Enabling cxx interop on Arch with GCC 15 causes lots of errors

[gonsolo]

Description

Enabling cxx interop on a simple example generates lots of errors with latest GCC on Arch Linux:

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:100:3: error: redefinition of 'acos'
  98 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
  99 |   inline _GLIBCXX_CONSTEXPR float
 100 |   acos(float __x)
     |   |- error: redefinition of 'acos'
     |   `- note: previous definition is here
 101 |   { return __builtin_acosf(__x); }
 102 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:104:3: error: redefinition of 'acos'
 102 | 
 103 |   inline _GLIBCXX_CONSTEXPR long double
 104 |   acos(long double __x)
     |   |- error: redefinition of 'acos'
     |   `- note: previous definition is here
 105 |   { return __builtin_acosl(__x); }
 106 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:112:5: error: redefinition of 'acos'
 110 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value, 
 111 |                                     double>::__type
 112 |     acos(_Tp __x)
     |     |- error: redefinition of 'acos'
     |     `- note: previous definition is here
 113 |     { return __builtin_acos(__x); }
 114 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:119:3: error: redefinition of 'asin'
 117 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 118 |   inline _GLIBCXX_CONSTEXPR float
 119 |   asin(float __x)
     |   |- error: redefinition of 'asin'
     |   `- note: previous definition is here
 120 |   { return __builtin_asinf(__x); }
 121 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:123:3: error: redefinition of 'asin'
 121 | 
 122 |   inline _GLIBCXX_CONSTEXPR long double
 123 |   asin(long double __x)
     |   |- error: redefinition of 'asin'
     |   `- note: previous definition is here
 124 |   { return __builtin_asinl(__x); }
 125 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:131:5: error: redefinition of 'asin'
 129 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
 130 |                                     double>::__type
 131 |     asin(_Tp __x)
     |     |- error: redefinition of 'asin'
     |     `- note: previous definition is here
 132 |     { return __builtin_asin(__x); }
 133 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:138:3: error: redefinition of 'atan'
 136 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 137 |   inline _GLIBCXX_CONSTEXPR float
 138 |   atan(float __x)
     |   |- error: redefinition of 'atan'
     |   `- note: previous definition is here
 139 |   { return __builtin_atanf(__x); }
 140 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:142:3: error: redefinition of 'atan'
 140 | 
 141 |   inline _GLIBCXX_CONSTEXPR long double
 142 |   atan(long double __x)
     |   |- error: redefinition of 'atan'
     |   `- note: previous definition is here
 143 |   { return __builtin_atanl(__x); }
 144 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:150:5: error: redefinition of 'atan'
 148 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
 149 |                                     double>::__type
 150 |     atan(_Tp __x)
     |     |- error: redefinition of 'atan'
     |     `- note: previous definition is here
 151 |     { return __builtin_atan(__x); }
 152 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:157:3: error: redefinition of 'atan2'
 155 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 156 |   inline _GLIBCXX_CONSTEXPR float
 157 |   atan2(float __y, float __x)
     |   |- error: redefinition of 'atan2'
     |   `- note: previous definition is here
 158 |   { return __builtin_atan2f(__y, __x); }
 159 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:161:3: error: redefinition of 'atan2'
 159 | 
 160 |   inline _GLIBCXX_CONSTEXPR long double
 161 |   atan2(long double __y, long double __x)
     |   |- error: redefinition of 'atan2'
     |   `- note: previous definition is here
 162 |   { return __builtin_atan2l(__y, __x); }
 163 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:169:3: error: redefinition of 'ceil'
 167 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 168 |   inline _GLIBCXX_CONSTEXPR float
 169 |   ceil(float __x)
     |   |- error: redefinition of 'ceil'
     |   `- note: previous definition is here
 170 |   { return __builtin_ceilf(__x); }
 171 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:173:3: error: redefinition of 'ceil'
 171 | 
 172 |   inline _GLIBCXX_CONSTEXPR long double
 173 |   ceil(long double __x)
     |   |- error: redefinition of 'ceil'
     |   `- note: previous definition is here
 174 |   { return __builtin_ceill(__x); }
 175 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:181:5: error: redefinition of 'ceil'
 179 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value, 
 180 |                                     double>::__type
 181 |     ceil(_Tp __x)
     |     |- error: redefinition of 'ceil'
     |     `- note: previous definition is here
 182 |     { return __builtin_ceil(__x); }
 183 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:188:3: error: redefinition of 'cos'
 186 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 187 |   inline _GLIBCXX_CONSTEXPR float
 188 |   cos(float __x)
     |   |- error: redefinition of 'cos'
     |   `- note: previous definition is here
 189 |   { return __builtin_cosf(__x); }
 190 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:192:3: error: redefinition of 'cos'
 190 | 
 191 |   inline _GLIBCXX_CONSTEXPR long double
 192 |   cos(long double __x)
     |   |- error: redefinition of 'cos'
     |   `- note: previous definition is here
 193 |   { return __builtin_cosl(__x); }
 194 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:200:5: error: redefinition of 'cos'
 198 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
 199 |                                     double>::__type
 200 |     cos(_Tp __x)
     |     |- error: redefinition of 'cos'
     |     `- note: previous definition is here
 201 |     { return __builtin_cos(__x); }
 202 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:207:3: error: redefinition of 'cosh'
 205 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 206 |   inline _GLIBCXX_CONSTEXPR float
 207 |   cosh(float __x)
     |   |- error: redefinition of 'cosh'
     |   `- note: previous definition is here
 208 |   { return __builtin_coshf(__x); }
 209 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "_FoundationCShims.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
15 | 
16 | #include "_CShimsTargetConditionals.h"
17 | #include "_CStdlib.h"
   |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_FoundationCShims.h:17:
18 | #include "CFUniCharBitmapData.inc.h"
19 | #include "CFUniCharBitmapData.h"

/usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:10: note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 53 | 
 54 | #if __has_include(<math.h>)
 55 | #include <math.h>
    |          `- note: in file included from /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h:55:
 56 | #endif
 57 | 

/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:11: note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/math.h:36:
 37 | 
 38 | using std::abs;

<unknown>:0: error: too many errors emitted, stopping now
<unknown>:0: error: could not build C module '_FoundationCShims'
/usr/lib64/gcc/x86_64-pc-linux-gnu/15.1.1/../../../../include/c++/15.1.1/cmath:211:3: error: redefinition of 'cosh'
 209 | 
 210 |   inline _GLIBCXX_CONSTEXPR long double
 211 |   cosh(long double __x)
     |   |- error: redefinition of 'cosh'
     |   `- note: previous definition is here
 212 |   { return __builtin_coshl(__x); }
 213 | #endif
make: *** [Makefile:3: all] Fehler 1

Reproduction

Expected behavior

Just compile without errors.

Environment

Swift version 6.1.1 (swift-6.1.1-RELEASE)
Target: x86_64-unknown-linux-gnu

Additional information

No response

[egorzhdan]

Seems like a modularization issue on the intersection of CoreFoundation and libstdc++.

[gonsolo]

This helps:

+ #if 0
#if __has_include(<math.h>)
#endif
+ #endif

In /usr/lib/swift/lib/swift/_FoundationCShims/_CStdlib.h +55

[gonsolo]

It should be noted that math related functions still work:

let x = sin(3.0)

[ADKaster]

This also impacts Fedora 42.

Looking at the history of libstdc++'s math.h and cmath headers from gcc 14.3.0 to 15.1.0, it seems like (?) the only possibly relevant change was this one:

libstdc++: #ifdef out #pragma GCC system_header
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=63a598deb0c9fcb8704af6ef90f0b905942b0276

@egorzhdan Is it possible that the clang module importer logic was relying on the presence of #pragma GCC system_header in <cmath> to properly de-duplicate definitions? The patch description asserts that "This doesn't affect installed libraries, as they get their system-header status from the lookup path."

Relatedly, is there a place to push for 'current gcc release testing'? It seems like every new release of libstdc++ reveals another fragile edge in the module graph for standard components.

[ADKaster]

Here's a minimal reproducer using a fedora 42 container:

Swift version 6.2-dev (LLVM 54efc8c61424404, Swift 2f920ce)
Target: x86_64-unknown-linux-gnu
Build config: +assertions

gcc (GCC) 15.1.1 20250521 (Red Hat 15.1.1-2)
libstdc++.x86_64 15.1.1-2.fc42

Inside docker run -it --rm fedora:42

repro.sh

# Install dependencies
dnf install -y file which g++ gpg

# Make sandbox directory
mkdir /tmp/files && \
cd /tmp/files

# download swiftly and swift toolchain snapshot
curl -O https://download.swift.org/swiftly/linux/swiftly-x86_64.tar.gz && \
tar -xzf swiftly-x86_64.tar.gz

./swiftly init --no-modify-profile --skip-install --assume-yes --platform ubi9 && \
. "/root/.local/share/swiftly/env.sh" && \
swiftly install main-snapshot-2025-06-17 && \
hash -r

# Build example project (3 files)
cat <<-EOF > Test.h
#pragma once
#include <math.h>
int foo() { return 42; }
EOF

cat <<-EOF > module.modulemap
module MyCxx {
  requires cplusplus
  header "Test.h"
}
EOF

cat <<-EOF > main.swift
import MyCxx
let x = foo()
EOF

# Fail to import a clang module that simply includes math.h
swiftc -I. -cxx-interoperability-mode=default main.swift

Produces this error log

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:100:3: error: redefinition of 'acos'
  98 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
  99 |   inline _GLIBCXX_CONSTEXPR float
 100 |   acos(float __x)
     |   |- error: redefinition of 'acos'
     |   `- note: previous definition is here
 101 |   { return __builtin_acosf(__x); }
 102 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:104:3: error: redefinition of 'acos'
 102 | 
 103 |   inline _GLIBCXX_CONSTEXPR long double
 104 |   acos(long double __x)
     |   |- error: redefinition of 'acos'
     |   `- note: previous definition is here
 105 |   { return __builtin_acosl(__x); }
 106 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:112:5: error: redefinition of 'acos'
 110 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value, 
 111 |                                     double>::__type
 112 |     acos(_Tp __x)
     |     |- error: redefinition of 'acos'
     |     `- note: previous definition is here
 113 |     { return __builtin_acos(__x); }
 114 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:119:3: error: redefinition of 'asin'
 117 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 118 |   inline _GLIBCXX_CONSTEXPR float
 119 |   asin(float __x)
     |   |- error: redefinition of 'asin'
     |   `- note: previous definition is here
 120 |   { return __builtin_asinf(__x); }
 121 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:123:3: error: redefinition of 'asin'
 121 | 
 122 |   inline _GLIBCXX_CONSTEXPR long double
 123 |   asin(long double __x)
     |   |- error: redefinition of 'asin'
     |   `- note: previous definition is here
 124 |   { return __builtin_asinl(__x); }
 125 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:131:5: error: redefinition of 'asin'
 129 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
 130 |                                     double>::__type
 131 |     asin(_Tp __x)
     |     |- error: redefinition of 'asin'
     |     `- note: previous definition is here
 132 |     { return __builtin_asin(__x); }
 133 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:138:3: error: redefinition of 'atan'
 136 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 137 |   inline _GLIBCXX_CONSTEXPR float
 138 |   atan(float __x)
     |   |- error: redefinition of 'atan'
     |   `- note: previous definition is here
 139 |   { return __builtin_atanf(__x); }
 140 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:142:3: error: redefinition of 'atan'
 140 | 
 141 |   inline _GLIBCXX_CONSTEXPR long double
 142 |   atan(long double __x)
     |   |- error: redefinition of 'atan'
     |   `- note: previous definition is here
 143 |   { return __builtin_atanl(__x); }
 144 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:150:5: error: redefinition of 'atan'
 148 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
 149 |                                     double>::__type
 150 |     atan(_Tp __x)
     |     |- error: redefinition of 'atan'
     |     `- note: previous definition is here
 151 |     { return __builtin_atan(__x); }
 152 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:157:3: error: redefinition of 'atan2'
 155 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 156 |   inline _GLIBCXX_CONSTEXPR float
 157 |   atan2(float __y, float __x)
     |   |- error: redefinition of 'atan2'
     |   `- note: previous definition is here
 158 |   { return __builtin_atan2f(__y, __x); }
 159 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:161:3: error: redefinition of 'atan2'
 159 | 
 160 |   inline _GLIBCXX_CONSTEXPR long double
 161 |   atan2(long double __y, long double __x)
     |   |- error: redefinition of 'atan2'
     |   `- note: previous definition is here
 162 |   { return __builtin_atan2l(__y, __x); }
 163 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:169:3: error: redefinition of 'ceil'
 167 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 168 |   inline _GLIBCXX_CONSTEXPR float
 169 |   ceil(float __x)
     |   |- error: redefinition of 'ceil'
     |   `- note: previous definition is here
 170 |   { return __builtin_ceilf(__x); }
 171 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:173:3: error: redefinition of 'ceil'
 171 | 
 172 |   inline _GLIBCXX_CONSTEXPR long double
 173 |   ceil(long double __x)
     |   |- error: redefinition of 'ceil'
     |   `- note: previous definition is here
 174 |   { return __builtin_ceill(__x); }
 175 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:181:5: error: redefinition of 'ceil'
 179 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value, 
 180 |                                     double>::__type
 181 |     ceil(_Tp __x)
     |     |- error: redefinition of 'ceil'
     |     `- note: previous definition is here
 182 |     { return __builtin_ceil(__x); }
 183 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:188:3: error: redefinition of 'cos'
 186 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 187 |   inline _GLIBCXX_CONSTEXPR float
 188 |   cos(float __x)
     |   |- error: redefinition of 'cos'
     |   `- note: previous definition is here
 189 |   { return __builtin_cosf(__x); }
 190 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:192:3: error: redefinition of 'cos'
 190 | 
 191 |   inline _GLIBCXX_CONSTEXPR long double
 192 |   cos(long double __x)
     |   |- error: redefinition of 'cos'
     |   `- note: previous definition is here
 193 |   { return __builtin_cosl(__x); }
 194 | #endif

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:200:5: error: redefinition of 'cos'
 198 |     typename __gnu_cxx::__enable_if<__is_integer<_Tp>::__value,
 199 |                                     double>::__type
 200 |     cos(_Tp __x)
     |     |- error: redefinition of 'cos'
     |     `- note: previous definition is here
 201 |     { return __builtin_cos(__x); }
 202 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:207:3: error: redefinition of 'cosh'
 205 | #ifndef __CORRECT_ISO_CPP_MATH_H_PROTO
 206 |   inline _GLIBCXX_CONSTEXPR float
 207 |   cosh(float __x)
     |   |- error: redefinition of 'cosh'
     |   `- note: previous definition is here
 208 |   { return __builtin_coshf(__x); }
 209 | 

<module-includes>:1:10: note: in file included from <module-includes>:1:
1 | #include "Test.h"
  |          `- note: in file included from <module-includes>:1:
2 | 

/tmp/files/./Test.h:3:10: note: in file included from /tmp/files/./Test.h:3:
1 | #pragma once
2 | 
3 | #include <math.h>
  |          `- note: in file included from /tmp/files/./Test.h:3:
4 | 
5 | int foo() { return 42; }

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:11: note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 34 | #define _GLIBCXX_MATH_H 1
 35 | 
 36 | # include <cmath>
    |           `- note: in file included from /usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/math.h:36:
 37 | 
 38 | using std::abs;

/usr/lib/gcc/x86_64-redhat-linux/15/../../../../include/c++/15/cmath:211:3: error: redefinition of 'cosh'
 209 | 
 210 |   inline _GLIBCXX_CONSTEXPR long double
 211 |   cosh(long double __x)
     |   |- error: redefinition of 'cosh'
     |   `- note: previous definition is here
 212 |   { return __builtin_coshl(__x); }
 213 | #endif

<unknown>:0: error: too many errors emitted, stopping now
main.swift:1:8: error: could not build C module 'MyCxx'
1 | import MyCxx
  |        `- error: could not build C module 'MyCxx'
2 | 
3 |

[ADKaster]

It should be noted that given the repro I posted, this is not actually a CoreFoundation + libstdc++ issue, but a more general clang modules + libstdc++ issue. Any clang module that has the statement #include "math.h" in one of its imported headers will cause this failure with libstdc++-15.