[clang-format] Disallow breaking before/after ## (#200721)

owenca · web-flow · commit 26ffc71afa7c · 2026-06-05T22:09:59.000-07:00
Fixes #199775
diff --git a/clang/lib/Format/TokenAnnotator.cpp b/clang/lib/Format/TokenAnnotator.cpp
@@ -6495,6 +6495,8 @@ bool TokenAnnotator::canBreakBefore(const AnnotatedLine &Line,
             !(Right.Next &&
               Right.Next->isOneOf(TT_FunctionDeclarationName, tok::kw_const)));
   }
+  if (Left.is(tok::hashhash) || Right.is(tok::hashhash))
+    return false;
   if (Right.isOneOf(TT_StartOfName, TT_FunctionDeclarationName,
                     TT_ClassHeadName, TT_QtProperty, tok::kw_operator)) {
     return true;
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
@@ -5967,22 +5967,33 @@ TEST_F(FormatTest, HashInMacroDefinition) {
   verifyFormat("#define A(c) uR#c");
   verifyFormat("#define A(c) UR#c");
   verifyFormat("#define A(c) u8R#c");
-  verifyFormat("#define A \\\n  b #c;", getLLVMStyleWithColumns(11));
+
+  auto Style = getLLVMStyleWithColumns(11);
+  verifyFormat("#define A \\\n  b #c;", Style);
   verifyFormat("#define A  \\\n"
                "  {        \\\n"
                "    f(#c); \\\n"
                "  }",
-               getLLVMStyleWithColumns(11));
+               Style);
 
+  Style.ColumnLimit = 22;
   verifyFormat("#define A(X)         \\\n"
                "  void function##X()",
-               getLLVMStyleWithColumns(22));
-
+               Style);
   verifyFormat("#define A(a, b, c)   \\\n"
                "  void a##b##c()",
-               getLLVMStyleWithColumns(22));
+               Style);
+  verifyFormat("#define A void # ## #", Style);
 
-  verifyFormat("#define A void # ## #", getLLVMStyleWithColumns(22));
+  Style.ColumnLimit = 60;
+  Style.AlignEscapedNewlines = FormatStyle::ENAS_DontAlign;
+  verifyFormat(
+      "#define MACRO(Name) \\\n"
+      "  struct LongPrefix##Name##LongSuffix< \\\n"
+      "      VeryLongTemplateArgument> {};",
+      "#define MACRO(Name) \\\n"
+      "  struct LongPrefix##Name##LongSuffix<VeryLongTemplateArgument> {};",
+      Style);
 
   verifyFormat("{\n"
                "  {\n"

Original file line number	Diff line number	Diff line change
`@@ -6495,6 +6495,8 @@ bool TokenAnnotator::canBreakBefore(const AnnotatedLine &Line,`
`6495`	`6495`	`!(Right.Next &&`
`6496`	`6496`	`Right.Next->isOneOf(TT_FunctionDeclarationName, tok::kw_const)));`
`6497`	`6497`	`}`
	`6498`	`+ if (Left.is(tok::hashhash) \|\| Right.is(tok::hashhash))`
	`6499`	`+ return false;`
`6498`	`6500`	`if (Right.isOneOf(TT_StartOfName, TT_FunctionDeclarationName,`
`6499`	`6501`	`TT_ClassHeadName, TT_QtProperty, tok::kw_operator)) {`
`6500`	`6502`	`return true;`