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[C23] AST equivalence of attributes #151196

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Jul 29, 2025
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[C23] AST equivalence of attributes #151196

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cf6982b
[C23] AST equivalence of attributes
AaronBallman Jul 29, 2025
77d6984
Merge remote-tracking branch 'origin/main' into aballman-c23-attr-equ…
AaronBallman Jul 29, 2025
7288995
Update the test
AaronBallman Jul 29, 2025
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6 changes: 4 additions & 2 deletions clang/lib/AST/ASTStructuralEquivalence.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -456,7 +456,9 @@ CheckStructurallyEquivalentAttributes(StructuralEquivalenceContext &Context,
const Decl *D1, const Decl *D2,
const Decl *PrimaryDecl = nullptr) {
// If either declaration has an attribute on it, we treat the declarations
// as not being structurally equivalent.
// as not being structurally equivalent unless both declarations are implicit
// (ones generated by the compiler like __NSConstantString_tag).
//
// FIXME: this should be handled on a case-by-case basis via tablegen in
// Attr.td. There are multiple cases to consider: one declaration with the
// attribute, another without it; different attribute syntax|spellings for
Expand All @@ -468,7 +470,7 @@ CheckStructurallyEquivalentAttributes(StructuralEquivalenceContext &Context,
D1Attr = *D1->getAttrs().begin();
if (D2->hasAttrs())
D2Attr = *D2->getAttrs().begin();
if (D1Attr || D2Attr) {
if ((D1Attr || D2Attr) && !D1->isImplicit() && !D2->isImplicit()) {
const auto *DiagnoseDecl = cast<TypeDecl>(PrimaryDecl ? PrimaryDecl : D2);
Context.Diag2(DiagnoseDecl->getLocation(),
diag::warn_odr_tag_type_with_attributes)
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6 changes: 2 additions & 4 deletions clang/test/ASTMerge/enum/test2.c
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@@ -1,9 +1,7 @@
// RUN: %clang_cc1 -std=c23 -emit-pch -o %t.1.ast %S/Inputs/enum3.c
// RUN: %clang_cc1 -std=c23 -emit-pch -o %t.2.ast %S/Inputs/enum4.c
// RUN: not %clang_cc1 -std=c23 -ast-merge %t.1.ast -ast-merge %t.2.ast -fsyntax-only %s 2>&1 | FileCheck %s
// RUN: %clang_cc1 -std=c23 -ast-merge %t.1.ast -ast-merge %t.2.ast -fsyntax-only %s 2>&1 | FileCheck %s

// FIXME: this error should not happen!
// CHECK: error: type 'struct __NSConstantString_tag' has an attribute which currently causes the types to be treated as though they are incompatible
// CHECK: enum3.c:2:6: warning: type 'enum E1' has incompatible definitions in different translation units
// CHECK: enum4.c:2:6: note: enumeration 'E1' missing fixed underlying type here
// CHECK: enum3.c:2:6: note: enumeration 'E1' has fixed underlying type here
Expand All @@ -12,5 +10,5 @@
// CHECK: enum3.c:6:6: note: enumeration 'E2' missing fixed underlying type here
// CHECK: enum3.c:11:6: warning: type 'enum E3' has incompatible definitions in different translation units
// CHECK: enum3.c:11:6: note: enumeration 'E3' declared with incompatible fixed underlying types ('long' vs. 'short')
// CHECK: 3 warnings and 1 error generated
// CHECK: 3 warnings generated