Use impl Tag for $T syntax for impl_tag!

Author: WaffleLapkin

compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs

@@ -23,7 +23,7 @@
 ///
 /// impl_tag! {
 ///     // The type for which the `Tag` will be implemented
-///     for SomeTag;
+///     impl Tag for SomeTag;
 ///     // You need to specify the `{value_of_the_type} <=> {tag}` relationship
 ///     SomeTag::A <=> 0,
 ///     SomeTag::B <=> 1,
@@ -54,7 +54,7 @@
 /// struct Flags { a: bool, b: bool }
 ///
 /// impl_tag! {
-///     for Flags;
+///     impl Tag for Flags;
 ///     Flags { a: true,  b: true  } <=> 3,
 ///     Flags { a: false, b: true  } <=> 2,
 ///     Flags { a: true,  b: false } <=> 1,
@@ -73,7 +73,7 @@
 // struct Unit;
 //
 // impl_tag! {
-//     for Unit;
+//     impl Tag for Unit;
 //     Unit <=> 0,
 //     Unit <=> 1,
 // }
@@ -87,7 +87,7 @@
 // enum E { A, B };
 //
 // impl_tag! {
-//     for E;
+//     impl Tag for E;
 //     E::A <=> 0,
 //     E::B <=> 0,
 // }
@@ -104,14 +104,14 @@
 /// }
 ///
 /// impl_tag! {
-///     for E;
+///     impl Tag for E;
 ///     E::A <=> 0,
 /// }
 /// ```
 #[macro_export]
 macro_rules! impl_tag {
     (
-        for $Self:ty;
+        impl Tag for $Self:ty;
         $(
             $($path:ident)::* $( { $( $fields:tt )* })? <=> $tag:literal,
         )*

compiler/rustc_data_structures/src/tagged_ptr/impl_tag/tests.rs

@@ -4,22 +4,22 @@ fn bits_constant() {
 
     #[derive(Copy, Clone)]
     struct Unit;
-    impl_tag! { for Unit; Unit <=> 0, }
+    impl_tag! { impl Tag for Unit; Unit <=> 0, }
     assert_eq!(Unit::BITS, 0);
 
     #[derive(Copy, Clone)]
     struct Unit1;
-    impl_tag! { for Unit1; Unit1 <=> 1, }
+    impl_tag! { impl Tag for Unit1; Unit1 <=> 1, }
     assert_eq!(Unit1::BITS, 1);
 
     #[derive(Copy, Clone)]
     struct Unit2;
-    impl_tag! { for Unit2; Unit2 <=> 0b10, }
+    impl_tag! { impl Tag for Unit2; Unit2 <=> 0b10, }
     assert_eq!(Unit2::BITS, 2);
 
     #[derive(Copy, Clone)]
     struct Unit3;
-    impl_tag! { for Unit3; Unit3 <=> 0b100, }
+    impl_tag! { impl Tag for Unit3; Unit3 <=> 0b100, }
     assert_eq!(Unit3::BITS, 3);
 
     #[derive(Copy, Clone)]
@@ -28,6 +28,6 @@ fn bits_constant() {
         B,
         C,
     }
-    impl_tag! { for Enum; Enum::A <=> 0b1, Enum::B <=> 0b1000, Enum::C <=> 0b10, }
+    impl_tag! { impl Tag for Enum; Enum::A <=> 0b1, Enum::B <=> 0b1000, Enum::C <=> 0b10, }
     assert_eq!(Enum::BITS, 4);
 }

compiler/rustc_middle/src/ty/mod.rs

@@ -1627,7 +1627,7 @@ struct ParamTag {
 }
 
 impl_tag! {
-    for ParamTag;
+    impl Tag for ParamTag;
     ParamTag { reveal: traits::Reveal::UserFacing, constness: hir::Constness::NotConst } <=> 0,
     ParamTag { reveal: traits::Reveal::All,        constness: hir::Constness::NotConst } <=> 1,
     ParamTag { reveal: traits::Reveal::UserFacing, constness: hir::Constness::Const    } <=> 2,