https://github.com/zwuis updated
https://github.com/llvm/llvm-project/pull/143492
>From 658f3d3cb72ff9fbdb2315f894f39956eeabf135 Mon Sep 17 00:00:00 2001
From: Yanzuo Liu <zw...@outlook.com>
Date: Tue, 10 Jun 2025 16:41:57 +0800
Subject: [PATCH 1/2] Apply CWG400 'Using-declarations and the "struct hack"'
to C++98 mode
---
clang/docs/ReleaseNotes.rst | 2 +
clang/lib/Sema/SemaDeclCXX.cpp | 92 +++++--------------
.../CXX/class.access/class.access.dcl/p1.cpp | 7 +-
.../basic.namespace/namespace.udecl/p3.cpp | 25 ++---
.../basic.namespace/namespace.udecl/p4.cpp | 12 +--
5 files changed, 35 insertions(+), 103 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index beed0da6883d6..d8f09a275c1f0 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -840,6 +840,8 @@ Bug Fixes to C++ Support
- Fixed a pack substitution bug in deducing class template partial
specializations. (#GH53609)
- Fixed a crash when constant evaluating some explicit object member
assignment operators. (#GH142835)
- Fixed an access checking bug when substituting into concepts (#GH115838)
+- Correctly rejects invalid member using-declaration whose nested name
specifier
+ refers to its own class in C++98 mode.
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 5ef2ae3ee857f..84c666578b79a 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -13632,82 +13632,36 @@ bool Sema::CheckUsingDeclQualifier(SourceLocation
UsingLoc, bool HasTypename,
RequireCompleteDeclContext(const_cast<CXXScopeSpec&>(SS), NamedContext))
return true;
- if (getLangOpts().CPlusPlus11) {
- // C++11 [namespace.udecl]p3:
- // In a using-declaration used as a member-declaration, the
- // nested-name-specifier shall name a base class of the class
- // being defined.
+ // CWG400 [namespace.udecl]p3:
+ // In a using-declaration used as a member-declaration, the
+ // nested-name-specifier shall name a base class of the class being
defined.
- if (cast<CXXRecordDecl>(CurContext)->isProvablyNotDerivedFrom(
- cast<CXXRecordDecl>(NamedContext))) {
+ if (cast<CXXRecordDecl>(CurContext)
+ ->isProvablyNotDerivedFrom(cast<CXXRecordDecl>(NamedContext))) {
- if (Cxx20Enumerator) {
- Diag(NameLoc, diag::warn_cxx17_compat_using_decl_non_member_enumerator)
- << SS.getRange();
- return false;
- }
-
- if (CurContext == NamedContext) {
- Diag(SS.getBeginLoc(),
- diag::err_using_decl_nested_name_specifier_is_current_class)
- << SS.getRange();
- return !getLangOpts().CPlusPlus20;
- }
-
- if (!cast<CXXRecordDecl>(NamedContext)->isInvalidDecl()) {
- Diag(SS.getBeginLoc(),
- diag::err_using_decl_nested_name_specifier_is_not_base_class)
- << SS.getScopeRep() << cast<CXXRecordDecl>(CurContext)
- << SS.getRange();
- }
- return true;
+ if (Cxx20Enumerator) {
+ Diag(NameLoc, diag::warn_cxx17_compat_using_decl_non_member_enumerator)
+ << SS.getRange();
+ return false;
}
- return false;
- }
-
- // C++03 [namespace.udecl]p4:
- // A using-declaration used as a member-declaration shall refer
- // to a member of a base class of the class being defined [etc.].
-
- // Salient point: SS doesn't have to name a base class as long as
- // lookup only finds members from base classes. Therefore we can
- // diagnose here only if we can prove that can't happen,
- // i.e. if the class hierarchies provably don't intersect.
-
- // TODO: it would be nice if "definitely valid" results were cached
- // in the UsingDecl and UsingShadowDecl so that these checks didn't
- // need to be repeated.
+ if (CurContext == NamedContext) {
+ Diag(SS.getBeginLoc(),
+ diag::err_using_decl_nested_name_specifier_is_current_class)
+ << SS.getRange();
+ return !getLangOpts().CPlusPlus20;
+ }
- llvm::SmallPtrSet<const CXXRecordDecl *, 4> Bases;
- auto Collect = [&Bases](const CXXRecordDecl *Base) {
- Bases.insert(Base);
+ if (!cast<CXXRecordDecl>(NamedContext)->isInvalidDecl()) {
+ Diag(SS.getBeginLoc(),
+ diag::err_using_decl_nested_name_specifier_is_not_base_class)
+ << SS.getScopeRep() << cast<CXXRecordDecl>(CurContext)
+ << SS.getRange();
+ }
return true;
- };
-
- // Collect all bases. Return false if we find a dependent base.
- if (!cast<CXXRecordDecl>(CurContext)->forallBases(Collect))
- return false;
-
- // Returns true if the base is dependent or is one of the accumulated base
- // classes.
- auto IsNotBase = [&Bases](const CXXRecordDecl *Base) {
- return !Bases.count(Base);
- };
-
- // Return false if the class has a dependent base or if it or one
- // of its bases is present in the base set of the current context.
- if (Bases.count(cast<CXXRecordDecl>(NamedContext)) ||
- !cast<CXXRecordDecl>(NamedContext)->forallBases(IsNotBase))
- return false;
-
- Diag(SS.getRange().getBegin(),
- diag::err_using_decl_nested_name_specifier_is_not_base_class)
- << SS.getScopeRep()
- << cast<CXXRecordDecl>(CurContext)
- << SS.getRange();
+ }
- return true;
+ return false;
}
Decl *Sema::ActOnAliasDeclaration(Scope *S, AccessSpecifier AS,
diff --git a/clang/test/CXX/class.access/class.access.dcl/p1.cpp
b/clang/test/CXX/class.access/class.access.dcl/p1.cpp
index fdb1373dd9b12..1ad4135e32ba5 100644
--- a/clang/test/CXX/class.access/class.access.dcl/p1.cpp
+++ b/clang/test/CXX/class.access/class.access.dcl/p1.cpp
@@ -323,21 +323,18 @@ namespace test4 {
// expected-warning@-2 {{access declarations are deprecated; use using
declarations instead}}
#else
// expected-error@-4 {{ISO C++11 does not allow access declarations; use
using declarations instead}}
- // expected-error@-5 {{using declaration refers to its own class}}
#endif
+ // expected-error@-6 {{using declaration refers to its own class}}
Subclass::foo; // legal in C++03
#if __cplusplus <= 199711L
// expected-warning@-2 {{access declarations are deprecated; use using
declarations instead}}
#else
// expected-error@-4 {{ISO C++11 does not allow access declarations; use
using declarations instead}}
- // expected-error@-5 {{using declaration refers into 'Subclass', which is
not a base class of 'C'}}
#endif
+ // expected-error@-6 {{using declaration refers into 'Subclass', which is
not a base class of 'C'}}
int bar();
-#if __cplusplus <= 199711L
- //expected-note@-2 {{target of using declaration}}
-#endif
C::bar;
#if __cplusplus <= 199711L
// expected-warning@-2 {{access declarations are deprecated; use using
declarations instead}}
diff --git a/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p3.cpp
b/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p3.cpp
index 657695657e0f7..bcc26bf4f4356 100644
--- a/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p3.cpp
+++ b/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p3.cpp
@@ -30,17 +30,10 @@ class D2 : public B {
using B::x;
using C::g; // expected-error{{using declaration refers into 'C', which is
not a base class of 'D2'}}
- // These are valid in C++98 but not in C++11.
- using D::f2;
- using D::E2;
- using D::e2;
- using D::x2;
-#if __cplusplus >= 201103L
- // expected-error@-5 {{using declaration refers into 'D', which is not a
base class of 'D2'}}
- // expected-error@-5 {{using declaration refers into 'D', which is not a
base class of 'D2'}}
- // expected-error@-5 {{using declaration refers into 'D', which is not a
base class of 'D2'}}
- // expected-error@-5 {{using declaration refers into 'D', which is not a
base class of 'D2'}}
-#endif
+ using D::f2; // expected-error {{using declaration refers into 'D', which is
not a base class of 'D2'}}
+ using D::E2; // expected-error {{using declaration refers into 'D', which is
not a base class of 'D2'}}
+ using D::e2; // expected-error {{using declaration refers into 'D', which is
not a base class of 'D2'}}
+ using D::x2; // expected-error {{using declaration refers into 'D', which is
not a base class of 'D2'}}
using B::EC;
using B::EC::ec; // expected-warning {{a C++20 extension}} expected-warning
0-1 {{C++11}}
@@ -71,13 +64,7 @@ namespace test1 {
using Base::bar; // expected-error {{no member named 'bar'}}
using Unrelated::foo; // expected-error {{not a base class}}
- // In C++98, it's hard to see that these are invalid, because indirect
- // references to base class members are permitted.
- using C::foo;
- using Subclass::foo;
-#if __cplusplus >= 201103L
- // expected-error@-3 {{refers to its own class}}
- // expected-error@-3 {{not a base class}}
-#endif
+ using C::foo; // expected-error {{refers to its own class}}
+ using Subclass::foo; // expected-error {{not a base class}}
};
}
diff --git a/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p4.cpp
b/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p4.cpp
index 973cd77279f19..26b66350b86d9 100644
--- a/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p4.cpp
+++ b/clang/test/CXX/dcl.dcl/basic.namespace/namespace.udecl/p4.cpp
@@ -206,17 +206,9 @@ namespace test4 {
using InnerNS::foo; // expected-error {{not a class}}
using Base::bar; // expected-error {{no member named 'bar'}}
using Unrelated::foo; // expected-error {{not a base class}}
- using C::foo; // legal in C++03
- using Subclass::foo; // legal in C++03
-#if __cplusplus >= 201103L
- // expected-error@-3 {{refers to its own class}}
- // expected-error@-3 {{refers into 'Subclass', which is not a base class}}
-#endif
-
+ using C::foo; // expected-error {{refers to its own class}}
+ using Subclass::foo; // expected-error {{refers into 'Subclass', which is
not a base class}}
int bar();
-#if __cplusplus < 201103L
- // expected-note@-2 {{target of using declaration}}
-#endif
using C::bar; // expected-error {{refers to its own class}}
};
}
>From 380eb58f7ec1180caf0d5d143b9d3b9720231a66 Mon Sep 17 00:00:00 2001
From: Yanzuo Liu <zw...@outlook.com>
Date: Mon, 16 Jun 2025 21:14:31 +0800
Subject: [PATCH 2/2] Add tests, modify comments and release notes
---
clang/docs/ReleaseNotes.rst | 7 +++++--
clang/lib/Sema/SemaDeclCXX.cpp | 10 +++++++---
clang/test/CXX/class.access/class.access.dcl/p1.cpp | 4 ++--
clang/test/CXX/drs/cwg4xx.cpp | 7 +++++++
4 files changed, 21 insertions(+), 7 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index d8f09a275c1f0..10f2e0bd8c0a4 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -159,6 +159,11 @@ Resolutions to C++ Defect Reports
- Implemented `CWG2496 ref-qualifiers and virtual overriding
<https://wg21.link/CWG2496>`_.
+- Fully implemented `CWG400 Using-declarations and the "struct hack" `
+ `<https://wg21.link/CWG400>`_. Correctly rejected invalid member
+ using-declaration whose nested-name-specifier doesn't refer to a base class
of
+ the current class in C++98 mode.
+
C Language Changes
------------------
@@ -840,8 +845,6 @@ Bug Fixes to C++ Support
- Fixed a pack substitution bug in deducing class template partial
specializations. (#GH53609)
- Fixed a crash when constant evaluating some explicit object member
assignment operators. (#GH142835)
- Fixed an access checking bug when substituting into concepts (#GH115838)
-- Correctly rejects invalid member using-declaration whose nested name
specifier
- refers to its own class in C++98 mode.
Bug Fixes to AST Handling
^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 84c666578b79a..841c245da1714 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -13632,9 +13632,13 @@ bool Sema::CheckUsingDeclQualifier(SourceLocation
UsingLoc, bool HasTypename,
RequireCompleteDeclContext(const_cast<CXXScopeSpec&>(SS), NamedContext))
return true;
- // CWG400 [namespace.udecl]p3:
- // In a using-declaration used as a member-declaration, the
- // nested-name-specifier shall name a base class of the class being
defined.
+ // C++26 [namespace.udecl]p3:
+ // In a using-declaration used as a member-declaration, each
+ // using-declarator shall either name an enumerator or have a
+ // nested-name-specifier naming a base class of the current class
+ // ([expr.prim.this]). ...
+ // "have a nested-name-specifier naming a base class of the current class"
+ // was introduced by CWG400.
if (cast<CXXRecordDecl>(CurContext)
->isProvablyNotDerivedFrom(cast<CXXRecordDecl>(NamedContext))) {
diff --git a/clang/test/CXX/class.access/class.access.dcl/p1.cpp
b/clang/test/CXX/class.access/class.access.dcl/p1.cpp
index 1ad4135e32ba5..b7ee6c9a7c04b 100644
--- a/clang/test/CXX/class.access/class.access.dcl/p1.cpp
+++ b/clang/test/CXX/class.access/class.access.dcl/p1.cpp
@@ -318,7 +318,7 @@ namespace test4 {
// expected-error@-4 {{ISO C++11 does not allow access declarations; use
using declarations instead}}
#endif
- C::foo; // legal in C++03
+ C::foo;
#if __cplusplus <= 199711L
// expected-warning@-2 {{access declarations are deprecated; use using
declarations instead}}
#else
@@ -326,7 +326,7 @@ namespace test4 {
#endif
// expected-error@-6 {{using declaration refers to its own class}}
- Subclass::foo; // legal in C++03
+ Subclass::foo;
#if __cplusplus <= 199711L
// expected-warning@-2 {{access declarations are deprecated; use using
declarations instead}}
#else
diff --git a/clang/test/CXX/drs/cwg4xx.cpp b/clang/test/CXX/drs/cwg4xx.cpp
index 210f7ae71ec04..0f8b684eebdd1 100644
--- a/clang/test/CXX/drs/cwg4xx.cpp
+++ b/clang/test/CXX/drs/cwg4xx.cpp
@@ -36,6 +36,13 @@ namespace cwg400 { // cwg400: 2.7
// expected-error@-1 {{member 'a' found in multiple base classes of
different types}}
// expected-note@#cwg400-A {{member type 'cwg400::A::a' found by ambiguous
name lookup}}
// expected-note@#cwg400-B {{member type 'cwg400::B::a' found by ambiguous
name lookup}}
+ struct F : A {};
+ struct G : A {
+ using G::A;
+ // expected-error@-1 {{using declaration refers to its own class}}
+ using F::a;
+ // expected-error@-1 {{using declaration refers into 'F', which is not a
base class of 'G'}}
+ };
} // namespace cwg400
namespace cwg401 { // cwg401: 2.8
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