[include-cleaner] Add handling for FriendDecls (llvm#72125)

Fixes llvm#64382.

Author: kadircet

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

@@ -11,6 +11,7 @@
 #include "clang/AST/ASTFwd.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
+#include "clang/AST/DeclFriend.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
@@ -243,6 +244,14 @@ class ASTWalker : public RecursiveASTVisitor<ASTWalker> {
     return true;
   }
 
+  bool VisitFriendDecl(FriendDecl *D) {
+    // We already visit the TypeLoc properly, but need to special case the decl
+    // case.
+    if (auto *FD = D->getFriendDecl())
+      report(D->getLocation(), FD);
+    return true;
+  }
+
   bool VisitConceptReference(const ConceptReference *CR) {
     report(CR->getConceptNameLoc(), CR->getFoundDecl());
     return true;

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

@@ -550,5 +550,10 @@ TEST(WalkAST, Concepts) {
   // FIXME: Foo should be explicitly referenced.
   testWalk("template<typename T> concept Foo = true;", "void func() { ^Foo auto x = 1; }");
 }
+
+TEST(WalkAST, FriendDecl) {
+  testWalk("void $explicit^foo();", "struct Bar { friend void ^foo(); };");
+  testWalk("struct $explicit^Foo {};", "struct Bar { friend struct ^Foo; };");
+}
 } // namespace
 } // namespace clang::include_cleaner