[clang-format] Fix repeated backslash insertion in macro line comments

[ZhongRuoyu]

Line comments in preprocessor directives were incorrectly marked as continuing the directive, causing clang-format to add backslashes after them on repeated runs. Backslashes appended after line comments in this way do not continue the PP directive because the following line would also become part of the comment.

Fix by unsetting InPPDirective in WhitespaceManager::replaceWhitespace for line comments in two places: when breaking lines and when formatting tokens on the same line. This stops the spurious backslash insertion for both standalone line comments after PP directives and trailing line comments after macro bodies.

Fixes #164282.

[llvmbot]

@llvm/pr-subscribers-clang-format

Author: Ruoyu Zhong (ZhongRuoyu)

Changes

Line comments in preprocessor directives were incorrectly marked as continuing the directive, causing clang-format to add backslashes after them on repeated runs. Line comments cannot span multiple lines with backslashes, so they should not be treated as PP directive continuations.

Fix by unsetting InPPDirective in WhitespaceManager::replaceWhitespace for line comments in two places: when breaking lines and when formatting tokens on the same line. This stops the spurious backslash insertion for both standalone line comments after preprocessor directives and trailing line comments after macro bodies.

Fixes #164282.

---

Full diff: https://github.com/llvm/llvm-project/pull/164300.diff

2 Files Affected:

• (modified) clang/lib/Format/ContinuationIndenter.cpp (+6-3)
• (modified) clang/unittests/Format/FormatTestComments.cpp (+19)

diff --git a/clang/lib/Format/ContinuationIndenter.cpp b/clang/lib/Format/ContinuationIndenter.cpp
index 26a95421775f3..1b0a2f001474d 100644
--- a/clang/lib/Format/ContinuationIndenter.cpp
+++ b/clang/lib/Format/ContinuationIndenter.cpp
@@ -798,9 +798,11 @@ void ContinuationIndenter::addTokenOnCurrentLine(LineState &State, bool DryRun,
   }
 
   if (!DryRun) {
+    bool ContinuePPDirective =
+        State.Line->InMacroBody && Current.isNot(TT_LineComment);
     Whitespaces.replaceWhitespace(Current, /*Newlines=*/0, Spaces,
                                   State.Column + Spaces + PPColumnCorrection,
-                                  /*IsAligned=*/false, State.Line->InMacroBody);
+                                  /*IsAligned=*/false, ContinuePPDirective);
   }
 
   // If "BreakBeforeInheritanceComma" mode, don't break within the inheritance
@@ -1178,8 +1180,9 @@ unsigned ContinuationIndenter::addTokenOnNewLine(LineState &State,
     }
     unsigned Newlines =
         std::max(1u, std::min(Current.NewlinesBefore, MaxEmptyLinesToKeep));
-    bool ContinuePPDirective =
-        State.Line->InPPDirective && State.Line->Type != LT_ImportStatement;
+    bool ContinuePPDirective = State.Line->InPPDirective &&
+                               State.Line->Type != LT_ImportStatement &&
+                               Current.isNot(TT_LineComment);
     Whitespaces.replaceWhitespace(Current, Newlines, State.Column, State.Column,
                                   CurrentState.IsAligned, ContinuePPDirective);
   }
diff --git a/clang/unittests/Format/FormatTestComments.cpp b/clang/unittests/Format/FormatTestComments.cpp
index fc80bf4024fd9..f5c791a29ba02 100644
--- a/clang/unittests/Format/FormatTestComments.cpp
+++ b/clang/unittests/Format/FormatTestComments.cpp
@@ -839,6 +839,25 @@ TEST_F(FormatTestComments, MultiLineCommentsInDefines) {
                    getLLVMStyleWithColumns(17)));
 }
 
+TEST_F(FormatTestComments, LineCommentsInMacrosDoNotGetEscapedNewlines) {
+  FormatStyle Style = getLLVMStyleWithColumns(0);
+  Style.ReflowComments = FormatStyle::RCS_Never;
+  verifyFormat("#define FOO (1U) // comment\n"
+               "                 // comment",
+               Style);
+
+  Style.ColumnLimit = 32;
+  EXPECT_EQ("#define SOME_MACRO(x) x\n"
+            "#define FOO                    \\\n"
+            "  SOME_MACRO(1) +              \\\n"
+            "      SOME_MACRO(2) // comment\n"
+            "                    // comment",
+            format("#define SOME_MACRO(x) x\n"
+                   "#define FOO SOME_MACRO(1) + SOME_MACRO(2) // comment\n"
+                   "                                          // comment",
+                   Style));
+}
+
 TEST_F(FormatTestComments, ParsesCommentsAdjacentToPPDirectives) {
   EXPECT_EQ("namespace {}\n// Test\n#define A",
             format("namespace {}\n   // Test\n#define A"));

[HazardyKnusperkeks]

You may also want to update the commit message, because line comments can be continued with \. https://godbolt.org/z/GP8YnoTqb

[ZhongRuoyu]

You may also want to update the commit message, because line comments can be continued with \. https://godbolt.org/z/GP8YnoTqb

Thanks -- didn't think about that! I updated the PR description as well.