Ensure extend op stays sequential when copying px #3928

docs/changelog.md

@@ -10,6 +10,9 @@ Requires libvips v8.15.0
   [#3914](https://github.com/lovell/sharp/pull/3914)
   [@abhi0498](https://github.com/abhi0498)
 
+* Ensure `extend` operation stays sequential when copying (regression in 0.32.0).
+  [#3928](https://github.com/lovell/sharp/issues/3928)
+
 ### v0.33.1 - 17th December 2023
 
 * Add support for Yarn Plug'n'Play filesystem layout.

src/pipeline.cc

@@ -561,6 +561,7 @@ class PipelineWorker : public Napi::AsyncWorker {
                 VImage::option()->set("extend", baton->extendWith)->set("background", background));
         } else {
           std::vector<double> ignoredBackground(1);
+          image = sharp::StaySequential(image, baton->input->access);
           image = nPages > 1
             ? sharp::EmbedMultiPage(image,
                 baton->extendLeft, baton->extendTop, baton->width, baton->height,

test/unit/extend.js

@@ -73,6 +73,20 @@ describe('Extend', function () {
         });
     });
 
+    it('extend top with mirroring uses ordered read', async () => {
+      const data = await sharp(fixtures.inputJpg)
+        .extend({
+          extendWith: 'mirror',
+          top: 1
+        })
+        .png({ compressionLevel: 0 })
+        .toBuffer();
+
+      const { width, height } = await sharp(data).metadata();
+      assert.strictEqual(2725, width);
+      assert.strictEqual(2226, height);
+    });
+
     it(`extend sides unequally with RGBA (${extendWith})`, function (done) {
       sharp(fixtures.inputPngWithTransparency16bit)
         .resize(120)