[include-cleaner] Generate references from explicit functiontemplate specializations (#83392)

Author: kadircet

clang-tools-extra/include-cleaner/lib/WalkAST.cpp

@@ -228,6 +228,11 @@ class ASTWalker : public RecursiveASTVisitor<ASTWalker> {
     // Mark declaration from definition as it needs type-checking.
     if (FD->isThisDeclarationADefinition())
       report(FD->getLocation(), FD);
+    // Explicit specializaiton/instantiations of a function template requires
+    // primary template.
+    if (clang::isTemplateExplicitInstantiationOrSpecialization(
+            FD->getTemplateSpecializationKind()))
+      report(FD->getLocation(), FD->getPrimaryTemplate());
     return true;
   }
   bool VisitVarDecl(VarDecl *VD) {

clang-tools-extra/include-cleaner/unittests/WalkASTTest.cpp

@@ -229,13 +229,9 @@ TEST(WalkAST, FunctionTemplates) {
   EXPECT_THAT(testWalk("template<typename T> void foo(T) {}",
                        "template void ^foo<int>(int);"),
               ElementsAre());
-  // FIXME: Report specialized template as used from explicit specializations.
-  EXPECT_THAT(testWalk("template<typename T> void foo(T);",
+  EXPECT_THAT(testWalk("template<typename T> void $explicit^foo(T);",
                        "template<> void ^foo<int>(int);"),
-              ElementsAre());
-  EXPECT_THAT(testWalk("template<typename T> void foo(T) {}",
-                       "template<typename T> void ^foo(T*) {}"),
-              ElementsAre());
+              ElementsAre(Decl::FunctionTemplate));
 
   // Implicit instantiations references most relevant template.
   EXPECT_THAT(testWalk(R"cpp(
@@ -510,6 +506,8 @@ TEST(WalkAST, Functions) {
   // Definition uses declaration, not the other way around.
   testWalk("void $explicit^foo();", "void ^foo() {}");
   testWalk("void foo() {}", "void ^foo();");
+  testWalk("template <typename> void $explicit^foo();",
+           "template <typename> void ^foo() {}");
 
   // Unresolved calls marks all the overloads.
   testWalk("void $ambiguous^foo(int); void $ambiguous^foo(char);",