Create an interactive porting tool

`blueprint-compiler port` interactively ports a project to blueprint.
It will create the subproject wrap file, add it to .gitignore, decompile
your GtkBuilder XML files, emit code to copy and paste into your
meson.build file, and update POTFILES.in.

It can't quite handle all of the features the forward compiler can, so
it will skip those files.

tests/samples/accessibility_dec.blp

@@ -0,0 +1,12 @@
+using Gtk 4.0;
+
+Widget {
+  accessibility {
+    label: _("Hello, world!");
+    labelled_by: my_label;
+    checked: true;
+  }
+}
+
+Label my_label {
+}

tests/samples/id_prop.blp

@@ -4,4 +4,5 @@ Scale {
   adjustment: adj;
 }
 
-Adjustment adj {}
+Adjustment adj {
+}

tests/samples/layout_dec.blp

@@ -0,0 +1,10 @@
+using Gtk 4.0;
+
+Grid {
+  Label {
+    layout {
+      column: "0";
+      row: "1";
+    }
+  }
+}

tests/samples/menu.ui

@@ -25,4 +25,4 @@
       </item>
     </submenu>
   </menu>
-</interface>
+</interface>

tests/samples/menu_dec.blp

@@ -0,0 +1,31 @@
+using Gtk 4.0;
+
+menu {
+  label: _("menu label");
+  test-custom-attribute: "3.1415";
+
+  submenu {
+    section {
+      label: "test section";
+    }
+
+    item {
+      label: "test item";
+    }
+
+    item {
+      label: "test item shorthand 1";
+    }
+
+    item {
+      label: "test item shorthand 2";
+      action: "app.test-action";
+    }
+
+    item {
+      label: "test item shorthand 3";
+      action: "app.test-action";
+      icon: "test-symbolic";
+    }
+  }
+}

tests/samples/style_dec.blp

@@ -0,0 +1,8 @@
+using Gtk 4.0;
+
+Label {
+  styles [
+    "class-1",
+    "class-2",
+  ]
+}

tests/samples/translated.blp

@@ -3,6 +3,7 @@ using Gtk 4.0;
 Label {
   label: _("Hello, world!");
 }
+
 Label {
   label: C_("translation context", "Hello");
 }

tests/samples/using.blp

@@ -1,4 +1,5 @@
 using Gtk 4.0;
 using GObject 2.0;
 
-GObject.Object {}
+GObject.Object {
+}

tests/test_samples.py

@@ -23,7 +23,7 @@ from pathlib import Path
 import traceback
 import unittest
 
-from blueprintcompiler import tokenizer, parser
+from blueprintcompiler import tokenizer, parser, decompiler
 from blueprintcompiler.errors import PrintableError, MultipleErrors, CompileError
 from blueprintcompiler.tokenizer import Token, TokenType, tokenize
 from blueprintcompiler import utils
@@ -91,6 +91,25 @@ class TestSamples(unittest.TestCase):
             raise AssertionError()
 
 
+    def assert_decompile(self, name):
+        try:
+            with open((Path(__file__).parent / f"samples/{name}.blp").resolve()) as f:
+                expected = f.read()
+
+            name = name.removesuffix("_dec")
+            ui_path = (Path(__file__).parent / f"samples/{name}.ui").resolve()
+
+            actual = decompiler.decompile(ui_path)
+
+            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("accessibility")
         self.assert_sample("binding")
@@ -143,3 +162,20 @@ class TestSamples(unittest.TestCase):
         self.assert_sample_error("uint")
         self.assert_sample_error("using_invalid_namespace")
         self.assert_sample_error("widgets_in_non_size_group")
+
+
+    def test_decompiler(self):
+        self.assert_decompile("accessibility_dec")
+        self.assert_decompile("binding")
+        self.assert_decompile("child_type")
+        self.assert_decompile("flags")
+        self.assert_decompile("id_prop")
+        self.assert_decompile("layout_dec")
+        self.assert_decompile("menu_dec")
+        self.assert_decompile("property")
+        self.assert_decompile("signal")
+        self.assert_decompile("strings")
+        self.assert_decompile("style_dec")
+        self.assert_decompile("template")
+        self.assert_decompile("translated")
+        self.assert_decompile("using")