Remove the mixin modifiers no longer supported in the latest proposal. (#1196)

Author: munificent

CHANGELOG.md

@@ -3,6 +3,8 @@
 * Hide `--fix` and related options in `--help`. The options are still there and
   supported, but are no longer shown by default. Eventually, we would like all
   users to move to using `dart fix` instead of `dart format --fix`.
+* Don't format `sealed`, `interface`, and `final` keywords on mixin
+  declarations. The proposal was updated to no longer support them.
 
 # 2.3.0
 

lib/src/source_visitor.dart

@@ -2215,9 +2215,6 @@ class SourceVisitor extends ThrowingAstVisitor {
 
     builder.nestExpression();
     modifier(node.baseKeyword);
-    modifier(node.interfaceKeyword);
-    modifier(node.finalKeyword);
-    modifier(node.sealedKeyword);
     token(node.mixinKeyword);
     space();
     token(node.name);

test/whitespace/metadata.unit

@@ -444,6 +444,11 @@ enum Foo {
 <<<
 @meta
 mixin M {}
+>>> metadata on mixin
+@meta  base   mixin M {}
+<<<
+@meta
+base mixin M {}
 >>> metadata on extension
 @meta extension A on B {}
 <<<

test/whitespace/mixins.unit

@@ -25,15 +25,7 @@ mixin M1 on UnaryNum {
 mixin M<   A  ,B  >on   C  implements    D{ }
 <<<
 mixin M<A, B> on C implements D {}
->>> mixin modifiers
-mixin  M1 {}
-base  mixin M2 {}
-interface  mixin M3 {}
-final  mixin M4 {}
-sealed  mixin M5 {}
+>>> base modifier
+base  mixin M {}
 <<<
-mixin M1 {}
-base mixin M2 {}
-interface mixin M3 {}
-final mixin M4 {}
-sealed mixin M5 {}
+base mixin M {}