glnx-errors.h: add a glnx_throw_prefix() variant

For completeness. It just looks much cleaner than doing the `, FALSE`
trick. It also takes care of appending the ': ' for you like its errno
version.

1 files changed, 34 insertions, 3 deletions

diff --git a/glnx-errors.h b/glnx-errors.h
index 2f6b962..e26a513 100644
--- a/glnx-errors.h
+++ b/glnx-errors.h
@@ -30,7 +30,7 @@ G_BEGIN_DECLS
  * This function returns %FALSE so it can be used conveniently in a single
  * statement:
  *
- * ``
+ * ```
  *   if (strcmp (foo, "somevalue") != 0)
  *     return glnx_throw (error, "key must be somevalue, not '%s'", foo);
  * ```
@@ -49,16 +49,47 @@ glnx_throw (GError **error, const char *fmt, ...)
   return FALSE;
 }
 
-/* Like glnx_throw(), but yields a NULL pointer. */
+/* Like `glnx_throw ()`, but returns %NULL. */
 #define glnx_null_throw(error, args...) \
   ({glnx_throw (error, args); NULL;})
 
+/* Implementation detail of glnx_throw_prefix() */
+void glnx_real_set_prefix_error_va (GError     *error,
+                                    const char *format,
+                                    va_list     args) G_GNUC_PRINTF (2,0);
+
+/* Prepend to @error's message by `$prefix: ` where `$prefix` is computed via
+ * printf @fmt. Returns %FALSE so it can be used conveniently in a single
+ * statement:
+ *
+ * ```
+ *   if (!function_that_fails (s, error))
+ *     return glnx_throw_prefix (error, "while handling '%s'", s);
+ * ```
+ * */
+static inline gboolean G_GNUC_PRINTF (2,3)
+glnx_prefix_error (GError **error, const char *fmt, ...)
+{
+  if (error == NULL)
+    return FALSE;
+
+  va_list args;
+  va_start (args, fmt);
+  glnx_real_set_prefix_error_va (*error, fmt, args);
+  va_end (args);
+  return FALSE;
+}
+
+/* Like `glnx_prefix_error ()`, but returns %NULL. */
+#define glnx_prefix_error_null(error, args...) \
+  ({glnx_prefix_error (error, args); NULL;})
+
 /* Set @error using the value of `g_strerror (errno)`.
  *
  * This function returns %FALSE so it can be used conveniently in a single
  * statement:
  *
- * ``
+ * ```
  *   if (unlinkat (fd, somepathname) < 0)
  *     return glnx_throw_errno (error);
  * ```