tokenizer: Allow escaped newlines

The docs said multi-line strings were possible by escaping the newline
character, but this was not actually implemented.

Fixes #132.

blueprintcompiler/tokenizer.py

@@ -39,8 +39,8 @@ class TokenType(Enum):
 
 _tokens = [
     (TokenType.IDENT, r"[A-Za-z_][\d\w\-_]*"),
-    (TokenType.QUOTED, r'"(\\.|[^\\"\n])*"'),
+    (TokenType.QUOTED, r'"(\\(.|\n)|[^\\"\n])*"'),
-    (TokenType.QUOTED, r"'(\\.|[^\\'\n])*'"),
+    (TokenType.QUOTED, r"'(\\(.|\n)|[^\\'\n])*'"),
     (TokenType.NUMBER, r"0x[A-Za-z0-9_]+"),
     (TokenType.NUMBER, r"[\d_]+(\.[\d_]+)?"),
     (TokenType.NUMBER, r"\.[\d_]+"),

blueprintcompiler/utils.py

@@ -124,6 +124,7 @@ def unescape_quote(string: str) -> str:
     string = string[1:-1]
 
     REPLACEMENTS = {
+        "\n": "\n",
         "\\": "\\",
         "n": "\n",
         "t": "\t",

tests/samples/multiline_string.blp

@@ -0,0 +1,6 @@
+using Gtk 4.0;
+
+Label {
+  label: "Hello,\
+world!";
+}

tests/samples/multiline_string.ui

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT!
+This file was @generated by blueprint-compiler. Instead, edit the
+corresponding .blp file and regenerate this file with blueprint-compiler.
+-->
+<interface>
+  <requires lib="gtk" version="4.0"/>
+  <object class="GtkLabel">
+    <property name="label">Hello,
+world!</property>
+  </object>
+</interface>