[libvirt PATCH v2] Do not disable incompatible-pointer-types-discards-qualifiers

[Martin Kletzander]

This reverts commit b3710e9a2af402a2b620de570b062294e11190eb.

That check is very valuable for our code, but it causes issue with glib >=
2.67.0 when building with clang.

The reason is a combination of two commits in glib, firstly fdda405b6b1b which
adds a g_atomic_pointer_{set,get} variants that enforce stricter type
checking (by removing an extra cast) for compilers that support __typeof__, and
commit dce24dc4492d which effectively enabled the new variant of glib's atomic
code for clang.  This will not be necessary when glib's issue #600 [0] (8 years
old) is fixed.  Thankfully, MR #1719 [1], which is supposed to deal with this
issue was opened 3 weeks ago, so there is a slight sliver of hope.

[0] https://gitlab.gnome.org/GNOME/glib/-/issues/600
[1] https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1719

Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
---
 meson.build           |  3 ---
 src/util/glibcompat.h | 24 ++++++++++++++++++++++++
 2 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/meson.build b/meson.build
index cecaad199d4c..04646e3a078c 100644
--- a/meson.build
+++ b/meson.build
@@ -405,9 +405,6 @@ cc_flags += [
   # so use this Clang-specific arg to keep it quiet
   '-Wno-typedef-redefinition',
 
-  # Clang complains about casts in G_DEFINE_TYPE(...)
-  '-Wno-incompatible-pointer-types-discards-qualifiers',
-
   # We don't use -Wc++-compat so we have to enable it explicitly
   '-Wjump-misses-init',
 
diff --git a/src/util/glibcompat.h b/src/util/glibcompat.h
index 6f50a76f3c2b..f4867f3eadbc 100644
--- a/src/util/glibcompat.h
+++ b/src/util/glibcompat.h
@@ -20,6 +20,30 @@
 
 #include <glib.h>
 #include <glib/gstdio.h>
+#include <glib-object.h>
+
+#ifdef __clang__
+/*
+ * Clang detects (valid) issue in G_DEFINE_TYPE and derivatives starting with
+ * glib >= 2.67.0.  See https://gitlab.gnome.org/GNOME/glib/-/issues/600
+ *
+ * For that we need to disable the one check that produces an error in our
+ * builds when using any G_DEFINE_TYPE* macro.  Thankfully all those macros end
+ * up using _G_DEFINE_TYPE_EXTENDED_BEGIN.  Because with that we can redefine
+ * this one macro to cover all use cases.  The macro is defined the same way it
+ * is defined in glib (with a very low probability of being changed thanks to a
+ * comment above it).
+ */
+# undef _G_DEFINE_TYPE_EXTENDED_BEGIN
+
+# define _G_DEFINE_TYPE_EXTENDED_BEGIN(TypeName, type_name, TYPE_PARENT, flags) \
+    _Pragma("GCC diagnostic push") \
+    _Pragma("GCC diagnostic ignored \"-Wincompatible-pointer-types-discards-qualifiers\"") \
+    _G_DEFINE_TYPE_EXTENDED_BEGIN_PRE(TypeName, type_name, TYPE_PARENT) \
+    _G_DEFINE_TYPE_EXTENDED_BEGIN_REGISTER(TypeName, type_name, TYPE_PARENT, flags) \
+    _Pragma("GCC diagnostic pop")
+
+#endif /* __clang__ */
 
 gchar * vir_g_canonicalize_filename(const gchar *filename,
                                     const gchar *relative_to);
-- 
2.29.2