[clang-format] Fix a crash in EnumTrailingComma (llvm#135903)

Fix llvm#135819

Author: owenca

clang/lib/Format/Format.cpp

@@ -2427,19 +2427,23 @@ class EnumTrailingCommaEditor : public TokenAnalyzer {
 private:
   void editEnumTrailingComma(SmallVectorImpl<AnnotatedLine *> &Lines,
                              tooling::Replacements &Result) {
+    bool InEnumBraces = false;
+    const FormatToken *BeforeRBrace = nullptr;
     const auto &SourceMgr = Env.getSourceManager();
     for (auto *Line : Lines) {
       if (!Line->Children.empty())
         editEnumTrailingComma(Line->Children, Result);
-      if (!Line->Affected)
-        continue;
       for (const auto *Token = Line->First; Token && !Token->Finalized;
            Token = Token->Next) {
-        if (Token->isNot(TT_EnumRBrace))
+        if (Token->isNot(TT_EnumRBrace)) {
+          if (Token->is(TT_EnumLBrace))
+            InEnumBraces = true;
+          else if (InEnumBraces && Token->isNot(tok::comment))
+            BeforeRBrace = Line->Affected ? Token : nullptr;
           continue;
-        const auto *BeforeRBrace = Token->getPreviousNonComment();
-        assert(BeforeRBrace);
-        if (BeforeRBrace->is(TT_EnumLBrace)) // Empty braces.
+        }
+        InEnumBraces = false;
+        if (!BeforeRBrace) // Empty braces or Line not affected.
           continue;
         if (BeforeRBrace->is(tok::comma)) {
           if (Style.EnumTrailingComma == FormatStyle::ETC_Remove)
@@ -2448,6 +2452,7 @@ class EnumTrailingCommaEditor : public TokenAnalyzer {
           cantFail(Result.add(tooling::Replacement(
               SourceMgr, BeforeRBrace->Tok.getEndLoc(), 0, ",")));
         }
+        BeforeRBrace = nullptr;
       }
     }
   }

clang/unittests/Format/FormatTest.cpp

@@ -27992,6 +27992,33 @@ TEST_F(FormatTest, EnumTrailingComma) {
                "};\n"
                "enum Color { red, green, blue /**/ };",
                Code, Style);
+
+  EXPECT_TRUE(Style.AllowShortEnumsOnASingleLine);
+  Style.AllowShortEnumsOnASingleLine = false;
+
+  constexpr StringRef Input("enum {\n"
+                            "  //\n"
+                            "  a,\n"
+                            "  /**/\n"
+                            "  b,\n"
+                            "};");
+  verifyFormat(Input, Input, Style, {tooling::Range(12, 3)}); // line 3
+  verifyFormat("enum {\n"
+               "  //\n"
+               "  a,\n"
+               "  /**/\n"
+               "  b\n"
+               "};",
+               Input, Style, {tooling::Range(24, 3)}); // line 5
+
+  Style.EnumTrailingComma = FormatStyle::ETC_Insert;
+  verifyFormat("enum class MyEnum_E {\n"
+               "  MY_ENUM = 0U,\n"
+               "};",
+               "enum class MyEnum_E {\n"
+               "  MY_ENUM = 0U\n"
+               "};",
+               Style);
 }
 
 TEST_F(FormatTest, BreakAfterAttributes) {