[clangd] Don't navigate to forward class declaration when go to definition.

[hokein]

Summary

For some cases, GoToDefinition will navigate to the forward class
declaration, we should always navigate to the class definition.

[sammccall]

clangd/XRefs.cpp

54

Can you add some motivation here? e.g. the forward decl example

[hokein]

• Revise the way of checking definition.
• Add a test for function declaration.

[hokein]

With more test, it turns out that ASTNode.OrigD is not always pointed to the definition, so we can't rely on D or ASTNode.OrigD :(.

I revised the way of checking definition, it should works for major cases. Please review it again.

[ilya-biryukov]

clangd/XRefs.cpp

59

That seems like a useful helper on its own, maybe create a helper called Decl* getDefinition(Decl* D) and use it instead?
It's implementation can be as short as the one we currently have for IsDefinition, since all interesting Decl types have getDefinition method.

[hokein]

Use getDefinition to simply the code.

[hokein]

clangd/XRefs.cpp

59

Good point!

clangd/XRefs.cpp

public:
   }
 
   bool
   handleDeclOccurence(const Decl *D, index::SymbolRoleSet Roles,
                       ArrayRef<index::SymbolRelation> Relations, FileID FID,
                       unsigned Offset,
                       index::IndexDataConsumer::ASTNodeInfo ASTNode) override {
     if (isSearchedLocation(FID, Offset))
-      Decls.push_back(D);
+      Decls.push_back(ASTNode.OrigD);
     return true;
   }
 
 private:
   bool isSearchedLocation(FileID FID, unsigned Offset) const {
     const SourceManager &SourceMgr = AST.getSourceManager();
     return SourceMgr.getFileOffset(SearchedLocation) == Offset &&
            SourceMgr.getFileID(SearchedLocation) == FID;
   }
 
   void finish() override {
     // Also handle possible macro at the searched location.
     Token Result;

unittests/clangd/XRefsTests.cpp

const char *Tests[] = {
 
       R"cpp(// Macro
         #define MACRO 0
         #define [[MACRO 1]]
         int main() { return ^MACRO; }
         #define MACRO 2
         #undef macro
       )cpp",
+
+      R"cpp(// Forward class declaration
+        class Foo;
+        [[class Foo {}]];
+        F^oo* foo();
+      )cpp",
   };
   for (const char *Test : Tests) {
     Annotations T(Test);
     auto AST = build(T.code());
     EXPECT_THAT(findDefinitions(Context::empty(), AST, T.point()),
                 ElementsAre(RangeIs(T.range())))
         << Test;
   }
 }
 
 } // namespace
 } // namespace clangd
 } // namespace clang