Fix unintentional locale dependency (#3358)

Avoid unintentional locale dependency

hb_variation_to_string uses sprintf with %g, which will produce
a locale-dependent decimal point, which is not desired here.

The output is supposed to be compatible with CSS syntax, and
that always uses '.' for the decimal point.

Fix this by changing the per-thread locale to "C" around sprintf call.

Fixes https://github.com/harfbuzz/harfbuzz/issues/3355
Fixes https://github.com/harfbuzz/harfbuzz/pull/3357
Fixes https://github.com/harfbuzz/harfbuzz/pull/3358

Co-authored-by: Matthias Clasen <mclasen@redhat.com>

configure.ac

@@ -68,8 +68,8 @@ GTK_DOC_CHECK([1.15],[--flavour no-tmpl])
 ])
 
 # Functions and headers
-AC_CHECK_FUNCS(atexit mprotect sysconf getpagesize mmap isatty)
-AC_CHECK_HEADERS(unistd.h sys/mman.h stdbool.h)
+AC_CHECK_FUNCS(atexit mprotect sysconf getpagesize mmap isatty newlocale uselocale)
+AC_CHECK_HEADERS(unistd.h sys/mman.h stdbool.h xlocale.h)
 
 # Compiler flags
 AC_CANONICAL_HOST

meson.build

@@ -61,6 +61,7 @@ check_headers = [
   ['unistd.h'],
   ['sys/mman.h'],
   ['stdbool.h'],
+  ['xlocale.h'],
 ]
 
 check_funcs = [
@@ -70,6 +71,8 @@ check_funcs = [
   ['getpagesize'],
   ['mmap'],
   ['isatty'],
+  ['uselocale'],
+  ['newlocale'],
 ]
 
 m_dep = cpp.find_library('m', required: false)

src/hb-common.cc

@@ -31,6 +31,10 @@
 
 #include <locale.h>
 
+#ifdef HAVE_XLOCALE_H
+#include <xlocale.h> // Needed on BSD/OS X for uselocale
+#endif
+
 #ifdef HB_NO_SETLOCALE
 #define setlocale(Category, Locale) "C"
 #endif
@@ -1039,6 +1043,56 @@ hb_variation_from_string (const char *str, int len,
   return false;
 }
 
+#if !defined(HARFBUZZ_NO_SETLOCALE) && defined(HAVE_NEWLOCALE) && defined(HAVE_USELOCALE)
+
+#ifdef WIN32
+using locale_t = _locale_t;
+#endif
+
+static inline void free_static_C_locale ();
+
+static struct hb_C_locale_lazy_loader_t : hb_lazy_loader_t<hb_remove_pointer<locale_t>,
+							     hb_C_locale_lazy_loader_t>
+{
+  static locale_t create ()
+  {
+    locale_t l = newlocale (LC_ALL_MASK, "C", NULL);
+    if (!l)
+      return l;
+
+    hb_atexit (free_static_C_locale);
+
+    return l;
+  }
+  static void destroy (locale_t l)
+  {
+    freelocale (l);
+  }
+  static locale_t get_null ()
+  {
+    return (locale_t) 0;
+  }
+} static_C_locale;
+
+static inline
+void free_static_C_locale ()
+{
+  static_C_locale.free_instance ();
+}
+
+static locale_t
+get_C_locale ()
+{
+  return static_C_locale.get_unconst ();
+}
+
+#else
+#ifdef WIN32
+#define locale_t void *
+#endif
+#define uselocale(Locale) ((locale_t) 0)
+#endif
+
 /**
  * hb_variation_to_string:
  * @variation: an #hb_variation_t to convert
@@ -1064,7 +1118,11 @@ hb_variation_to_string (hb_variation_t *variation,
   while (len && s[len - 1] == ' ')
     len--;
   s[len++] = '=';
+
+  locale_t oldlocale HB_UNUSED;
+  oldlocale = uselocale (get_C_locale ());
   len += hb_max (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%g", (double) variation->value));
+  (void) uselocale (oldlocale);
 
   assert (len < ARRAY_LENGTH (s));
   len = hb_min (len, size - 1);