Rollup merge of rust-lang#123101 - Bryanskiy:delegation-fixes-2, r=petrochenkov

Delegation: fix ICE on wrong `Self` instantiation

fixes rust-lang#119921
fixes rust-lang#119919

There is no way to instantiate `Self` param for caller in delegation item if

1. callee is a trait method && callee contains `Self` param
2. delegation item isn't an associative item

In general, we can consider `Self` param as independent type param in these cases:

```rust

trait Trait {
    fn foo(_: Option<&Self>) {...}
}

reuse Trait::foo;
// will be desugared to:
fn foo<T: Trait>(x: Option<&T>) { Trait::foo(x) }
```

But this requires early bound parameters support. For now, I suggest banning such cases to avoid ICE's.

r? `@petrochenkov`

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2212,6 +2212,17 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             try_emit("delegation with early bound generics");
         }
 
+        // There is no way to instantiate `Self` param for caller if
+        // 1. callee is a trait method
+        // 2. delegation item isn't an associative item
+        if let DefKind::AssocFn = self.tcx().def_kind(sig_id)
+            && let DefKind::Fn = self.tcx().def_kind(self.item_def_id())
+            && self.tcx().associated_item(sig_id).container
+                == ty::AssocItemContainer::TraitContainer
+        {
+            try_emit("delegation to a trait method from a free function");
+        }
+
         if self.tcx().asyncness(sig_id) == ty::Asyncness::Yes {
             try_emit("delegation to async functions");
         }

tests/ui/delegation/bad-resolve.rs

@@ -1,5 +1,5 @@
 #![feature(fn_delegation)]
-//~^ WARN the feature `fn_delegation` is incomplete
+#![allow(incomplete_features)]
 
 trait Trait {
     const C: u32 = 0;
@@ -34,14 +34,6 @@ impl Trait for S {
 
     reuse foo { &self.0 }
     //~^ ERROR cannot find function `foo` in this scope
-    reuse F::foo { &self.0 }
-    //~^ ERROR cannot find function `foo` in `F`
-    //~| ERROR duplicate definitions with name `foo`
-}
-
-impl S {
-    reuse F::foo { &self.0 }
-    //~^ ERROR cannot find function `foo` in `F`
 }
 
 fn main() {}

tests/ui/delegation/bad-resolve.stderr

@@ -25,18 +25,6 @@ LL |     reuse <F as Trait>::baz;
    |     |                   help: there is an associated function with a similar name: `bar`
    |     not a member of trait `Trait`
 
-error[E0201]: duplicate definitions with name `foo`:
-  --> $DIR/bad-resolve.rs:37:5
-   |
-LL |     fn foo(&self, x: i32) -> i32 { x }
-   |     ---------------------------------- item in trait
-...
-LL |     reuse foo { &self.0 }
-   |     --------------------- previous definition here
-LL |
-LL |     reuse F::foo { &self.0 }
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^ duplicate definition
-
 error[E0423]: expected function, found associated constant `Trait::C`
   --> $DIR/bad-resolve.rs:24:11
    |
@@ -66,27 +54,6 @@ error[E0425]: cannot find function `foo` in this scope
 LL |     reuse foo { &self.0 }
    |           ^^^ not found in this scope
 
-error[E0425]: cannot find function `foo` in `F`
-  --> $DIR/bad-resolve.rs:37:14
-   |
-LL |     reuse F::foo { &self.0 }
-   |              ^^^ not found in `F`
-
-error[E0425]: cannot find function `foo` in `F`
-  --> $DIR/bad-resolve.rs:43:14
-   |
-LL |     reuse F::foo { &self.0 }
-   |              ^^^ not found in `F`
-
-warning: the feature `fn_delegation` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/bad-resolve.rs:1:12
-   |
-LL | #![feature(fn_delegation)]
-   |            ^^^^^^^^^^^^^
-   |
-   = note: see issue #118212 <https://github.com/rust-lang/rust/issues/118212> for more information
-   = note: `#[warn(incomplete_features)]` on by default
-
 error[E0046]: not all trait items implemented, missing: `Type`
   --> $DIR/bad-resolve.rs:22:1
    |
@@ -96,7 +63,7 @@ LL |     type Type;
 LL | impl Trait for S {
    | ^^^^^^^^^^^^^^^^ missing `Type` in implementation
 
-error: aborting due to 11 previous errors; 1 warning emitted
+error: aborting due to 8 previous errors
 
-Some errors have detailed explanations: E0046, E0201, E0324, E0407, E0423, E0425, E0575, E0576.
+Some errors have detailed explanations: E0046, E0324, E0407, E0423, E0425, E0575, E0576.
 For more information about an error, try `rustc --explain E0046`.

tests/ui/delegation/duplicate-definition-inside-trait-impl.rs

@@ -1,5 +1,5 @@
 #![feature(fn_delegation)]
-//~^ WARN the feature `fn_delegation` is incomplete
+#![allow(incomplete_features)]
 
 trait Trait {
     fn foo(&self) -> u32 { 0 }

tests/ui/delegation/duplicate-definition-inside-trait-impl.stderr

@@ -9,15 +9,6 @@ LL |     reuse to_reuse::foo { self }
 LL |     reuse Trait::foo;
    |     ^^^^^^^^^^^^^^^^^ duplicate definition
 
-warning: the feature `fn_delegation` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/duplicate-definition-inside-trait-impl.rs:1:12
-   |
-LL | #![feature(fn_delegation)]
-   |            ^^^^^^^^^^^^^
-   |
-   = note: see issue #118212 <https://github.com/rust-lang/rust/issues/118212> for more information
-   = note: `#[warn(incomplete_features)]` on by default
-
-error: aborting due to 1 previous error; 1 warning emitted
+error: aborting due to 1 previous error
 
 For more information about this error, try `rustc --explain E0201`.

tests/ui/delegation/explicit-paths-in-traits-pass.rs

@@ -1,7 +1,7 @@
 //@ run-pass
 
 #![feature(fn_delegation)]
-//~^ WARN the feature `fn_delegation` is incomplete
+#![allow(incomplete_features)]
 
 trait ToReuse {
     fn foo(&self, x: i32) -> i32 { x }

tests/ui/delegation/explicit-paths-in-traits-pass.stderr

@@ -1,7 +1,7 @@
 //@ run-pass
 
 #![feature(fn_delegation)]
-//~^ WARN the feature `fn_delegation` is incomplete
+#![allow(incomplete_features)]
 
 trait Trait {
     fn bar(&self, x: i32) -> i32 { x }
@@ -10,7 +10,6 @@ trait Trait {
     }
     fn static_method(x: i32) -> i32 { x }
     fn static_method2(x: i32, y: i32) -> i32 { x + y }
-    fn baz<'a>(&self, x: &'a i32) -> &'a i32 { x }
 }
 
 struct F;
@@ -29,11 +28,9 @@ impl Trait for S {
     reuse Trait::description { &self.0 }
     reuse <F as Trait>::static_method;
     reuse <F as Trait>::static_method2 { S::static_method(self) }
-    reuse Trait::baz { &self.0 }
 }
 
 impl S {
-    reuse Trait::baz { &self.0 }
     reuse <F as Trait>::static_method { to_reuse::foo(self) }
 }
 
@@ -49,16 +46,8 @@ fn main() {
     assert_eq!(42, <S as Trait>::static_method(42));
     assert_eq!(21, S::static_method2(10, 10));
 
-    reuse <S as Trait>::static_method;
-    reuse <S as Trait>::static_method2 { static_method(self) }
     #[inline]
     reuse to_reuse::foo;
-    assert_eq!(42, static_method(42));
-    assert_eq!(21, static_method2(10, 10));
     assert_eq!(43, foo(42));
     assert_eq!(15, zero_args());
-
-    let x: i32 = 15;
-    assert_eq!(&x, <S as Trait>::baz(&s, &x));
-    assert_eq!(&x, S::baz(&s, &x));
 }

tests/ui/delegation/explicit-paths-pass.rs

@@ -1,7 +1,7 @@
 //@ run-pass
 
 #![feature(fn_delegation)]
-//~^ WARN the feature `fn_delegation` is incomplete
+#![allow(incomplete_features)]
 
 mod to_reuse {
     use crate::S;