Fix Path.from. (#15268)

* Fix Path.from to deep copy. Add regression test.

Author: ferhatb

lib/web_ui/lib/src/engine/surface/painting.dart

@@ -287,10 +287,28 @@ class SurfacePath implements ui.Path {
   /// This copy is fast and does not require additional memory unless either
   /// the `source` path or the path returned by this constructor are modified.
   SurfacePath.from(SurfacePath source)
+      : subpaths = _deepCopy(source.subpaths);
+
+  SurfacePath._shallowCopy(SurfacePath source)
       : subpaths = List<Subpath>.from(source.subpaths);
 
   SurfacePath._clone(this.subpaths, this._fillType);
 
+  static List<Subpath> _deepCopy(List<Subpath> source) {
+    // The last sub path can potentially still be mutated by calling ops.
+    // Copy all sub paths except the last active one which needs a deep copy.
+    final List<Subpath> paths = [];
+    int len = source.length;
+    if (len != 0) {
+      --len;
+      for (int i = 0; i < len; i++) {
+        paths.add(source[i]);
+      }
+      paths.add(source[len].shift(const ui.Offset(0, 0)));
+    }
+    return paths;
+  }
+
   /// Determines how the interior of this path is calculated.
   ///
   /// Defaults to the non-zero winding rule, [PathFillType.nonZero].

lib/web_ui/lib/src/engine/surface/recording_canvas.dart

@@ -309,7 +309,7 @@ class RecordingCanvas {
     }
     _paintBounds.grow(pathBounds);
     // Clone path so it can be reused for subsequent draw calls.
-    final ui.Path clone = ui.Path.from(path);
+    final ui.Path clone = SurfacePath._shallowCopy(path);
     clone.fillType = path.fillType;
     _commands.add(PaintDrawPath(clone, paint.paintData));
   }

lib/web_ui/test/path_test.dart

@@ -238,4 +238,18 @@ void main() {
             distance: 0.1,
             from: const Rect.fromLTRB(220.0, 124.1, 382.9, 300.0)));
   });
+
+  // Regression test for https://github.com/flutter/flutter/issues/46813.
+  test('Should deep copy path', () {
+    final SurfacePath path = SurfacePath();
+    path.moveTo(25, 30);
+    path.lineTo(100, 200);
+    expect(path.getBounds(), const Rect.fromLTRB(25, 30, 100, 200));
+
+    final SurfacePath path2 = SurfacePath.from(path);
+    path2.lineTo(250, 300);
+    expect(path2.getBounds(), const Rect.fromLTRB(25, 30, 250, 300));
+    // Expect original path to stay the same.
+    expect(path.getBounds(), const Rect.fromLTRB(25, 30, 100, 200));
+  });
 }