[glib: 1/2] Improve g_ascii_formatd docs and preconditions

[Philip Withnall <pwithnall src gnome org>]

commit 6749b343fefc199fa3a5d800c5baf59dc8a130c2
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jan 19 00:14:55 2022 +0000

    Improve g_ascii_formatd docs and preconditions

 glib/gstrfuncs.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/glib/gstrfuncs.c b/glib/gstrfuncs.c
index e486251ab..07d0dcd5a 100644
--- a/glib/gstrfuncs.c
+++ b/glib/gstrfuncs.c
@@ -927,7 +927,7 @@ g_ascii_dtostr (gchar       *buffer,
  * @buffer: A buffer to place the resulting string in
  * @buf_len: The length of the buffer.
  * @format: The printf()-style format to use for the
- *          code to use for converting.
+ *   code to use for converting
  * @d: The #gdouble to convert
  *
  * Converts a #gdouble to a string, using the '.' as
@@ -935,6 +935,9 @@ g_ascii_dtostr (gchar       *buffer,
  * a printf()-style format string. Allowed conversion
  * specifiers are 'e', 'E', 'f', 'F', 'g' and 'G'.
  *
+ * The @format must just be a single format specifier
+ * starting with `%`, expecting a #gdouble argument.
+ *
  * The returned buffer is guaranteed to be nul-terminated.
  *
  * If you just want to want to serialize the value into a
@@ -951,6 +954,10 @@ g_ascii_formatd (gchar       *buffer,
 #ifdef USE_XLOCALE
   locale_t old_locale;
 
+  g_return_val_if_fail (buffer != NULL, NULL);
+  g_return_val_if_fail (format[0] == '%', NULL);
+  g_return_val_if_fail (strpbrk (format + 1, "'l%") == NULL, NULL);
+
   old_locale = uselocale (get_C_locale ());
    _g_snprintf (buffer, buf_len, format, d);
   uselocale (old_locale);