From 09bf526b19e498aa2c4e8861affd59d2982e1559 Mon Sep 17 00:00:00 2001
From: Cong-Cong Pan <dacongsama@live.com>
Date: Tue, 8 Sep 2026 16:36:56 +0800
Subject: [PATCH 1/2] fix: deduplicate mask image prefixes

---
 src/lib.rs                | 196 ++++++++++++++++++++++++++++++++++++++
 src/properties/masking.rs |  51 +++++++++-
 2 files changed, 244 insertions(+), 3 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 6416b7bae..504f5b52b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -28460,6 +28460,202 @@ mod tests {
     assert_eq!(property, Property::ColorInterpolation(svg::ColorInterpolation::SRGB));
   }
 
+  #[test]
+  fn test_mask_image_prefix_duplicates() {
+    let targets = Browsers {
+      chrome: Some(90 << 16),
+      ..Browsers::default()
+    };
+
+    for (source, expected) in [
+      (
+        r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: var(--image);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: var(--image);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            mask-image: linear-gradient(red, blue);
+            mask-image: linear-gradient(var(--start, red), blue);
+            -webkit-mask-image: linear-gradient(red, blue);
+            -webkit-mask-image: linear-gradient(var(--start, red), blue);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            mask-image: linear-gradient(red, #00f);
+            mask-image: linear-gradient(var(--start, red), blue);
+            -webkit-mask-image: linear-gradient(red, #00f);
+            -webkit-mask-image: linear-gradient(var(--start, red), blue);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            mask-image: var(--first, none);
+            mask-image: var(--second, none);
+            -webkit-mask-image: var(--first, none);
+            -webkit-mask-image: var(--second, none);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            mask-image: var(--first, none);
+            mask-image: var(--second, none);
+            -webkit-mask-image: var(--first, none);
+            -webkit-mask-image: var(--second, none);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            mask-image: var(--first);
+            -webkit-mask-image: var(--second);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--first);
+            mask-image: var(--first);
+            -webkit-mask-image: var(--second);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: none;
+            -webkit-mask-image: var(--image);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: none;
+            -webkit-mask-image: var(--image);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            mask-image: var(--image);
+            mask-position: center;
+            -webkit-mask-image: var(--image);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: var(--image);
+            -webkit-mask-position: center;
+            mask-position: center;
+            -webkit-mask-image: var(--image);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            mask-image: var(--image);
+            mask: none;
+            -webkit-mask-image: var(--image);
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: var(--image);
+            -webkit-mask: none;
+            mask: none;
+            -webkit-mask-image: var(--image);
+          }
+        "#},
+      ),
+      (
+        r#"
+          .foo {
+            mask-image: var(--image) !important;
+            -webkit-mask-image: var(--image);
+            -webkit-mask-image: var(--image) !important;
+          }
+        "#,
+        indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: var(--image) !important;
+            -webkit-mask-image: var(--image) !important;
+          }
+        "#},
+      ),
+    ] {
+      prefix_test(source, expected, targets);
+      prefix_test(expected, expected, targets);
+    }
+
+    prefix_test(
+      r#"
+          .foo {
+            mask-image: var(--image);
+            mask: var(--mask);
+            -webkit-mask-image: var(--image);
+          }
+        "#,
+      indoc! { r#"
+          .foo {
+            -webkit-mask-image: var(--image);
+            mask-image: var(--image);
+            -webkit-mask: var(--mask);
+            mask: var(--mask);
+            -webkit-mask-image: var(--image);
+          }
+        "#},
+      targets,
+    );
+
+    let source = r#"
+      .foo {
+        -webkit-mask-image: var(--image);
+        mask-image: var(--image);
+      }
+    "#;
+    test(
+      source,
+      indoc! { r#"
+        .foo {
+          -webkit-mask-image: var(--image);
+          mask-image: var(--image);
+        }
+      "#},
+    );
+    prefix_test(
+      source,
+      indoc! { r#"
+        .foo {
+          -webkit-mask-image: var(--image);
+          mask-image: var(--image);
+        }
+      "#},
+      Browsers {
+        chrome: Some(130 << 16),
+        ..Browsers::default()
+      },
+    );
+  }
+
   #[test]
   fn test_filter() {
     minify_test(
diff --git a/src/properties/masking.rs b/src/properties/masking.rs
index ff05e1f63..0b2cda2a0 100644
--- a/src/properties/masking.rs
+++ b/src/properties/masking.rs
@@ -703,7 +703,11 @@ impl<'i> PropertyHandler<'i> for MaskHandler<'i> {
         self
           .flushed_properties
           .insert(MaskProperty::try_from(&val.property_id).unwrap());
-        dest.push(Property::Unparsed(unparsed));
+        if matches!(unparsed.property_id, PropertyId::MaskImage(_)) {
+          self.push_mask_image(Property::Unparsed(unparsed), dest);
+        } else {
+          dest.push(Property::Unparsed(unparsed));
+        }
       }
       Property::MaskBorderSource(val) => property!(border_source, val, &VendorPrefix::None),
       Property::WebKitMaskBoxImageSource(val, _) => property!(border_source, val, &VendorPrefix::WebKit),
@@ -903,7 +907,7 @@ impl<'i> MaskHandler<'i> {
             if p.is_empty() {
               p = prefix;
             }
-            dest.push(Property::MaskImage(fallback, p))
+            self.push_mask_image(Property::MaskImage(fallback, p), dest)
           }
 
           let p = images
@@ -916,7 +920,7 @@ impl<'i> MaskHandler<'i> {
           }
         }
 
-        dest.push(Property::MaskImage(images, prefix));
+        self.push_mask_image(Property::MaskImage(images, prefix), dest);
         self.flushed_properties.insert(MaskProperty::MaskImage);
       }
     }
@@ -953,6 +957,47 @@ impl<'i> MaskHandler<'i> {
     }
   }
 
+  fn push_mask_image(&self, property: Property<'i>, dest: &mut DeclarationList<'i>) {
+    let prefix = property.property_id().prefix();
+    for i in (0..dest.len()).rev() {
+      let adjacent = i == dest.len() - 1;
+      let previous_prefix = match (&mut dest[i], &property) {
+        (Property::MaskImage(previous, previous_prefix), Property::MaskImage(value, _)) => {
+          if previous != value {
+            continue;
+          }
+          previous_prefix
+        }
+        (Property::Unparsed(previous), Property::Unparsed(value)) => {
+          let PropertyId::MaskImage(previous_prefix) = &mut previous.property_id else {
+            break;
+          };
+          if previous.value != value.value {
+            continue;
+          }
+          previous_prefix
+        }
+        (Property::MaskImage(..), _) => continue,
+        (Property::Unparsed(previous), _) if matches!(previous.property_id, PropertyId::MaskImage(_)) => continue,
+        _ => break,
+      };
+
+      // Keep the last occurrence of each prefix in an image fallback chain.
+      // Moving a later declaration earlier could change the cascade in browsers
+      // that treat the prefixed and unprefixed properties as aliases.
+      // Preserve nonadjacent declarations if no prefixes would remain, so the
+      // first value in the fallback chain does not change on a second minify.
+      if !adjacent && (*previous_prefix - prefix).is_empty() {
+        continue;
+      }
+      previous_prefix.remove(prefix);
+      if previous_prefix.is_empty() {
+        dest.remove(i);
+      }
+    }
+    dest.push(property);
+  }
+
   fn flush_mask_shorthand(
     &self,
     masks: SmallVec<[Mask<'i>; 1]>,

From 0e6ec3ab091a5b72bade9729ba15498b7ddfe3c8 Mon Sep 17 00:00:00 2001
From: Cong-Cong Pan <dacongsama@live.com>
Date: Thu, 8 Oct 2026 11:33:32 +0800
Subject: [PATCH 2/2] fix: simplify mask image prefix deduplication

---
 src/lib.rs                | 138 ++------------------------------------
 src/properties/masking.rs |  60 ++++-------------
 2 files changed, 20 insertions(+), 178 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 504f5b52b..09c95e8d5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -28469,12 +28469,7 @@ mod tests {
 
     for (source, expected) in [
       (
-        r#"
-          .foo {
-            -webkit-mask-image: var(--image);
-            mask-image: var(--image);
-          }
-        "#,
+        ".foo { -webkit-mask-image: var(--image); mask-image: var(--image) }",
         indoc! { r#"
           .foo {
             -webkit-mask-image: var(--image);
@@ -28483,80 +28478,18 @@ mod tests {
         "#},
       ),
       (
-        r#"
-          .foo {
-            mask-image: linear-gradient(red, blue);
-            mask-image: linear-gradient(var(--start, red), blue);
-            -webkit-mask-image: linear-gradient(red, blue);
-            -webkit-mask-image: linear-gradient(var(--start, red), blue);
-          }
-        "#,
-        indoc! { r#"
-          .foo {
-            mask-image: linear-gradient(red, #00f);
-            mask-image: linear-gradient(var(--start, red), blue);
-            -webkit-mask-image: linear-gradient(red, #00f);
-            -webkit-mask-image: linear-gradient(var(--start, red), blue);
-          }
-        "#},
-      ),
-      (
-        r#"
-          .foo {
-            mask-image: var(--first, none);
-            mask-image: var(--second, none);
-            -webkit-mask-image: var(--first, none);
-            -webkit-mask-image: var(--second, none);
-          }
-        "#,
-        indoc! { r#"
-          .foo {
-            mask-image: var(--first, none);
-            mask-image: var(--second, none);
-            -webkit-mask-image: var(--first, none);
-            -webkit-mask-image: var(--second, none);
-          }
-        "#},
-      ),
-      (
-        r#"
-          .foo {
-            mask-image: var(--first);
-            -webkit-mask-image: var(--second);
-          }
-        "#,
+        ".foo { mask-image: var(--first); mask-image: var(--second) }",
         indoc! { r#"
           .foo {
             -webkit-mask-image: var(--first);
             mask-image: var(--first);
             -webkit-mask-image: var(--second);
+            mask-image: var(--second);
           }
         "#},
       ),
       (
-        r#"
-          .foo {
-            -webkit-mask-image: var(--image);
-            mask-image: none;
-            -webkit-mask-image: var(--image);
-          }
-        "#,
-        indoc! { r#"
-          .foo {
-            -webkit-mask-image: var(--image);
-            mask-image: none;
-            -webkit-mask-image: var(--image);
-          }
-        "#},
-      ),
-      (
-        r#"
-          .foo {
-            mask-image: var(--image);
-            mask-position: center;
-            -webkit-mask-image: var(--image);
-          }
-        "#,
+        ".foo { mask-image: var(--image); mask-position: center; -webkit-mask-image: var(--image) }",
         indoc! { r#"
           .foo {
             -webkit-mask-image: var(--image);
@@ -28568,36 +28501,12 @@ mod tests {
         "#},
       ),
       (
-        r#"
-          .foo {
-            mask-image: var(--image);
-            mask: none;
-            -webkit-mask-image: var(--image);
-          }
-        "#,
+        ".foo { mask-image: var(--image) !important; -webkit-mask-image: var(--image) }",
         indoc! { r#"
           .foo {
-            -webkit-mask-image: var(--image);
-            mask-image: var(--image);
-            -webkit-mask: none;
-            mask: none;
-            -webkit-mask-image: var(--image);
-          }
-        "#},
-      ),
-      (
-        r#"
-          .foo {
-            mask-image: var(--image) !important;
             -webkit-mask-image: var(--image);
             -webkit-mask-image: var(--image) !important;
-          }
-        "#,
-        indoc! { r#"
-          .foo {
-            -webkit-mask-image: var(--image);
             mask-image: var(--image) !important;
-            -webkit-mask-image: var(--image) !important;
           }
         "#},
       ),
@@ -28607,42 +28516,7 @@ mod tests {
     }
 
     prefix_test(
-      r#"
-          .foo {
-            mask-image: var(--image);
-            mask: var(--mask);
-            -webkit-mask-image: var(--image);
-          }
-        "#,
-      indoc! { r#"
-          .foo {
-            -webkit-mask-image: var(--image);
-            mask-image: var(--image);
-            -webkit-mask: var(--mask);
-            mask: var(--mask);
-            -webkit-mask-image: var(--image);
-          }
-        "#},
-      targets,
-    );
-
-    let source = r#"
-      .foo {
-        -webkit-mask-image: var(--image);
-        mask-image: var(--image);
-      }
-    "#;
-    test(
-      source,
-      indoc! { r#"
-        .foo {
-          -webkit-mask-image: var(--image);
-          mask-image: var(--image);
-        }
-      "#},
-    );
-    prefix_test(
-      source,
+      ".foo { -webkit-mask-image: var(--image); mask-image: var(--image) }",
       indoc! { r#"
         .foo {
           -webkit-mask-image: var(--image);
diff --git a/src/properties/masking.rs b/src/properties/masking.rs
index 0b2cda2a0..050e0d1f7 100644
--- a/src/properties/masking.rs
+++ b/src/properties/masking.rs
@@ -703,9 +703,18 @@ impl<'i> PropertyHandler<'i> for MaskHandler<'i> {
         self
           .flushed_properties
           .insert(MaskProperty::try_from(&val.property_id).unwrap());
-        if matches!(unparsed.property_id, PropertyId::MaskImage(_)) {
-          self.push_mask_image(Property::Unparsed(unparsed), dest);
-        } else {
+        let mut merged = false;
+        if let (PropertyId::MaskImage(prefix), Some(Property::Unparsed(previous))) =
+          (&unparsed.property_id, dest.last_mut())
+        {
+          if let PropertyId::MaskImage(previous_prefix) = &mut previous.property_id {
+            if previous.value == unparsed.value {
+              *previous_prefix |= *prefix;
+              merged = true;
+            }
+          }
+        }
+        if !merged {
           dest.push(Property::Unparsed(unparsed));
         }
       }
@@ -907,7 +916,7 @@ impl<'i> MaskHandler<'i> {
             if p.is_empty() {
               p = prefix;
             }
-            self.push_mask_image(Property::MaskImage(fallback, p), dest)
+            dest.push(Property::MaskImage(fallback, p))
           }
 
           let p = images
@@ -920,7 +929,7 @@ impl<'i> MaskHandler<'i> {
           }
         }
 
-        self.push_mask_image(Property::MaskImage(images, prefix), dest);
+        dest.push(Property::MaskImage(images, prefix));
         self.flushed_properties.insert(MaskProperty::MaskImage);
       }
     }
@@ -957,47 +966,6 @@ impl<'i> MaskHandler<'i> {
     }
   }
 
-  fn push_mask_image(&self, property: Property<'i>, dest: &mut DeclarationList<'i>) {
-    let prefix = property.property_id().prefix();
-    for i in (0..dest.len()).rev() {
-      let adjacent = i == dest.len() - 1;
-      let previous_prefix = match (&mut dest[i], &property) {
-        (Property::MaskImage(previous, previous_prefix), Property::MaskImage(value, _)) => {
-          if previous != value {
-            continue;
-          }
-          previous_prefix
-        }
-        (Property::Unparsed(previous), Property::Unparsed(value)) => {
-          let PropertyId::MaskImage(previous_prefix) = &mut previous.property_id else {
-            break;
-          };
-          if previous.value != value.value {
-            continue;
-          }
-          previous_prefix
-        }
-        (Property::MaskImage(..), _) => continue,
-        (Property::Unparsed(previous), _) if matches!(previous.property_id, PropertyId::MaskImage(_)) => continue,
-        _ => break,
-      };
-
-      // Keep the last occurrence of each prefix in an image fallback chain.
-      // Moving a later declaration earlier could change the cascade in browsers
-      // that treat the prefixed and unprefixed properties as aliases.
-      // Preserve nonadjacent declarations if no prefixes would remain, so the
-      // first value in the fallback chain does not change on a second minify.
-      if !adjacent && (*previous_prefix - prefix).is_empty() {
-        continue;
-      }
-      previous_prefix.remove(prefix);
-      if previous_prefix.is_empty() {
-        dest.remove(i);
-      }
-    }
-    dest.push(property);
-  }
-
   fn flush_mask_shorthand(
     &self,
     masks: SmallVec<[Mask<'i>; 1]>,