[path] Strip Windows Extended-Length Path prefixes in absolutePathToUri

pkgs/path/CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 1.9.2-wip
 
+- `WindowsStyle.absolutePathToUri` (and therefore `toUri()`) now strips Windows
+  Extended-Length Path prefixes (`\\?\` and `\\?\UNC\`) instead of
+  throwing a `FormatException`. This aligns `path.toUri()` with
+  `Uri.file()` / `Uri.directory()` from `dart:io`.
 - Make `Url` style better at recognizing schemes and authorities.
   Only consider a path as being a schemed URL if it starts with a
   valid scheme.

pkgs/path/lib/src/style/windows.dart

@@ -103,6 +103,24 @@ class WindowsStyle extends InternalStyle {
 
   @override
   Uri absolutePathToUri(String path) {
+    // Strip Windows Extended-Length Path prefixes so that `toUri()` aligns
+    // with `Uri.file()` / `Uri.directory()` from `dart:io`.
+    //
+    // `\\?\C:\path`           -> `C:\path`
+    // `\\?\UNC\server\share` -> `\\server\share`
+    //
+    // The `\\?\` prefix is a Win32 API artifact (enables paths > 260 chars
+    // and disables DOS device-name interpretation). It is not user intent and
+    // should not leak into the resulting file URI. See:
+    // https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#win32-file-namespaces
+    if (path.startsWith(r'\\?\')) {
+      if (path.startsWith(r'UNC\', r'\\?\'.length)) {
+        path = path.replaceRange(0, r'\\?\UNC'.length, r'\');
+      } else {
+        path = path.substring(r'\\?\'.length);
+      }
+    }
+
     final parsed = ParsedPath.parse(path, this);
     if (parsed.root!.startsWith(r'\\')) {
       // Network paths become "file://server/share/path/to/file".
@@ -119,10 +137,7 @@ class WindowsStyle extends InternalStyle {
       }
 
       return Uri(
-        scheme: 'file',
-        host: rootParts.first,
-        pathSegments: parsed.parts,
-      );
+          scheme: 'file', host: rootParts.first, pathSegments: parsed.parts);
     } else {
       // Drive-letter paths become "file:///C:/path/to/file".
 
@@ -136,10 +151,8 @@ class WindowsStyle extends InternalStyle {
 
       // Get rid of the trailing "\" in "C:\" because the URI constructor will
       // add a separator on its own.
-      parsed.parts.insert(
-        0,
-        parsed.root!.replaceAll('/', '').replaceAll('\\', ''),
-      );
+      parsed.parts
+          .insert(0, parsed.root!.replaceAll('/', '').replaceAll('\\', ''));
 
       return Uri(scheme: 'file', pathSegments: parsed.parts);
     }

pkgs/path/test/windows_test.dart

@@ -1058,6 +1058,31 @@ void main() {
       Uri.parse('_%7B_%7D_%60_%5E_%20_%22_%25_'),
     );
     expect(context.toUri(''), Uri.parse(''));
+
+    // Windows Extended-Length Path prefixes are stripped to align with
+    // `Uri.file()` from `dart:io`. See:
+    // https://learn.microsoft.com/en-us/windows/win32/fileio/naming-a-file#win32-file-namespaces
+    expect(
+      context.toUri(r'\\?\UNC\server\share\path\to\foo'),
+      Uri.parse('file://server/share/path/to/foo'),
+    );
+    expect(
+      context.toUri(r'\\?\UNC\wsl.localhost\Ubuntu-24.04\tmp\foo'),
+      Uri.parse('file://wsl.localhost/Ubuntu-24.04/tmp/foo'),
+    );
+    expect(
+      context.toUri(r'\\?\UNC\server\share'),
+      Uri.parse('file://server/share'),
+    );
+    expect(
+      context.toUri(r'\\?\UNC\server\share\'),
+      Uri.parse('file://server/share/'),
+    );
+    expect(
+      context.toUri(r'\\?\C:\path\to\foo'),
+      Uri.parse('file:///C:/path/to/foo'),
+    );
+    expect(context.toUri(r'\\?\C:\'), Uri.parse('file:///C:/'));
   });
 
   group('prettyUri', () {