[clang-format] Fix invalid-code-generation by RemoveBracesLLVM

[owenpan]

Summary

When removing an r_brace that is the first token of an annotated line, if the
line above ends with a line comment, clang-format generates invalid code by
merging the tokens after the r_brace into the line comment.

Fixes https://github.com/llvm/llvm-project/issues/56488.

clang/lib/Format/Format.cpp

analyze(TokenAnnotator &Annotator,
     removeBraces(AnnotatedLines, Result);
     return {Result, 0};
   }
 
 private:
   void removeBraces(SmallVectorImpl<AnnotatedLine *> &Lines,
                     tooling::Replacements &Result) {
     const auto &SourceMgr = Env.getSourceManager();
+    bool EndsWithComment = false;
     for (AnnotatedLine *Line : Lines) {
       removeBraces(Line->Children, Result);
-      if (!Line->Affected)
-        continue;
+      if (Line->Affected) {
         for (FormatToken *Token = Line->First; Token && !Token->Finalized;
              Token = Token->Next) {
           if (!Token->Optional)
             continue;
           assert(Token->isOneOf(tok::l_brace, tok::r_brace));
-        assert(Token->Next || Token == Line->Last);
+          assert(Token->Previous || Token == Line->First);
+          const FormatToken *Next = Token->Next;
+          assert(Next || Token == Line->Last);
           const auto Start =
-            Token == Line->Last ||
-                    (Token->Next->isOneOf(tok::kw_else, tok::comment) &&
-                     Token->Next->NewlinesBefore > 0)
-                ? Token->WhitespaceRange.getBegin()
-                : Token->Tok.getLocation();
+              (!Token->Previous && EndsWithComment) ||
+                      (Next && !(Next->isOneOf(tok::kw_else, tok::comment) &&
+                                 Next->NewlinesBefore > 0))
+                  ? Token->Tok.getLocation()
+                  : Token->WhitespaceRange.getBegin();
           const auto Range =
               CharSourceRange::getCharRange(Start, Token->Tok.getEndLoc());
           cantFail(Result.add(tooling::Replacement(SourceMgr, Range, "")));
         }
       }
+      assert(Line->Last);
+      EndsWithComment = Line->Last->is(tok::comment);
+    }
   }
 };
 
 class JavaScriptRequoter : public TokenAnalyzer {
 public:
   JavaScriptRequoter(const Environment &Env, const FormatStyle &Style)
       : TokenAnalyzer(Env, Style) {}
 

clang/unittests/Format/FormatTest.cpp

verifyFormat("if (a)\n"
                "}\n"
                "// comment\n"
                "else {\n"
                "  bar();\n"
                "}",
                Style);
 
   verifyFormat("if (a) {\n"
+               "  if (b)\n"
+               "    c = 1; // comment\n"
+               "}",
+               "if (a) {\n"
+               "  if (b) {\n"
+               "    c = 1; // comment\n"
+               "  }\n"
+               "}",
+               Style);
+
+  verifyFormat("if (a) {\n"
                "Label:\n"
                "}",
                Style);
 
   verifyFormat("if (a) {\n"
                "Label:\n"
                "  f();\n"
                "}",