[Clang] show attribute namespace in diagnostics #138519

a-tarasyuk · 2025-05-05T12:36:17Z

This patch enhances Clang's diagnosis of an unknown attribute by printing the attribute's namespace in the diagnostic text. e.g.,

[[foo::nodiscard]] int f(); // warning: unknown attribute 'foo::nodiscard' ignored

llvmbot · 2025-05-05T12:36:55Z

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-modules

Author: Oleksandr T. (a-tarasyuk)

Changes

This patch enhances Clang's attribute handling by diagnosing unknown attribute namespaces

[[foo::nodiscard]] int f(); // warning: unknown attribute namespace 'unknown'; attribute 'unknown::foo' ignored

Full diff: https://github.com/llvm/llvm-project/pull/138519.diff

9 Files Affected:

(modified) clang/docs/ReleaseNotes.rst (+2)
(modified) clang/include/clang/Basic/AttributeCommonInfo.h (+3-1)
(modified) clang/include/clang/Basic/DiagnosticCommonKinds.td (+3)
(modified) clang/lib/Basic/Attributes.cpp (+8-1)
(modified) clang/lib/Sema/SemaDeclAttr.cpp (+12-7)
(modified) clang/test/CXX/module/module.interface/p3.cpp (+1-1)
(modified) clang/test/Parser/c2x-attributes.c (+1-1)
(modified) clang/test/Parser/cxx0x-attributes.cpp (+3-3)
(added) clang/test/Sema/unknown-attributes.c (+12)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index a80fedebf8f89..d01fc5d1bf46f 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -385,6 +385,8 @@ related warnings within the method body.
 - Clang now disallows the use of attributes applied before an
   ``extern template`` declaration (#GH79893).
 
+- Clang now diagnoses unknown attribute namespaces
+
 Improvements to Clang's diagnostics
 -----------------------------------
 
diff --git a/clang/include/clang/Basic/AttributeCommonInfo.h b/clang/include/clang/Basic/AttributeCommonInfo.h
index 4af5a8fd1852c..ddb022c493bdf 100644
--- a/clang/include/clang/Basic/AttributeCommonInfo.h
+++ b/clang/include/clang/Basic/AttributeCommonInfo.h
@@ -67,7 +67,7 @@ class AttributeCommonInfo {
     IgnoredAttribute,
     UnknownAttribute,
   };
-  enum class Scope { NONE, CLANG, GNU, MSVC, OMP, HLSL, GSL, RISCV };
+  enum class Scope { NONE, CLANG, GNU, MSVC, OMP, HLSL, GSL, RISCV, UNKNOWN };
   enum class AttrArgsInfo {
     None,
     Optional,
@@ -234,6 +234,8 @@ class AttributeCommonInfo {
     return SyntaxUsed == AS_ContextSensitiveKeyword;
   }
 
+  bool isUnknownScopeName() const;
+
   unsigned getAttributeSpellingListIndex() const {
     assert((isAttributeSpellingListCalculated() || AttrName) &&
            "Spelling cannot be found");
diff --git a/clang/include/clang/Basic/DiagnosticCommonKinds.td b/clang/include/clang/Basic/DiagnosticCommonKinds.td
index f26c906b46447..63f4c229b2e76 100644
--- a/clang/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/clang/include/clang/Basic/DiagnosticCommonKinds.td
@@ -177,6 +177,9 @@ def err_opencl_unknown_type_specifier : Error<
   "%0 does not support the '%1' "
   "%select{type qualifier|storage class specifier}2">;
 
+def warn_unknown_attribute_namespace : Warning<
+  "unknown attribute namespace '%0'; attribute '%0::%1' ignored">,
+  InGroup<UnknownAttributes>;
 def warn_unknown_attribute_ignored : Warning<
   "unknown attribute %0 ignored">, InGroup<UnknownAttributes>;
 def warn_attribute_ignored : Warning<"%0 attribute ignored">,
diff --git a/clang/lib/Basic/Attributes.cpp b/clang/lib/Basic/Attributes.cpp
index 6a070a99c8d96..c41cbf0fb61f6 100644
--- a/clang/lib/Basic/Attributes.cpp
+++ b/clang/lib/Basic/Attributes.cpp
@@ -191,7 +191,8 @@ getScopeFromNormalizedScopeName(StringRef ScopeName) {
       .Case("hlsl", AttributeCommonInfo::Scope::HLSL)
       .Case("msvc", AttributeCommonInfo::Scope::MSVC)
       .Case("omp", AttributeCommonInfo::Scope::OMP)
-      .Case("riscv", AttributeCommonInfo::Scope::RISCV);
+      .Case("riscv", AttributeCommonInfo::Scope::RISCV)
+      .Default(AttributeCommonInfo::Scope::UNKNOWN);
 }
 
 unsigned AttributeCommonInfo::calculateAttributeSpellingListIndex() const {
@@ -206,3 +207,9 @@ unsigned AttributeCommonInfo::calculateAttributeSpellingListIndex() const {
 
 #include "clang/Sema/AttrSpellingListIndex.inc"
 }
+
+bool AttributeCommonInfo::isUnknownScopeName() const {
+  return getScopeFromNormalizedScopeName(
+             normalizeAttrScopeName(getScopeName(), getSyntax())) ==
+         AttributeCommonInfo::Scope::UNKNOWN;
+}
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index bfb3ee9dcbd16..7dc5a04923946 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -6861,13 +6861,18 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
   // though they were unknown attributes.
   if (AL.getKind() == ParsedAttr::UnknownAttribute ||
       !AL.existsInTarget(S.Context.getTargetInfo())) {
-    S.Diag(AL.getLoc(),
-           AL.isRegularKeywordAttribute()
-               ? (unsigned)diag::err_keyword_not_supported_on_target
-           : AL.isDeclspecAttribute()
-               ? (unsigned)diag::warn_unhandled_ms_attribute_ignored
-               : (unsigned)diag::warn_unknown_attribute_ignored)
-        << AL << AL.getRange();
+    if (AL.isUnknownScopeName())
+      S.Diag(AL.getScopeLoc(), diag::warn_unknown_attribute_namespace)
+          << AL.getScopeName()->getName() << AL.getAttrName()->getName()
+          << SourceRange(AL.getScopeLoc(), AL.getRange().getEnd());
+    else
+      S.Diag(AL.getLoc(),
+             AL.isRegularKeywordAttribute()
+                 ? (unsigned)diag::err_keyword_not_supported_on_target
+             : AL.isDeclspecAttribute()
+                 ? (unsigned)diag::warn_unhandled_ms_attribute_ignored
+                 : (unsigned)diag::warn_unknown_attribute_ignored)
+          << AL << AL.getRange();
     return;
   }
 
diff --git a/clang/test/CXX/module/module.interface/p3.cpp b/clang/test/CXX/module/module.interface/p3.cpp
index 32819b2dccb11..18758edaf1be7 100644
--- a/clang/test/CXX/module/module.interface/p3.cpp
+++ b/clang/test/CXX/module/module.interface/p3.cpp
@@ -40,7 +40,7 @@ export { // No diagnostic after P2615R1 DR
   extern "C++" {} // No diagnostic after P2615R1 DR
 }
 export [[]]; // No diagnostic after P2615R1 DR
-export [[example::attr]]; // expected-warning {{unknown attribute 'attr'}}
+export [[example::attr]]; // expected-warning {{unknown attribute namespace 'example'; attribute 'example::attr' ignored}}
 
 // [...] shall not declare a name with internal linkage
 export static int a; // expected-error {{declaration of 'a' with internal linkage cannot be exported}}
diff --git a/clang/test/Parser/c2x-attributes.c b/clang/test/Parser/c2x-attributes.c
index be039e40f98ef..b5f502c5790d3 100644
--- a/clang/test/Parser/c2x-attributes.c
+++ b/clang/test/Parser/c2x-attributes.c
@@ -133,7 +133,7 @@ void f11(void) {
 }
 
 [[attr]] void f12(void); // expected-warning {{unknown attribute 'attr' ignored}}
-[[vendor::attr]] void f13(void); // expected-warning {{unknown attribute 'attr' ignored}}
+[[vendor::attr]] void f13(void); // expected-warning {{unknown attribute namespace 'vendor'; attribute 'vendor::attr' ignored}}
 
 // Ensure that asm statements properly handle double colons.
 void test_asm(void) {
diff --git a/clang/test/Parser/cxx0x-attributes.cpp b/clang/test/Parser/cxx0x-attributes.cpp
index fad3010c98b9c..7a0a8b989851f 100644
--- a/clang/test/Parser/cxx0x-attributes.cpp
+++ b/clang/test/Parser/cxx0x-attributes.cpp
@@ -46,7 +46,7 @@ int & [[noreturn]] ref_attr_3 = after_attr; // expected-error {{'noreturn' attri
 int && [[]] rref_attr = 0;
 int array_attr [1] [[]];
 alignas(8) int aligned_attr;
-[[test::valid(for 42 [very] **** '+' symbols went on a trip and had a "good"_time; the end.)]] int garbage_attr; // expected-warning {{unknown attribute 'valid' ignored}}
+[[test::valid(for 42 [very] **** '+' symbols went on a trip and had a "good"_time; the end.)]] int garbage_attr; // expected-warning {{unknown attribute namespace 'test'; attribute 'test::valid' ignored}}
 [[,,,static, class, namespace,, inline, constexpr, mutable,, bitand, bitor::compl(!.*_ Cx.!U^*R),,,]] int more_garbage_attr; // expected-warning {{unknown attribute 'static' ignored}} \
     // expected-warning {{unknown attribute 'class' ignored}} \
     // expected-warning {{unknown attribute 'namespace' ignored}} \
@@ -54,7 +54,7 @@ alignas(8) int aligned_attr;
     // expected-warning {{unknown attribute 'constexpr' ignored}} \
     // expected-warning {{unknown attribute 'mutable' ignored}} \
     // expected-warning {{unknown attribute 'bitand' ignored}} \
-    // expected-warning {{unknown attribute 'compl' ignored}}
+    // expected-warning {{unknown attribute namespace 'bitor'; attribute 'bitor::compl' ignored}}
 [[u8"invalid!"]] int invalid_string_attr; // expected-error {{expected ']'}}
 void fn_attr () [[]];
 void noexcept_fn_attr () noexcept [[]];
@@ -269,7 +269,7 @@ template <int... Is> void variadic_nttp() {
   void baz [[clang::no_sanitize(Is...)]] ();          // expected-error {{expected string literal as argument of 'no_sanitize' attribute}}
   void bor [[clang::annotate("A", "V" ...)]] ();      // expected-error {{pack expansion does not contain any unexpanded parameter packs}}
   void bir [[clang::annotate("B", {1, 2, 3, 4})]] (); // expected-error {{'annotate' attribute requires parameter 1 to be a constant expression}} expected-note {{subexpression not valid in a constant expression}}
-  void boo [[unknown::foo(Is...)]] ();                // expected-warning {{unknown attribute 'foo' ignored}}
+  void boo [[unknown::foo(Is...)]] ();                // expected-warning {{unknown attribute namespace 'unknown'; attribute 'unknown::foo' ignored}}
   void faz [[clang::annotate("C", (Is + ...))]] ();   // expected-warning {{pack fold expression is a C++17 extension}}
   void far [[clang::annotate("D", Is...)]] ();
   void foz [[clang::annotate("E", 1, 2, 3, Is...)]] ();
diff --git a/clang/test/Sema/unknown-attributes.c b/clang/test/Sema/unknown-attributes.c
new file mode 100644
index 0000000000000..833ac2f919ea6
--- /dev/null
+++ b/clang/test/Sema/unknown-attributes.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -Wunknown-attributes -fsyntax-only -verify %s
+// RUN: %clang_cc1 -x c++ -fsyntax-only -Wunknown-attributes -verify %s
+
+[[foo::a]] // expected-warning {{unknown attribute namespace 'foo'; attribute 'foo::a' ignored}}
+int f1(void) {
+  return 0;
+}
+
+[[clan::deprecated]] // expected-warning {{unknown attribute namespace 'clan'; attribute 'clan::deprecated' ignored}}
+int f2(void) {
+  return 0;
+}

erichkeane

I believe our feedback on the last one was to emit the namespace in all attribute ignored diagnostics, not just if we don't know the namespace. So unknown attribute clang::whatever as well?

Otherwise, I think this is a reasonable patch that makes this diagnostic somewhat more clear.

clang/docs/ReleaseNotes.rst

erichkeane

So I don't believe this is correct either. We want it to always say the namespace. So clang::unknown will diagnose as unknown attribute 'clang::unknown' ignored AFAIK. Right @AaronBallman ?

AaronBallman · 2025-05-05T16:34:17Z

So I don't believe this is correct either. We want it to always say the namespace. So clang::unknown will diagnose as unknown attribute 'clang::unknown' ignored AFAIK. Right @AaronBallman ?

I think what I'm seeing is correct, unless I'm missing something. Attributes without namespaces are printed as foo and attributes with namespaces are now being printed as bar::foo instead of foo.

clang/lib/Sema/SemaDeclAttr.cpp

…/unknown-attribute-namespaces

a-tarasyuk · 2025-05-06T21:57:40Z

So I don't believe this is correct either. We want it to always say the namespace. So clang::unknown will diagnose as unknown attribute 'clang::unknown' ignored

@erichkeane @AaronBallman Thanks for the feedback. I've made changes to include the scope in the diagnostic.

AaronBallman · 2025-05-07T11:26:28Z

I think the summary and title should be updated to something more like:

[Clang] Show attribute namespace in diagnostics

This patch enhances Clang's diagnosing of an unknown attribute by also printing the namespace of the attribute in the diagnostic text. e.g.,

[[foo::nodiscard]] int f(); // warning: unknown attribute 'foo::nodiscard' ignored

clang/test/OpenMP/openmp_attribute_parsing.cpp

clang/docs/ReleaseNotes.rst

clang/lib/Sema/SemaDeclAttr.cpp

AaronBallman

As far as the changes go, this LGTM. We can generalize in another PR (which will update some parts of this patch but not enough to be worried we're wasting effort).

clang/lib/Sema/SemaDeclAttr.cpp

a-tarasyuk requested review from AaronBallman and erichkeane May 5, 2025 12:36

llvmbot added clang Clang issues not falling into any other category clang:frontend Language frontend issues, e.g. anything involving "Sema" clang:modules C++20 modules and Clang Header Modules labels May 5, 2025

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a-tarasyuk requested review from AaronBallman and erichkeane May 5, 2025 18:53

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a-tarasyuk added 2 commits May 7, 2025 00:46

[Clang] diagnose unknown attribute namespaces

cbbca4d

Merge branch 'main' of https://github.com/llvm/llvm-project into feat…

8acf144

…/unknown-attribute-namespaces

a-tarasyuk force-pushed the feat/unknown-attribute-namespaces branch from 7835772 to 8acf144 Compare May 6, 2025 21:47

llvmbot added clang:modules C++20 modules and Clang Header Modules clang:openmp OpenMP related changes to Clang labels May 6, 2025

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update release notes

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llvmbot added clang:modules C++20 modules and Clang Header Modules clang:openmp OpenMP related changes to Clang labels May 7, 2025

a-tarasyuk changed the title ~~[Clang] diagnose unknown attribute namespaces~~ [Clang] show attribute namespace in diagnostics May 7, 2025

a-tarasyuk requested a review from AaronBallman May 7, 2025 12:02

a-tarasyuk removed clang:modules C++20 modules and Clang Header Modules clang:openmp OpenMP related changes to Clang labels May 7, 2025

AaronBallman approved these changes May 7, 2025

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Merge branch 'main' into feat/unknown-attribute-namespaces

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llvmbot added clang:modules C++20 modules and Clang Header Modules clang:openmp OpenMP related changes to Clang labels May 7, 2025

a-tarasyuk removed clang:modules C++20 modules and Clang Header Modules clang:openmp OpenMP related changes to Clang labels May 7, 2025

erichkeane approved these changes May 8, 2025

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a-tarasyuk merged commit 61b435e into llvm:main May 8, 2025
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