[clang] Suppress octal literal diagnostics from system macros (PR #192481)
Aaron Ballman via cfe-commits
cfe-commits at lists.llvm.org
Thu Apr 16 09:27:41 PDT 2026
https://github.com/AaronBallman updated https://github.com/llvm/llvm-project/pull/192481
>From 338b888f8478afc8a4e5d2c688038d88342e82f8 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Thu, 16 Apr 2026 12:04:54 -0400
Subject: [PATCH 1/3] Suppress octal literal diagnostics from system macros
We emit two kinds of diagnostics related to octal literals. One is a
compat/extension warning for use of 0o as the literal prefix and the
other is a deprecation warning for use of 0 as the literal prefix.
Clang now suppresses both of those diagnostics when the octal literal
comes from a macro expansion of a macro defined in a system header.
Those are not uses of the literal the user has any control over,
generally, so the diagnostics are not helpful in that case.
Fixes #192389
---
clang/docs/ReleaseNotes.rst | 6 ++++++
clang/lib/Lex/LiteralSupport.cpp | 13 ++++++++++---
clang/test/C/C2y/n3353.c | 30 ++++++++++++++++++++++++++----
3 files changed, 42 insertions(+), 7 deletions(-)
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 8d74dd8bc9699..e8edf36f39af5 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -382,6 +382,12 @@ Improvements to Clang's diagnostics
code can automatically be made portable to other host platforms that don't
support backslashes.
+- No longer emitting a ``-Wpre-c2y-compat`` or extension diagnostic about use
+ of octal literals with a ``0o`` prefix, and no longer emitting a
+ ``-Wdeprecated-octal-literals`` diagnostic for use of octal literals without
+ a ``0o`` prefix, when the literal is expanded from a macro defined in a
+ system header. (#GH192389)
+
Improvements to Clang's time-trace
----------------------------------
diff --git a/clang/lib/Lex/LiteralSupport.cpp b/clang/lib/Lex/LiteralSupport.cpp
index a6b895e842c80..c93e9e33786cc 100644
--- a/clang/lib/Lex/LiteralSupport.cpp
+++ b/clang/lib/Lex/LiteralSupport.cpp
@@ -1429,7 +1429,11 @@ void NumericLiteralParser::ParseNumberStartingWithZero(SourceLocation TokLoc) {
DiagId = diag::ext_cpp_octal_literal;
else
DiagId = diag::ext_octal_literal;
- Diags.Report(TokLoc, DiagId);
+ // If the token location is from a macro expansion where the macro was
+ // defined in a system header, suppress the diagnostic.
+ if (!SM.isInSystemMacro(TokLoc))
+ Diags.Report(TokLoc, DiagId);
+
++s;
DigitsBegin = s;
radix = 8;
@@ -1450,8 +1454,11 @@ void NumericLiteralParser::ParseNumberStartingWithZero(SourceLocation TokLoc) {
llvm::scope_exit _([&] {
// If we still have an octal value but we did not see an octal prefix,
- // diagnose as being an obsolescent feature starting in C2y.
- if (radix == 8 && LangOpts.C2y && !hadError && !IsSingleZero)
+ // diagnose as being an obsolescent feature starting in C2y. If the token
+ // location is from a macro expansion where the macro was defined in a
+ // system header, suppress the diagnostic.
+ if (radix == 8 && LangOpts.C2y && !hadError && !IsSingleZero &&
+ !SM.isInSystemMacro(TokLoc))
Diags.Report(TokLoc, diag::warn_unprefixed_octal_deprecated);
});
diff --git a/clang/test/C/C2y/n3353.c b/clang/test/C/C2y/n3353.c
index a2e08cf6344db..f396d4e6182bf 100644
--- a/clang/test/C/C2y/n3353.c
+++ b/clang/test/C/C2y/n3353.c
@@ -1,7 +1,7 @@
-// RUN: %clang_cc1 -verify=expected,c2y,c -pedantic -std=c2y %s
-// RUN: %clang_cc1 -verify=expected,c2y,compat -Wpre-c2y-compat -std=c2y %s
-// RUN: %clang_cc1 -verify=expected,ext,c -pedantic -std=c23 %s
-// RUN: %clang_cc1 -verify=expected,cpp -pedantic -x c++ -Wno-c11-extensions %s
+// RUN: %clang_cc1 -verify=expected,c2y,c -pedantic -std=c2y -Wno-gnu-line-marker %s
+// RUN: %clang_cc1 -verify=expected,c2y,compat -Wpre-c2y-compat -std=c2y -Wno-gnu-line-marker %s
+// RUN: %clang_cc1 -verify=expected,ext,c -pedantic -std=c23 -Wno-gnu-line-marker %s
+// RUN: %clang_cc1 -verify=expected,cpp -pedantic -x c++ -Wno-c11-extensions -Wno-gnu-line-marker %s
/* WG14 N3353: Clang 21
@@ -166,5 +166,27 @@ void foo() {
}
#endif
+#172 "system_header.c" 3
+#define SYS_HEADER_MACRO_1 0o02
+#define SYS_HEADER_MACRO_2 02
+#174 "n3353.c" 1
+
+#define USER_HEADER_MACRO_1 0o02
+#define USER_HEADER_MACRO_2 02
+
+void test_macro_behavior(void) {
+ // No diagnostic because these expanded from a macro defined in a system
+ // header.
+ int i = SYS_HEADER_MACRO_1;
+ int j = SYS_HEADER_MACRO_2;
+
+ // Diagnose other macro expansions though.
+ int a = USER_HEADER_MACRO_1; /* ext-warning {{octal integer literals are a C2y extension}}
+ cpp-warning {{octal integer literals are a Clang extension}}
+ compat-warning {{octal integer literals are incompatible with standards before C2y}}
+ */
+ int b = USER_HEADER_MACRO_2; // c2y-warning {{octal literals without a '0o' prefix are deprecated}}
+}
+
#line 0123 // expected-warning {{#line directive interprets number as decimal, not octal}}
#line 0o123 // expected-error {{#line directive requires a simple digit sequence}}
>From a52081c90f2c4a18f1b3f01083d70dd3fe849a48 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Thu, 16 Apr 2026 12:18:08 -0400
Subject: [PATCH 2/3] Use .h as the extension for the header in the line marker
---
clang/test/C/C2y/n3353.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/clang/test/C/C2y/n3353.c b/clang/test/C/C2y/n3353.c
index f396d4e6182bf..10c8449124fe4 100644
--- a/clang/test/C/C2y/n3353.c
+++ b/clang/test/C/C2y/n3353.c
@@ -166,7 +166,7 @@ void foo() {
}
#endif
-#172 "system_header.c" 3
+#172 "system_header.h" 3
#define SYS_HEADER_MACRO_1 0o02
#define SYS_HEADER_MACRO_2 02
#174 "n3353.c" 1
>From b46920d13a6748502d30337e19619d05b59a374d Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Thu, 16 Apr 2026 12:27:08 -0400
Subject: [PATCH 3/3] Add some more test cases
---
clang/test/C/C2y/n3353.c | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/clang/test/C/C2y/n3353.c b/clang/test/C/C2y/n3353.c
index 10c8449124fe4..84620a2cb8425 100644
--- a/clang/test/C/C2y/n3353.c
+++ b/clang/test/C/C2y/n3353.c
@@ -166,19 +166,31 @@ void foo() {
}
#endif
+int other_func(int i, ...);
#172 "system_header.h" 3
#define SYS_HEADER_MACRO_1 0o02
#define SYS_HEADER_MACRO_2 02
+#define SYS_HEADER_MACRO_FN1(...) other_func(0o02, __VA_ARGS__)
+#define SYS_HEADER_MACRO_FN2(...) other_func(2, __VA_ARGS__)
#174 "n3353.c" 1
#define USER_HEADER_MACRO_1 0o02
#define USER_HEADER_MACRO_2 02
+#define USER_HEADER_MACRO_FN1(...) other_func(0o02, __VA_ARGS__)
+#define USER_HEADER_MACRO_FN2(...) other_func(2, __VA_ARGS__)
void test_macro_behavior(void) {
// No diagnostic because these expanded from a macro defined in a system
// header.
int i = SYS_HEADER_MACRO_1;
int j = SYS_HEADER_MACRO_2;
+ int k = SYS_HEADER_MACRO_FN1(12);
+
+ // This one diagnoses because the literal is not in the system header.
+ int l = SYS_HEADER_MACRO_FN2(0o02); /* ext-warning {{octal integer literals are a C2y extension}}
+ cpp-warning {{octal integer literals are a Clang extension}}
+ compat-warning {{octal integer literals are incompatible with standards before C2y}}
+ */
// Diagnose other macro expansions though.
int a = USER_HEADER_MACRO_1; /* ext-warning {{octal integer literals are a C2y extension}}
@@ -186,6 +198,14 @@ void test_macro_behavior(void) {
compat-warning {{octal integer literals are incompatible with standards before C2y}}
*/
int b = USER_HEADER_MACRO_2; // c2y-warning {{octal literals without a '0o' prefix are deprecated}}
+ int c = USER_HEADER_MACRO_FN1(12); /* ext-warning {{octal integer literals are a C2y extension}}
+ cpp-warning {{octal integer literals are a Clang extension}}
+ compat-warning {{octal integer literals are incompatible with standards before C2y}}
+ */
+ int d = USER_HEADER_MACRO_FN2(0o02); /* ext-warning {{octal integer literals are a C2y extension}}
+ cpp-warning {{octal integer literals are a Clang extension}}
+ compat-warning {{octal integer literals are incompatible with standards before C2y}}
+ */
}
#line 0123 // expected-warning {{#line directive interprets number as decimal, not octal}}
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