{fix} fail when encountering illegal unicode escapes

Fixes #8

src/string-utils.js

@@ -265,7 +265,19 @@ function replaceEscapes(ctx, value, token) {
 			hadError = true;
 			return "";
 		} else if (unicode) {
-			return String.fromCodePoint(parseInt(unicode, 16));
+			const codePoint = parseInt(unicode, 16);
+
+			// Non-scalar values
+			if (codePoint >= 0xd800 && codePoint <= 0xdfff) {
+				ctx.errors.push(
+					new InvalidKdlError(
+						String.raw`Invalid unicode escape "\u{${unicode}}, only scalar values can be added using an escape`,
+						{token},
+					),
+				);
+			}
+
+			return String.fromCodePoint(codePoint);
 		} else {
 			const replacement = escapedValues.get(escape);
 

test/issues.js

@@ -45,4 +45,27 @@ test("issue #5: trailing comments", () => {
 	assert.doesNotThrow(() => parse(`node "arg"\n\n// test\n`));
 });
 
+test("issue #8: escaped surrogates", () => {
+	assert.throws(
+		() => {
+			parse(
+				String.raw`no "Surrogtates high\u{D800}\u{D911}\u{DABB}\u{DBFF} low\u{DC00}\u{DEAD}\u{DFFF}"`,
+			);
+		},
+		(err) => {
+			assert(err instanceof AggregateError);
+			assert.equal(err.errors.length, 7);
+
+			for (let i = 0; i < 7; i++) {
+				assert.match(
+					err.errors[i].message,
+					/only scalar values can be added using an escape/,
+				);
+			}
+
+			return true;
+		},
+	);
+});
+
 test.run();