[Bug 218657] Usage of I (_Complex_I) from complex.h results in unexpected warnings with clang -pedantic

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D218657

Mark Millard <[email protected]> changed:

           What    |Removed                     |Added
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                 CC|                            |[email protected]

--- Comment #2 from Mark Millard <[email protected]> ---
(In reply to Andrey Alexeyev from comment #0)

As main [so: 16] is now llvm 21 based, retesting for
c99, c11, c23, and c2y follows. The messages show
that, as stands for this context, the notation 1.0i
still ends up in use and is reported for c99 .. C23
but not for c2y. It now says "C2y" instead of "GNU"
in front of "extension" when it is reported. Also:
-Wc2y-extensions vs. -Wgnu-imaginary-constant


# cat complexI.c=20
// clang -std=3Dc11 -pedantic complexI.c
// ./a.out
//
#include <stdio.h>
#include <complex.h>

int main(void) {
    complex double c =3D 1.0 + 2.0 * I;
    printf("c =3D %f+%fi\n", creal(c), cimag(c));
    return 0;
}

# clang -std=3Dc99 -pedantic complexI.c
complexI.c:12:36: warning: imaginary constants are a C2y extension
[-Wc2y-extensions]
   12 |     complex double c =3D 1.0 + 2.0 * I;
      |                                    ^
/usr/include/complex.h:47:12: note: expanded from macro 'I'
   47 | #define I               _Complex_I
      |                         ^
/usr/include/complex.h:38:37: note: expanded from macro '_Complex_I'
   38 | #define _Complex_I      ((float _Complex)1.0i)
      |                                          ^
1 warning generated.


# clang -std=3Dc11 -pedantic complexI.c
complexI.c:8:36: warning: imaginary constants are a C2y extension
[-Wc2y-extensions]
    8 |     complex double c =3D 1.0 + 2.0 * I;
      |                                    ^
/usr/include/complex.h:47:12: note: expanded from macro 'I'
   47 | #define I               _Complex_I
      |                         ^
/usr/include/complex.h:38:37: note: expanded from macro '_Complex_I'
   38 | #define _Complex_I      ((float _Complex)1.0i)
      |                                          ^
1 warning generated.

# ./a.out
c =3D 1.000000+2.000000i


# clang -std=3Dc23 -pedantic complexI.c
complexI.c:12:36: warning: imaginary constants are a C2y extension
[-Wc2y-extensions]
   12 |     complex double c =3D 1.0 + 2.0 * I;
      |                                    ^
/usr/include/complex.h:47:12: note: expanded from macro 'I'
   47 | #define I               _Complex_I
      |                         ^
/usr/include/complex.h:38:37: note: expanded from macro '_Complex_I'
   38 | #define _Complex_I      ((float _Complex)1.0i)
      |                                          ^
1 warning generated.


# clang -std=3Dc2y -pedantic complexI.c
#=20

(So -std=3Dc2y does not complain.)

--=20
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