[clang-tools-extra] [include-cleaner] Use FoundDecl only for using-shadow-decls (PR #82615)

[kadir çetinkaya via cfe-commits]

https://github.com/kadircet updated https://github.com/llvm/llvm-project/pull/82615

>From 32c8199fb9ffb9180b666e0837aa73aa6151cebc Mon Sep 17 00:00:00 2001
From: Kadir Cetinkaya <kadircet at google.com>
Date: Thu, 22 Feb 2024 13:52:42 +0100
Subject: [PATCH] [include-cleaner] Use FoundDecl only for using-shadow-decls

---
 .../include-cleaner/lib/WalkAST.cpp           |  5 +++
 .../include-cleaner/unittests/WalkASTTest.cpp | 34 +++++++++++--------
 2 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/clang-tools-extra/include-cleaner/lib/WalkAST.cpp b/clang-tools-extra/include-cleaner/lib/WalkAST.cpp
index 6c4d9b7862d915..277e6ec5b08900 100644
--- a/clang-tools-extra/include-cleaner/lib/WalkAST.cpp
+++ b/clang-tools-extra/include-cleaner/lib/WalkAST.cpp
@@ -128,6 +128,11 @@ class ASTWalker : public RecursiveASTVisitor<ASTWalker> {
 
   bool VisitDeclRefExpr(DeclRefExpr *DRE) {
     auto *FD = DRE->getFoundDecl();
+    // Prefer the underlying decl if FoundDecl isn't a shadow decl, e.g:
+    // - For templates, found-decl is always primary template, but we want the
+    // specializaiton itself.
+    if (!llvm::isa<UsingShadowDecl>(FD))
+      FD = DRE->getDecl();
     // For refs to non-meber-like decls, use the found decl.
     // For member-like decls, we should have a reference from the qualifier to
     // the container decl instead, which is preferred as it'll handle
diff --git a/clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp b/clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp
index 0be5db36b1fc51..e238dc3d902bbe 100644
--- a/clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp
+++ b/clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp
@@ -200,24 +200,26 @@ TEST(WalkAST, VarTemplates) {
   EXPECT_THAT(testWalk(R"cpp(
     template <typename T> T $explicit^Foo = 0;)cpp",
                        "int z = ^Foo<int>;"),
-              ElementsAre(Decl::VarTemplate));
+              ElementsAre(Decl::VarTemplateSpecialization));
   EXPECT_THAT(testWalk(R"cpp(
-    template<typename T> T $explicit^Foo = 0;
-    template<> int Foo<int> = 1;)cpp",
+    template<typename T> T Foo = 0;
+    template<> int $explicit^Foo<int> = 1;)cpp",
                        "int x = ^Foo<int>;"),
-              ElementsAre(Decl::VarTemplate));
+              ElementsAre(Decl::VarTemplateSpecialization));
   // FIXME: This points at implicit specialization, instead we should point to
   // explicit partial specializaiton pattern.
   EXPECT_THAT(testWalk(R"cpp(
-    template<typename T> T $explicit^Foo = 0;
-    template<typename T> T* Foo<T*> = nullptr;)cpp",
+    template<typename T> T Foo = 0;
+    template<typename T> T* $explicit^Foo<T*> = nullptr;)cpp",
                        "int *x = ^Foo<int *>;"),
-              ElementsAre(Decl::VarTemplate));
+              ElementsAre(Decl::VarTemplateSpecialization));
+  // Implicit specializations through explicit instantiations has source
+  // locations pointing at the primary template.
   EXPECT_THAT(testWalk(R"cpp(
     template<typename T> T $explicit^Foo = 0;
     template int Foo<int>;)cpp",
                        "int x = ^Foo<int>;"),
-              ElementsAre(Decl::VarTemplate));
+              ElementsAre(Decl::VarTemplateSpecialization));
 }
 TEST(WalkAST, FunctionTemplates) {
   // Explicit instantiation and (partial) specialization references primary
@@ -239,18 +241,19 @@ TEST(WalkAST, FunctionTemplates) {
   EXPECT_THAT(testWalk(R"cpp(
     template <typename T> void $explicit^foo() {})cpp",
                        "auto x = []{ ^foo<int>(); };"),
-              ElementsAre(Decl::FunctionTemplate));
-  // FIXME: DeclRefExpr points at primary template, not the specialization.
+              ElementsAre(Decl::Function));
   EXPECT_THAT(testWalk(R"cpp(
-    template<typename T> void $explicit^foo() {}
-    template<> void foo<int>(){})cpp",
+    template<typename T> void foo() {}
+    template<> void $explicit^foo<int>(){})cpp",
                        "auto x = []{ ^foo<int>(); };"),
-              ElementsAre(Decl::FunctionTemplate));
+              ElementsAre(Decl::Function));
+  // The decl is actually the specialization, but explicit instantations point
+  // at the primary template.
   EXPECT_THAT(testWalk(R"cpp(
     template<typename T> void $explicit^foo() {};
     template void foo<int>();)cpp",
                        "auto x = [] { ^foo<int>(); };"),
-              ElementsAre(Decl::FunctionTemplate));
+              ElementsAre(Decl::Function));
 }
 TEST(WalkAST, TemplateSpecializationsFromUsingDecl) {
   // Class templates
@@ -548,7 +551,8 @@ TEST(WalkAST, Concepts) {
   testWalk(Concept, "template<typename T> void func() requires ^Foo<T> {}");
   testWalk(Concept, "void func(^Foo auto x) {}");
   // FIXME: Foo should be explicitly referenced.
-  testWalk("template<typename T> concept Foo = true;", "void func() { ^Foo auto x = 1; }");
+  testWalk("template<typename T> concept Foo = true;",
+           "void func() { ^Foo auto x = 1; }");
 }
 
 TEST(WalkAST, FriendDecl) {