style: Add a declaration iterator to AllShorthand for simplify code.

Bug: 1461285
Reviewed-by: emilio
MozReview-Commit-ID: 9w2B3SpdkQo

components/style/properties/declaration_block.rs

@@ -455,34 +455,9 @@ impl PropertyDeclarationBlock {
                 mode,
             );
         }
-        match drain.all_shorthand {
+        drain.all_shorthand.declarations().fold(changed, |changed, decl| {
-            AllShorthand::NotSet => {}
+            changed | self.push(decl, importance, mode)
-            AllShorthand::CSSWideKeyword(keyword) => {
+        })
-                for id in ShorthandId::All.longhands() {
-                    let decl = PropertyDeclaration::CSSWideKeyword(
-                        WideKeywordDeclaration { id, keyword },
-                    );
-                    changed |= self.push(
-                        decl,
-                        importance,
-                        mode,
-                    );
-                }
-            }
-            AllShorthand::WithVariables(unparsed) => {
-                for id in ShorthandId::All.longhands() {
-                    let decl = PropertyDeclaration::WithVariables(
-                        VariableDeclaration { id, value: unparsed.clone() },
-                    );
-                    changed |= self.push(
-                        decl,
-                        importance,
-                        mode,
-                    );
-                }
-            }
-        }
-        changed
     }
 
     /// Adds or overrides the declaration for a given property in this block.

components/style/properties/properties.mako.rs

@@ -2222,6 +2222,50 @@ enum AllShorthand {
     WithVariables(Arc<UnparsedValue>)
 }
 
+impl AllShorthand {
+    /// Iterates property declarations from the given all shorthand value.
+    #[inline]
+    fn declarations(&self) -> AllShorthandDeclarationIterator {
+        AllShorthandDeclarationIterator {
+            all_shorthand: self,
+            longhands: ShorthandId::All.longhands(),
+        }
+    }
+}
+
+struct AllShorthandDeclarationIterator<'a> {
+    all_shorthand: &'a AllShorthand,
+    longhands: NonCustomPropertyIterator<LonghandId>,
+}
+
+impl<'a> Iterator for AllShorthandDeclarationIterator<'a> {
+    type Item = PropertyDeclaration;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        match *self.all_shorthand {
+            AllShorthand::NotSet => None,
+            AllShorthand::CSSWideKeyword(ref keyword) => {
+                Some(PropertyDeclaration::CSSWideKeyword(
+                    WideKeywordDeclaration {
+                        id: self.longhands.next()?,
+                        keyword: *keyword
+                    }
+                ))
+            }
+            AllShorthand::WithVariables(ref unparsed) => {
+                let id = self.longhands.next()?;
+                Some(PropertyDeclaration::WithVariables(
+                    VariableDeclaration {
+                        id: self.longhands.next()?,
+                        value: unparsed.clone()
+                    }
+                ))
+            }
+        }
+    }
+}
+
 #[cfg(feature = "gecko")]
 pub use gecko_properties::style_structs;