Fix DevFS to understand missing files in _stat() (#22844)

Fixes #22451

packages/flutter_tools/lib/src/devfs.dart

@@ -83,20 +83,32 @@ class DevFSFileContent extends DevFSContent {
   void _stat() {
     if (_linkTarget != null) {
       // Stat the cached symlink target.
-      _fileStat = _linkTarget.statSync();
+      final FileStat fileStat = _linkTarget.statSync();
+      if (fileStat.type == FileSystemEntityType.notFound) {
+        _linkTarget = null;
+      } else {
+        _fileStat = fileStat;
         return;
       }
-    _fileStat = file.statSync();
-    if (_fileStat.type == FileSystemEntityType.link) {
+    }
+    final FileStat fileStat = file.statSync();
+    _fileStat = fileStat.type == FileSystemEntityType.notFound ? null : fileStat;
+    if (_fileStat != null && _fileStat.type == FileSystemEntityType.link) {
       // Resolve, stat, and maybe cache the symlink target.
       final String resolved = file.resolveSymbolicLinksSync();
       final FileSystemEntity linkTarget = fs.file(resolved);
       // Stat the link target.
-      _fileStat = linkTarget.statSync();
-      if (devFSConfig.cacheSymlinks) {
+      final FileStat fileStat = linkTarget.statSync();
+      if (fileStat.type == FileSystemEntityType.notFound) {
+        _fileStat = null;
+        _linkTarget = null;
+      } else if (devFSConfig.cacheSymlinks) {
         _linkTarget = linkTarget;
       }
     }
+    if (_fileStat == null) {
+      printError('Unable to get status of file "${file.path}": file not found.');
+    }
   }
 
   @override
@@ -106,21 +118,29 @@ class DevFSFileContent extends DevFSContent {
   bool get isModified {
     final FileStat _oldFileStat = _fileStat;
     _stat();
-    return _oldFileStat == null || _fileStat.modified.isAfter(_oldFileStat.modified);
+    if (_oldFileStat == null && _fileStat == null)
+      return false;
+    return _oldFileStat == null || _fileStat == null || _fileStat.modified.isAfter(_oldFileStat.modified);
   }
 
   @override
   bool isModifiedAfter(DateTime time) {
     final FileStat _oldFileStat = _fileStat;
     _stat();
-    return _oldFileStat == null || time == null || _fileStat.modified.isAfter(time);
+    if (_oldFileStat == null && _fileStat == null)
+      return false;
+    return time == null
+        || _oldFileStat == null
+        || _fileStat == null
+        || _fileStat.modified.isAfter(time);
   }
 
   @override
   int get size {
     if (_fileStat == null)
       _stat();
-    return _fileStat.size;
+    // Can still be null if the file wasn't found.
+    return _fileStat?.size ?? 0;
   }
 
   @override

packages/flutter_tools/test/devfs_test.dart

@@ -62,6 +62,36 @@ void main() {
       expect(content.isModified, isTrue);
       expect(content.isModified, isFalse);
     });
+    testUsingContext('file', () async {
+      final File file = fs.file(filePath);
+      final DevFSFileContent content = DevFSFileContent(file);
+      expect(content.isModified, isFalse);
+      expect(content.isModified, isFalse);
+
+      file.parent.createSync(recursive: true);
+      file.writeAsBytesSync(<int>[1, 2, 3]);
+
+      final DateTime fiveSecondsAgo = DateTime.now().subtract(Duration(seconds:5));
+      expect(content.isModifiedAfter(fiveSecondsAgo), isTrue);
+      expect(content.isModifiedAfter(fiveSecondsAgo), isTrue);
+      expect(content.isModifiedAfter(null), isTrue);
+
+      file.writeAsBytesSync(<int>[2, 3, 4]);
+      expect(content.fileDependencies, <String>[filePath]);
+      expect(content.isModified, isTrue);
+      expect(content.isModified, isFalse);
+      expect(await content.contentsAsBytes(), <int>[2, 3, 4]);
+      updateFileModificationTime(file.path, fiveSecondsAgo, 0);
+      expect(content.isModified, isFalse);
+      expect(content.isModified, isFalse);
+
+      file.deleteSync();
+      expect(content.isModified, isTrue);
+      expect(content.isModified, isFalse);
+      expect(content.isModified, isFalse);
+    }, overrides: <Type, Generator>{
+      FileSystem: () => fs,
+    });
   });
 
   group('devfs local', () {