[clang] Fix isInStdNamespace for Decl flagged extern c++

[frederic-tingaud-sonarsource]

The MSVC STL implementation declares multiple classes using:

namespace std {
  extern "C++" class locale {
    ...
  };
}

isInStdNamespace uses the first DeclContext to check whether a Decl is inside the std namespace. Here, the first DeclContext of the locale Decl is a LinkageSpecDecl so the method will return false.
We need to skip this LinkageSpecDecl to find the first DeclContext of type Namespace and actually check whether we're in the std namespace.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Fred Tingaud (frederic-tingaud-sonarsource)

Changes

The MSVC STL implementation declares multiple classes using:

namespace std {
  extern "C++" class locale {
    ...
  };
}

isInStdNamespace uses the first DeclContext to check whether a Decl is inside the std namespace. Here, the first DeclContext of the locale Decl is a LinkageSpecDecl so the method will return false.
We need to skip this LinkageSpecDecl to find the first DeclContext of type Namespace and actually check whether we're in the std namespace.

---

Full diff: https://github.com/llvm/llvm-project/pull/81776.diff

2 Files Affected:

• (modified) clang/lib/AST/DeclBase.cpp (+3)
• (modified) clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp (+5)

diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index 8163f9bdaf8d97..4cfe9ed3340735 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -402,6 +402,9 @@ bool Decl::isInAnonymousNamespace() const {
 
 bool Decl::isInStdNamespace() const {
   const DeclContext *DC = getDeclContext();
+  while (auto const LD = dyn_cast_or_null<LinkageSpecDecl>(DC)) {
+    DC = LD->getDeclContext();
+  }
   return DC && DC->isStdNamespace();
 }
 
diff --git a/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp b/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
index edcdae4559d970..b75da7bc1ed069 100644
--- a/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
+++ b/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
@@ -3637,6 +3637,11 @@ TEST_P(ASTMatchersTest, InStdNamespace) {
                       "  class vector {};"
                       "}",
                       cxxRecordDecl(hasName("vector"), isInStdNamespace())));
+
+  EXPECT_TRUE(matches("namespace std {"
+                      "  extern \"C++\" class vector {};"
+                      "}",
+                      cxxRecordDecl(hasName("vector"), isInStdNamespace())));
 }
 
 TEST_P(ASTMatchersTest, InAnonymousNamespace) {

[cor3ntin]

Looks good.
Can you add an entry to clang/docs/ReleseNotes.rst?
There is an ast matchers section.

Thanks

[cor3ntin]

LGTM, thanks!

[cor3ntin]

Hum, should we use getNonTransparentContext instead? That would be cleaner

[frederic-tingaud-sonarsource]

Oh, I didn't know about this, but it does look better. Thanks!

[cor3ntin]

Thanks! Do you need me to merge this for you?

[frederic-tingaud-sonarsource]

Yes please :)