[ASTMatchers] HasNameMatcher handles `extern "C"`

[njames93]

Summary

Fixes hasName AST matcher is confused by extern "C" in namespace.

[aaron.ballman]

LGTM!

clang/lib/ASTMatchers/ASTMatchersInternal.cpp

518

I would imagine we'd want to skip an ExternCContextDecl for similar reasons, though I am struggling to find a test case that actually generates that context.

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

1648

As another test:

namespace foo {
extern "C" {
void test();
}
}

[njames93]

• Add extra test case

[njames93]

clang/lib/ASTMatchers/ASTMatchersInternal.cpp

518

I couldn't figure a way to generate one of those either. However if a context type that isnt found matched the assertions should go off and we can look into the issue again

clang/lib/ASTMatchers/ASTMatchersInternal.cpp

bool HasNameMatcher::matchesNodeFullFast(const NamedDecl &Node) const {
 
   // Try to match each declaration context.
   // We are allowed to skip anonymous and inline namespaces if they don't match.
   const DeclContext *Ctx = Node.getDeclContext();
 
   if (Ctx->isFunctionOrMethod())
     return Patterns.foundMatch(/*AllowFullyQualified=*/false);
 
-  for (; Ctx && isa<NamedDecl>(Ctx); Ctx = Ctx->getParent()) {
+  for (; Ctx; Ctx = Ctx->getParent()) {
+    // Linkage Spec can just be ignored
+    // FIXME: Any other DeclContext kinds that can be safely disregarded
+    if (isa<LinkageSpecDecl>(Ctx))
+      continue;
+    if (!isa<NamedDecl>(Ctx))
+      break;
     if (Patterns.foundMatch(/*AllowFullyQualified=*/false))
       return true;
 
     if (const auto *ND = dyn_cast<NamespaceDecl>(Ctx)) {
       // If it matches (or we can skip it), continue.
       if (Patterns.consumeNameSuffix(getNodeName(*ND, Scratch),
                                      /*CanSkip=*/ND->isAnonymousNamespace() ||
                                          ND->isInline()))

clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp

TEST(Matcher, HasNameSupportsFunctionScope) {
 
   EXPECT_TRUE(matches(code, fieldDecl(hasName("m"))));
   EXPECT_TRUE(matches(code, fieldDecl(hasName("S::m"))));
   EXPECT_TRUE(matches(code, fieldDecl(hasName("F(int)::S::m"))));
   EXPECT_TRUE(matches(code, fieldDecl(hasName("a::F(int)::S::m"))));
   EXPECT_TRUE(matches(code, fieldDecl(hasName("::a::F(int)::S::m"))));
 }
 
+TEST(Matcher, HasNameQualifiedSupportsLinkage) {
+  // https://bugs.llvm.org/show_bug.cgi?id=42193
+  std::string code = R"cpp(namespace foo { extern "C" void test(); })cpp";
+  EXPECT_TRUE(matches(code, functionDecl(hasName("test"))));
+  EXPECT_TRUE(matches(code, functionDecl(hasName("foo::test"))));
+  EXPECT_TRUE(matches(code, functionDecl(hasName("::foo::test"))));
+  EXPECT_TRUE(notMatches(code, functionDecl(hasName("::test"))));
+
+  code = R"cpp(namespace foo { extern "C" { void test(); } })cpp";
+  EXPECT_TRUE(matches(code, functionDecl(hasName("test"))));
+  EXPECT_TRUE(matches(code, functionDecl(hasName("foo::test"))));
+  EXPECT_TRUE(matches(code, functionDecl(hasName("::foo::test"))));
+  EXPECT_TRUE(notMatches(code, functionDecl(hasName("::test"))));
+}
+
 TEST(Matcher, HasAnyName) {
   const std::string Code = "namespace a { namespace b { class C; } }";
 
   EXPECT_TRUE(matches(Code, recordDecl(hasAnyName("XX", "a::b::C"))));
   EXPECT_TRUE(matches(Code, recordDecl(hasAnyName("a::b::C", "XX"))));
   EXPECT_TRUE(matches(Code, recordDecl(hasAnyName("XX::C", "a::b::C"))));
   EXPECT_TRUE(matches(Code, recordDecl(hasAnyName("XX", "C"))));