From 512aa8485010009f6ec1b8d9deea3effe67e0106 Mon Sep 17 00:00:00 2001
From: Kadir Cetinkaya <kadircet@google.com>
Date: Thu, 30 Sep 2021 15:25:42 +0200
Subject: [PATCH] [clangd] Handle members of anon structs in SelectionTree

References to fields inside anon structs contain an implicit children
for the container, which has the same SourceLocation with the field.
This was resulting in SelectionTree always picking the anon-struct rather than
the field as the selection.

This patch prevents that by claiming the range for the field early.

https://github.com/clangd/clangd/issues/877.

Differential Revision: https://reviews.llvm.org/D110825
---
 clang-tools-extra/clangd/Selection.cpp        |  9 ++++++++
 .../clangd/unittests/XRefsTests.cpp           | 21 +++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/clang-tools-extra/clangd/Selection.cpp b/clang-tools-extra/clangd/Selection.cpp
index e3a2e3199766..a53673e07480 100644
--- a/clang-tools-extra/clangd/Selection.cpp
+++ b/clang-tools-extra/clangd/Selection.cpp
@@ -443,6 +443,15 @@ bool isImplicit(const Stmt *S) {
   if (auto *CTI = llvm::dyn_cast<CXXThisExpr>(S))
     if (CTI->isImplicit())
       return true;
+  // Make sure implicit access of anonymous structs don't end up owning tokens.
+  if (auto *ME = llvm::dyn_cast<MemberExpr>(S)) {
+    if (auto *FD = llvm::dyn_cast<FieldDecl>(ME->getMemberDecl()))
+      if (FD->isAnonymousStructOrUnion())
+        // If Base is an implicit CXXThis, then the whole MemberExpr has no
+        // tokens. If it's a normal e.g. DeclRef, we treat the MemberExpr like
+        // an implicit cast.
+        return isImplicit(ME->getBase());
+  }
   // Refs to operator() and [] are (almost?) always implicit as part of calls.
   if (auto *DRE = llvm::dyn_cast<DeclRefExpr>(S)) {
     if (auto *FD = llvm::dyn_cast<FunctionDecl>(DRE->getDecl())) {
diff --git a/clang-tools-extra/clangd/unittests/XRefsTests.cpp b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
index 6a9d355792a6..e8b64e9200bb 100644
--- a/clang-tools-extra/clangd/unittests/XRefsTests.cpp
+++ b/clang-tools-extra/clangd/unittests/XRefsTests.cpp
@@ -365,6 +365,27 @@ TEST(LocateSymbol, WithIndex) {
       ElementsAre(Sym("Forward", SymbolHeader.range("forward"), Test.range())));
 }
 
+TEST(LocateSymbol, AnonymousStructFields) {
+  auto Code = Annotations(R"cpp(
+    struct $2[[Foo]] {
+      struct { int $1[[x]]; };
+      void foo() {
+        // Make sure the implicit base is skipped.
+        $1^x = 42;
+      }
+    };
+    // Check that we don't skip explicit bases.
+    int a = $2^Foo{}.x;
+  )cpp");
+  TestTU TU = TestTU::withCode(Code.code());
+  auto AST = TU.build();
+  EXPECT_THAT(locateSymbolAt(AST, Code.point("1"), TU.index().get()),
+              UnorderedElementsAre(Sym("x", Code.range("1"), Code.range("1"))));
+  EXPECT_THAT(
+      locateSymbolAt(AST, Code.point("2"), TU.index().get()),
+      UnorderedElementsAre(Sym("Foo", Code.range("2"), Code.range("2"))));
+}
+
 TEST(LocateSymbol, FindOverrides) {
   auto Code = Annotations(R"cpp(
     class Foo {