validation: Writable/construct-only properties

Add two new errors, one for non-writable properties and another for
binding construct-only properties.

blueprintcompiler/gir.py

@@ -184,6 +184,14 @@ class Property(GirNode):
     def signature(self):
         return f"{self.type_name} {self.container.name}.{self.name}"
 
+    @property
+    def writable(self):
+        return self.xml["writable"] == "1"
+
+    @property
+    def construct_only(self):
+        return self.xml["construct-only"] == "1"
+
 
 class Parameter(GirNode):
     def __init__(self, container: GirNode, xml: xml_reader.Element):

blueprintcompiler/language/gobject_property.py

@@ -29,7 +29,7 @@ class Property(AstNode):
         Statement(
             UseIdent("name"),
             ":",
-            "bind",
+            Keyword("bind"),
             UseIdent("bind_source").expected("the ID of a source object to bind from"),
             ".",
             UseIdent("bind_property").expected("a property name to bind from"),
@@ -85,6 +85,19 @@ class Property(AstNode):
                 did_you_mean=(self.tokens["name"], self.gir_class.properties.keys())
             )
 
+    @validate("bind")
+    def property_bindable(self):
+        if self.tokens["bind"] and self.gir_property is not None and self.gir_property.construct_only:
+            raise CompileError(
+                f"{self.gir_property.full_name} can't be bound because it is construct-only",
+                hints=["construct-only properties may only be set to a static value"]
+            )
+
+    @validate("name")
+    def property_writable(self):
+        if self.gir_property is not None and not self.gir_property.writable:
+            raise CompileError(f"{self.gir_property.full_name} is not writable")
+
 
     @validate()
     def obj_property_type(self):

tests/sample_errors/read_only_properties.blp

@@ -0,0 +1,6 @@
+using Gtk 4.0;
+
+ComboBox combo_box {
+  has-entry: bind combo_box.visible;
+  scale-factor: 2;
+}

tests/sample_errors/read_only_properties.err

@@ -0,0 +1,2 @@
+4,14,4,ComboBox.has-entry can't be bound because it is construct-only
+5,3,12,Widget.scale-factor is not writable

tests/test_samples.py

@@ -190,6 +190,7 @@ class TestSamples(unittest.TestCase):
         self.assert_sample_error("obj_in_string_list")
         self.assert_sample_error("obj_prop_type")
         self.assert_sample_error("property_dne")
+        self.assert_sample_error("read_only_properties")
         self.assert_sample_error("signal_dne")
         self.assert_sample_error("signal_object_dne")
         self.assert_sample_error("size_group_non_widget")