[Clang] show attribute namespace in diagnostics (llvm#138519)

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

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

Author: a-tarasyuk

clang/docs/ReleaseNotes.rst

@@ -506,6 +506,8 @@ Improvements to Clang's diagnostics
   behavior of the C99 feature as it was introduced into C++20. Fixes #GH47037
 - ``-Wreserved-identifier`` now fires on reserved parameter names in a function
   declaration which is not a definition.
+- Clang now prints the namespace for an attribute, if any,
+  when emitting an unknown attribute diagnostic.
 
 - Several compatibility diagnostics that were incorrectly being grouped under
   ``-Wpre-c++20-compat`` are now part of ``-Wc++20-compat``. (#GH138775)

clang/include/clang/Basic/AttributeCommonInfo.h

@@ -196,6 +196,7 @@ class AttributeCommonInfo {
   /// with surrounding underscores removed as appropriate (e.g.
   /// __gnu__::__attr__ will be normalized to gnu::attr).
   std::string getNormalizedFullName() const;
+  SourceRange getNormalizedRange() const;
 
   bool isDeclspecAttribute() const { return SyntaxUsed == AS_Declspec; }
   bool isMicrosoftAttribute() const { return SyntaxUsed == AS_Microsoft; }

clang/lib/Basic/Attributes.cpp

@@ -181,6 +181,10 @@ std::string AttributeCommonInfo::getNormalizedFullName() const {
       normalizeName(getAttrName(), getScopeName(), getSyntax()));
 }
 
+SourceRange AttributeCommonInfo::getNormalizedRange() const {
+  return hasScope() ? SourceRange(ScopeLoc, AttrRange.getEnd()) : AttrRange;
+}
+
 static AttributeCommonInfo::Scope
 getScopeFromNormalizedScopeName(StringRef ScopeName) {
   return llvm::StringSwitch<AttributeCommonInfo::Scope>(ScopeName)

clang/lib/Sema/SemaDeclAttr.cpp

@@ -6862,13 +6862,16 @@ 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.isRegularKeywordAttribute() || AL.isDeclspecAttribute()) {
+      S.Diag(AL.getLoc(), AL.isRegularKeywordAttribute()
+                              ? diag::err_keyword_not_supported_on_target
+                              : diag::warn_unhandled_ms_attribute_ignored)
+          << AL.getAttrName() << AL.getRange();
+    } else {
+      S.Diag(AL.getNormalizedRange().getBegin(),
+             diag::warn_unknown_attribute_ignored)
+          << "'" + AL.getNormalizedFullName() + "'" << AL.getNormalizedRange();
+    }
     return;
   }
 

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 '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}}

clang/test/OpenMP/openmp_attribute_parsing.cpp

@@ -10,9 +10,9 @@
 // attribute name. So this means we never hit the omp-specific parsing and
 // instead handle this through the usual Sema attribute handling in
 // SemaDeclAttr.cpp, which diagnoses this as an unknown attribute.
-[[omp::directive]]; // expected-warning {{unknown attribute 'directive' ignored}}
-[[omp::sequence]]; // expected-warning {{unknown attribute 'sequence' ignored}}
-[[omp::unknown]]; // expected-warning {{unknown attribute 'unknown' ignored}}
+[[omp::directive]]; // expected-warning {{unknown attribute 'omp::directive' ignored}}
+[[omp::sequence]]; // expected-warning {{unknown attribute 'omp::sequence' ignored}}
+[[omp::unknown]]; // expected-warning {{unknown attribute 'omp::unknown' ignored}}
 
 [[omp::directive()]]; // expected-error {{expected an OpenMP directive}}
 [[omp::sequence()]]; // expected-error {{expected an OpenMP 'directive' or 'sequence' attribute argument}}
@@ -49,8 +49,8 @@
 
 // Test that we give a sensible error on an unknown attribute in the omp
 // namespace that has an argument list.
-[[omp::unknown()]]; // expected-warning {{unknown attribute 'unknown' ignored}}
-[[using omp: unknown()]]; // expected-warning {{unknown attribute 'unknown' ignored}}
+[[omp::unknown()]]; // expected-warning {{unknown attribute 'omp::unknown' ignored}}
+[[using omp: unknown()]]; // expected-warning {{unknown attribute 'omp::unknown' ignored}}
 
 // Test that unknown arguments to the omp::sequence are rejected, regardless of
 // what level they're at.

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 'vendor::attr' ignored}}
 
 // Ensure that asm statements properly handle double colons.
 void test_asm(void) {

clang/test/Parser/cxx0x-attributes.cpp

@@ -46,15 +46,15 @@ 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 '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}} \
     // expected-warning {{unknown attribute 'inline' ignored}} \
     // 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 '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 '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...)]] ();

clang/test/Sema/patchable-function-entry-attr.cpp

@@ -15,5 +15,5 @@
 // silence-no-diagnostics
 
 // AIX-error@+2 {{'patchable_function_entry' attribute is not yet supported on AIX}}
-// expected-warning@+1 {{unknown attribute 'patchable_function_entry' ignored}}
+// expected-warning@+1 {{unknown attribute 'gnu::patchable_function_entry' ignored}}
 [[gnu::patchable_function_entry(0)]] void f();

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 'foo::a' ignored}}
+int f1(void) {
+  return 0;
+}
+
+[[clan::deprecated]] // expected-warning {{unknown attribute 'clan::deprecated' ignored}}
+int f2(void) {
+  return 0;
+}