[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Krystian Stasiowski via cfe-commits]

sdkrystian wrote:

@zyn0217 Yes, both examples are of uninstantiable templates & are intended to 
be diagnosed by #90152.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

> It seems this change cause https://godbolt.org/z/311nb6xYe to fail. Could you 
> please take look?

> Also:
> https://godbolt.org/z/bYs7Y9v11

I don't see any justification that these examples should compile: the first 
example is a typical one handled by #90152
(from the release note):
```rst
- Clang now looks up members of the current instantiation in the template 
definition context
  if the current instantiation has no dependent base classes.

 template
 struct A {
   int f() {
 return this->x; // error: no member named 'x' in 'A'
   }
 };

```
and the second one would also be rejected by GCC once the inner class `b` gets 
instantiated. This earlier diagnostic is probably also triggered by #90152, but 
I'm not sure. @sdkrystian, is this behavior intended and from your recent 
patches?

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

jyu2-git wrote:

Hi @zyn0217, I am not sure.  But if I revert your patch, two tests compiles.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@jyu2-git Are you sure this is the patch you’re looking for? The diagnostic 
there is completely unrelated and I think the right patch is 
https://github.com/llvm/llvm-project/pull/90152.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

jyu2-git wrote:

Hi @zyn0217.
It seems this change cause https://godbolt.org/z/311nb6xYe to fail.  Could you 
please take look?

Thanks.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@aganea Oops, this is an oversight I think, because I don't build lldb locally 
nor run its tests...
I'm proposing a PR https://github.com/llvm/llvm-project/pull/91132, can you 
help me confirm if that works?



https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Alexandre Ganea via cfe-commits]

aganea wrote:

Hello,
This causes a warning when building LLDB on Windows, 
`clang::BuiltinType::UnresolvedTemplate` isn't handled in the case in the file 
indicated below (sorry my locale is French). Would you have a chance to take a 
look @zyn0217 please?
```
[6325/7521] Building CXX object 
tools\lldb\source\Plugins\TypeSystem\Clang\CMakeFiles\lldbPluginTypeSystemClang.dir\TypeSystemClang.cpp.obj
C:\src\git\llvm-project\lldb\source\Plugins\TypeSystem\Clang\TypeSystemClang.cpp(4999):
 warning C4062: L'énumérateur 'clang::BuiltinType::UnresolvedTemplate' dans le 
commutateur de l'énumération 'clang::BuiltinType::Kind' n'est pas géré.
C:\src\git\llvm-project\clang\include\clang/AST/Type.h(2983): note: voir la 
déclaration de 'clang::BuiltinType::Kind'
```

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 closed 
https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/7] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/7] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Michael Maitland via cfe-commits]

https://github.com/michaelmaitland updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/7] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

https://github.com/erichkeane approved this pull request.


https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

> This is introducing a new type that has a pretty subtle difference vs others. 
> Can we have some documentation in the internals manual explaining the 
> difference?
> 
> Code wise, I think this looks fine.

Yeah, I added some explanation to the document of `UnresolvedLookupExpr`; 
further, I didn't see anything specific to the topic of `UnresolvedLookupExpr` 
in the `InternalsManual.rst`, so I hope this is sufficient?

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/6] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This is introducing a new type that has a pretty subtle difference vs others.  
Can we have some documentation in the internals manual explaining the 
difference?

Code wise, I think this looks fine.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@cor3ntin @erichkeane Any chance we can move forward with this review? I 
appreciate your feedback!

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}
+  }
+};
+
+int bar() {
+  return Q().foo(); // expected-note-re {{function template specialization 
{{.*}} requested here}}
+}
+
+} // namespace PR88832
+#endif
+
+namespace PR63243 {
+
+namespace std {
+template  struct add_pointer { // #add_pointer
+};
+} // namespace std
+
+class A {};
+
+int main() {
+  std::__add_pointer::type ptr; // #ill-formed-decl
+  // expected-error@#ill-formed-decl {{no template named '__add_pointer'}}
+  // expected-note@#add_pointer {{'add_pointer' declared here}}
+  // expected-error@#ill-formed-decl {{expected ';' after expression}}
+  // expected-error@#ill-formed-decl {{no type named 'type' in the global 
namespace}}
+  // expected-error@#ill-formed-decl {{'std::add_pointer' is expected to be a 
non-type template, but instantiated to a class template}}

zyn0217 wrote:

@cor3ntin do you have any thoughts here? thanks!

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/5] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}
+  }
+};
+
+int bar() {
+  return Q().foo(); // expected-note-re {{function template specialization 
{{.*}} requested here}}
+}
+
+} // namespace PR88832
+#endif
+
+namespace PR63243 {
+
+namespace std {
+template  struct add_pointer { // #add_pointer
+};
+} // namespace std
+
+class A {};
+
+int main() {
+  std::__add_pointer::type ptr; // #ill-formed-decl
+  // expected-error@#ill-formed-decl {{no template named '__add_pointer'}}
+  // expected-note@#add_pointer {{'add_pointer' declared here}}
+  // expected-error@#ill-formed-decl {{expected ';' after expression}}
+  // expected-error@#ill-formed-decl {{no type named 'type' in the global 
namespace}}
+  // expected-error@#ill-formed-decl {{'std::add_pointer' is expected to be a 
non-type template, but instantiated to a class template}}

erichkeane wrote:

I think that would be OK?  But  @cor3ntin would be our expert there.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/4] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}
+  }
+};
+
+int bar() {
+  return Q().foo(); // expected-note-re {{function template specialization 
{{.*}} requested here}}
+}
+
+} // namespace PR88832
+#endif
+
+namespace PR63243 {
+
+namespace std {
+template  struct add_pointer { // #add_pointer
+};
+} // namespace std
+
+class A {};
+
+int main() {
+  std::__add_pointer::type ptr; // #ill-formed-decl
+  // expected-error@#ill-formed-decl {{no template named '__add_pointer'}}
+  // expected-note@#add_pointer {{'add_pointer' declared here}}
+  // expected-error@#ill-formed-decl {{expected ';' after expression}}
+  // expected-error@#ill-formed-decl {{no type named 'type' in the global 
namespace}}
+  // expected-error@#ill-formed-decl {{'std::add_pointer' is expected to be a 
non-type template, but instantiated to a class template}}

zyn0217 wrote:

> As far as this diagnostic, can you spend a little time to evaluate how much 
> work it is to fix that? It is particularly awkward.

I have looked into it a bit more, and I found it is a consequence of not 
handling `TRANSFORM_TYPE_TRAIT`s as scope specifiers, which was introduced in 
e9ef45635.

Let's explain the difference with an example:
```cpp
namespace std {
struct add_pointer {};
}
void foo() {
  std::__add_pointer::type ptr;
  std::Add_pointer::type ptr2;
}
```
we would end up seeing different diagnostics on two declarations `ptr` and 
`ptr2`: the first is what was crashing previously, because `__add_pointer` is 
actually a keyword rather than an identifier like `Add_pointer`. As a result, 
we would bail out when we see `__add_pointer` in 
`ParseOptionalCXXScopeSpecifier`, and we would continue parsing it as a 
`TemplateIdExpr`, which gave us a crash as well as a spurious diagnostic saying 
we're missing a semicolon after ``.

For comparison, the second case would keep parsing until we encounter the 
semicolon after `ptr2`. This results in a better diagnostic even after the typo 
correction.

I think a fix would be to add a handling logic to 
`ParseOptionalCXXScopeSpecifier` like what we did in e9ef45635:
```cpp
switch (Tok.getKind()) {
#define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) case tok::kw___##Trait:
#include "clang/Basic/TransformTypeTraits.def"
  if (NextToken().is(tok::less)) {
Tok.setKind(tok::identifier);
Diag(Tok, diag::ext_keyword_as_ident)
<< Tok.getIdentifierInfo()->getName() << 0;
   continue;
  }
  LLVM_FALLTHROUGH;
default:
  break;
}
```


https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

erichkeane wrote:

FWIW, I think I'm the 'first' person who has really been pushing for using the 
bookmarks for notes, no one ever has before, but when reviewing template stuff 
in particular, it is REALLY bad, so as code-owner, its one of the things I push 
for in new commits :)  

So you'll see very few that do it, but hopefully more happening.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

Sirraide wrote:

That’s true; I’ve run into cases before where the notes just ended up being a 
mess...

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

erichkeane wrote:

Yeah, it doesn't make sense for errors/warnings: Those should be "right next" 
to the thing that caused them (so I prefer the  +/- Numeral for those).  
However, with Notes, it makes a TON of sense, and IMO, should nearly ALWAYS be 
used.

Without them, we end up getting 'errors' and their notes are completely 
unintelligible, because they are spread out around the file and in no 
reasonable order.  It makes it so figuring out "this is an error only because 
of these instantiations" is impossible.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

Sirraide wrote:

>  It makes it easier to determine which error is causing the note.

Iirc last time this came up in a discussion the consensus was that it was 
better not to use markers, but I think that was more about actual errors than 
notes, because this makes sense, yeah.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}
+  }
+};
+
+int bar() {
+  return Q().foo(); // expected-note-re {{function template specialization 
{{.*}} requested here}}
+}
+
+} // namespace PR88832
+#endif
+
+namespace PR63243 {
+
+namespace std {
+template  struct add_pointer { // #add_pointer
+};
+} // namespace std
+
+class A {};
+
+int main() {
+  std::__add_pointer::type ptr; // #ill-formed-decl
+  // expected-error@#ill-formed-decl {{no template named '__add_pointer'}}
+  // expected-note@#add_pointer {{'add_pointer' declared here}}
+  // expected-error@#ill-formed-decl {{expected ';' after expression}}
+  // expected-error@#ill-formed-decl {{no type named 'type' in the global 
namespace}}
+  // expected-error@#ill-formed-decl {{'std::add_pointer' is expected to be a 
non-type template, but instantiated to a class template}}

erichkeane wrote:

This is a case where just doing the `-N` positioning is fine, since it is on 
the same thing here.  

As far as this diagnostic, can you spend a little time to evaluate how much 
work it is to fix that?  It is particularly awkward.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Erich Keane via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

erichkeane wrote:

I VASTLY prefer the markers.  It makes it easier to determine which error is 
causing the note.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

zyn0217 wrote:

> Can you add some more tests that involve an expression with this new type as 
> the argument to a function call?

Done. Thanks for the feedback.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

zyn0217 wrote:

I think this is more of a preference - subjectively, I feel like using markers 
makes the diagnostics concentrated, and one can see them in a somewhat 
consistent block without guessing what else notes/warnings an error diagnostic 
would also provide, though this looks a bit untidy. :(

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/3] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH 1/2] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

https://github.com/Sirraide edited 
https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

Sirraide wrote:

The same applies to the other diagnostics using markers below.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}

Sirraide wrote:

I’d suggest putting this on the line where the note is emitted rather than 
using markers whenever possible.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

https://github.com/Sirraide commented:

I think the general approach of this makes sense. 

Can you add some more tests that involve an expression with this new type as 
the argument to a function call? You’ve taken care of handling that case from 
what I’ve seen, but having tests for that would probably be a good idea.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

llvmbot wrote:




@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)


Changes

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673

---
Full diff: https://github.com/llvm/llvm-project/pull/89019.diff


14 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+1) 
- (modified) clang/include/clang/AST/ASTContext.h (+2-1) 
- (modified) clang/include/clang/AST/BuiltinTypes.def (+3) 
- (modified) clang/include/clang/Serialization/ASTBitCodes.h (+4-1) 
- (modified) clang/lib/AST/ASTContext.cpp (+3) 
- (modified) clang/lib/AST/NSAPI.cpp (+1) 
- (modified) clang/lib/AST/Type.cpp (+3) 
- (modified) clang/lib/AST/TypeLoc.cpp (+1) 
- (modified) clang/lib/Sema/SemaExpr.cpp (+19) 
- (modified) clang/lib/Sema/SemaTemplate.cpp (+10-3) 
- (modified) clang/lib/Serialization/ASTCommon.cpp (+3) 
- (modified) clang/lib/Serialization/ASTReader.cpp (+3) 
- (modified) clang/test/SemaCXX/PR62533.cpp (+1-1) 
- (modified) clang/test/SemaTemplate/template-id-expr.cpp (+71) 


``diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 
b/clang/include/clang/Serialization/ASTBitCodes.h
index 500098dd3dab1d..2f0a122fdfde14 100644
--- a/clang/include/clang/Serialization/ASTBitCodes.h
+++ b/clang/include/clang/Serialization/ASTBitCodes.h
@@ 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[via cfe-commits]

llvmbot wrote:




@llvm/pr-subscribers-clang-modules

Author: Younan Zhang (zyn0217)


Changes

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673

---
Full diff: https://github.com/llvm/llvm-project/pull/89019.diff


14 Files Affected:

- (modified) clang/docs/ReleaseNotes.rst (+1) 
- (modified) clang/include/clang/AST/ASTContext.h (+2-1) 
- (modified) clang/include/clang/AST/BuiltinTypes.def (+3) 
- (modified) clang/include/clang/Serialization/ASTBitCodes.h (+4-1) 
- (modified) clang/lib/AST/ASTContext.cpp (+3) 
- (modified) clang/lib/AST/NSAPI.cpp (+1) 
- (modified) clang/lib/AST/Type.cpp (+3) 
- (modified) clang/lib/AST/TypeLoc.cpp (+1) 
- (modified) clang/lib/Sema/SemaExpr.cpp (+19) 
- (modified) clang/lib/Sema/SemaTemplate.cpp (+10-3) 
- (modified) clang/lib/Serialization/ASTCommon.cpp (+3) 
- (modified) clang/lib/Serialization/ASTReader.cpp (+3) 
- (modified) clang/test/SemaCXX/PR62533.cpp (+1-1) 
- (modified) clang/test/SemaTemplate/template-id-expr.cpp (+71) 


``diff
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 
b/clang/include/clang/Serialization/ASTBitCodes.h
index 500098dd3dab1d..2f0a122fdfde14 100644
--- a/clang/include/clang/Serialization/ASTBitCodes.h
+++ b/clang/include/clang/Serialization/ASTBitCodes.h

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 ready_for_review 
https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

zyn0217 wrote:

The pre-commit CI is still clogging after a few hours, and I'm opening it for 
feedback anyway.

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

@@ -186,3 +186,74 @@ class E {
 #endif
 template using D = int; // expected-note {{declared here}} 
 E ed; // expected-note {{instantiation of}}
+
+namespace non_functions {
+
+#if __cplusplus >= 201103L
+namespace PR88832 {
+template  struct O {
+  static const T v = 0;
+};
+
+struct P {
+  template  using I = typename O::v; // #TypeAlias
+};
+
+struct Q {
+  template  int foo() {
+return T::template I; // expected-error {{'P::I' is expected to be a 
non-type template, but instantiated to a type alias template}}
+// expected-note@#TypeAlias {{type alias template declared here}}
+  }
+};
+
+int bar() {
+  return Q().foo(); // expected-note-re {{function template specialization 
{{.*}} requested here}}
+}
+
+} // namespace PR88832
+#endif
+
+namespace PR63243 {
+
+namespace std {
+template  struct add_pointer { // #add_pointer
+};
+} // namespace std
+
+class A {};
+
+int main() {
+  std::__add_pointer::type ptr; // #ill-formed-decl
+  // expected-error@#ill-formed-decl {{no template named '__add_pointer'}}
+  // expected-note@#add_pointer {{'add_pointer' declared here}}
+  // expected-error@#ill-formed-decl {{expected ';' after expression}}
+  // expected-error@#ill-formed-decl {{no type named 'type' in the global 
namespace}}
+  // expected-error@#ill-formed-decl {{'std::add_pointer' is expected to be a 
non-type template, but instantiated to a class template}}

zyn0217 wrote:

RFC: this diagnostic is probably not optimal (and maybe confusing), since 
`CheckPlaceholderExpr` is called almost everywhere apart from a full 
expression. I was considering moving the diagnostic out of that function, but 
that requires much work I think. (and I'm a bit lazy :)

https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 edited 
https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 updated 
https://github.com/llvm/llvm-project/pull/89019

>From 89a5bbcc89c1e43ac7f2e60f3c234c2c42928c86 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

This patch revolves around the misuse of UnresolvedLookupExpr in
BuildTemplateIdExpr.

Basically, we build up an UnresolvedLookupExpr not only for function
overloads but for "unresolved" templates wherever we need an expression
for template decls. For example, a dependent VarTemplateDecl can be
wrapped with such an expression before template instantiation. (See
https://github.com/llvm/llvm-project/commit/617007240cbfb97c8ccf6d61b0c4ca0bb62d43c9)

Also, one important thing is that UnresolvedLookupExpr uses a "canonical"
QualType to describe the containing unresolved decls: a DependentTy is
for dependent expressions and an OverloadTy otherwise. Therefore, this
modeling for non-dependent templates leaves a problem in that the expression
is marked and perceived as if describing overload functions. The consumer then
expects functions for every such expression, although the fact is the reverse.
Hence, we run into crashes.

As to the patch, I added a new canonical type "UnresolvedTemplateTy" to
model these cases. Given that we have been using this model (intentionally or
accidentally) and it is pretty baked in throughout the code, I think
extending the role of UnresolvedLookupExpr is reasonable. Further, I added
some diagnostics for the direct occurrence of these expressions, which
are supposed to be ill-formed.

As a bonus, this patch also fixes some typos in the diagnostics and creates
RecoveryExprs rather than nothing in the hope of a better error-recovery
for clangd.

Fixes https://github.com/llvm/llvm-project/issues/88832
Fixes https://github.com/llvm/llvm-project/issues/63243
Fixes https://github.com/llvm/llvm-project/issues/48673
---
 clang/docs/ReleaseNotes.rst   |  1 +
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  3 +
 .../include/clang/Serialization/ASTBitCodes.h |  5 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 13 +++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 14 files changed, 125 insertions(+), 6 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index efc32212f300cf..8c50988083faa6 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -535,6 +535,7 @@ Bug Fixes to C++ Support
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member 
function. Fixes (#GH84020).
 - Placement new initializes typedef array with correct size (#GH41441)
+- Fixed a misuse of ``UnresolvedLookupExpr`` for ill-formed templated 
expressions. Fixes (#GH48673), (#GH63243) and (#GH88832).
 
 Bug Fixes to AST Handling
 ^
diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..fd0cc10be8ebca 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,9 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+// The type of an unresolved template. Used in UnresolvedLookupExpr.
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 

[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 edited 
https://github.com/llvm/llvm-project/pull/89019
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[clang] [clang] Distinguish unresolved templates in UnresolvedLookupExpr (PR #89019)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 created 
https://github.com/llvm/llvm-project/pull/89019

None

>From e510a76d231de0e22ba52584a80f18deb6af91c6 Mon Sep 17 00:00:00 2001
From: Younan Zhang 
Date: Wed, 17 Apr 2024 12:24:56 +0800
Subject: [PATCH] [clang] Distinguish unresolved templates in
 UnresolvedLookupExpr

---
 clang/include/clang/AST/ASTContext.h  |  3 +-
 clang/include/clang/AST/BuiltinTypes.def  |  2 +
 .../include/clang/Serialization/ASTBitCodes.h |  4 +-
 clang/lib/AST/ASTContext.cpp  |  3 +
 clang/lib/AST/NSAPI.cpp   |  1 +
 clang/lib/AST/Type.cpp|  3 +
 clang/lib/AST/TypeLoc.cpp |  1 +
 clang/lib/Sema/SemaExpr.cpp   | 19 +
 clang/lib/Sema/SemaTemplate.cpp   | 11 ++-
 clang/lib/Serialization/ASTCommon.cpp |  3 +
 clang/lib/Serialization/ASTReader.cpp |  3 +
 clang/test/SemaCXX/PR62533.cpp|  2 +-
 clang/test/SemaTemplate/template-id-expr.cpp  | 71 +++
 13 files changed, 120 insertions(+), 6 deletions(-)

diff --git a/clang/include/clang/AST/ASTContext.h 
b/clang/include/clang/AST/ASTContext.h
index 28f8d67811f0a2..e9a22f04cfe764 100644
--- a/clang/include/clang/AST/ASTContext.h
+++ b/clang/include/clang/AST/ASTContext.h
@@ -1116,7 +1116,8 @@ class ASTContext : public RefCountedBase {
   CanQualType BFloat16Ty;
   CanQualType Float16Ty; // C11 extension ISO/IEC TS 18661-3
   CanQualType VoidPtrTy, NullPtrTy;
-  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnknownAnyTy;
+  CanQualType DependentTy, OverloadTy, BoundMemberTy, UnresolvedTemplateTy,
+  UnknownAnyTy;
   CanQualType BuiltinFnTy;
   CanQualType PseudoObjectTy, ARCUnbridgedCastTy;
   CanQualType ObjCBuiltinIdTy, ObjCBuiltinClassTy, ObjCBuiltinSelTy;
diff --git a/clang/include/clang/AST/BuiltinTypes.def 
b/clang/include/clang/AST/BuiltinTypes.def
index c04f6f6f127191..eb72bf0f866247 100644
--- a/clang/include/clang/AST/BuiltinTypes.def
+++ b/clang/include/clang/AST/BuiltinTypes.def
@@ -285,6 +285,8 @@ PLACEHOLDER_TYPE(Overload, OverloadTy)
 //   x->foo   # if only contains non-static members
 PLACEHOLDER_TYPE(BoundMember, BoundMemberTy)
 
+PLACEHOLDER_TYPE(UnresolvedTemplate, UnresolvedTemplateTy)
+
 // The type of an expression which refers to a pseudo-object,
 // such as those introduced by Objective C's @property or
 // VS.NET's __property declarations.  A placeholder type.  The
diff --git a/clang/include/clang/Serialization/ASTBitCodes.h 
b/clang/include/clang/Serialization/ASTBitCodes.h
index 500098dd3dab1d..a0feb3a317611e 100644
--- a/clang/include/clang/Serialization/ASTBitCodes.h
+++ b/clang/include/clang/Serialization/ASTBitCodes.h
@@ -1099,6 +1099,8 @@ enum PredefinedTypeIDs {
 // \brief WebAssembly reference types with auto numeration
 #define WASM_TYPE(Name, Id, SingletonId) PREDEF_TYPE_##Id##_ID,
 #include "clang/Basic/WebAssemblyReferenceTypes.def"
+
+  PREDEF_TYPE_UNRESOLVED_TEMPLATE,
   // Sentinel value. Considered a predefined type but not useable as one.
   PREDEF_TYPE_LAST_ID
 };
@@ -1108,7 +1110,7 @@ enum PredefinedTypeIDs {
 ///
 /// Type IDs for non-predefined types will start at
 /// NUM_PREDEF_TYPE_IDs.
-const unsigned NUM_PREDEF_TYPE_IDS = 502;
+const unsigned NUM_PREDEF_TYPE_IDS = 503;
 
 // Ensure we do not overrun the predefined types we reserved
 // in the enum PredefinedTypeIDs above.
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 6ce233704a5885..e9fba116cff559 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -1306,6 +1306,9 @@ void ASTContext::InitBuiltinTypes(const TargetInfo 
,
   // Placeholder type for bound members.
   InitBuiltinType(BoundMemberTy,   BuiltinType::BoundMember);
 
+  // Placeholder type for unresolved templates.
+  InitBuiltinType(UnresolvedTemplateTy, BuiltinType::UnresolvedTemplate);
+
   // Placeholder type for pseudo-objects.
   InitBuiltinType(PseudoObjectTy,  BuiltinType::PseudoObject);
 
diff --git a/clang/lib/AST/NSAPI.cpp b/clang/lib/AST/NSAPI.cpp
index ecc56c13fb7573..4e09b27b0f76cd 100644
--- a/clang/lib/AST/NSAPI.cpp
+++ b/clang/lib/AST/NSAPI.cpp
@@ -454,6 +454,7 @@ NSAPI::getNSNumberFactoryMethodKind(QualType T) const {
 #define WASM_TYPE(Name, Id, SingletonId) case BuiltinType::Id:
 #include "clang/Basic/WebAssemblyReferenceTypes.def"
   case BuiltinType::BoundMember:
+  case BuiltinType::UnresolvedTemplate:
   case BuiltinType::Dependent:
   case BuiltinType::Overload:
   case BuiltinType::UnknownAny:
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index cb22c91a12aa89..4751d73184262f 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -3381,6 +3381,8 @@ StringRef BuiltinType::getName(const PrintingPolicy 
) const {
 return "";
   case BoundMember:
 return "";
+  case UnresolvedTemplate:
+return "";
   case PseudoObject:
 return "";
   case Dependent:
@@ -4673,6 +4675,7 @@ bool