delegation: rename Self generic param to This in recursive delegations

compiler/rustc_ast_lowering/src/delegation.rs

@@ -508,7 +508,7 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
 
             // FIXME(fn_delegation): proper support for parent generics propagation
             // in method call scenario.
-            let segment = self.process_segment(span, &segment, &mut generics.child, false);
+            let segment = self.process_segment(span, &segment, &mut generics.child);
             let segment = self.arena.alloc(segment);
 
             self.arena.alloc(hir::Expr {
@@ -534,14 +534,10 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
 
                     new_path.segments = self.arena.alloc_from_iter(
                         new_path.segments.iter().enumerate().map(|(idx, segment)| {
-                            let mut process_segment = |result, add_lifetimes| {
-                                self.process_segment(span, segment, result, add_lifetimes)
-                            };
-
                             if idx + 2 == len {
-                                process_segment(&mut generics.parent, true)
+                                self.process_segment(span, segment, &mut generics.parent)
                             } else if idx + 1 == len {
-                                process_segment(&mut generics.child, false)
+                                self.process_segment(span, segment, &mut generics.child)
                             } else {
                                 segment.clone()
                             }
@@ -551,7 +547,7 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
                     hir::QPath::Resolved(ty, self.arena.alloc(new_path))
                 }
                 hir::QPath::TypeRelative(ty, segment) => {
-                    let segment = self.process_segment(span, segment, &mut generics.child, false);
+                    let segment = self.process_segment(span, segment, &mut generics.child);
 
                     hir::QPath::TypeRelative(ty, self.arena.alloc(segment))
                 }
@@ -584,13 +580,12 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
         span: Span,
         segment: &hir::PathSegment<'hir>,
         result: &mut GenericsGenerationResult<'hir>,
-        add_lifetimes: bool,
     ) -> hir::PathSegment<'hir> {
         let details = result.generics.args_propagation_details();
 
         let segment = if details.should_propagate {
             let generics = result.generics.into_hir_generics(self, span);
-            let args = generics.into_generic_args(self, add_lifetimes, span);
+            let args = generics.into_generic_args(self, span);
 
             // Needed for better error messages (`trait-impl-wrong-args-count.rs` test).
             let args = if args.is_empty() { None } else { Some(args) };

compiler/rustc_ast_lowering/src/delegation/generics.rs

@@ -6,7 +6,7 @@ use rustc_hir::def_id::DefId;
 use rustc_middle::ty::GenericParamDefKind;
 use rustc_middle::{bug, ty};
 use rustc_span::symbol::kw;
-use rustc_span::{Ident, Span};
+use rustc_span::{Ident, Span, sym};
 
 use crate::{LoweringContext, ResolverAstLoweringExt};
 
@@ -25,22 +25,37 @@ pub(super) enum DelegationGenericsKind {
     TraitImpl(bool /* Has user-specified args */),
 }
 
+#[derive(Debug, Clone, Copy)]
+pub(super) enum GenericsPosition {
+    Parent,
+    Child,
+}
+
 pub(super) struct DelegationGenerics<T> {
     generics: T,
     kind: DelegationGenericsKind,
+    pos: GenericsPosition,
 }
 
 impl<'hir> DelegationGenerics<&'hir [ty::GenericParamDef]> {
-    fn default(generics: &'hir [ty::GenericParamDef]) -> Self {
-        DelegationGenerics { generics, kind: DelegationGenericsKind::Default }
+    fn default(generics: &'hir [ty::GenericParamDef], pos: GenericsPosition) -> Self {
+        DelegationGenerics { generics, pos, kind: DelegationGenericsKind::Default }
     }
 
-    fn user_specified(generics: &'hir [ty::GenericParamDef]) -> Self {
-        DelegationGenerics { generics, kind: DelegationGenericsKind::UserSpecified }
+    fn user_specified(generics: &'hir [ty::GenericParamDef], pos: GenericsPosition) -> Self {
+        DelegationGenerics { generics, pos, kind: DelegationGenericsKind::UserSpecified }
     }
 
-    fn trait_impl(generics: &'hir [ty::GenericParamDef], user_specified: bool) -> Self {
-        DelegationGenerics { generics, kind: DelegationGenericsKind::TraitImpl(user_specified) }
+    fn trait_impl(
+        generics: &'hir [ty::GenericParamDef],
+        user_specified: bool,
+        pos: GenericsPosition,
+    ) -> Self {
+        DelegationGenerics {
+            generics,
+            pos,
+            kind: DelegationGenericsKind::TraitImpl(user_specified),
+        }
     }
 }
 
@@ -103,8 +118,14 @@ impl<'hir> HirOrTyGenerics<'hir> {
         span: Span,
     ) -> &mut HirOrTyGenerics<'hir> {
         if let HirOrTyGenerics::Ty(ty) = self {
-            let params = ctx.uplift_delegation_generic_params(span, ty.generics);
-            *self = HirOrTyGenerics::Hir(DelegationGenerics { generics: params, kind: ty.kind });
+            let rename_self = matches!(ty.pos, GenericsPosition::Child);
+            let params = ctx.uplift_delegation_generic_params(span, ty.generics, rename_self);
+
+            *self = HirOrTyGenerics::Hir(DelegationGenerics {
+                generics: params,
+                kind: ty.kind,
+                pos: ty.pos,
+            });
         }
 
         self
@@ -120,14 +141,14 @@ impl<'hir> HirOrTyGenerics<'hir> {
     pub(super) fn into_generic_args(
         &self,
         ctx: &mut LoweringContext<'_, 'hir, impl ResolverAstLoweringExt<'hir>>,
-        add_lifetimes: bool,
         span: Span,
     ) -> &'hir hir::GenericArgs<'hir> {
         match self {
             HirOrTyGenerics::Ty(_) => {
                 bug!("Attempting to get generic args before uplifting to HIR")
             }
             HirOrTyGenerics::Hir(hir) => {
+                let add_lifetimes = matches!(hir.pos, GenericsPosition::Parent);
                 ctx.create_generics_args_from_params(hir.generics.params, add_lifetimes, span)
             }
         }
@@ -227,10 +248,15 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
         if matches!(delegation_parent_kind, DefKind::Impl { of_trait: true }) {
             // Considering parent generics, during signature inheritance
             // we will take those args that are in trait impl header trait ref.
-            let parent = DelegationGenerics::trait_impl(&[], true);
+            let parent = DelegationGenerics::trait_impl(&[], true, GenericsPosition::Parent);
             let parent = GenericsGenerationResult::new(parent);
 
-            let child = DelegationGenerics::trait_impl(sig_params, child_user_specified);
+            let child = DelegationGenerics::trait_impl(
+                sig_params,
+                child_user_specified,
+                GenericsPosition::Child,
+            );
+
             let child = GenericsGenerationResult::new(child);
 
             return GenericsGenerationResults {
@@ -263,25 +289,32 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
                     DelegationGenerics {
                         kind: DelegationGenericsKind::SelfAndUserSpecified,
                         generics: &sig_parent_params[..1],
+                        pos: GenericsPosition::Parent,
                     }
                 } else {
-                    DelegationGenerics::user_specified(&[])
+                    DelegationGenerics::user_specified(&[], GenericsPosition::Parent)
                 }
             } else {
                 let skip_self = usize::from(!generate_self);
-                DelegationGenerics::default(&sig_parent_params[skip_self..])
+                DelegationGenerics::default(
+                    &sig_parent_params[skip_self..],
+                    GenericsPosition::Parent,
+                )
             }
         } else {
-            DelegationGenerics::default(&[])
+            DelegationGenerics::default(&[], GenericsPosition::Parent)
         };
 
         let child_generics = if child_user_specified {
             let synth_params_index =
                 sig_params.iter().position(|p| p.kind.is_synthetic()).unwrap_or(sig_params.len());
 
-            DelegationGenerics::user_specified(&sig_params[synth_params_index..])
+            DelegationGenerics::user_specified(
+                &sig_params[synth_params_index..],
+                GenericsPosition::Child,
+            )
         } else {
-            DelegationGenerics::default(sig_params)
+            DelegationGenerics::default(sig_params, GenericsPosition::Child)
         };
 
         GenericsGenerationResults {
@@ -296,6 +329,7 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
         &mut self,
         span: Span,
         params: &'hir [ty::GenericParamDef],
+        rename_self: bool,
     ) -> &'hir hir::Generics<'hir> {
         let params = self.arena.alloc_from_iter(params.iter().map(|p| {
             let def_kind = match p.kind {
@@ -304,7 +338,20 @@ impl<'hir, R: ResolverAstLoweringExt<'hir>> LoweringContext<'_, 'hir, R> {
                 GenericParamDefKind::Const { .. } => DefKind::ConstParam,
             };
 
-            let param_ident = Ident::new(p.name, span);
+            // Rename Self generic param to This so it is properly propagated.
+            // If the user will create a function `fn foo<Self>() {}` with generic
+            // param "Self" then it will not be generated in HIR, the same thing
+            // applies to traits, `trait Trait<Self> {}` will be represented as
+            // `trait Trait {}` in HIR and "unexpected keyword `Self` in generic parameters"
+            // error will be emitted.
+            // Note that we do not rename `Self` to `This` after non-recursive reuse
+            // from Trait, in this case the `Self` should not be propagated
+            // (we rely that implicit `Self` generic param of a trait is named "Self")
+            // and it is OK to have Self generic param generated during lowering.
+            let param_name =
+                if rename_self && p.name == kw::SelfUpper { sym::This } else { p.name };
+
+            let param_ident = Ident::new(param_name, span);
             let def_name = Some(param_ident.name);
             let node_id = self.next_node_id();
 

tests/pretty/delegation-self-rename.pp

@@ -0,0 +1,55 @@
+#![attr = Feature([fn_delegation#0])]
+extern crate std;
+#[attr = PreludeImport]
+use ::std::prelude::rust_2015::*;
+//@ pretty-compare-only
+//@ pretty-mode:hir
+//@ pp-exact:delegation-self-rename.pp
+
+
+trait Trait<'a, A, const B: bool> {
+    fn foo<'b, const B2: bool, T, U,
+        impl FnOnce() -> usize>(&self, f: impl FnOnce() -> usize) -> usize
+        where impl FnOnce() -> usize: FnOnce() -> usize { f() + 1 }
+}
+
+struct X;
+impl <'a, A, const B: bool> Trait<'a, A, B> for X { }
+
+#[attr = Inline(Hint)]
+fn foo<'a, Self, A, const B: _, const B2: _, T, U,
+    impl FnOnce() -> usize>(self: _, arg1: _) -> _ where
+    'a:'a { self.foo::<B2, T, U>(arg1) }
+#[attr = Inline(Hint)]
+fn bar<Self, impl FnOnce() -> usize>(self: _, arg1: _)
+    -> _ { Trait::<'static, (), true>::foo::<true, (), ()>(self, arg1) }
+
+#[attr = Inline(Hint)]
+fn foo2<'a, This, A, const B: _, const B2: _, T, U,
+    impl FnOnce() -> usize>(arg0: _, arg1: _) -> _ where
+    'a:'a { foo::<This, A, B, B2, T, U>(arg0, arg1) }
+#[attr = Inline(Hint)]
+fn bar2<This, impl FnOnce() -> usize>(arg0: _, arg1: _)
+    -> _ { bar::<This>(arg0, arg1) }
+
+trait Trait2 {
+    #[attr = Inline(Hint)]
+    fn foo3<'a, This, A, const B: _, const B2: _, T, U,
+        impl FnOnce() -> usize>(arg0: _, arg1: _) -> _ where
+        'a:'a { foo2::<This, A, B, B2, T, U>(arg0, arg1) }
+    #[attr = Inline(Hint)]
+    fn bar3<This, impl FnOnce() -> usize>(arg0: _, arg1: _)
+        -> _ { bar2::<This>(arg0, arg1) }
+}
+
+impl Trait2 for () { }
+
+#[attr = Inline(Hint)]
+fn foo4<'a, This, A, const B: _, const B2: _, T, U,
+    impl FnOnce() -> usize>(arg0: _, arg1: _) -> _ where
+    'a:'a { <() as Trait2>::foo3::<This, A, B, B2, T, U>(arg0, arg1) }
+#[attr = Inline(Hint)]
+fn bar4<This, impl FnOnce() -> usize>(arg0: _, arg1: _)
+    -> _ { <() as Trait2>::bar3::<This>(arg0, arg1) }
+
+fn main() { }

tests/pretty/delegation-self-rename.rs

@@ -0,0 +1,32 @@
+//@ pretty-compare-only
+//@ pretty-mode:hir
+//@ pp-exact:delegation-self-rename.pp
+
+#![feature(fn_delegation)]
+
+trait Trait<'a, A, const B: bool> {
+    fn foo<'b, const B2: bool, T, U>(&self, f: impl FnOnce() -> usize) -> usize {
+        f() + 1
+    }
+}
+
+struct X;
+impl<'a, A, const B: bool> Trait<'a, A, B> for X {}
+
+reuse Trait::foo;
+reuse Trait::<'static, (), true>::foo::<true, (), ()> as bar;
+
+reuse foo as foo2;
+reuse bar as bar2;
+
+trait Trait2 {
+    reuse foo2 as foo3;
+    reuse bar2 as bar3;
+}
+
+impl Trait2 for () {}
+
+reuse <() as Trait2>::foo3 as foo4;
+reuse <() as Trait2>::bar3 as bar4;
+
+fn main() {}

tests/ui/delegation/generics/self-rename.rs

@@ -0,0 +1,45 @@
+//@ run-pass
+
+#![feature(fn_delegation)]
+
+trait Trait<'a, A, const B: bool> {
+    fn foo<'b, const B2: bool, T, U>(&self, f: impl FnOnce() -> usize) -> usize {
+        f() + 1
+    }
+}
+
+struct X;
+impl<'a, A, const B: bool> Trait<'a, A, B> for X {}
+
+reuse Trait::foo;
+reuse Trait::<'static, (), true>::foo::<true, (), ()> as bar;
+
+reuse foo as foo2;
+reuse bar as bar2;
+
+trait Trait2 {
+    reuse foo2 as foo3;
+    reuse bar2 as bar3;
+}
+
+impl Trait2 for () {}
+
+reuse <() as Trait2>::foo3 as foo4;
+reuse <() as Trait2>::bar3 as bar4;
+
+fn main() {
+    assert_eq!(foo::<'static, X, (), true, false, (), ()>(&X, || 123), 124);
+    assert_eq!(foo2::<'static, X, (), true, false, (), ()>(&X, || 123), 124);
+    assert_eq!(<()>::foo3::<'static, X, (), true, false, (), ()>(&X, || 123), 124);
+    assert_eq!(foo4::<'static, X, (), true, false, (), ()>(&X, || 123), 124);
+
+    assert_eq!(bar::<X>(&X, || 123), 124);
+    assert_eq!(bar2::<X>(&X, || 123), 124);
+    assert_eq!(<()>::bar3::<X>(&X, || 123), 124);
+    assert_eq!(bar4::<X>(&X, || 123), 124);
+
+    assert_eq!(bar(&X, || 123), 124);
+    assert_eq!(bar2(&X, || 123), 124);
+    assert_eq!(<()>::bar3(&X, || 123), 124);
+    assert_eq!(bar4::<X>(&X, || 123), 124);
+}