[clangd] Also perform merging for symbol definitions

[kadircet]

Summary

clangd currently prefers declarations from codegen files. This patch
implements that behavior for definition locations. If we have definiton
locations both coming from AST and index, clangd will perform a merging to show
the codegen file if that's the case.

[kadircet]

• Get rid of debug comments

[kadircet]

• Update diff

[sammccall]

clang-tools-extra/clangd/XRefs.cpp

350

Maybe move this below the PreferredDeclaration assignment?

It might just be me, but the generated code case seems much more obscure than the AST/index conflict case.

350

The connection between the comment and the code seems a little obscure to me.
maybe. // We may still prefer the definition from the index, e.g. for generated symbols.

clang-tools-extra/clangd/XRefs.cpp

std::vector<LocatedSymbol> locateSymbolAt(ParsedAST &AST, Position Pos,
   if (Index && !ResultIndex.empty()) {
     LookupRequest QueryRequest;
     for (auto It : ResultIndex)
       QueryRequest.IDs.insert(It.first);
     std::string Scratch;
     Index->lookup(QueryRequest, [&](const Symbol &Sym) {
       auto &R = Result[ResultIndex.lookup(Sym.ID)];
 
-      // Special case: if the AST yielded a definition, then it may not be
-      // the right *declaration*. Prefer the one from the index.
       if (R.Definition) { // from AST
-        if (auto Loc = toLSPLocation(Sym.CanonicalDeclaration, *MainFilePath))
-          R.PreferredDeclaration = *Loc;
+        // In case of generated files we prefer to omit the definition in the
+        // generated code.
         if (auto Loc = toLSPLocation(
                 getPreferredLocation(*R.Definition, Sym.Definition, Scratch),
                 *MainFilePath))
           R.Definition = *Loc;
+
+        // Special case: if the AST yielded a definition, then it may not be
+        // the right *declaration*. Prefer the one from the index.
+        if (auto Loc = toLSPLocation(Sym.CanonicalDeclaration, *MainFilePath))
+          R.PreferredDeclaration = *Loc;
       } else {
         R.Definition = toLSPLocation(Sym.Definition, *MainFilePath);
 
-        if (Sym.CanonicalDeclaration) {
-          // Use merge logic to choose AST or index declaration.
-          // We only do this for declarations as definitions from AST
-          // is generally preferred (e.g. definitions in main file).
-          if (auto Loc = toLSPLocation(
-                  getPreferredLocation(R.PreferredDeclaration,
-                                       Sym.CanonicalDeclaration, Scratch),
-                  *MainFilePath))
-            R.PreferredDeclaration = *Loc;
-        }
-      }
     });
   }
 
   return Result;
 }
 
 namespace {
 

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

Test = Annotations(R"cpp(// defintion in AST.
       )cpp");
   EXPECT_THAT(
       LocateWithIndex(Test),
       ElementsAre(Sym("Forward", SymbolHeader.range("forward"), Test.range())));
 }
 
 TEST(LocateSymbol, WithIndexPreferredLocation) {
   Annotations SymbolHeader(R"cpp(
-        class $[[Proto]] {};
+        class $p[[Proto]] {};
+        void $f[[func]]() {};
       )cpp");
   TestTU TU;
   TU.HeaderCode = SymbolHeader.code();
   TU.HeaderFilename = "x.proto"; // Prefer locations in codegen files.
   auto Index = TU.index();
 
   Annotations Test(R"cpp(// only declaration in AST.
         // Shift to make range different.
-        class [[Proto]];
-        P^roto* create();
+        class Proto;
+        void func() {}
+        P$p^roto* create() {
+          fu$f^nc();
+          return nullptr;
+        }
       )cpp");
 
   auto AST = TestTU::withCode(Test.code()).build();
-  auto Locs = clangd::locateSymbolAt(AST, Test.point(), Index.get());
-  EXPECT_THAT(Locs, ElementsAre(Sym("Proto", SymbolHeader.range())));
+  {
+    auto Locs = clangd::locateSymbolAt(AST, Test.point("p"), Index.get());
+    auto CodeGenLoc = SymbolHeader.range("p");
+    EXPECT_THAT(Locs, ElementsAre(Sym("Proto", CodeGenLoc, CodeGenLoc)));
+  }
+  {
+    auto Locs = clangd::locateSymbolAt(AST, Test.point("f"), Index.get());
+    auto CodeGenLoc = SymbolHeader.range("f");
+    EXPECT_THAT(Locs, ElementsAre(Sym("func", CodeGenLoc, CodeGenLoc)));
+  }
 }
 
 TEST(LocateSymbol, All) {
   // Ranges in tests:
   //   $decl is the declaration location (if absent, no symbol is located)
   //   $def is the definition location (if absent, symbol has no definition)
   //   unnamed range becomes both $decl and $def.
   const char *Tests[] = {