[xdg_directories] Return null from getUserDirectory instead of throwing exception (#3033)

* fix: xdg.getUserDirectory to return null on missing executable

* Update changelog

* Fix review comments

packages/xdg_directories/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.2.0+3
+
+* Returns null instead of throwing exception from getUserDirectory when xdg-user-dir executable is missing.
+
 ## 0.2.0+2
 
 * Fixes unit tests on Windows.

packages/xdg_directories/lib/xdg_directories.dart

@@ -149,7 +149,12 @@ Directory? get runtimeDir => _directoryFromEnvironment('XDG_RUNTIME_DIR');
 /// Gets the xdg user directory named by `dirName`.
 ///
 /// Use [getUserDirectoryNames] to find out the list of available names.
+///
+/// If the `xdg-user-dir` executable is not present this returns null.
 Directory? getUserDirectory(String dirName) {
+  if (!_processManager.canRun('xdg-user-dir')) {
+    return null;
+  }
   final ProcessResult result = _processManager.runSync(
     <String>['xdg-user-dir', dirName],
     stdoutEncoding: utf8,

packages/xdg_directories/pubspec.yaml

@@ -2,7 +2,7 @@ name: xdg_directories
 description: A Dart package for reading XDG directory configuration information on Linux.
 repository: https://github.com/flutter/packages/tree/main/packages/xdg_directories
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+xdg_directories%22
-version: 0.2.0+2
+version: 0.2.0+3
 
 environment:
   sdk: ">=2.12.0 <3.0.0"

packages/xdg_directories/test/xdg_directories_test.dart

@@ -113,6 +113,16 @@ XDG_VIDEOS_DIR="$HOME/Videos"
     xdg.xdgProcessManager = const LocalProcessManager();
   });
 
+  test('Returns null when xdg-user-dir executable is not present', () {
+    xdg.xdgProcessManager = FakeProcessManager(
+      <String, String>{},
+      canRunExecutable: false,
+    );
+    expect(xdg.getUserDirectory('DESKTOP'), isNull,
+        reason: 'Found xdg user directory without access to xdg-user-dir');
+    xdg.xdgProcessManager = const LocalProcessManager();
+  });
+
   test('Throws StateError when HOME not set', () {
     fakeEnv.clear();
     expect(() {
@@ -122,9 +132,10 @@ XDG_VIDEOS_DIR="$HOME/Videos"
 }
 
 class FakeProcessManager extends Fake implements ProcessManager {
-  FakeProcessManager(this.expected);
+  FakeProcessManager(this.expected, {this.canRunExecutable = true});
 
   Map<String, String> expected;
+  final bool canRunExecutable;
 
   @override
   ProcessResult runSync(
@@ -138,4 +149,9 @@ class FakeProcessManager extends Fake implements ProcessManager {
   }) {
     return ProcessResult(0, 0, expected[command[1]], '');
   }
+
+  @override
+  bool canRun(dynamic executable, {String? workingDirectory}) {
+    return canRunExecutable;
+  }
 }