diagnostics missing from -Wc++-compat #21898

zygoloid · 2014-11-11T05:46:06Z


Bugzilla Link	21524
Version	trunk
OS	Linux
CC	@DougGregor

Extended Description

From http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-November/039875.html

clang doesn't print warning for following test-case:

compiled with: clang -fsyntax-only -Wc++-compat

int new;
struct A
{
struct B
{
int x;
}bs;
int y;
};
struct B b;

gcc -fsyntax-only -Wc++-compat prints following warnings (gcc-4.9.1 ubuntu):

t.c:1:5: warning: identifier ‘new’ conflicts with C++ keyword [-Wc++-compat]
int new;
^
t.c:13:8: warning: struct defined in struct or union is not visible in
C++ [-Wc++-compat]
struct B b;
^
t.c:5:10: note: struct defined here
struct B
^

llvmbot · 2023-12-07T02:57:34Z

@llvm/issue-subscribers-c

Author: None (ec04fc15-fa35-46f2-80e1-5d271f2ef708)

| | | | --- | --- | | Bugzilla Link | [21524](https://llvm.org/bz21524) | | Version | trunk | | OS | Linux | | CC | @DougGregor |

Extended Description

From http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-November/039875.html

clang doesn't print warning for following test-case:

compiled with: clang -fsyntax-only -Wc++-compat

int new;
struct A
{
struct B
{
int x;
}bs;
int y;
};
struct B b;

gcc -fsyntax-only -Wc++-compat prints following warnings (gcc-4.9.1 ubuntu):

t.c:1:5: warning: identifier ‘new’ conflicts with C++ keyword [-Wc++-compat]
int new;
^
t.c:13:8: warning: struct defined in struct or union is not visible in
C++ [-Wc++-compat]
struct B b;
^
t.c:5:10: note: struct defined here
struct B
^

wheatman · 2023-12-07T02:58:06Z

This still exists in post 17 trunk(e68c265)

https://godbolt.org/z/fGcnGTrn5

code

int new;
struct A {
  struct B  { int x; } bs;
  int y;
};
struct B b;

clang gives no warnings with -Wc++-compat

on the other hand gcc gives the following warning

<source>:1:5: warning: identifier 'new' conflicts with C++ keyword [-Wc++-compat]
    1 | int new;
      |     ^~~
<source>:6:8: warning: struct defined in struct or union is not visible in C++ [-Wc++-compat]
    6 | struct B b;
      |        ^
<source>:3:10: note: struct defined here
    3 |   struct B  { int x; } bs;
      |          ^
Compiler returned: 0

This adds a new diagnostic group, -Widentifier-is-c++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists. Partially fixes llvm#21898

This introduces a new diagnostic, -Wc++-hidden-decl, which is grouped under -Wc++-compat, that diagnoses declarations which are valid in C but invalid in C++ due to the type being at the wrong scope. e.g., struct S { struct T { int x; } t; }; struct T t; // Valid C, invalid C++ This is implementing the other half of llvm#21898

This introduces a new diagnostic, -Wc++-hidden-decl, which is grouped under -Wc++-compat, that diagnoses declarations which are valid in C but invalid in C++ due to the type being at the wrong scope. e.g., ``` struct S { struct T { int x; } t; }; struct T t; // Valid C, invalid C++ ``` This is implementing the other half of #21898

This adds a new diagnostic group, -Wc++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists in a function declaration which is not a definition. Fixes #21898

This introduces a new diagnostic, -Wc++-hidden-decl, which is grouped under -Wc++-compat, that diagnoses declarations which are valid in C but invalid in C++ due to the type being at the wrong scope. e.g., ``` struct S { struct T { int x; } t; }; struct T t; // Valid C, invalid C++ ``` This is implementing the other half of llvm#21898

This adds a new diagnostic group, -Wc++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists in a function declaration which is not a definition. Fixes llvm#21898

This introduces a new diagnostic, -Wc++-hidden-decl, which is grouped under -Wc++-compat, that diagnoses declarations which are valid in C but invalid in C++ due to the type being at the wrong scope. e.g., ``` struct S { struct T { int x; } t; }; struct T t; // Valid C, invalid C++ ``` This is implementing the other half of llvm#21898

This adds a new diagnostic group, -Wc++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists in a function declaration which is not a definition. Fixes llvm#21898

This introduces a new diagnostic, -Wc++-hidden-decl, which is grouped under -Wc++-compat, that diagnoses declarations which are valid in C but invalid in C++ due to the type being at the wrong scope. e.g., ``` struct S { struct T { int x; } t; }; struct T t; // Valid C, invalid C++ ``` This is implementing the other half of llvm#21898

This adds a new diagnostic group, -Wc++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists in a function declaration which is not a definition. Fixes llvm#21898

This adds a new diagnostic group, -Wc++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists in a function declaration which is not a definition. Fixes llvm/llvm-project#21898

This introduces a new diagnostic, -Wc++-hidden-decl, which is grouped under -Wc++-compat, that diagnoses declarations which are valid in C but invalid in C++ due to the type being at the wrong scope. e.g., ``` struct S { struct T { int x; } t; }; struct T t; // Valid C, invalid C++ ``` This is implementing the other half of llvm#21898

This adds a new diagnostic group, -Wc++-keyword, which is off by default and grouped under -Wc++-compat. The diagnostic catches use of C++ keywords in C code. This change additionally fixes an issue with -Wreserved-identifier not diagnosing use of reserved identifiers in function parameter lists in a function declaration which is not a definition. Fixes llvm#21898

llvmbot transferred this issue from llvm/llvm-bugzilla-archive Dec 9, 2021

wheatman added clang:diagnostics New/improved warning or error message in Clang, but not in clang-tidy or static analyzer confirmed Verified by a second party c labels Dec 7, 2023

AaronBallman mentioned this issue Apr 24, 2025

[C] Diagnose use of C++ keywords in C #137234

Merged

AaronBallman mentioned this issue Apr 25, 2025

[C] Diagnose declarations hidden in C++ #137368

Merged

AaronBallman closed this as completed in #137234 May 2, 2025

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diagnostics missing from -Wc++-compat #21898

diagnostics missing from -Wc++-compat #21898

zygoloid mannequin commented Nov 11, 2014

llvmbot commented Dec 7, 2023

Extended Description

wheatman commented Dec 7, 2023

diagnostics missing from -Wc++-compat #21898

diagnostics missing from -Wc++-compat #21898

Comments

zygoloid mannequin commented Nov 11, 2014

Extended Description

llvmbot commented Dec 7, 2023

Extended Description

wheatman commented Dec 7, 2023