meson: crypt.h must always exist

We require at least crypt_r() exists, and it is provided since glibc-2.0
(and dropped in glibc-2.39) or by libxcrypt, and the function is
provided in crypt.h regardless it is provided by glibc or libxcrypt.
Hence, we cannot fallback to unistd.h.

This makes the condition about crypt.h more strict, and stop compilation
earlier when crypt.h does not exist.

README

@@ -212,6 +212,7 @@ REQUIREMENTS:
         newer though. TL;DR: turn audit off, still.
 
         glibc >= 2.31
+        libxcrypt or glibc (<= 2.38 built with --enable-crypt)
         libcap
         libmount >= 2.30 (from util-linux)
                 (util-linux *must* be built without --enable-libmount-support-mtab)

meson.build

@@ -685,15 +685,22 @@ conf.set('GPERF_LEN_TYPE', gperf_len_type,
 
 #####################################################################
 
-if not cc.has_header('sys/capability.h')
-        error('POSIX caps headers not found')
-endif
-foreach header : ['crypt.h',
-                  'sys/sdt.h',
-                  'threads.h',
-                  'valgrind/memcheck.h',
-                  'valgrind/valgrind.h',
-                 ]
+foreach header : [
+        'crypt.h',
+        'sys/capability.h',
+]
+
+        if not cc.has_header(header)
+                error('Header file @0@ not found.'.format(header))
+        endif
+endforeach
+
+foreach header : [
+        'sys/sdt.h',
+        'threads.h',
+        'valgrind/memcheck.h',
+        'valgrind/valgrind.h',
+]
 
         conf.set10('HAVE_' + header.underscorify().to_upper(),
                    cc.has_header(header))
@@ -989,11 +996,6 @@ threads = dependency('threads')
 librt = cc.find_library('rt')
 libm = cc.find_library('m')
 libdl = cc.find_library('dl')
-libcrypt = dependency('libcrypt', 'libxcrypt', required : false)
-if not libcrypt.found()
-        # fallback to use find_library() if libcrypt is provided by glibc, e.g. for LibreELEC.
-        libcrypt = cc.find_library('crypt')
-endif
 libcap = dependency('libcap')
 
 # On some architectures, libatomic is required. But on some installations,
@@ -1007,15 +1009,21 @@ else
         libatomic = []
 endif
 
-crypt_header = conf.get('HAVE_CRYPT_H') == 1 ? '''#include <crypt.h>''' : '''#include <unistd.h>'''
-foreach ident : [
-        ['crypt_ra',               crypt_header],
-        ['crypt_preferred_method', crypt_header],
-        ['crypt_gensalt_ra',       crypt_header]]
+libcrypt = dependency('libcrypt', 'libxcrypt', required : false)
+if not libcrypt.found()
+        # fallback to use find_library() if libcrypt is provided by glibc, e.g. for LibreELEC.
+        libcrypt = cc.find_library('crypt')
+endif
 
-        have = cc.has_function(ident[0], prefix : ident[1], args : '-D_GNU_SOURCE',
+foreach func : [
+        'crypt_ra',               # since libxcrypt-4.0.0
+        'crypt_gensalt_ra',       # since libxcrypt-4.0.0
+        'crypt_preferred_method', # since libxcrypt-4.4.0
+]
+
+        have = cc.has_function(func, prefix : '''#include <crypt.h>''', args : '-D_GNU_SOURCE',
                                dependencies : libcrypt)
-        conf.set10('HAVE_' + ident[0].to_upper(), have)
+        conf.set10('HAVE_' + func.to_upper(), have)
 endforeach
 
 bpf_framework = get_option('bpf-framework')

src/shared/libcrypt-util.c

@@ -1,20 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#if HAVE_CRYPT_H
-/* libxcrypt is a replacement for glibc's libcrypt, and libcrypt might be
- * removed from glibc at some point. As part of the removal, defines for
- * crypt(3) are dropped from unistd.h, and we must include crypt.h instead.
- *
- * Newer versions of glibc (v2.0+) already ship crypt.h with a definition
- * of crypt(3) as well, so we simply include it if it is present.  MariaDB,
- * MySQL, PostgreSQL, Perl and some other wide-spread packages do it the
- * same way since ages without any problems.
- */
-#  include <crypt.h>
-#else
-#  include <unistd.h>
-#endif
-
+#include <crypt.h>
 #include <stdlib.h>
 
 #include "alloc-util.h"

src/test/test-libcrypt-util.c

@@ -1,10 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#if HAVE_CRYPT_H
-#  include <crypt.h>
-#else
-#  include <unistd.h>
-#endif
+#include <crypt.h>
 
 #include "libcrypt-util.h"
 #include "strv.h"