hard_locale on Android

[Bruno Haible <bruno@clisp.org>]

Given the strange behaviour of the "C" locale on Android, it is no wonder
that I see a test failure:

FAIL: test-hard-locale
======================

The initial locale should not be hard!
FAIL test-hard-locale (exit status: 1)


This patch adjusts the function hard_locale in a conservative way (i.e.
hard_locale(category) returns 1 if the locale has UTF-8 encoding or
may behave in an unknown way in the future), and updates the unit test
accordingly.

I don't expect coreutils malfunctions on Android due to this, but we'll see.


2023-01-17  Bruno Haible  <bruno@clisp.org>

	hard-locale: Port to Android ≥ 5.0.
	* lib/hard-locale.c: Include <stdlib.h>.
	(hard_locale): On Android, consider also MB_CUR_MAX, even if the
	locale's name is "C".
	* tests/test-hard-locale.c (test_one, main): Assume that on Android,
	even the "C" locale is hard.

diff --git a/lib/hard-locale.c b/lib/hard-locale.c
index 0a28552e75..c01fce5344 100644
--- a/lib/hard-locale.c
+++ b/lib/hard-locale.c
@@ -21,6 +21,7 @@
 #include "hard-locale.h"
 
 #include <locale.h>
+#include <stdlib.h>
 #include <string.h>
 
 bool
@@ -31,5 +32,16 @@ hard_locale (int category)
   if (setlocale_null_r (category, locale, sizeof (locale)))
     return false;
 
-  return !(strcmp (locale, "C") == 0 || strcmp (locale, "POSIX") == 0);
+  if (!(strcmp (locale, "C") == 0 || strcmp (locale, "POSIX") == 0))
+    return true;
+
+#if defined __ANDROID__
+  /* On Android 5.0 or newer, it is possible to set a locale that has the same
+     name as the "C" locale but in fact uses UTF-8 encoding.  Cf. test case 2 in
+     <https://lists.gnu.org/archive/html/bug-gnulib/2023-01/msg00141.html>.  */
+  if (MB_CUR_MAX > 1)
+    return true;
+#endif
+
+  return false;
 }
diff --git a/tests/test-hard-locale.c b/tests/test-hard-locale.c
index eb02f4f6e6..6f94e6c3ac 100644
--- a/tests/test-hard-locale.c
+++ b/tests/test-hard-locale.c
@@ -38,8 +38,10 @@ test_one (const char *name, int failure_bitmask)
       /* musl libc has special code for the C.UTF-8 locale; other than that,
          all locale names are accepted and all locales are trivial.
          OpenBSD returns the locale name that was set, but we don't know how it
-         behaves under the hood.  Likewise for Haiku.  */
-#if defined MUSL_LIBC || defined __OpenBSD__ || defined __HAIKU__
+         behaves under the hood.  Likewise for Haiku.
+         On Android >= 5.0, the "C" locale may have UTF-8 encoding, and we don't
+         know how it will behave in the future.  */
+#if defined MUSL_LIBC || defined __OpenBSD__ || defined __HAIKU__ || defined __ANDROID__
       expected = true;
 #else
       expected = !all_trivial;
@@ -57,12 +59,14 @@ test_one (const char *name, int failure_bitmask)
 
       /* On NetBSD 7.0, some locales such as de_DE.ISO8859-1 and de_DE.UTF-8
          have the LC_COLLATE category set to "C".
-         Similarly, on musl libc, with the C.UTF-8 locale.  */
+         Similarly, on musl libc, with the C.UTF-8 locale.
+         On Android >= 5.0, the "C" locale may have UTF-8 encoding, and we don't
+         know how it will behave in the future.  */
 #if defined __NetBSD__
       expected = false;
 #elif defined MUSL_LIBC
       expected = strcmp (name, "C.UTF-8") != 0;
-#elif (defined __OpenBSD__ && HAVE_DUPLOCALE) || defined __HAIKU__ /* OpenBSD >= 6.2, Haiku */
+#elif (defined __OpenBSD__ && HAVE_DUPLOCALE) || defined __HAIKU__ || defined __ANDROID__ /* OpenBSD >= 6.2, Haiku, Android */
       expected = true;
 #else
       expected = !all_trivial;
@@ -86,12 +90,16 @@ main ()
 {
   int fail = 0;
 
-  /* The initial locale is the "C" or "POSIX" locale.  */
+  /* The initial locale is the "C" or "POSIX" locale.
+     On Android >= 5.0, it is equivalent to the "C.UTF-8" locale, cf.
+     <https://lists.gnu.org/archive/html/bug-gnulib/2023-01/msg00141.html>.  */
+#if ! defined __ANDROID__
   if (hard_locale (LC_CTYPE) || hard_locale (LC_COLLATE))
     {
       fprintf (stderr, "The initial locale should not be hard!\n");
       fail |= 1;
     }
+#endif
 
   all_trivial = (setlocale (LC_ALL, "foobar") != NULL);