Prevent double unpremultiply with some composite blends

docs/changelog.md

@@ -4,6 +4,11 @@
 
 Requires libvips v8.12.2
 
+### v0.30.3 - TBD
+
+* Prevent double unpremultiply with some composite blend modes (regression in 0.30.2).
+  [#3118](https://github.com/lovell/sharp/issues/3118)
+
 ### v0.30.2 - 2nd March 2022
 
 * Improve performance and accuracy when compositing multiple images.

src/pipeline.cc

@@ -354,7 +354,7 @@ class PipelineWorker : public Napi::AsyncWorker {
       }
 
       bool const shouldPremultiplyAlpha = sharp::HasAlpha(image) &&
-        (shouldResize || shouldBlur || shouldConv || shouldSharpen || shouldComposite);
+        (shouldResize || shouldBlur || shouldConv || shouldSharpen);
 
       // Premultiply image alpha channel before all transformations to avoid
       // dark fringing around bright pixels

test/unit/extend.js

@@ -158,6 +158,6 @@ describe('Extend', function () {
       })
       .raw()
       .toBuffer();
-    assert.deepStrictEqual(Array.from(data), [191, 25, 65, 204, 238, 31, 82, 204]);
+    assert.deepStrictEqual(Array.from(data), [191, 25, 66, 204, 191, 25, 66, 204]);
   });
 });