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, 2 deletions

diff --git a/src/common/parse_manifest.c b/src/common/parse_manifest.c
index 05858578207..71973af199b 100644
--- a/src/common/parse_manifest.c
+++ b/src/common/parse_manifest.c
@@ -114,8 +114,8 @@ static void json_manifest_finalize_wal_range(JsonManifestParseState *parse);
 static void verify_manifest_checksum(JsonManifestParseState *parse,
 									 const char *buffer, size_t size,
 									 pg_cryptohash_ctx *incr_ctx);
-static void json_manifest_parse_failure(JsonManifestParseContext *context,
-										char *msg);
+pg_noreturn static void json_manifest_parse_failure(JsonManifestParseContext *context,
+													char *msg);
 
 static int	hexdecode_char(char c);
 static bool hexdecode_string(uint8 *result, char *input, int nbytes);
@@ -889,6 +889,7 @@ static void
 json_manifest_parse_failure(JsonManifestParseContext *context, char *msg)
 {
 	context->error_cb(context, "could not parse backup manifest: %s", msg);
+	pg_unreachable();
 }
 
 /*