Handle escaped colons in Windows file:// URIs

lib/src/style/url.dart

@@ -64,8 +64,7 @@ class UrlStyle extends InternalStyle {
         // See https://url.spec.whatwg.org/#file-slash-state.
         if (!withDrive || path.length < index + 3) return index;
         if (!path.startsWith('file://')) return index;
-        if (!isDriveLetter(path, index + 1)) return index;
-        return path.length == index + 3 ? index + 3 : index + 4;
+        return driveLetterEnd(path, index + 1) ?? index;
       }
     }
 

lib/src/utils.dart

@@ -15,10 +15,25 @@ bool isNumeric(int char) => char >= chars.zero && char <= chars.nine;
 
 /// Returns whether [path] has a URL-formatted Windows drive letter beginning at
 /// [index].
-bool isDriveLetter(String path, int index) {
-  if (path.length < index + 2) return false;
-  if (!isAlphabetic(path.codeUnitAt(index))) return false;
-  if (path.codeUnitAt(index + 1) != chars.colon) return false;
-  if (path.length == index + 2) return true;
-  return path.codeUnitAt(index + 2) == chars.slash;
+bool isDriveLetter(String path, int index) =>
+    driveLetterEnd(path, index) != null;
+
+/// Returns the index of the first character after the drive letter, or `null`
+/// if [index] is not the start of a drive letter.
+int? driveLetterEnd(String path, int index) {
+  if (path.length < index + 2) return null;
+  if (!isAlphabetic(path.codeUnitAt(index))) return null;
+  if (path.codeUnitAt(index + 1) != chars.colon) {
+    // If not a raw colon, check for escaped colon
+    if (path.length < index + 4) return null;
+    if (path.substring(index + 1, index + 4).toLowerCase() != '%3a') {
+      return null;
+    }
+    // Offset the index to account for the extra 2 characters from the
+    // colon encoding.
+    index += 2;
+  }
+  if (path.length == index + 2) return index + 2;
+  if (path.codeUnitAt(index + 2) != chars.slash) return null;
+  return index + 3;
 }

test/url_test.dart

@@ -301,6 +301,19 @@ void main() {
           'file://host/c:/baz/qux');
     });
 
+    test(
+        'treats drive letters as part of the root for file: URLs '
+        'with encoded colons', () {
+      expect(context.join('file:///c%3A/foo/bar', '/baz/qux'),
+          'file:///c%3A/baz/qux');
+      expect(context.join('file:///D%3A/foo/bar', '/baz/qux'),
+          'file:///D%3A/baz/qux');
+      expect(context.join('file:///c%3A/', '/baz/qux'), 'file:///c%3A/baz/qux');
+      expect(context.join('file:///c%3A', '/baz/qux'), 'file:///c%3A/baz/qux');
+      expect(context.join('file://host/c%3A/foo/bar', '/baz/qux'),
+          'file://host/c%3A/baz/qux');
+    });
+
     test('treats drive letters as normal components for non-file: URLs', () {
       expect(context.join('http://foo.com/c:/foo/bar', '/baz/qux'),
           'http://foo.com/baz/qux');
@@ -884,7 +897,7 @@ void main() {
     expect(context.withoutExtension('a/b.c//'), 'a/b//');
   });
 
-  test('withoutExtension', () {
+  test('setExtension', () {
     expect(context.setExtension('', '.x'), '.x');
     expect(context.setExtension('a', '.x'), 'a.x');
     expect(context.setExtension('.a', '.x'), '.a.x');

test/windows_test.dart

@@ -761,7 +761,7 @@ void main() {
     expect(context.withoutExtension(r'a\b.c\'), r'a\b\');
   });
 
-  test('withoutExtension', () {
+  test('setExtension', () {
     expect(context.setExtension('', '.x'), '.x');
     expect(context.setExtension('a', '.x'), 'a.x');
     expect(context.setExtension('.a', '.x'), '.a.x');
@@ -784,9 +784,12 @@ void main() {
     test('with a URI', () {
       expect(context.fromUri(Uri.parse('file:///C:/path/to/foo')),
           r'C:\path\to\foo');
+      expect(context.fromUri(Uri.parse('file:///C%3A/path/to/foo')),
+          r'C:\path\to\foo');
       expect(context.fromUri(Uri.parse('file://server/share/path/to/foo')),
           r'\\server\share\path\to\foo');
       expect(context.fromUri(Uri.parse('file:///C:/')), r'C:\');
+      expect(context.fromUri(Uri.parse('file:///C%3A/')), r'C:\');
       expect(
           context.fromUri(Uri.parse('file://server/share')), r'\\server\share');
       expect(context.fromUri(Uri.parse('foo/bar')), r'foo\bar');
@@ -797,6 +800,8 @@ void main() {
           r'\\server\share\path\to\foo');
       expect(context.fromUri(Uri.parse('file:///C:/path/to/foo%23bar')),
           r'C:\path\to\foo#bar');
+      expect(context.fromUri(Uri.parse('file:///C%3A/path/to/foo%23bar')),
+          r'C:\path\to\foo#bar');
       expect(
           context.fromUri(Uri.parse('file://server/share/path/to/foo%23bar')),
           r'\\server\share\path\to\foo#bar');
@@ -809,6 +814,7 @@ void main() {
 
     test('with a string', () {
       expect(context.fromUri('file:///C:/path/to/foo'), r'C:\path\to\foo');
+      expect(context.fromUri('file:///C%3A/path/to/foo'), r'C:\path\to\foo');
     });
   });
 
@@ -845,6 +851,16 @@ void main() {
       expect(context.prettyUri('file:///C:/root/other'), r'..\other');
     });
 
+    test('with a file: URI with encoded colons', () {
+      expect(context.prettyUri('file:///C%3A/root/path/a/b'), r'a\b');
+      expect(context.prettyUri('file:///C%3A/root/path/a/../b'), r'b');
+      expect(context.prettyUri('file:///C%3A/other/path/a/b'),
+          r'C:\other\path\a\b');
+      expect(
+          context.prettyUri('file:///D%3A/root/path/a/b'), r'D:\root\path\a\b');
+      expect(context.prettyUri('file:///C%3A/root/other'), r'..\other');
+    });
+
     test('with an http: URI', () {
       expect(context.prettyUri('https://dart.dev/a/b'), 'https://dart.dev/a/b');
     });