[clang] Support function pointer types with attributes when extracting parameter names for signature help

Fixes clangd/clangd#1729

Differential Revision: https://reviews.llvm.org/D157952

Author: HighCommander4

clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp

@@ -1397,20 +1397,37 @@ TEST(SignatureHelpTest, Overloads) {
 }
 
 TEST(SignatureHelpTest, FunctionPointers) {
-  auto FunctionPointerResults = signatures(R"cpp(
+  llvm::StringLiteral Tests[] = {
+      // Variable of function pointer type
+      R"cpp(
     void (*foo)(int x, int y);
     int main() { foo(^); }
-  )cpp");
-  EXPECT_THAT(FunctionPointerResults.signatures,
-              UnorderedElementsAre(sig("([[int x]], [[int y]]) -> void")));
-
-  auto FunctionPointerTypedefResults = signatures(R"cpp(
+  )cpp",
+      // Wrapped in an AttributedType
+      R"cpp(
+    void (__stdcall *foo)(int x, int y);
+    int main() { foo(^); }
+  )cpp",
+      // Another syntax for an AttributedType
+      R"cpp(
+    void (__attribute__(stdcall) *foo)(int x, int y);
+    int main() { foo(^); },
+  )cpp",
+      // Wrapped in a typedef
+      R"cpp(
     typedef void (*fn)(int x, int y);
     fn foo;
     int main() { foo(^); }
-  )cpp");
-  EXPECT_THAT(FunctionPointerTypedefResults.signatures,
-              UnorderedElementsAre(sig("([[int x]], [[int y]]) -> void")));
+  )cpp",
+      // Wrapped in both a typedef and an AttributedTyped
+      R"cpp(
+    typedef void (__stdcall *fn)(int x, int y);
+    fn foo;
+    int main() { foo(^); }
+  )cpp"};
+  for (auto Test : Tests)
+    EXPECT_THAT(signatures(Test).signatures,
+                UnorderedElementsAre(sig("([[int x]], [[int y]]) -> void")));
 }
 
 TEST(SignatureHelpTest, Constructors) {

clang/lib/Sema/SemaCodeComplete.cpp

@@ -6066,12 +6066,21 @@ static FunctionProtoTypeLoc GetPrototypeLoc(Expr *Fn) {
   if (!Target)
     return {};
 
-  if (auto P = Target.getAs<PointerTypeLoc>()) {
-    Target = P.getPointeeLoc();
-  }
-
-  if (auto P = Target.getAs<ParenTypeLoc>()) {
-    Target = P.getInnerLoc();
+  // Unwrap types that may be wrapping the function type
+  while (true) {
+    if (auto P = Target.getAs<PointerTypeLoc>()) {
+      Target = P.getPointeeLoc();
+      continue;
+    }
+    if (auto A = Target.getAs<AttributedTypeLoc>()) {
+      Target = A.getModifiedLoc();
+      continue;
+    }
+    if (auto P = Target.getAs<ParenTypeLoc>()) {
+      Target = P.getInnerLoc();
+      continue;
+    }
+    break;
   }
 
   if (auto F = Target.getAs<FunctionProtoTypeLoc>()) {