Register a dummy candidate for failed structural normalization during…

… candiate assembly

compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs

@@ -6,6 +6,7 @@ use derive_where::derive_where;
 use rustc_type_ir::fold::TypeFoldable;
 use rustc_type_ir::inherent::*;
 use rustc_type_ir::lang_items::TraitSolverLangItem;
+use rustc_type_ir::solve::inspect;
 use rustc_type_ir::visit::TypeVisitableExt as _;
 use rustc_type_ir::{self as ty, Interner, Upcast as _, elaborate};
 use tracing::{debug, instrument};
@@ -288,6 +289,25 @@ where
         let Ok(normalized_self_ty) =
             self.structurally_normalize_ty(goal.param_env, goal.predicate.self_ty())
         else {
+            // HACK: Register a fake candidate when normalization fails so that
+            // we can point at the reason for *why*. I'm tempted to say that this
+            // is the wrong way to do this, though.
+            let result =
+                self.probe(|&result| inspect::ProbeKind::RigidAlias { result }).enter(|this| {
+                    let normalized_ty = this.next_ty_infer();
+                    let alias_relate_goal = Goal::new(
+                        this.cx(),
+                        goal.param_env,
+                        ty::PredicateKind::AliasRelate(
+                            goal.predicate.self_ty().into(),
+                            normalized_ty.into(),
+                            ty::AliasRelationDirection::Equate,
+                        ),
+                    );
+                    this.add_goal(GoalSource::AliasWellFormed, alias_relate_goal);
+                    this.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
+                });
+            assert_eq!(result, Err(NoSolution));
             return vec![];
         };
 

tests/ui/impl-trait/method-resolution4.next.stderr

@@ -1,28 +1,9 @@
 error[E0282]: type annotations needed
-  --> $DIR/method-resolution4.rs:14:9
+  --> $DIR/method-resolution4.rs:13:9
    |
 LL |         foo(false).next().unwrap();
    |         ^^^^^^^^^^ cannot infer type
 
-error[E0277]: the size for values of type `impl Iterator<Item = ()>` cannot be known at compilation time
-  --> $DIR/method-resolution4.rs:11:20
-   |
-LL | fn foo(b: bool) -> impl Iterator<Item = ()> {
-   |                    ^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl Iterator<Item = ()>`
-   = note: the return type of a function must have a statically known size
-
-error[E0277]: the size for values of type `impl Iterator<Item = ()>` cannot be known at compilation time
-  --> $DIR/method-resolution4.rs:14:9
-   |
-LL |         foo(false).next().unwrap();
-   |         ^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl Iterator<Item = ()>`
-   = note: the return type of a function must have a statically known size
-
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0277, E0282.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0282`.

tests/ui/impl-trait/method-resolution4.rs

@@ -9,11 +9,9 @@
 //@[current] check-pass
 
 fn foo(b: bool) -> impl Iterator<Item = ()> {
-    //[next]~^ ERROR the size for values of type `impl Iterator<Item = ()>` cannot be known at compilation time
     if b {
         foo(false).next().unwrap();
         //[next]~^ type annotations needed
-        //[next]~| ERROR the size for values of type `impl Iterator<Item = ()>` cannot be known at compilation time
     }
     std::iter::empty()
 }

tests/ui/impl-trait/recursive-coroutine-boxed.next.stderr

@@ -1,9 +1,9 @@
 error[E0282]: type annotations needed
-  --> $DIR/recursive-coroutine-boxed.rs:16:23
+  --> $DIR/recursive-coroutine-boxed.rs:14:23
    |
 LL |         let mut gen = Box::pin(foo());
    |                       ^^^^^^^^ cannot infer type of the type parameter `T` declared on the struct `Box`
-...
+LL |
 LL |         let mut r = gen.as_mut().resume(());
    |                         ------ type must be known at this point
    |
@@ -12,25 +12,6 @@ help: consider specifying the generic argument
 LL |         let mut gen = Box::<T>::pin(foo());
    |                          +++++
 
-error[E0277]: the size for values of type `impl Coroutine<Yield = (), Return = ()>` cannot be known at compilation time
-  --> $DIR/recursive-coroutine-boxed.rs:9:13
-   |
-LL | fn foo() -> impl Coroutine<Yield = (), Return = ()> {
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl Coroutine<Yield = (), Return = ()>`
-   = note: the return type of a function must have a statically known size
-
-error[E0277]: the size for values of type `impl Coroutine<Yield = (), Return = ()>` cannot be known at compilation time
-  --> $DIR/recursive-coroutine-boxed.rs:16:32
-   |
-LL |         let mut gen = Box::pin(foo());
-   |                                ^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl Coroutine<Yield = (), Return = ()>`
-   = note: the return type of a function must have a statically known size
-
-error: aborting due to 3 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0277, E0282.
-For more information about an error, try `rustc --explain E0277`.
+For more information about this error, try `rustc --explain E0282`.

tests/ui/impl-trait/recursive-coroutine-boxed.rs

@@ -7,15 +7,12 @@
 use std::ops::{Coroutine, CoroutineState};
 
 fn foo() -> impl Coroutine<Yield = (), Return = ()> {
-    //[next]~^ ERROR the size for values of type `impl Coroutine<Yield = (), Return = ()>` cannot be known at compilation time
-
     // FIXME(-Znext-solver): this fails with a mismatched types as the
     // hidden type of the opaque ends up as {type error}. We should not
     // emit errors for such goals.
     #[coroutine] || {
         let mut gen = Box::pin(foo());
         //[next]~^ ERROR type annotations needed
-        //[next]~| ERROR the size for values of type `impl Coroutine<Yield = (), Return = ()>` cannot be known at compilation time
         let mut r = gen.as_mut().resume(());
         while let CoroutineState::Yielded(v) = r {
             yield v;

tests/ui/traits/negative-bounds/opaque-type-unsatisfied-bound.rs

@@ -15,15 +15,12 @@ fn main() {
 fn weird0() -> impl Sized + !Sized {}
 //~^ ERROR the size for values of type `()` cannot be known at compilation time [E0277]
 //~| ERROR the size for values of type `()` cannot be known at compilation time [E0277]
-//~| ERROR the size for values of type `impl !Sized + Sized` cannot be known at compilation time [E0277]
 //~| ERROR the size for values of type `()` cannot be known at compilation time [E0277]
 fn weird1() -> impl !Sized + Sized {}
 //~^ ERROR the size for values of type `()` cannot be known at compilation time [E0277]
 //~| ERROR the size for values of type `()` cannot be known at compilation time [E0277]
-//~| ERROR the size for values of type `impl !Sized + Sized` cannot be known at compilation time [E0277]
 //~| ERROR the size for values of type `()` cannot be known at compilation time [E0277]
 fn weird2() -> impl !Sized {}
 //~^ ERROR the size for values of type `()` cannot be known at compilation time [E0277]
 //~| ERROR the size for values of type `()` cannot be known at compilation time [E0277]
-//~| ERROR the size for values of type `impl !Sized` cannot be known at compilation time [E0277]
 //~| ERROR the size for values of type `()` cannot be known at compilation time [E0277]

tests/ui/traits/negative-bounds/opaque-type-unsatisfied-bound.stderr

@@ -14,15 +14,6 @@ LL | fn weird0() -> impl Sized + !Sized {}
    |
    = help: the trait bound `(): !Sized` is not satisfied
 
-error[E0277]: the size for values of type `impl !Sized + Sized` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:15:16
-   |
-LL | fn weird0() -> impl Sized + !Sized {}
-   |                ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl !Sized + Sized`
-   = note: the return type of a function must have a statically known size
-
 error[E0277]: the size for values of type `()` cannot be known at compilation time
   --> $DIR/opaque-type-unsatisfied-bound.rs:15:1
    |
@@ -32,65 +23,47 @@ LL | fn weird0() -> impl Sized + !Sized {}
    = help: the trait bound `(): !Sized` is not satisfied
 
 error[E0277]: the size for values of type `()` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:20:16
+  --> $DIR/opaque-type-unsatisfied-bound.rs:19:16
    |
 LL | fn weird1() -> impl !Sized + Sized {}
    |                ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait bound `(): !Sized` is not satisfied
 
 error[E0277]: the size for values of type `()` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:20:36
+  --> $DIR/opaque-type-unsatisfied-bound.rs:19:36
    |
 LL | fn weird1() -> impl !Sized + Sized {}
    |                                    ^^ doesn't have a size known at compile-time
    |
    = help: the trait bound `(): !Sized` is not satisfied
 
-error[E0277]: the size for values of type `impl !Sized + Sized` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:20:16
-   |
-LL | fn weird1() -> impl !Sized + Sized {}
-   |                ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl !Sized + Sized`
-   = note: the return type of a function must have a statically known size
-
 error[E0277]: the size for values of type `()` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:20:1
+  --> $DIR/opaque-type-unsatisfied-bound.rs:19:1
    |
 LL | fn weird1() -> impl !Sized + Sized {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait bound `(): !Sized` is not satisfied
 
 error[E0277]: the size for values of type `()` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:25:16
+  --> $DIR/opaque-type-unsatisfied-bound.rs:23:16
    |
 LL | fn weird2() -> impl !Sized {}
    |                ^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait bound `(): !Sized` is not satisfied
 
 error[E0277]: the size for values of type `()` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:25:28
+  --> $DIR/opaque-type-unsatisfied-bound.rs:23:28
    |
 LL | fn weird2() -> impl !Sized {}
    |                            ^^ doesn't have a size known at compile-time
    |
    = help: the trait bound `(): !Sized` is not satisfied
 
-error[E0277]: the size for values of type `impl !Sized` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:25:16
-   |
-LL | fn weird2() -> impl !Sized {}
-   |                ^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl !Sized`
-   = note: the return type of a function must have a statically known size
-
 error[E0277]: the size for values of type `()` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-bound.rs:25:1
+  --> $DIR/opaque-type-unsatisfied-bound.rs:23:1
    |
 LL | fn weird2() -> impl !Sized {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
@@ -111,6 +84,6 @@ note: required by a bound in `consume`
 LL | fn consume(_: impl Trait) {}
    |                    ^^^^^ required by this bound in `consume`
 
-error: aborting due to 13 previous errors
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/negative-bounds/opaque-type-unsatisfied-fn-bound.rs

@@ -5,7 +5,6 @@
 fn produce() -> impl !Fn<(u32,)> {}
 //~^ ERROR expected a `Fn(u32)` closure, found `()`
 //~| ERROR expected a `Fn(u32)` closure, found `()`
-//~| ERROR the size for values of type `impl !Fn<(u32,)>` cannot be known at compilation time
 //~| ERROR expected a `Fn(u32)` closure, found `()`
 
 fn main() {}

tests/ui/traits/negative-bounds/opaque-type-unsatisfied-fn-bound.stderr

@@ -14,15 +14,6 @@ LL | fn produce() -> impl !Fn<(u32,)> {}
    |
    = help: the trait bound `(): !Fn(u32)` is not satisfied
 
-error[E0277]: the size for values of type `impl !Fn<(u32,)>` cannot be known at compilation time
-  --> $DIR/opaque-type-unsatisfied-fn-bound.rs:5:17
-   |
-LL | fn produce() -> impl !Fn<(u32,)> {}
-   |                 ^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `impl !Fn<(u32,)>`
-   = note: the return type of a function must have a statically known size
-
 error[E0277]: expected a `Fn(u32)` closure, found `()`
   --> $DIR/opaque-type-unsatisfied-fn-bound.rs:5:1
    |
@@ -31,6 +22,6 @@ LL | fn produce() -> impl !Fn<(u32,)> {}
    |
    = help: the trait bound `(): !Fn(u32)` is not satisfied
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/next-solver/dyn-incompatibility.rs

@@ -13,7 +13,6 @@ pub fn copy_any<T>(t: &T) -> T {
     //~^ ERROR the trait bound `T: Copy` is not satisfied in `dyn Setup<From = T>`
     //~| ERROR mismatched types
     //~| ERROR the trait bound `T: Copy` is not satisfied
-    //~| ERROR the size for values of type `<dyn Setup<From = T> as Setup>::From` cannot be known at compilation time
 
     // FIXME(-Znext-solver): These error messages are horrible and some of them
     // are even simple fallout from previous error.

tests/ui/traits/next-solver/dyn-incompatibility.stderr

@@ -43,20 +43,7 @@ help: consider restricting type parameter `T`
 LL | pub fn copy_any<T: std::marker::Copy>(t: &T) -> T {
    |                  +++++++++++++++++++
 
-error[E0277]: the size for values of type `<dyn Setup<From = T> as Setup>::From` cannot be known at compilation time
-  --> $DIR/dyn-incompatibility.rs:12:5
-   |
-LL |     copy::<dyn Setup<From=T>>(t)
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `<dyn Setup<From = T> as Setup>::From`
-   = note: the return type of a function must have a statically known size
-help: consider further restricting the associated type
-   |
-LL | pub fn copy_any<T>(t: &T) -> T where <dyn Setup<From = T> as Setup>::From: Sized {
-   |                                +++++++++++++++++++++++++++++++++++++++++++++++++
-
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0277, E0308.
 For more information about an error, try `rustc --explain E0277`.