Emit deprecation warnings

tests/sample_errors/deprecations.blp

@@ -0,0 +1,10 @@
+using Gtk 4.0;
+using Gio 2.0;
+
+Dialog {
+  use-header-bar: 1;
+}
+
+Window {
+  keys-changed => $on_window_keys_changed();
+}

tests/sample_errors/deprecations.err

@@ -0,0 +1 @@
+4,1,6,Gtk.Dialog is deprecated

tests/sample_errors/legacy_template.err

@@ -1,2 +1,3 @@
 3,10,12,Use type syntax here (introduced in blueprint 0.8.0)
+8,1,6,Gtk.Dialog is deprecated
 9,18,12,Use 'template' instead of the class name (introduced in 0.8.0)

tests/test_samples.py

@@ -54,6 +54,14 @@ class TestSamples(unittest.TestCase):
             tokens = tokenizer.tokenize(blueprint)
             ast, errors, warnings = parser.parse(tokens)
 
+            # Ignore deprecation warnings because some of the things we're testing
+            # are deprecated
+            warnings = [
+                warning
+                for warning in warnings
+                if "is deprecated" not in warning.message
+            ]
+
             if errors:
                 raise errors
             if len(warnings):