[clang][Diagnostics] Don't expand label fixit to the next line

[tbaeder]

Summary

Now that we print >1 line of code snippet, we printed another line of
code for now reason, because the source range we created for the fixit
expanded to the next line, if the next token was there. Don't do that.

[tbaeder]

As far as the fixit goes, I guess the previous version was better, since it didn't leave an empty line behind?

[aaron.ballman]

In D152525#4408902, @tbaeder wrote:

As far as the fixit goes, I guess the previous version was better, since it didn't leave an empty line behind?

Yes, but that's a formatting-related concern with the output, and we traditionally leave that to another tool like clang-format to address.

LGTM, but add a release note since there technically is a change in behavior with the fix-it?

[cjdb]

Thanks for fixing this, it'll hopefully cause less frustration for devs :)

clang/docs/ReleaseNotes.rst

 - Clang now diagnoses unused const-qualified variable template as
   "unused variable template" rather than "unused variable".
 - When diagnosing a constant expression where an enum without a fixed underlying
   type is set to a value outside the range of the enum's values, clang will now
   print the name of the enum in question.
 - Clang no longer diagnoses a read of an empty structure as use of an
   uninitialized variable.
   (`#26842: <https://github.com/llvm/llvm-project/issues/26842>`_)
+- The Fix-It emitted for unused labels used to expand to the next line, which caused
+  visual oddities now that Clang shows more than one line of code snippet. This has
+  been fixed and the Fix-It now only spans to the end of the ``:``.
 
 Bug Fixes in This Version
 -------------------------
 
 - Fix segfault while running clang-rename on a non existing file.
   (`#36471 <https://github.com/llvm/llvm-project/issues/36471>`_)
 - Fix crash when diagnosing incorrect usage of ``_Nullable`` involving alias
   templates.

clang/lib/Sema/SemaDecl.cpp

static bool ShouldDiagnoseUnusedDecl(const NamedDecl *D) {
   return true;
 }
 
 static void GenerateFixForUnusedDecl(const NamedDecl *D, ASTContext &Ctx,
                                      FixItHint &Hint) {
   if (isa<LabelDecl>(D)) {
     SourceLocation AfterColon = Lexer::findLocationAfterToken(
         D->getEndLoc(), tok::colon, Ctx.getSourceManager(), Ctx.getLangOpts(),
-        true);
+        /*SkipTrailingWhitespaceAndNewline=*/false);
     if (AfterColon.isInvalid())
       return;
     Hint = FixItHint::CreateRemoval(
         CharSourceRange::getCharRange(D->getBeginLoc(), AfterColon));
   }
 }
 
 void Sema::DiagnoseUnusedNestedTypedefs(const RecordDecl *D) {

clang/test/FixIt/fixit-newline-style.c

 // RUN: %clang_cc1 -pedantic -Wunused-label -fno-diagnostics-show-line-numbers -x c %s 2>&1 | FileCheck %s -strict-whitespace
 
 // This file intentionally uses a CRLF newline style
 // <rdar://problem/12639047>
 // CHECK: warning: unused label 'ddd'
 // CHECK-NEXT: {{^  ddd:}}
 // CHECK-NEXT: {{^  \^~~~$}}
+// CHECK-NOT: {{^  ;}}
 void f(void) {
   ddd:
   ;
 }