https://github.com/vbvictor created
https://github.com/llvm/llvm-project/pull/144270
Before this patch, the following code gave misleading diagnostics about absence
of `#include <new>`:
```cpp
struct X { int n; };
int foo() {
const X cx = {5};
// error: no matching 'operator new' function for non-allocating placement
new expression; include <new>
(void)new(&cx) X{10};
};
```
Now it gives correct diagnostics about constness of passed argument:
```cpp
struct X { int n; };
int foo() {
const X cx = {5};
// error: placement new expression with a const-qualified argument of type
'const X *' is not allowed
(void)new(&cx) X{10};
};
```
Fixes https://github.com/llvm/llvm-project/issues/143708.
>From 07392e16740d3d89700da43e22b4d90197bb4d4a Mon Sep 17 00:00:00 2001
From: Victor Baranov <bar.victor.2...@gmail.com>
Date: Sun, 15 Jun 2025 19:56:05 +0300
Subject: [PATCH] [Clang] Improve diagnostics when 'placement new' was called
with const storage argument
---
clang/docs/ReleaseNotes.rst | 2 ++
clang/include/clang/Basic/DiagnosticSemaKinds.td | 3 +++
clang/lib/Sema/SemaExprCXX.cpp | 10 +++++++++-
clang/test/SemaCXX/new-delete.cpp | 7 +++++++
4 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 33ee8a53b5f37..9fdc8660a981e 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -629,6 +629,8 @@ Improvements to Clang's diagnostics
#GH69470, #GH59391, #GH58172, #GH46215, #GH45915, #GH45891, #GH44490,
#GH36703, #GH32903, #GH23312, #GH69874.
+- Improve the diagnostics for placement new expression when const-qualified
+ object was passed as the storage argument.
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td
b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 8fe7ad6138aa0..0bc1e7deff5ab 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8285,6 +8285,9 @@ def err_need_header_before_typeid : Error<
def err_need_header_before_placement_new : Error<
"no matching %0 function for non-allocating placement new expression; "
"include <new>">;
+def err_placement_new_into_const_qualified_storage : Error<
+ "placement new expression with a const-qualified argument of type %0 "
+ "is not allowed">;
def err_ms___leave_not_in___try : Error<
"'__leave' statement not in __try block">;
def err_uuidof_without_guid : Error<
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index ba52e8f8932d3..e9cd40b9061d0 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -2753,10 +2753,18 @@ static bool resolveAllocationOverloadInterior(
if (Diagnose) {
// If this is an allocation of the form 'new (p) X' for some object
// pointer p (or an expression that will decay to such a pointer),
- // diagnose the missing inclusion of <new>.
+ // diagnose potential error.
if (!R.isClassLookup() && Args.size() == 2 &&
(Args[1]->getType()->isObjectPointerType() ||
Args[1]->getType()->isArrayType())) {
+ if (Args[1]->getType()->isPointerType()) {
+ if (Args[1]->getType()->getPointeeType().isConstQualified()) {
+ S.Diag(Args[1]->getExprLoc(),
+ diag::err_placement_new_into_const_qualified_storage)
+ << Args[1]->getType() << Args[1]->getSourceRange();
+ return true;
+ }
+ }
S.Diag(R.getNameLoc(), diag::err_need_header_before_placement_new)
<< R.getLookupName() << Range;
// Listing the candidates is unlikely to be useful; skip it.
diff --git a/clang/test/SemaCXX/new-delete.cpp
b/clang/test/SemaCXX/new-delete.cpp
index 9bbee32c58c36..fae9487cbe2c1 100644
--- a/clang/test/SemaCXX/new-delete.cpp
+++ b/clang/test/SemaCXX/new-delete.cpp
@@ -160,6 +160,13 @@ void bad_news(int *ip)
#if __cplusplus < 201103L
(void)new int[]{}; // expected-error {{array size must be specified in new
expression with no initializer}}
#endif
+ struct X { int n; };
+ const X cx = {5};
+ (void)new(&cx) X{10}; // expected-error {{placement new expression with a
const-qualified argument of type 'const X *' is not allowed}}
+ const X* const cx2 = 0;
+ (void)new(cx2) X{10}; // expected-error {{placement new expression with a
const-qualified argument of type 'const X *const' is not allowed}}
+ const int arr[1] = {1};
+ (void)new(&arr[0]) int(10); // expected-error {{placement new expression
with a const-qualified argument of type 'const int *' is not allowed}}
}
void no_matching_placement_new() {
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