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

[Owen Pan via cfe-commits]

https://github.com/owenca created https://github.com/llvm/llvm-project/pull/135903

Fix #135819

>From 8f79ecf3e3f32b6b735a478eb1d3a48b7a6fa640 Mon Sep 17 00:00:00 2001
From: Owen Pan <owenpiano at gmail.com>
Date: Tue, 15 Apr 2025 21:02:28 -0700
Subject: [PATCH] [clang-format] Fix a crash in EnumTrailingComma

Fix #135819
---
 clang/lib/Format/Format.cpp           | 17 +++++++++++------
 clang/unittests/Format/FormatTest.cpp | 11 +++++++++++
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
index c601967a8715c..b8d55871ab932 100644
--- a/clang/lib/Format/Format.cpp
+++ b/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 && Line->Affected && Token->isNot(tok::comment))
+            BeforeRBrace = Token;
           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;
       }
     }
   }
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index b62d49e17c83f..be0343efb4b83 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -27962,6 +27962,7 @@ TEST_F(FormatTest, EnumTrailingComma) {
   verifyFormat(Code);
 
   auto Style = getLLVMStyle();
+  EXPECT_TRUE(Style.AllowShortEnumsOnASingleLine);
   Style.EnumTrailingComma = FormatStyle::ETC_Insert;
   verifyFormat("enum : int { /**/ };\n"
                "enum {\n"
@@ -27972,6 +27973,16 @@ TEST_F(FormatTest, EnumTrailingComma) {
                "enum Color { red, green, blue, /**/ };",
                Code, Style);
 
+  Style.AllowShortEnumsOnASingleLine = false;
+  verifyFormat("enum class MyEnum_E {\n"
+               "  MY_ENUM = 0U,\n"
+               "};",
+               "enum class MyEnum_E {\n"
+               "  MY_ENUM = 0U\n"
+               "};",
+               Style);
+  Style.AllowShortEnumsOnASingleLine = true;
+
   Style.EnumTrailingComma = FormatStyle::ETC_Remove;
   verifyFormat("enum : int { /**/ };\n"
                "enum {\n"