llvm · AaronBallman · Apr 11, 2025 · Apr 11, 2025 · Apr 14, 2025 · Apr 15, 2025
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
@@ -51,6 +51,11 @@ C/C++ Language Potentially Breaking Changes
   ensure they are not caught by these optimizations.  It is also possible to use
   ``-fwrapv-pointer`` or   ``-fno-delete-null-pointer-checks`` to make pointer arithmetic
   on null pointers well-defined. (#GH130734, #GH130742, #GH130952)
+- Use of the dollar sign (``$``) in an identifier is no longer a conforming
+  extension in either C or C++, so ``-fdollars-in-identifiers`` is no longer
+  enabled by default. Use of the dollar sign in an identifier will now be
+  diagnosed as an error unless ``-fdollars-in-identifiers`` is explicitly
+  enabled.
 
 C++ Specific Potentially Breaking Changes
 -----------------------------------------

diff --git a/clang/include/clang/Basic/DiagnosticLexKinds.td b/clang/include/clang/Basic/DiagnosticLexKinds.td
@@ -57,6 +57,9 @@ def warn_no_newline_eof : Warning<"no newline at end of file">,
 
 def ext_dollar_in_identifier : Extension<"'$' in identifier">,
   InGroup<DiagGroup<"dollar-in-identifier-extension">>;
+def warn_dollar_in_identifier : Warning<
+  "'$' in identifier; did you mean to enable '-fdollars-in-identifiers'?">,
+  InGroup<DiagGroup<"dollar-in-identifier">>;
 def ext_charize_microsoft : Extension<
   "charizing operator #@ is a Microsoft extension">,
   InGroup<MicrosoftCharize>;

diff --git a/clang/include/clang/Basic/LangOptions.def b/clang/include/clang/Basic/LangOptions.def
@@ -119,7 +119,7 @@ LANGOPT(WChar             , 1, 0, "wchar_t keyword")
 LANGOPT(Char8             , 1, 0, "char8_t keyword")
 LANGOPT(IEEE128           , 1, 0, "__ieee128 keyword")
 LANGOPT(DeclSpecKeyword   , 1, 0, "__declspec keyword")
-BENIGN_LANGOPT(DollarIdents   , 1, 1, "'$' in identifiers")
+COMPATIBLE_LANGOPT(DollarIdents, 1, 0, "'$' in identifiers")
 BENIGN_LANGOPT(AsmPreprocessor, 1, 0, "preprocessor in asm mode")
 LANGOPT(GNUMode           , 1, 1, "GNU extensions")
 LANGOPT(GNUKeywords       , 1, 1, "GNU keywords")

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -632,7 +632,6 @@ defvar open_cl = LangOpts<"OpenCL">;
 defvar cuda = LangOpts<"CUDA">;
 defvar hip = LangOpts<"HIP">;
 defvar gnu_mode = LangOpts<"GNUMode">;
-defvar asm_preprocessor = LangOpts<"AsmPreprocessor">;
 defvar hlsl = LangOpts<"HLSL">;
 
 defvar std = !strconcat("LangStandard::getLangStandardForKind(", lang_std.KeyPath, ")");
@@ -2092,7 +2091,7 @@ def fno_discard_value_names : Flag<["-"], "fno-discard-value-names">,
   Group<f_clang_Group>, Visibility<[ClangOption, DXCOption]>,
   HelpText<"Do not discard value names in LLVM IR">;
 defm dollars_in_identifiers : BoolFOption<"dollars-in-identifiers",
-  LangOpts<"DollarIdents">, Default<!strconcat("!", asm_preprocessor.KeyPath)>,
+  LangOpts<"DollarIdents">, DefaultFalse,
   PosFlag<SetTrue, [], [ClangOption], "Allow">,
   NegFlag<SetFalse, [], [ClangOption], "Disallow">,
   BothFlags<[], [ClangOption, CC1Option], " '$' in identifiers">>;

diff --git a/clang/lib/Format/Format.cpp b/clang/lib/Format/Format.cpp
@@ -4035,6 +4035,7 @@ LangOptions getFormattingLangOpts(const FormatStyle &Style) {
   LangOpts.MicrosoftExt = 1;    // To get kw___try, kw___finally.
   LangOpts.DeclSpecKeyword = 1; // To get __declspec.
   LangOpts.C99 = 1; // To get kw_restrict for non-underscore-prefixed restrict.
+  LangOpts.DollarIdents = 1; // To allow $ in identifiers.
 
   return LangOpts;
 }

diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
@@ -4036,8 +4036,11 @@ bool Lexer::LexTokenInternal(Token &Result, bool TokAtPhysicalStartOfLine) {
       MIOpt.ReadToken();
       return LexIdentifierContinue(Result, CurPtr);
     }
-
     Kind = tok::unknown;
+    // We do not want to diagnose in ASM preprocessor mode because the
+    // assembler isn't necessarily trying to lex identifiers to begin with.
+    if (!isLexingRawMode() && !LangOpts.AsmPreprocessor)
+      Diag(CurPtr - 1, diag::warn_dollar_in_identifier);
     break;
 
   // C99 6.4.4: Character Constants.

diff --git a/clang/test/AST/ByteCode/codegen.m b/clang/test/AST/ByteCode/codegen.m
@@ -3,7 +3,7 @@
 /// See test/CodeGenObjC/constant-strings.m
 /// Test that we let the APValue we create for ObjCStringLiterals point to the right expression.
 
-// RUN: %clang_cc1 -triple x86_64-macho -emit-llvm -o %t %s -fexperimental-new-constant-interpreter
+// RUN: %clang_cc1 -triple x86_64-macho -fdollars-in-identifiers  -emit-llvm -o %t %s -fexperimental-new-constant-interpreter
 // RUN: FileCheck --check-prefix=CHECK-NEXT < %t %s
 
 // Check that we set alignment 1 on the string.

diff --git a/clang/test/C/C99/n717.c b/clang/test/C/C99/n717.c
@@ -37,7 +37,7 @@ M(\U123456789) // Okay-ish, two tokens (valid-per-spec-but-actually-invalid UCN
 // GH87106.
 M(\u0024) // expected-error {{character '$' cannot be specified by a universal character name}}
 M(\U00000024) // expected-error {{character '$' cannot be specified by a universal character name}}
-M($)
+M($)      // expected-warning {{'$' in identifier; did you mean to enable '-fdollars-in-identifiers'?}}
 
 // These should always be rejected because they're not valid identifier
 // characters.

diff --git a/clang/test/C/drs/dr0xx.c b/clang/test/C/drs/dr0xx.c
@@ -1,9 +1,9 @@
-/* RUN: %clang_cc1 -std=c89 -fsyntax-only -verify=expected,c89only -pedantic -Wno-declaration-after-statement -Wno-c11-extensions %s
-   RUN: %clang_cc1 -std=c89 -fsyntax-only -verify=expected,c89only -pedantic -Wno-declaration-after-statement -Wno-c11-extensions -fno-signed-char %s
-   RUN: %clang_cc1 -std=c99 -fsyntax-only -verify=expected,c99untilc2x -pedantic -Wno-c11-extensions %s
-   RUN: %clang_cc1 -std=c11 -fsyntax-only -verify=expected,c99untilc2x -pedantic %s
-   RUN: %clang_cc1 -std=c17 -fsyntax-only -verify=expected,c99untilc2x -pedantic %s
-   RUN: %clang_cc1 -std=c2x -fsyntax-only -verify=expected,c2xandup -pedantic %s
+/* RUN: %clang_cc1 -std=c89 -fdollars-in-identifiers -fsyntax-only -verify=expected,c89only -pedantic -Wno-declaration-after-statement -Wno-c11-extensions %s
+   RUN: %clang_cc1 -std=c89 -fdollars-in-identifiers -fsyntax-only -verify=expected,c89only -pedantic -Wno-declaration-after-statement -Wno-c11-extensions -fno-signed-char %s
+   RUN: %clang_cc1 -std=c99 -fdollars-in-identifiers -fsyntax-only -verify=expected,c99untilc2x -pedantic -Wno-c11-extensions %s
+   RUN: %clang_cc1 -std=c11 -fdollars-in-identifiers -fsyntax-only -verify=expected,c99untilc2x -pedantic %s
+   RUN: %clang_cc1 -std=c17 -fdollars-in-identifiers -fsyntax-only -verify=expected,c99untilc2x -pedantic %s
+   RUN: %clang_cc1 -std=c2x -fdollars-in-identifiers -fsyntax-only -verify=expected,c2xandup -pedantic %s
  */
 
 /* The following are DRs which do not require tests to demonstrate

diff --git a/clang/test/CodeGen/ms-inline-asm.c b/clang/test/CodeGen/ms-inline-asm.c
@@ -1,5 +1,5 @@
 // REQUIRES: x86-registered-target
-// RUN: %clang_cc1 %s -triple i386-apple-darwin10 -fasm-blocks -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -triple i386-apple-darwin10 -fdollars-in-identifiers -fasm-blocks -emit-llvm -o - | FileCheck %s
 
 void t1(void) {
 // CHECK: @t1

diff --git a/clang/test/CodeGenObjC/extern-void-class-decl.m b/clang/test/CodeGenObjC/extern-void-class-decl.m
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 -fdollars-in-identifiers %s -emit-llvm -o - | FileCheck %s
 
 extern void OBJC_CLASS_$_f;
 Class c = (Class)&OBJC_CLASS_$_f;

diff --git a/clang/test/Lexer/dollar-idents.c b/clang/test/Lexer/dollar-idents.c
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -dump-tokens %s 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -dump-tokens -fdollars-in-identifiers %s 2>&1 | FileCheck %s
 // RUN: %clang_cc1 -dump-tokens -x assembler-with-cpp %s 2>&1 | FileCheck %s --check-prefix=CHECK-ASM
 // PR3808
 

diff --git a/clang/test/Lexer/gh128939.cpp b/clang/test/Lexer/gh128939.cpp
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -E -fdollars-in-identifiers %s 2>&1 | FileCheck %s --check-prefix=CHECK-DOLLARS
+// RUN: %clang_cc1 -E %s 2>&1 | FileCheck %s --check-prefix=CHECK-NO-DOLLARS
+// RUN: %clang_cc1 -verify -x assembler-with-cpp %s
+// GH128939
+
+#define FOO$ 10 // expected-warning {{ISO C99 requires whitespace after the macro name}}
+#define STR(x) #x
+#define STR2(x) STR(x)
+const char *p = STR2(FOO$);
+
+// CHECK-NO-DOLLARS: const char *p = "$ 10$";
+// CHECK-DOLLARS: const char *p = "10";
+
+#define STR3 STR(
+const char *q = STR3$10);
+
+// CHECK-NO-DOLLARS: const char *q = "$10";
+// CHECK-DOLLARS: const char *q = STR3$10);
diff --git a/clang/test/Preprocessor/c90.c b/clang/test/Preprocessor/c90.c
@@ -1,4 +1,4 @@
-/* RUN: %clang_cc1 %s -std=c89 -Eonly -verify -pedantic-errors 
+/* RUN: %clang_cc1 %s -std=c89 -Eonly -DTEST_THIS_TOO -verify -pedantic-errors
  * RUN: %clang_cc1 %s -std=c89 -E | FileCheck %s
  */
 
@@ -7,7 +7,18 @@
 #define foo`bar   /* expected-error {{whitespace required after macro name}} */
 #define foo2!bar  /* expected-warning {{whitespace recommended after macro name}} */
 
-#define foo3$bar  /* expected-error {{'$' in identifier}} */
+#define foo3$bar  /* expected-error {{whitespace required after macro name}}
+                     expected-warning {{'$' in identifier; did you mean to enable '-fdollars-in-identifiers'?}}
+                   */
+
+#define test$     /* expected-error {{whitespace required after macro name}}
+                     expected-warning {{'$' in identifier; did you mean to enable '-fdollars-in-identifiers'?}}
+                   */
+#ifdef TEST_THIS_TOO
+#define $         /* expected-error {{macro name must be an identifier}}
+                     expected-warning {{'$' in identifier; did you mean to enable '-fdollars-in-identifiers'?}}
+                   */
+#endif
 
 /* CHECK-NOT: this comment should be missing
  * CHECK: {{^}}// this comment should be present{{$}}

diff --git a/clang/test/SemaCXX/scope-check.cpp b/clang/test/SemaCXX/scope-check.cpp
@@ -434,7 +434,8 @@ namespace test_recovery {
     a0:;
 
     switch (c) {
-    case $: // expected-error {{}}
+    case $: // expected-error {{}} \
+               expected-warning {{'$' in identifier; did you mean to enable '-fdollars-in-identifiers'?}}
     case 0:
       int x = 56; // expected-note {{jump bypasses variable initialization}}
     case 1: // expected-error {{cannot jump}}

diff --git a/clang/unittests/Analysis/MacroExpansionContextTest.cpp b/clang/unittests/Analysis/MacroExpansionContextTest.cpp
@@ -41,6 +41,7 @@ class MacroExpansionContextTest : public ::testing::Test {
     TargetOpts->Triple = "x86_64-pc-linux-unknown";
     Target = TargetInfo::CreateTargetInfo(Diags, TargetOpts);
     LangOpts.CPlusPlus20 = 1; // For __VA_OPT__
+    LangOpts.DollarIdents = 1; // For $identifier$ testing.
   }
 
   IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> InMemoryFileSystem;