[clangd] Do not offer "Add using" tweak in header files.

[sammccall]

clang-tools-extra/clangd/refactor/tweaks/AddUsing.cpp

181

can you use isHeaderFile instead? (in SourceCode.h)

clang-tools-extra/clangd/unittests/TweakTests.cpp

2471

no need for this extra test if using isHeaderFile

[adamcz]

Addressed review comments

clang-tools-extra/clangd/unittests/TweakTests.cpp

2471

I'd argue there is a need for this test - if only to check that we are, in fact, using isHeaderFile() or something equivalent :-)

I can delete it if you want, but I think it's better this way.

clang-tools-extra/clangd/refactor/tweaks/AddUsing.cpp

findInsertionPoint(const Tweak::Selection &Inputs,
   InsertionPointData Out;
   Out.Loc = SM.getExpansionLoc(TLDs[0]->getBeginLoc());
   Out.Suffix = "\n\n";
   return Out;
 }
 
 bool AddUsing::prepare(const Selection &Inputs) {
   auto &SM = Inputs.AST->getSourceManager();
+
+  // Do not suggest "using" in header files. That way madness lies.
+  if (isHeaderFile(SM.getFileEntryForID(SM.getMainFileID())->getName(),
+                   Inputs.AST->getLangOpts()))
+    return false;
+
   auto *Node = Inputs.ASTSelection.commonAncestor();
   if (Node == nullptr)
     return false;
 
   // If we're looking at a type or NestedNameSpecifier, walk up the tree until
   // we find the "main" node we care about, which would be ElaboratedTypeLoc or
   // DeclRefExpr.
   for (; Node->Parent; Node = Node->Parent) {

clang-tools-extra/clangd/unittests/TweakTests.cpp

EXPECT_UNAVAILABLE(Header +
                      "void fun() { o^n^e^:^:^t^w^o^:^:^c^c^:^:^s^t inst; }");
   EXPECT_UNAVAILABLE(Header +
                      "void fun() { o^n^e^:^:^t^w^o^:^:^c^c^:^:^s^t inst; }");
   EXPECT_UNAVAILABLE(Header + "void fun() { N^S(c^c) inst; }");
   // This used to crash. Ideally we would support this case, but for now we just
   // test that we don't crash.
   EXPECT_UNAVAILABLE(Header +
                      "template<typename TT> using foo = one::tt<T^T>;");
+
+  // Check that we do not trigger in header files.
+  FileName = "test.h";
+  ExtraArgs.push_back("-xc++-header"); // .h file is treated a C by default.
+  EXPECT_UNAVAILABLE(Header + "void fun() { one::two::f^f(); }");
+  FileName = "test.hpp";
+  EXPECT_UNAVAILABLE(Header + "void fun() { one::two::f^f(); }");
 }
 
 TEST_F(AddUsingTest, Apply) {
   FileName = "test.cpp";
   struct {
     llvm::StringRef TestSource;
     llvm::StringRef ExpectedSource;
   } Cases[]{{