tests/ref-test: Allow updating only non-existing reference images

This makes it a bit more reliable to add more reference images, but be
sure not to touch any existing ones.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3859>

src/tests/meta-ref-test-utils.c

@@ -315,6 +315,7 @@ meta_ref_test_verify (MetaRefTestAdaptor  adaptor,
   g_autofree char *ref_image_path = NULL;
   cairo_surface_t *ref_image;
   cairo_status_t ref_status;
+  gboolean maybe_update;
 
   image = adaptor (adaptor_data);
 
@@ -330,11 +331,21 @@ meta_ref_test_verify (MetaRefTestAdaptor  adaptor,
   g_assert_nonnull (ref_image);
   ref_status = cairo_surface_status (ref_image);
 
-  if (flags & META_REFTEST_FLAG_UPDATE_REF)
+  g_assert_true (ref_status == CAIRO_STATUS_FILE_NOT_FOUND ||
-    {
+                 ref_status == CAIRO_STATUS_SUCCESS);
-      g_assert_true (ref_status == CAIRO_STATUS_FILE_NOT_FOUND ||
-                ref_status == CAIRO_STATUS_SUCCESS);
 
+  if (ref_status == CAIRO_STATUS_FILE_NOT_FOUND)
+    {
+      maybe_update = ((flags & META_REFTEST_FLAG_UPDATE_REF) ||
+                      (flags & META_REFTEST_FLAG_ENSURE_REF));
+    }
+  else
+    {
+      maybe_update = !!(flags & META_REFTEST_FLAG_UPDATE_REF);
+    }
+
+  if (maybe_update)
+    {
       if (ref_status == CAIRO_STATUS_SUCCESS)
         ensure_expected_format (&ref_image);
 
@@ -428,6 +439,10 @@ meta_ref_test_verify (MetaRefTestAdaptor  adaptor,
                       result_image_path,
                       diff_image_path);
         }
+      else
+        {
+          g_message ("Image matched the reference image '%s'.", ref_image_path);
+        }
     }
 
   cairo_surface_destroy (image);

src/tests/meta-ref-test-utils.h

@@ -24,6 +24,7 @@ typedef enum _MetaReftestFlag
 {
   META_REFTEST_FLAG_NONE = 0,
   META_REFTEST_FLAG_UPDATE_REF = 1 << 0,
+  META_REFTEST_FLAG_ENSURE_REF = 1 << 1,
 } MetaReftestFlag;
 
 typedef cairo_surface_t * (* MetaRefTestAdaptor) (gpointer adaptor_data);

src/tests/meta-ref-test.c

@@ -24,6 +24,10 @@
  * expressions, the test reference image will be updated, unless the
  * existing reference image is pixel identical to the newly created one.
  *
+ * If MUTTER_REF_TEST_ENSURE_ONLY is set to "1", in combination with
+ * MUTTER_REF_TEST_UPDATE being set, only reference images that doesn't already
+ * exist are updated.
+ *
  * Updating test reference images also requires using a software OpenGL
  * renderer, which can be achieved using MESA_LOADER_DRIVER_OVERRIDE=swrast
  *
@@ -210,18 +214,24 @@ meta_ref_test_verify_view (ClutterStageView *view,
 MetaReftestFlag
 meta_ref_test_determine_ref_test_flag (void)
 {
+  gboolean ensure_only;
   const char *update_tests;
   char **update_test_rules;
   int n_update_test_rules;
   MetaReftestFlag flags;
   int i;
 
+  ensure_only = g_strcmp0 (getenv ("MUTTER_REF_TEST_ENSURE_ONLY"), "1") == 0;
+
   update_tests = g_getenv ("MUTTER_REF_TEST_UPDATE");
   if (!update_tests)
     return META_REFTEST_FLAG_NONE;
 
   if (strcmp (update_tests, "all") == 0)
-    return META_REFTEST_FLAG_UPDATE_REF;
+    {
+      return ensure_only ? META_REFTEST_FLAG_ENSURE_REF
+                         : META_REFTEST_FLAG_UPDATE_REF;
+    }
 
   update_test_rules = g_strsplit (update_tests, ",", -1);
   n_update_test_rules = g_strv_length (update_test_rules);
@@ -234,7 +244,8 @@ meta_ref_test_determine_ref_test_flag (void)
 
       if (g_regex_match_simple (rule, g_test_get_path (), 0, 0))
         {
-          flags |= META_REFTEST_FLAG_UPDATE_REF;
+          flags |= ensure_only ? META_REFTEST_FLAG_ENSURE_REF
+                               : META_REFTEST_FLAG_UPDATE_REF;
           break;
         }
     }