pg_noreturn to replace pg_attribute_noreturn()

We want to support a "noreturn" decoration on more compilers besides
just GCC-compatible ones, but for that we need to move the decoration
in front of the function declaration instead of either behind it or
wherever, which is the current style afforded by GCC-style attributes.
Also rename the macro to "pg_noreturn" to be similar to the C11
standard "noreturn".

pg_noreturn is now supported on all compilers that support C11 (using
_Noreturn), as well as GCC-compatible ones (using __attribute__, as
before), as well as MSVC (using __declspec).  (When PostgreSQL
requires C11, the latter two variants can be dropped.)

Now, all supported compilers effectively support pg_noreturn, so the
extra code for !HAVE_PG_ATTRIBUTE_NORETURN can be dropped.

This also fixes a possible problem if third-party code includes
stdnoreturn.h, because then the current definition of

    #define pg_attribute_noreturn() __attribute__((noreturn))

would cause an error.

Note that the C standard does not support a noreturn attribute on
function pointer types.  So we have to drop these here.  There are
only two instances at this time, so it's not a big loss.  In one case,
we can make up for it by adding the pg_noreturn to a wrapper function
and adding a pg_unreachable(), in the other case, the latter was
already done before.

Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/flat/pxr5b3z7jmkpenssra5zroxi7qzzp6eswuggokw64axmdixpnk@zbwxuq7gbbcw

1 files changed, 3 insertions, 3 deletions

diff --git a/src/include/utils/float.h b/src/include/utils/float.h
index 9233fa479c6..0e2e9ec5347 100644
--- a/src/include/utils/float.h
+++ b/src/include/utils/float.h
@@ -37,9 +37,9 @@ extern PGDLLIMPORT int extra_float_digits;
 /*
  * Utility functions in float.c
  */
-extern void float_overflow_error(void) pg_attribute_noreturn();
-extern void float_underflow_error(void) pg_attribute_noreturn();
-extern void float_zero_divide_error(void) pg_attribute_noreturn();
+pg_noreturn extern void float_overflow_error(void);
+pg_noreturn extern void float_underflow_error(void);
+pg_noreturn extern void float_zero_divide_error(void);
 extern int	is_infinite(float8 val);
 extern float8 float8in_internal(char *num, char **endptr_p,
 								const char *type_name, const char *orig_string,