Improve value parsing

Parse values as different AST nodes rather than just strings. This
allows for better validation and will eventually make expressions
possible.

tests/test_samples.py

@@ -20,38 +20,44 @@
 
 import difflib # I love Python
 from pathlib import Path
+import traceback
 import unittest
 
 from gtkblueprinttool import tokenizer, parser
-from gtkblueprinttool.errors import PrintableError
+from gtkblueprinttool.errors import PrintableError, MultipleErrors
 from gtkblueprinttool.tokenizer import Token, TokenType, tokenize
 
 
 class TestSamples(unittest.TestCase):
     def assert_sample(self, name):
-        with open((Path(__file__).parent / f"samples/{name}.blp").resolve()) as f:
-            blueprint = f.read()
-        with open((Path(__file__).parent / f"samples/{name}.ui").resolve()) as f:
-            expected = f.read()
+        try:
+            with open((Path(__file__).parent / f"samples/{name}.blp").resolve()) as f:
+                blueprint = f.read()
+            with open((Path(__file__).parent / f"samples/{name}.ui").resolve()) as f:
+                expected = f.read()
 
-        tokens = tokenizer.tokenize(blueprint)
-        ast, errors = parser.parse(tokens)
+            tokens = tokenizer.tokenize(blueprint)
+            ast, errors = parser.parse(tokens)
 
-        if errors:
-            raise errors
-        if len(ast.errors):
-            raise MultipleErrors(ast.errors)
+            if errors:
+                raise errors
+            if len(ast.errors):
+                raise MultipleErrors(ast.errors)
 
-        actual = ast.generate()
-        if actual.strip() != expected.strip():
-            diff = difflib.unified_diff(expected.splitlines(), actual.splitlines())
-            print("\n".join(diff))
+            actual = ast.generate()
+            if actual.strip() != expected.strip():
+                diff = difflib.unified_diff(expected.splitlines(), actual.splitlines())
+                print("\n".join(diff))
+                raise AssertionError()
+        except PrintableError as e:
+            e.pretty_print(name + ".blp", blueprint)
             raise AssertionError()
 
 
     def test_samples(self):
         self.assert_sample("binding")
         self.assert_sample("child_type")
+        self.assert_sample("flags")
         self.assert_sample("layout")
         self.assert_sample("menu")
         self.assert_sample("property")