Remove the special case of ::self after edition 2018

Author: mu001999

compiler/rustc_resolve/src/ident.rs

@@ -1838,12 +1838,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
             }
 
-            // Support `...::self`, but deny `::self` after edition 2018
-            let allow_trailing_self = is_last
-                && name == kw::SelfLower
-                && segment_idx > 0
-                && (path[segment_idx - 1].ident.name != kw::PathRoot
-                    || self.path_root_is_crate_root(path[segment_idx - 1].ident));
+            let allow_trailing_self = is_last && name == kw::SelfLower;
 
             // Report special messages for path segment keywords in wrong positions.
             if ident.is_path_segment_keyword() && segment_idx != 0 && !allow_trailing_self {

tests/ui/use/use-path-segment-kw.e2018.stderr

@@ -812,6 +812,12 @@ error[E0573]: expected type, found module `self`
 LL |         type D1 = self;
    |                   ^^^^ not a type
 
+error[E0425]: cannot find crate `self` in the list of imported crates
+  --> $DIR/use-path-segment-kw.rs:175:21
+   |
+LL |         type D2 = ::self;
+   |                     ^^^^ not found in the list of imported crates
+
 error[E0573]: expected type, found module `foobar::self`
   --> $DIR/use-path-segment-kw.rs:185:19
    |
@@ -978,13 +984,7 @@ error[E0433]: `super` in paths can only be used in start position
 LL |         type C4 = crate::super;
    |                          ^^^^^ can only be used in path start position
 
-error[E0433]: global paths cannot start with `self`
-  --> $DIR/use-path-segment-kw.rs:175:21
-   |
-LL |         type D2 = ::self;
-   |                     ^^^^ cannot start with this
-
 error: aborting due to 114 previous errors
 
-Some errors have detailed explanations: E0433, E0573.
-For more information about an error, try `rustc --explain E0433`.
+Some errors have detailed explanations: E0425, E0433, E0573.
+For more information about an error, try `rustc --explain E0425`.

tests/ui/use/use-path-segment-kw.rs

@@ -174,7 +174,7 @@ pub mod foo {
 
         type D2 = ::self;
         //[e2015]~^ ERROR expected type, found module `::self`
-        //[e2018]~^^ ERROR global paths cannot start with `self`
+        //[e2018]~^^ ERROR cannot find crate `self` in the list of imported crates
         use ::self; //[e2018]~ ERROR extern prelude cannot be imported
         //[e2015]~^ ERROR imports need to be explicitly named
         use ::self as _self2; //[e2018]~ ERROR extern prelude cannot be imported

tests/ui/use/use-self-at-end.e2018.stderr

@@ -266,6 +266,12 @@ error[E0573]: expected type, found module `crate::x::self`
 LL |         type E = crate::x::self;
    |                  ^^^^^^^^^^^^^^ not a type
 
+error[E0425]: cannot find crate `self` in the list of imported crates
+  --> $DIR/use-self-at-end.rs:45:20
+   |
+LL |         type F = ::self;
+   |                    ^^^^ not found in the list of imported crates
+
 error[E0223]: ambiguous associated type
   --> $DIR/use-self-at-end.rs:62:18
    |
@@ -292,13 +298,7 @@ help: if this is a dyn-compatible trait, use `dyn`
 LL |         type J = dyn super::Trait::self;
    |                  +++
 
-error[E0433]: global paths cannot start with `self`
-  --> $DIR/use-self-at-end.rs:45:20
-   |
-LL |         type F = ::self;
-   |                    ^^^^ cannot start with this
-
 error: aborting due to 36 previous errors; 1 warning emitted
 
-Some errors have detailed explanations: E0223, E0252, E0432, E0433, E0573.
+Some errors have detailed explanations: E0223, E0252, E0425, E0432, E0433, E0573.
 For more information about an error, try `rustc --explain E0223`.

tests/ui/use/use-self-at-end.rs

@@ -44,7 +44,7 @@ pub mod x {
 
         type F = ::self;
         //[e2015]~^ ERROR expected type, found module `::self`
-        //[e2018]~^^ ERROR global paths cannot start with `self`
+        //[e2018]~^^ ERROR cannot find crate `self` in the list of imported crates
         pub use ::self;
         //[e2015]~^ ERROR imports need to be explicitly named
         //[e2018]~^^ ERROR extern prelude cannot be imported