[change-namespace] get insertion points of forward declarations correct.

[ioeric]

Summary

Previously, the insertion points would conflict with the old namespace
deletion.

[hokein]

unittests/change-namespace/ChangeNamespaceTests.cpp

354 ↗

(On Diff #90131)

I'd create a new test for the fix instead of modifying the current one.

[ioeric]

• Create a new test case. And slight refactor.

[hokein]

LGTM.

clang-tools-extra/trunk/change-namespace/ChangeNamespace.cpp

 //   namespace x {
 //   class A { a::FWD *fwd; }
 //   }  // x
 void ChangeNamespaceTool::moveClassForwardDeclaration(
     const ast_matchers::MatchFinder::MatchResult &Result,
     const NamedDecl *FwdDecl) {
   SourceLocation Start = FwdDecl->getLocStart();
   SourceLocation End = FwdDecl->getLocEnd();
+  const SourceManager &SM = *Result.SourceManager;
   SourceLocation AfterSemi = Lexer::findLocationAfterToken(
-      End, tok::semi, *Result.SourceManager, Result.Context->getLangOpts(),
+      End, tok::semi, SM, Result.Context->getLangOpts(),
       /*SkipTrailingWhitespaceAndNewLine=*/true);
   if (AfterSemi.isValid())
     End = AfterSemi.getLocWithOffset(-1);
   // Delete the forward declaration from the code to be moved.
-  addReplacementOrDie(Start, End, "", *Result.SourceManager,
-                      &FileToReplacements);
+  addReplacementOrDie(Start, End, "", SM, &FileToReplacements);
   llvm::StringRef Code = Lexer::getSourceText(
-      CharSourceRange::getTokenRange(
-          Result.SourceManager->getSpellingLoc(Start),
-          Result.SourceManager->getSpellingLoc(End)),
-      *Result.SourceManager, Result.Context->getLangOpts());
+      CharSourceRange::getTokenRange(SM.getSpellingLoc(Start),
+                                     SM.getSpellingLoc(End)),
+      SM, Result.Context->getLangOpts());
   // Insert the forward declaration back into the old namespace after moving the
   // code from old namespace to new namespace.
   // Insertion information is stored in `InsertFwdDecls` and actual
   // insertion will be performed in `onEndOfTranslationUnit`.
   // Get the (old) namespace that contains the forward declaration.
   const auto *NsDecl = Result.Nodes.getNodeAs<NamespaceDecl>("ns_decl");
   // The namespace contains the forward declaration, so it must not be empty.
   assert(!NsDecl->decls_empty());
-  const auto Insertion = createInsertion(NsDecl->decls_begin()->getLocStart(),
-                                         Code, *Result.SourceManager);
+  const auto Insertion = createInsertion(
+      getLocAfterNamespaceLBrace(NsDecl, SM, Result.Context->getLangOpts()),
+      Code, SM);
   InsertForwardDeclaration InsertFwd;
   InsertFwd.InsertionOffset = Insertion.getOffset();
   InsertFwd.ForwardDeclText = Insertion.getReplacementText().str();
   InsertFwdDecls[Insertion.getFilePath()].push_back(InsertFwd);
 }
 
 // Replaces a qualified symbol (in \p DeclCtx) that refers to a declaration \p
 // FromDecl with the shortest qualified name possible when the reference is in

clang-tools-extra/trunk/unittests/change-namespace/ChangeNamespaceTests.cpp

std::string Expected = "namespace na {\n"
                          "class A {\n"
                          "  ::na::nb::FWD *fwd;\n"
                          "};\n"
                          "} // namespace y\n"
                          "} // namespace x\n";
   EXPECT_EQ(format(Expected), runChangeNamespaceOnCode(Code));
 }
 
+TEST_F(ChangeNamespaceTest, InsertForwardDeclsProperly) {
+  std::string Code = "namespace na {\n"
+                     "namespace nb {\n"
+                     "\n"
+                     "class FWD;\n"
+                     "class FWD2;\n"
+                     "class A {\n"
+                     "  FWD *fwd;\n"
+                     "};\n"
+                     "\n"
+                     "} // namespace nb\n"
+                     "} // namespace na\n";
+  std::string Expected = "namespace na {\n"
+                         "namespace nb {\n"
+                         "class FWD;\n"
+                         "class FWD2;\n"
+                         "} // namespace nb\n"
+                         "} // namespace na\n"
+                         "namespace x {\n"
+                         "namespace y {\n"
+                         "\n"
+                         "class A {\n"
+                         "  ::na::nb::FWD *fwd;\n"
+                         "};\n"
+                         "\n"
+                         "} // namespace y\n"
+                         "} // namespace x\n";
+  EXPECT_EQ(format(Expected), runChangeNamespaceOnCode(Code));
+}
+
 TEST_F(ChangeNamespaceTest, TemplateClassForwardDeclaration) {
   std::string Code = "namespace na {\n"
                      "namespace nb {\n"
                      "class FWD;\n"
                      "template<typename T> class FWD_TEMP;\n"
                      "class A {\n"
                      "  FWD *fwd;\n"
                      "};\n"