[flutter_tools] handle OSError 2 from current working directory (#78380)

packages/flutter_tools/lib/src/base/error_handling_io.dart

@@ -24,6 +24,10 @@ import 'platform.dart';
 // ToolExit and a message that is more clear than the FileSystemException by
 // itself.
 
+/// On windows this is error code 2: ERROR_FILE_NOT_FOUND, and on
+/// macOS/Linux it is error code 2/ENOENT: No such file or directory.
+const int kSystemCannotFindFile = 2;
+
 /// A [FileSystem] that throws a [ToolExit] on certain errors.
 ///
 /// If a [FileSystem] error is not caused by the Flutter tool, and can only be
@@ -83,10 +87,6 @@ class ErrorHandlingFileSystem extends ForwardingFileSystem {
       // Certain error codes indicate the file could not be found. It could have
       // been deleted by a different program while the tool was running.
       // if it still exists, the file likely exists on a read-only volume.
-      //
-      // On windows this is error code 2: ERROR_FILE_NOT_FOUND, and on
-      // macOS/Linux it is error code 2/ENOENT: No such file or directory.
-      const int kSystemCannotFindFile = 2;
       if (err?.osError?.errorCode != kSystemCannotFindFile || _noExitOnFailure) {
         rethrow;
       }
@@ -105,7 +105,18 @@ class ErrorHandlingFileSystem extends ForwardingFileSystem {
 
   @override
   Directory get currentDirectory {
-    return _runSync(() =>  directory(delegate.currentDirectory), platform: _platform);
+    try {
+      return _runSync(() =>  directory(delegate.currentDirectory), platform: _platform);
+    } on FileSystemException catch (err) {
+      // Special handling for OS error 2 for current directory only.
+      if (err.osError.errorCode == kSystemCannotFindFile) {
+        throwToolExit(
+          'Unable to read current working directory. This can happen if the directory the '
+          'Flutter tool was run from was moved or deleted.'
+        );
+      }
+      rethrow;
+    }
   }
 
   @override

packages/flutter_tools/test/general.shard/base/error_handling_io_test.dart

@@ -8,6 +8,7 @@ import 'dart:io' as io; // ignore: dart_io_import;
 
 import 'package:file/file.dart';
 import 'package:file/memory.dart';
+import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/error_handling_io.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -370,6 +371,7 @@ void main() {
     const int eperm = 1;
     const int enospc = 28;
     const int eacces = 13;
+
     MockFileSystem mockFileSystem;
     ErrorHandlingFileSystem fs;
 
@@ -475,6 +477,19 @@ void main() {
       expect(() => directory.existsSync(),
              throwsToolExit(message: expectedMessage));
     });
+
+    testWithoutContext('When the current working directory disappears', () async {
+      setupReadMocks(
+        mockFileSystem: mockFileSystem,
+        fs: fs,
+        errorCode: kSystemCannotFindFile,
+      );
+
+      expect(() => fs.currentDirectory, throwsToolExit(message: 'Unable to read current working directory'));
+
+      // Error is not caught by other operations.
+      expect(() => fs.file('foo').readAsStringSync(), throwsFileSystemException(kSystemCannotFindFile));
+    });
   });
 
   group('throws ToolExit on macOS', () {