mesa/fbobject: tweak attachment validation

now that st is available in this part of mesa, the texture's binds
can be checked directly in order to provide more detailed info about
why an attachment was marked invalid

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/28135>

src/mesa/main/fbobject.c

@@ -1195,7 +1195,15 @@ do_validate_attachment(struct gl_context *ctx,
                                        stObj->pt->nr_storage_samples,
                                        bindings);
    if (!valid) {
-      fbo_invalid("Invalid format");
+      /* this is the actual texture, so check the bind flags for more info */
+      if (stObj->pt->bind & (PIPE_BIND_RENDER_TARGET | PIPE_BIND_DEPTH_STENCIL)) {
+         if (_mesa_is_format_srgb(texFormat))
+            fbo_invalid("Invalid format: linear format supported for rendering but not sRGB");
+         else
+            fbo_invalid("Invalid format");
+      } else {
+         fbo_invalid("Format unsupported for rendering: RENDER_TARGET bind not applied");
+      }
    }
 
    return valid;