[clang] [clang] Diagnose when spelled 'abi_tag' on namespace doesn't match applied one. (PR #221039)
Volodymyr Sapsai via cfe-commits
cfe-commits at lists.llvm.org
Fri Oct 9 15:54:41 PDT 2026
https://github.com/vsapsai updated https://github.com/llvm/llvm-project/pull/221039
>From ca0d3577a12d3ff3a23377add7d02ad03add1fa9 Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at apple.com>
Date: Wed, 2 Sep 2026 23:52:33 -0700
Subject: [PATCH 1/8] [clang] Diagnose when spelled 'abi_tag' on namespace
doesn't match applied one.
'abi_tag' on a namespace means applying it to decls within this
namespace. You can reopen a namespace with the same name later. And in
this case clang uses 'abi_tag' from the canonical namespace decl, not
the attribute specified for this reopened namespace. This difference
between the spelled and applied 'abi_tag' can be unexpected and confusing.
Don't change the existing behavior but add a diagnostic notifying about
such mismatches.
---
clang/docs/ReleaseNotes.md | 5 ++
clang/include/clang/Basic/DiagnosticGroups.td | 2 +
.../clang/Basic/DiagnosticSemaKinds.td | 6 ++
clang/lib/Sema/SemaDecl.cpp | 61 ++++++++++++++-----
clang/lib/Sema/SemaDeclCXX.cpp | 3 +-
clang/test/SemaCXX/attr-abi-tag-syntax.cpp | 26 +++++++-
6 files changed, 85 insertions(+), 18 deletions(-)
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index a1f24a8caedae5..a5f8fb5a971f33 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -518,6 +518,11 @@ features cannot lower the translation-unit ABI level;
- Improve Clang diagnoses when unary `__imag` operator with non-complex type operand is used as lvalue. (GH222383)
+- Added `-Wabi-tag` to diagnose when the `abi_tag` attribute spelled on a
+ namespace declaration doesn't match the one actually applied, which is taken
+ from the first declaration of that namespace. The diagnostic is an error by
+ default and can be downgraded with `-Wno-error=abi-tag`.
+
### Improvements to Clang's time-trace
### Improvements to Coverage Mapping
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 1da7698944b24b..9435578145ddf2 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -1868,6 +1868,8 @@ def UnknownArgument : DiagGroup<"unknown-argument">;
def UnsupportedABI : DiagGroup<"unsupported-abi">;
+def IgnoredAbiTagAttr : DiagGroup<"abi-tag">;
+
// A warning group for warnings about code that clang accepts when
// compiling OpenCL C/C++ but which is not compatible with the SPIR(-V) spec.
def SpirCompat : DiagGroup<"spir-compat">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index fca68f292f6671..82911fa7a96019 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6492,6 +6492,12 @@ def err_redefinition_extern_inline : Error<
def warn_attr_abi_tag_namespace : Warning<
"'abi_tag' attribute on %select{non-inline|anonymous}0 namespace ignored">,
InGroup<IgnoredAttributes>;
+def warn_abi_tag_ignored_missing : Warning<
+ "absent 'abi_tag' attribute is ignored, applying 'abi_tag' %0">,
+ InGroup<IgnoredAbiTagAttr>, DefaultError;
+def warn_abi_tag_ignored_different : Warning<
+ "'abi_tag' %0 is ignored, applying %select{no 'abi_tag'|'abi_tag' %2}1">,
+ InGroup<IgnoredAbiTagAttr>, DefaultError;
def err_abi_tag_on_redeclaration : Error<
"cannot add 'abi_tag' attribute in a redeclaration">;
def err_new_abi_tag_on_redeclaration : Error<
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e52f99b4cd98db..9f6949d853f09a 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2961,11 +2961,13 @@ static bool mergeDeclAttribute(Sema &S, NamedDecl *D,
AA->getDeprecated(), AA->getObsoleted(), AA->getUnavailable(),
AA->getMessage(), AA->getStrict(), AA->getReplacement(), AMK,
AA->getPriority(), AA->getEnvironment(), InferredPlatformII);
- } else if (const auto *VA = dyn_cast<VisibilityAttr>(Attr))
- NewAttr = S.mergeVisibilityAttr(D, *VA, VA->getVisibility());
- else if (const auto *VA = dyn_cast<TypeVisibilityAttr>(Attr))
- NewAttr = S.mergeTypeVisibilityAttr(D, *VA, VA->getVisibility());
- else if (const auto *ImportA = dyn_cast<DLLImportAttr>(Attr))
+ } else if (const auto *VA = dyn_cast<VisibilityAttr>(Attr)) {
+ if (!isa<NamespaceDecl>(D))
+ NewAttr = S.mergeVisibilityAttr(D, *VA, VA->getVisibility());
+ } else if (const auto *VA = dyn_cast<TypeVisibilityAttr>(Attr)) {
+ if (!isa<NamespaceDecl>(D))
+ NewAttr = S.mergeTypeVisibilityAttr(D, *VA, VA->getVisibility());
+ } else if (const auto *ImportA = dyn_cast<DLLImportAttr>(Attr))
NewAttr = S.mergeDLLImportAttr(D, *ImportA);
else if (const auto *ExportA = dyn_cast<DLLExportAttr>(Attr))
NewAttr = S.mergeDLLExportAttr(D, *ExportA);
@@ -3368,20 +3370,47 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
}
}
- // Re-declaration cannot add abi_tag's.
- if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
- if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
- for (const auto &NewTag : NewAbiTagAttr->tags()) {
- if (!llvm::is_contained(OldAbiTagAttr->tags(), NewTag)) {
- Diag(NewAbiTagAttr->getLocation(),
- diag::err_new_abi_tag_on_redeclaration)
- << NewTag;
+ if (isa<NamespaceDecl>(New)) {
+ Decl *ComparedOld = Old->getCanonicalDecl();
+ if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
+ if (const auto *OldAbiTagAttr = ComparedOld->getAttr<AbiTagAttr>()) {
+ bool Diff = NewAbiTagAttr->tags_size() != OldAbiTagAttr->tags_size();
+ if (!Diff)
+ Diff = !llvm::all_of(NewAbiTagAttr->tags(), [OldAbiTagAttr](StringRef NewTag) {
+ return llvm::is_contained(OldAbiTagAttr->tags(), NewTag);
+ });
+ if (Diff) {
+ Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different) << llvm::join(NewAbiTagAttr->tags(), ", ") << true << llvm::join(OldAbiTagAttr->tags(), ", ");
Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
+ } else {
+ Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different) << llvm::join(NewAbiTagAttr->tags(), ", ") << false;
+ Diag(ComparedOld->getLocation(), diag::note_previous_declaration);
+ }
+ } else if (const auto *OldAbiTagAttr = ComparedOld->getAttr<AbiTagAttr>()) {
+ Diag(New->getLocation(), diag::warn_abi_tag_ignored_missing) << llvm::join(OldAbiTagAttr->tags(), ", ");
+ Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
+ }
+ } else {
+ // Re-declaration cannot add abi_tag's.
+ if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
+ if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
+ for (const auto &NewTag : NewAbiTagAttr->tags()) {
+ if (!llvm::is_contained(OldAbiTagAttr->tags(), NewTag)) {
+ if (isa<NamespaceDecl>(New)) {
+ Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different) << NewTag << true << llvm::join(OldAbiTagAttr->tags(), ", ");
+ } else {
+ Diag(NewAbiTagAttr->getLocation(),
+ diag::err_new_abi_tag_on_redeclaration)
+ << NewTag;
+ }
+ Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
+ }
+ }
+ } else {
+ Diag(NewAbiTagAttr->getLocation(), diag::err_abi_tag_on_redeclaration);
+ Diag(Old->getLocation(), diag::note_previous_declaration);
}
- } else {
- Diag(NewAbiTagAttr->getLocation(), diag::err_abi_tag_on_redeclaration);
- Diag(Old->getLocation(), diag::note_previous_declaration);
}
}
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 3639640f2886ab..e0c70ff07f447c 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -12102,9 +12102,10 @@ Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
AddPragmaAttributes(DeclRegionScope, Namespc);
ProcessAPINotes(Namespc);
- // FIXME: Should we be merging attributes?
if (const VisibilityAttr *Attr = Namespc->getAttr<VisibilityAttr>())
PushNamespaceVisibilityAttr(Attr, Loc);
+ if (PrevNS)
+ mergeDeclAttributes(Namespc, PrevNS);
if (IsStd)
StdNamespace = Namespc;
diff --git a/clang/test/SemaCXX/attr-abi-tag-syntax.cpp b/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
index 4f14a3c043b5cf..2ed24c83cc0b4b 100644
--- a/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
+++ b/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
@@ -17,7 +17,31 @@ inline namespace __attribute__((__abi_tag__)) {}
inline namespace N __attribute__((__abi_tag__)) {}
-} // namespcace N2
+} // namespace N2
+
+namespace N3 {
+inline namespace AbsentOld {}
+inline namespace AbsentOld __attribute__((__abi_tag__)) {}
+// expected-error at -1 {{'abi_tag' AbsentOld is ignored, applying no 'abi_tag'}}
+// expected-note at -3 {{previous declaration is here}}
+
+inline namespace AbsentNew __attribute__((__abi_tag__)) {}
+inline namespace AbsentNew {}
+// expected-error at -1 {{absent 'abi_tag' attribute is ignored, applying 'abi_tag' AbsentNew}}
+// expected-note at -3 {{previous declaration is here}}
+
+inline namespace Different __attribute__((abi_tag("A"))) {}
+inline namespace Different __attribute__((abi_tag("B"))) {}
+// expected-error at -1 {{'abi_tag' B is ignored, applying 'abi_tag' A}}
+// expected-note at -3 {{previous declaration is here}}
+inline namespace Different __attribute__((abi_tag("A"))) {}
+// No error as we compare with the canonical namespace decl, not with the previous one.
+
+inline namespace MultipleTags __attribute__((abi_tag("A", "B"))) {}
+inline namespace MultipleTags __attribute__((abi_tag("X", "Y", "B"))) {}
+// expected-error at -1 {{'abi_tag' B, X, Y is ignored, applying 'abi_tag' A, B}}
+// expected-note at -3 {{previous declaration is here}}
+} // namespace N3
__attribute__((abi_tag("B", "A"))) extern int a1;
>From b2df4615cdf6dd60d2f7a7fa5561b44d118ab227 Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at apple.com>
Date: Thu, 3 Sep 2026 13:33:59 -0700
Subject: [PATCH 2/8] Fix formatting.
---
clang/lib/Sema/SemaDecl.cpp | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 9f6949d853f09a..93a2b11a9e3dc1 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3376,19 +3376,25 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
if (const auto *OldAbiTagAttr = ComparedOld->getAttr<AbiTagAttr>()) {
bool Diff = NewAbiTagAttr->tags_size() != OldAbiTagAttr->tags_size();
if (!Diff)
- Diff = !llvm::all_of(NewAbiTagAttr->tags(), [OldAbiTagAttr](StringRef NewTag) {
- return llvm::is_contained(OldAbiTagAttr->tags(), NewTag);
- });
+ Diff = !llvm::all_of(
+ NewAbiTagAttr->tags(), [OldAbiTagAttr](StringRef NewTag) {
+ return llvm::is_contained(OldAbiTagAttr->tags(), NewTag);
+ });
if (Diff) {
- Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different) << llvm::join(NewAbiTagAttr->tags(), ", ") << true << llvm::join(OldAbiTagAttr->tags(), ", ");
+ Diag(NewAbiTagAttr->getLocation(),
+ diag::warn_abi_tag_ignored_different)
+ << llvm::join(NewAbiTagAttr->tags(), ", ") << true
+ << llvm::join(OldAbiTagAttr->tags(), ", ");
Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
} else {
- Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different) << llvm::join(NewAbiTagAttr->tags(), ", ") << false;
+ Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different)
+ << llvm::join(NewAbiTagAttr->tags(), ", ") << false;
Diag(ComparedOld->getLocation(), diag::note_previous_declaration);
}
} else if (const auto *OldAbiTagAttr = ComparedOld->getAttr<AbiTagAttr>()) {
- Diag(New->getLocation(), diag::warn_abi_tag_ignored_missing) << llvm::join(OldAbiTagAttr->tags(), ", ");
+ Diag(New->getLocation(), diag::warn_abi_tag_ignored_missing)
+ << llvm::join(OldAbiTagAttr->tags(), ", ");
Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
} else {
@@ -3398,11 +3404,13 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
for (const auto &NewTag : NewAbiTagAttr->tags()) {
if (!llvm::is_contained(OldAbiTagAttr->tags(), NewTag)) {
if (isa<NamespaceDecl>(New)) {
- Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different) << NewTag << true << llvm::join(OldAbiTagAttr->tags(), ", ");
+ Diag(NewAbiTagAttr->getLocation(),
+ diag::warn_abi_tag_ignored_different)
+ << NewTag << true << llvm::join(OldAbiTagAttr->tags(), ", ");
} else {
Diag(NewAbiTagAttr->getLocation(),
diag::err_new_abi_tag_on_redeclaration)
- << NewTag;
+ << NewTag;
}
Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
>From 323ec0b41afe9c6cc931ded69b1fe8971b30edfa Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at apple.com>
Date: Mon, 28 Sep 2026 15:21:04 -0700
Subject: [PATCH 3/8] Address review comments.
---
clang/include/clang/Basic/AttrDocs.td | 9 ++++++
clang/include/clang/Basic/DiagnosticGroups.td | 2 +-
.../clang/Basic/DiagnosticSemaKinds.td | 7 ++---
clang/lib/Sema/SemaDecl.cpp | 30 +++++++------------
clang/test/SemaCXX/attr-abi-tag-syntax.cpp | 15 +++++-----
5 files changed, 29 insertions(+), 34 deletions(-)
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
index 0a8977d3c6b14f..b2bc8ace9ca5ae 100644
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -6917,6 +6917,15 @@ could have a different set of data members and thus have a different size. Using
the `abi_tag` attribute, it is possible to have different mangled names for
a global variable of the class type. Therefore, the old code could keep using
the old mangled name and the new code will use the new mangled name with tags.
+
+On an inline namespace, the attribute does not change the namespace's mangled
+name. Instead, the tags are added to functions and variables whose type refers
+to an entity of that namespace, unless the tags already appear in the mangled
+name. As in GCC, the attribute is not limited to the namespace where it is
+written but affects subsequent reopenings. Specifying different tags on a
+reopening can make Clang and GCC produce different mangled names. So, for
+portability, it is recommended to use the same `abi_tag` on each namespace
+reopening.
}];
}
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 9435578145ddf2..136cadc9798245 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -1868,7 +1868,7 @@ def UnknownArgument : DiagGroup<"unknown-argument">;
def UnsupportedABI : DiagGroup<"unsupported-abi">;
-def IgnoredAbiTagAttr : DiagGroup<"abi-tag">;
+def IgnoredAbiTagAttr : DiagGroup<"abi-tag-redeclaration">;
// A warning group for warnings about code that clang accepts when
// compiling OpenCL C/C++ but which is not compatible with the SPIR(-V) spec.
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 903d8310ed8650..dedc1d5cea3c2a 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6486,12 +6486,9 @@ def err_redefinition_extern_inline : Error<
def warn_attr_abi_tag_namespace : Warning<
"'abi_tag' attribute on %select{non-inline|anonymous}0 namespace ignored">,
InGroup<IgnoredAttributes>;
-def warn_abi_tag_ignored_missing : Warning<
- "absent 'abi_tag' attribute is ignored, applying 'abi_tag' %0">,
- InGroup<IgnoredAbiTagAttr>, DefaultError;
def warn_abi_tag_ignored_different : Warning<
- "'abi_tag' %0 is ignored, applying %select{no 'abi_tag'|'abi_tag' %2}1">,
- InGroup<IgnoredAbiTagAttr>, DefaultError;
+ "%select{no 'abi_tag'|'abi_tag' %1}0 prevents applying 'abi_tag' %2 later">,
+ InGroup<IgnoredAbiTagAttr>;
def err_abi_tag_on_redeclaration : Error<
"cannot add 'abi_tag' attribute in a redeclaration">;
def err_new_abi_tag_on_redeclaration : Error<
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 11de40ef15d740..4b6985e210394b 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3381,21 +3381,17 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
return llvm::is_contained(OldAbiTagAttr->tags(), NewTag);
});
if (Diff) {
- Diag(NewAbiTagAttr->getLocation(),
+ Diag(OldAbiTagAttr->getLocation(),
diag::warn_abi_tag_ignored_different)
- << llvm::join(NewAbiTagAttr->tags(), ", ") << true
- << llvm::join(OldAbiTagAttr->tags(), ", ");
- Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
+ << true << llvm::join(OldAbiTagAttr->tags(), ", ")
+ << llvm::join(NewAbiTagAttr->tags(), ", ");
+ Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
}
} else {
- Diag(NewAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored_different)
- << llvm::join(NewAbiTagAttr->tags(), ", ") << false;
- Diag(ComparedOld->getLocation(), diag::note_previous_declaration);
+ Diag(ComparedOld->getLocation(), diag::warn_abi_tag_ignored_different)
+ << false << "" << llvm::join(NewAbiTagAttr->tags(), ", ");
+ Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
}
- } else if (const auto *OldAbiTagAttr = ComparedOld->getAttr<AbiTagAttr>()) {
- Diag(New->getLocation(), diag::warn_abi_tag_ignored_missing)
- << llvm::join(OldAbiTagAttr->tags(), ", ");
- Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
} else {
// Re-declaration cannot add abi_tag's.
@@ -3403,15 +3399,9 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
for (const auto &NewTag : NewAbiTagAttr->tags()) {
if (!llvm::is_contained(OldAbiTagAttr->tags(), NewTag)) {
- if (isa<NamespaceDecl>(New)) {
- Diag(NewAbiTagAttr->getLocation(),
- diag::warn_abi_tag_ignored_different)
- << NewTag << true << llvm::join(OldAbiTagAttr->tags(), ", ");
- } else {
- Diag(NewAbiTagAttr->getLocation(),
- diag::err_new_abi_tag_on_redeclaration)
- << NewTag;
- }
+ Diag(NewAbiTagAttr->getLocation(),
+ diag::err_new_abi_tag_on_redeclaration)
+ << NewTag;
Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
}
diff --git a/clang/test/SemaCXX/attr-abi-tag-syntax.cpp b/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
index 2ed24c83cc0b4b..1bf20f4d8cbed2 100644
--- a/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
+++ b/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
@@ -22,25 +22,24 @@ inline namespace N __attribute__((__abi_tag__)) {}
namespace N3 {
inline namespace AbsentOld {}
inline namespace AbsentOld __attribute__((__abi_tag__)) {}
-// expected-error at -1 {{'abi_tag' AbsentOld is ignored, applying no 'abi_tag'}}
-// expected-note at -3 {{previous declaration is here}}
+// expected-warning at -2 {{no 'abi_tag' prevents applying 'abi_tag' AbsentOld later}}
+// expected-note at -2 {{declared here}}
inline namespace AbsentNew __attribute__((__abi_tag__)) {}
inline namespace AbsentNew {}
-// expected-error at -1 {{absent 'abi_tag' attribute is ignored, applying 'abi_tag' AbsentNew}}
-// expected-note at -3 {{previous declaration is here}}
+// No tags on a namespace reopening can be deliberate, no diagnostic.
inline namespace Different __attribute__((abi_tag("A"))) {}
inline namespace Different __attribute__((abi_tag("B"))) {}
-// expected-error at -1 {{'abi_tag' B is ignored, applying 'abi_tag' A}}
-// expected-note at -3 {{previous declaration is here}}
+// expected-warning at -2 {{'abi_tag' A prevents applying 'abi_tag' B later}}
+// expected-note at -2 {{declared here}}
inline namespace Different __attribute__((abi_tag("A"))) {}
// No error as we compare with the canonical namespace decl, not with the previous one.
inline namespace MultipleTags __attribute__((abi_tag("A", "B"))) {}
inline namespace MultipleTags __attribute__((abi_tag("X", "Y", "B"))) {}
-// expected-error at -1 {{'abi_tag' B, X, Y is ignored, applying 'abi_tag' A, B}}
-// expected-note at -3 {{previous declaration is here}}
+// expected-warning at -2 {{'abi_tag' A, B prevents applying 'abi_tag' B, X, Y later}}
+// expected-note at -2 {{declared here}}
} // namespace N3
__attribute__((abi_tag("B", "A"))) extern int a1;
>From 2bed60a85f2103a7af980ac5f6ba954401916bfb Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at apple.com>
Date: Tue, 29 Sep 2026 09:30:51 -0700
Subject: [PATCH 4/8] Update release notes to reflect the latest code changes.
---
clang/docs/ReleaseNotes.md | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/clang/docs/ReleaseNotes.md b/clang/docs/ReleaseNotes.md
index 5766f764dc788b..ea78dd918b2b77 100644
--- a/clang/docs/ReleaseNotes.md
+++ b/clang/docs/ReleaseNotes.md
@@ -524,10 +524,8 @@ features cannot lower the translation-unit ABI level;
- Improve Clang diagnoses when unary `__imag` operator with non-complex type operand is used as lvalue. (GH222383)
-- Added `-Wabi-tag` to diagnose when the `abi_tag` attribute spelled on a
- namespace declaration doesn't match the one actually applied, which is taken
- from the first declaration of that namespace. The diagnostic is an error by
- default and can be downgraded with `-Wno-error=abi-tag`.
+- Added `-Wabi-tag-redeclaration` to diagnose when a forward namespace
+ declaration prevents applying `abi_tag` later on namespace reopening.
### Improvements to Clang's time-trace
>From 1d53da161003817111ea14925b4f99ff25bf242d Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at gmail.com>
Date: Thu, 1 Oct 2026 10:30:50 -0700
Subject: [PATCH 5/8] Update clang/include/clang/Basic/DiagnosticSemaKinds.td
Co-authored-by: Aaron Ballman <aaron at aaronballman.com>
---
clang/include/clang/Basic/DiagnosticSemaKinds.td | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index dedc1d5cea3c2a..95fb464cb96e62 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6488,7 +6488,7 @@ def warn_attr_abi_tag_namespace : Warning<
InGroup<IgnoredAttributes>;
def warn_abi_tag_ignored_different : Warning<
"%select{no 'abi_tag'|'abi_tag' %1}0 prevents applying 'abi_tag' %2 later">,
- InGroup<IgnoredAbiTagAttr>;
+ InGroup<DiagGroup<"abi-tag-redeclaration">>;
def err_abi_tag_on_redeclaration : Error<
"cannot add 'abi_tag' attribute in a redeclaration">;
def err_new_abi_tag_on_redeclaration : Error<
>From cd3bfeb6819bc91ebdeea5d87888fab93796fc23 Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at gmail.com>
Date: Thu, 1 Oct 2026 10:33:46 -0700
Subject: [PATCH 6/8] Update clang/include/clang/Basic/DiagnosticSemaKinds.td
Co-authored-by: Aaron Ballman <aaron at aaronballman.com>
---
clang/include/clang/Basic/DiagnosticSemaKinds.td | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 95fb464cb96e62..08dfa6575b7e82 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6487,7 +6487,7 @@ def warn_attr_abi_tag_namespace : Warning<
"'abi_tag' attribute on %select{non-inline|anonymous}0 namespace ignored">,
InGroup<IgnoredAttributes>;
def warn_abi_tag_ignored_different : Warning<
- "%select{no 'abi_tag'|'abi_tag' %1}0 prevents applying 'abi_tag' %2 later">,
+ "%select{no 'abi_tag'|'abi_tag(\"%1\")'}0 prevents applying 'abi_tag(\"%2\")' later">,
InGroup<DiagGroup<"abi-tag-redeclaration">>;
def err_abi_tag_on_redeclaration : Error<
"cannot add 'abi_tag' attribute in a redeclaration">;
>From ddb0f22c7588b0f6c10c442ba9806fe776ffe744 Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at apple.com>
Date: Thu, 1 Oct 2026 11:29:17 -0700
Subject: [PATCH 7/8] Address review comments, don't merge namespace
attributes.
---
clang/include/clang/Basic/DiagnosticGroups.td | 2 -
.../clang/Basic/DiagnosticSemaKinds.td | 2 +-
clang/lib/Sema/SemaDecl.cpp | 61 ++++++-------------
clang/lib/Sema/SemaDeclCXX.cpp | 28 ++++++++-
clang/test/SemaCXX/attr-abi-tag-syntax.cpp | 9 ++-
5 files changed, 50 insertions(+), 52 deletions(-)
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 136cadc9798245..1da7698944b24b 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -1868,8 +1868,6 @@ def UnknownArgument : DiagGroup<"unknown-argument">;
def UnsupportedABI : DiagGroup<"unsupported-abi">;
-def IgnoredAbiTagAttr : DiagGroup<"abi-tag-redeclaration">;
-
// A warning group for warnings about code that clang accepts when
// compiling OpenCL C/C++ but which is not compatible with the SPIR(-V) spec.
def SpirCompat : DiagGroup<"spir-compat">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 08dfa6575b7e82..c4686ae01f83f6 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6486,7 +6486,7 @@ def err_redefinition_extern_inline : Error<
def warn_attr_abi_tag_namespace : Warning<
"'abi_tag' attribute on %select{non-inline|anonymous}0 namespace ignored">,
InGroup<IgnoredAttributes>;
-def warn_abi_tag_ignored_different : Warning<
+def warn_abi_tag_ignored : Warning<
"%select{no 'abi_tag'|'abi_tag(\"%1\")'}0 prevents applying 'abi_tag(\"%2\")' later">,
InGroup<DiagGroup<"abi-tag-redeclaration">>;
def err_abi_tag_on_redeclaration : Error<
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 4b6985e210394b..db5e66cb96c3ec 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -2961,13 +2961,11 @@ static bool mergeDeclAttribute(Sema &S, NamedDecl *D,
AA->getDeprecated(), AA->getObsoleted(), AA->getUnavailable(),
AA->getMessage(), AA->getStrict(), AA->getReplacement(), AMK,
AA->getPriority(), AA->getEnvironment(), InferredPlatformII);
- } else if (const auto *VA = dyn_cast<VisibilityAttr>(Attr)) {
- if (!isa<NamespaceDecl>(D))
- NewAttr = S.mergeVisibilityAttr(D, *VA, VA->getVisibility());
- } else if (const auto *VA = dyn_cast<TypeVisibilityAttr>(Attr)) {
- if (!isa<NamespaceDecl>(D))
- NewAttr = S.mergeTypeVisibilityAttr(D, *VA, VA->getVisibility());
- } else if (const auto *ImportA = dyn_cast<DLLImportAttr>(Attr))
+ } else if (const auto *VA = dyn_cast<VisibilityAttr>(Attr))
+ NewAttr = S.mergeVisibilityAttr(D, *VA, VA->getVisibility());
+ else if (const auto *VA = dyn_cast<TypeVisibilityAttr>(Attr))
+ NewAttr = S.mergeTypeVisibilityAttr(D, *VA, VA->getVisibility());
+ else if (const auto *ImportA = dyn_cast<DLLImportAttr>(Attr))
NewAttr = S.mergeDLLImportAttr(D, *ImportA);
else if (const auto *ExportA = dyn_cast<DLLExportAttr>(Attr))
NewAttr = S.mergeDLLExportAttr(D, *ExportA);
@@ -3370,45 +3368,20 @@ void Sema::mergeDeclAttributes(NamedDecl *New, Decl *Old,
}
}
- if (isa<NamespaceDecl>(New)) {
- Decl *ComparedOld = Old->getCanonicalDecl();
- if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
- if (const auto *OldAbiTagAttr = ComparedOld->getAttr<AbiTagAttr>()) {
- bool Diff = NewAbiTagAttr->tags_size() != OldAbiTagAttr->tags_size();
- if (!Diff)
- Diff = !llvm::all_of(
- NewAbiTagAttr->tags(), [OldAbiTagAttr](StringRef NewTag) {
- return llvm::is_contained(OldAbiTagAttr->tags(), NewTag);
- });
- if (Diff) {
- Diag(OldAbiTagAttr->getLocation(),
- diag::warn_abi_tag_ignored_different)
- << true << llvm::join(OldAbiTagAttr->tags(), ", ")
- << llvm::join(NewAbiTagAttr->tags(), ", ");
- Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
+ // Re-declaration cannot add abi_tag's.
+ if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
+ if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
+ for (const auto &NewTag : NewAbiTagAttr->tags()) {
+ if (!llvm::is_contained(OldAbiTagAttr->tags(), NewTag)) {
+ Diag(NewAbiTagAttr->getLocation(),
+ diag::err_new_abi_tag_on_redeclaration)
+ << NewTag;
+ Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
}
- } else {
- Diag(ComparedOld->getLocation(), diag::warn_abi_tag_ignored_different)
- << false << "" << llvm::join(NewAbiTagAttr->tags(), ", ");
- Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
- }
- }
- } else {
- // Re-declaration cannot add abi_tag's.
- if (const auto *NewAbiTagAttr = New->getAttr<AbiTagAttr>()) {
- if (const auto *OldAbiTagAttr = Old->getAttr<AbiTagAttr>()) {
- for (const auto &NewTag : NewAbiTagAttr->tags()) {
- if (!llvm::is_contained(OldAbiTagAttr->tags(), NewTag)) {
- Diag(NewAbiTagAttr->getLocation(),
- diag::err_new_abi_tag_on_redeclaration)
- << NewTag;
- Diag(OldAbiTagAttr->getLocation(), diag::note_previous_declaration);
- }
- }
- } else {
- Diag(NewAbiTagAttr->getLocation(), diag::err_abi_tag_on_redeclaration);
- Diag(Old->getLocation(), diag::note_previous_declaration);
}
+ } else {
+ Diag(NewAbiTagAttr->getLocation(), diag::err_abi_tag_on_redeclaration);
+ Diag(Old->getLocation(), diag::note_previous_declaration);
}
}
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index f1ffdcef920b4c..9c3c530e9a86dd 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -12106,10 +12106,34 @@ Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
AddPragmaAttributes(DeclRegionScope, Namespc);
ProcessAPINotes(Namespc);
+ // FIXME: Should we be merging attributes?
if (const VisibilityAttr *Attr = Namespc->getAttr<VisibilityAttr>())
PushNamespaceVisibilityAttr(Attr, Loc);
- if (PrevNS)
- mergeDeclAttributes(Namespc, PrevNS);
+ if (Decl *PrevTagD = Namespc->getCanonicalDecl(); PrevTagD != Namespc) {
+ auto PrintableTags = [](ArrayRef<StringRef> Tags) {
+ return llvm::join(Tags, R"(", ")");
+ };
+ if (const auto *NewAbiTagAttr = Namespc->getAttr<AbiTagAttr>()) {
+ if (const auto *OldAbiTagAttr = PrevTagD->getAttr<AbiTagAttr>()) {
+ SmallVector<StringRef, 4> ExtraTags;
+ llvm::copy_if(NewAbiTagAttr->tags(), std::back_inserter(ExtraTags),
+ [OldAbiTagAttr](StringRef NewTag) {
+ return !llvm::is_contained(OldAbiTagAttr->tags(),
+ NewTag);
+ });
+ if (!ExtraTags.empty()) {
+ Diag(OldAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored)
+ << true << PrintableTags(OldAbiTagAttr->tags())
+ << PrintableTags(ExtraTags);
+ Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
+ }
+ } else {
+ Diag(PrevTagD->getLocation(), diag::warn_abi_tag_ignored)
+ << false << "" << PrintableTags(NewAbiTagAttr->tags());
+ Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
+ }
+ }
+ }
if (IsStd)
StdNamespace = Namespc;
diff --git a/clang/test/SemaCXX/attr-abi-tag-syntax.cpp b/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
index 1bf20f4d8cbed2..d0de37c1efde1d 100644
--- a/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
+++ b/clang/test/SemaCXX/attr-abi-tag-syntax.cpp
@@ -22,7 +22,7 @@ inline namespace N __attribute__((__abi_tag__)) {}
namespace N3 {
inline namespace AbsentOld {}
inline namespace AbsentOld __attribute__((__abi_tag__)) {}
-// expected-warning at -2 {{no 'abi_tag' prevents applying 'abi_tag' AbsentOld later}}
+// expected-warning at -2 {{no 'abi_tag' prevents applying 'abi_tag("AbsentOld")' later}}
// expected-note at -2 {{declared here}}
inline namespace AbsentNew __attribute__((__abi_tag__)) {}
@@ -31,15 +31,18 @@ inline namespace AbsentNew {}
inline namespace Different __attribute__((abi_tag("A"))) {}
inline namespace Different __attribute__((abi_tag("B"))) {}
-// expected-warning at -2 {{'abi_tag' A prevents applying 'abi_tag' B later}}
+// expected-warning at -2 {{'abi_tag("A")' prevents applying 'abi_tag("B")' later}}
// expected-note at -2 {{declared here}}
inline namespace Different __attribute__((abi_tag("A"))) {}
// No error as we compare with the canonical namespace decl, not with the previous one.
inline namespace MultipleTags __attribute__((abi_tag("A", "B"))) {}
inline namespace MultipleTags __attribute__((abi_tag("X", "Y", "B"))) {}
-// expected-warning at -2 {{'abi_tag' A, B prevents applying 'abi_tag' B, X, Y later}}
+// expected-warning at -2 {{'abi_tag("A", "B")' prevents applying 'abi_tag("X", "Y")' later}}
// expected-note at -2 {{declared here}}
+inline namespace MultipleTagsSubset __attribute__((abi_tag("A", "B"))) {}
+inline namespace MultipleTagsSubset __attribute__((abi_tag("A"))) {}
+// No diagnostic as tag "A" *is* applied.
} // namespace N3
__attribute__((abi_tag("B", "A"))) extern int a1;
>From c860d990967a32a92f456bc2139e975b534faa31 Mon Sep 17 00:00:00 2001
From: Volodymyr Sapsai <vsapsai at apple.com>
Date: Fri, 9 Oct 2026 15:54:03 -0700
Subject: [PATCH 8/8] Move ABI tag diagnostics to a separate function.
---
clang/lib/Sema/SemaDeclCXX.cpp | 56 +++++++++++++++++++---------------
1 file changed, 31 insertions(+), 25 deletions(-)
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index f2ef8fe678c274..5087836eae6141 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -12000,6 +12000,35 @@ static void DiagnoseNamespaceInlineMismatch(Sema &S, SourceLocation KeywordLoc,
*IsInline = PrevNS->isInline();
}
+/// Diagnose 'abi_tag' on a namespace rejecting a different tag on a subsequent
+/// namespace re-opening.
+static void DiagnoseNamespaceABITagMismatch(Sema &S, const Decl *NewD,
+ const Decl *OldD) {
+ assert(NewD != OldD);
+ auto PrintableTags = [](ArrayRef<StringRef> Tags) {
+ return llvm::join(Tags, R"(", ")");
+ };
+ if (const auto *NewAbiTagAttr = NewD->getAttr<AbiTagAttr>()) {
+ if (const auto *OldAbiTagAttr = OldD->getAttr<AbiTagAttr>()) {
+ SmallVector<StringRef, 4> ExtraTags;
+ llvm::copy_if(NewAbiTagAttr->tags(), std::back_inserter(ExtraTags),
+ [OldAbiTagAttr](StringRef NewTag) {
+ return !llvm::is_contained(OldAbiTagAttr->tags(), NewTag);
+ });
+ if (!ExtraTags.empty()) {
+ S.Diag(OldAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored)
+ << true << PrintableTags(OldAbiTagAttr->tags())
+ << PrintableTags(ExtraTags);
+ S.Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
+ }
+ } else {
+ S.Diag(OldD->getLocation(), diag::warn_abi_tag_ignored)
+ << false << "" << PrintableTags(NewAbiTagAttr->tags());
+ S.Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
+ }
+ }
+}
+
/// ActOnStartNamespaceDef - This is called at the start of a namespace
/// definition.
Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
@@ -12109,31 +12138,8 @@ Decl *Sema::ActOnStartNamespaceDef(Scope *NamespcScope,
// FIXME: Should we be merging attributes?
if (const VisibilityAttr *Attr = Namespc->getAttr<VisibilityAttr>())
PushNamespaceVisibilityAttr(Attr, Loc);
- if (Decl *PrevTagD = Namespc->getCanonicalDecl(); PrevTagD != Namespc) {
- auto PrintableTags = [](ArrayRef<StringRef> Tags) {
- return llvm::join(Tags, R"(", ")");
- };
- if (const auto *NewAbiTagAttr = Namespc->getAttr<AbiTagAttr>()) {
- if (const auto *OldAbiTagAttr = PrevTagD->getAttr<AbiTagAttr>()) {
- SmallVector<StringRef, 4> ExtraTags;
- llvm::copy_if(NewAbiTagAttr->tags(), std::back_inserter(ExtraTags),
- [OldAbiTagAttr](StringRef NewTag) {
- return !llvm::is_contained(OldAbiTagAttr->tags(),
- NewTag);
- });
- if (!ExtraTags.empty()) {
- Diag(OldAbiTagAttr->getLocation(), diag::warn_abi_tag_ignored)
- << true << PrintableTags(OldAbiTagAttr->tags())
- << PrintableTags(ExtraTags);
- Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
- }
- } else {
- Diag(PrevTagD->getLocation(), diag::warn_abi_tag_ignored)
- << false << "" << PrintableTags(NewAbiTagAttr->tags());
- Diag(NewAbiTagAttr->getLocation(), diag::note_declared_at);
- }
- }
- }
+ if (Decl *PrevTagDecl = Namespc->getCanonicalDecl(); PrevTagDecl != Namespc)
+ DiagnoseNamespaceABITagMismatch(*this, Namespc, PrevTagDecl);
if (IsStd)
StdNamespace = Namespc;
More information about the cfe-commits
mailing list