Improve Windows symlink instructions (#67029)

When the developer doesn't have permission to create symlinks, we
display specific instructions, but they were only correct for recent
versions of Windows 10. This improves them by:
- Giving the correct instructions for older versions.
- For recent versions, adds a command that will deep-link into the
  settings application so that developers don't have to figure out
  where/how to enable developer mode.

Fixes https://github.com/flutter/flutter/issues/66973

packages/flutter_tools/lib/src/plugins.dart

@@ -11,6 +11,9 @@ import 'android/gradle.dart';
 import 'base/common.dart';
 import 'base/error_handling_io.dart';
 import 'base/file_system.dart';
+import 'base/os.dart';
+import 'base/platform.dart';
+import 'base/version.dart';
 import 'convert.dart';
 import 'dart/package_map.dart';
 import 'features.dart';
@@ -1087,6 +1090,30 @@ void createPluginSymlinks(FlutterProject project, {bool force = false}) {
   }
 }
 
+/// Handler for symlink failures which provides specific instructions for known
+/// failure cases.
+@visibleForTesting
+void handleSymlinkException(FileSystemException e, {
+  @required Platform platform,
+  @required OperatingSystemUtils os,
+}) {
+  if (platform.isWindows && (e.osError?.errorCode ?? 0) == 1314) {
+    final String versionString = RegExp(r'[\d.]+').firstMatch(os.name)?.group(0);
+    final Version version = Version.parse(versionString);
+    // Window 10 14972 is the oldest version that allows creating symlinks
+    // just by enabling developer mode; before that it requires running the
+    // terminal as Administrator.
+    // https://blogs.windows.com/windowsdeveloper/2016/12/02/symlinks-windows-10/
+    final String instructions = (version != null && version >= Version(10, 0, 14972))
+        ? 'Please enable Developer Mode in your system settings. Run\n'
+          '  start ms-settings:developers\n'
+          'to open settings.'
+        : 'You must build from a terminal run as administrator.';
+    throwToolExit('Building with plugins requires symlink support.\n\n' +
+        instructions);
+  }
+}
+
 /// Creates [symlinkDirectory] containing symlinks to each plugin listed in [platformPlugins].
 ///
 /// If [force] is true, the directory will be created only if missing.
@@ -1109,12 +1136,7 @@ void _createPlatformPluginSymlinks(Directory symlinkDirectory, List<dynamic> pla
     try {
       link.createSync(path);
     } on FileSystemException catch (e) {
-      if (globals.platform.isWindows && (e.osError?.errorCode ?? 0) == 1314) {
-        throwToolExit(
-          'Building with plugins requires symlink support. '
-          'Please enable Developer Mode in your system settings.\n\n$e'
-        );
-      }
+      handleSymlinkException(e, platform: globals.platform, os: globals.os);
       rethrow;
     }
   }

packages/flutter_tools/test/general.shard/plugins_test.dart

@@ -7,6 +7,8 @@ import 'dart:convert';
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
 import 'package:file_testing/file_testing.dart';
+import 'package:flutter_tools/src/base/os.dart';
+import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/base/time.dart';
 import 'package:flutter_tools/src/base/utils.dart';
 import 'package:flutter_tools/src/features.dart';
@@ -1414,6 +1416,38 @@ flutter:
       });
 
     });
+
+    testWithoutContext('Symlink failures give developer mode instructions on recent versions of Windows', () async {
+      final Platform platform = FakePlatform(operatingSystem: 'windows');
+      final MockOperatingSystemUtils os = MockOperatingSystemUtils();
+      when(os.name).thenReturn('Microsoft Windows [Version 10.0.14972.1]');
+
+      const FileSystemException e = FileSystemException('', '', OSError('', 1314));
+
+      expect(() => handleSymlinkException(e, platform: platform, os: os),
+        throwsToolExit(message: 'start ms-settings:developers'));
+    });
+
+    testWithoutContext('Symlink failures instruct developers to run as administrator on older versions of Windows', () async {
+      final Platform platform = FakePlatform(operatingSystem: 'windows');
+      final MockOperatingSystemUtils os = MockOperatingSystemUtils();
+      when(os.name).thenReturn('Microsoft Windows [Version 10.0.14393]');
+
+      const FileSystemException e = FileSystemException('', '', OSError('', 1314));
+
+      expect(() => handleSymlinkException(e, platform: platform, os: os),
+        throwsToolExit(message: 'administrator'));
+    });
+
+    testWithoutContext('Symlink failures only give instructions for specific errors', () async {
+      final Platform platform = FakePlatform(operatingSystem: 'windows');
+      final MockOperatingSystemUtils os = MockOperatingSystemUtils();
+      when(os.name).thenReturn('Microsoft Windows [Version 10.0.14393]');
+
+      const FileSystemException e = FileSystemException('', '', OSError('', 999));
+
+      expect(() => handleSymlinkException(e, platform: platform, os: os), returnsNormally);
+    });
   });
 }
 
@@ -1426,3 +1460,4 @@ class MockXcodeProjectInterpreter extends Mock implements XcodeProjectInterprete
 class MockWebProject extends Mock implements WebProject {}
 class MockWindowsProject extends Mock implements WindowsProject {}
 class MockLinuxProject extends Mock implements LinuxProject {}
+class MockOperatingSystemUtils extends Mock implements OperatingSystemUtils {}