[gnome-builder] plugins/clang: use -Wno-unused-function for headers

[Christian Hergert <chergert src gnome org>]

commit 3d100228c4e0d37c00ff34022fbd0ad3e2203e7a
Author: Christian Hergert <chergert redhat com>
Date:   Sat Sep 24 16:21:22 2022 -0700

    plugins/clang: use -Wno-unused-function for headers
    
    Rather than use our hack for -Dinline, we can just disable the diagnostic
    for headers (but make sure we append it so it takes effect after other
    diagnostic values like -Wall).
    
    This makes sure we still warn in C/C++ files, but not headers like the
    original issue reported.
    
    Related #1807

 src/plugins/clang/ide-clang.c | 36 +++++++++++++++++++++++++++++-------
 1 file changed, 29 insertions(+), 7 deletions(-)
---
diff --git a/src/plugins/clang/ide-clang.c b/src/plugins/clang/ide-clang.c
index 8bcfff521..a12f0c89e 100644
--- a/src/plugins/clang/ide-clang.c
+++ b/src/plugins/clang/ide-clang.c
@@ -188,6 +188,26 @@ get_stdcpp_includes (void)
   return (const gchar * const *)stdcpp_includes;
 }
 
+static gboolean
+maybe_header (const char *path)
+{
+  const char *dot;
+
+  if (path == NULL)
+    return FALSE;
+
+  if (!(dot = strrchr (path, '.')))
+    return FALSE;
+
+  g_printerr ("%s\n", dot);
+
+  return strcmp (dot, ".h") == 0 ||
+         strcmp (dot, ".hh") == 0 ||
+         strcmp (dot, ".hpp") == 0 ||
+         strcmp (dot, ".h++") == 0 ||
+         strcmp (dot, ".hxx") == 0;
+}
+
 static gchar **
 ide_clang_cook_flags (const gchar         *path,
                       const gchar * const *flags)
@@ -209,13 +229,6 @@ ide_clang_cook_flags (const gchar         *path,
       include = g_strdup_printf ("-I%s", current);
     }
 
-  /* Work around Clang/GCC inconsistency on -Wunused-function with regards
-   * to static inline usage.
-   *
-   * See https://gitlab.gnome.org/GNOME/gnome-builder/issues/961
-   */
-  g_ptr_array_add (cooked, g_strdup ("-Dinline=inline __attribute__((unused))"));
-
   if (flags != NULL)
     {
       for (guint i = 0; flags[i]; i++)
@@ -250,6 +263,15 @@ ide_clang_cook_flags (const gchar         *path,
         g_ptr_array_insert (cooked, pos++, g_strdup (stdcpp_includes[i]));
     }
 
+  /* If this looks like a header, set -Wno-unused-function so that we
+   * don't get warnings "static inline" not being used. Set it last so
+   * that it applies after -Wall, etc.
+   *
+   * https://gitlab.gnome.org/GNOME/gnome-builder/-/issues/961
+   */
+  if (maybe_header (path))
+    g_ptr_array_add (cooked, g_strdup ("-Wno-unused-function"));
+
   g_ptr_array_add (cooked, NULL);
 
   return (gchar **)g_ptr_array_free (cooked, FALSE);