Auto merge of rust-lang#122317 - compiler-errors:fulfill-method-probe…

…, r=<try>

Use fulfillment in method probe, not evaluation

This PR reworks method probing to use fulfillment instead of a `for`-loop of `evaluate_predicate` calls, and moves normalization from method candidate assembly into the `consider_probe`, where it's applied to *all* candidates. This last part coincidentally fixes rust-lang#121643 (comment).

Regarding *why* this large rewrite is done: In general, it's an anti-pattern to do `for o in obligations { evaluate(o); }` because it's not compatible with the way that the new solver emits alias-relate obligations which constrain variables that may show up in other predicates.

Putting this up for vibe-check mostly. Tests aren't yet blessed, and there are some nuances about whether it's worthwhile to restore regressed diagnostics.

r? lcnr

compiler/rustc_hir_typeck/src/demand.rs

@@ -894,7 +894,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             [candidate] => format!(
                 "the method of the same name on {} `{}`",
                 match candidate.kind {
-                    probe::CandidateKind::InherentImplCandidate(..) => "the inherent impl for",
+                    probe::CandidateKind::InherentImplCandidate(_) => "the inherent impl for",
                     _ => "trait",
                 },
                 self.tcx.def_path_str(candidate.item.container_id(self.tcx))

tests/ui/derives/issue-91550.stderr

@@ -2,15 +2,13 @@ error[E0599]: the method `insert` exists for struct `HashSet<Value>`, but its tr
   --> $DIR/issue-91550.rs:8:8
    |
 LL | struct Value(u32);
-   | ------------ doesn't satisfy `Value: Eq`, `Value: Hash` or `Value: PartialEq`
+   | ------------ doesn't satisfy `Value: Eq` or `Value: Hash`
 ...
 LL |     hs.insert(Value(0));
    |        ^^^^^^
    |
    = note: the following trait bounds were not satisfied:
            `Value: Eq`
-           `Value: PartialEq`
-           which is required by `Value: Eq`
            `Value: Hash`
 help: consider annotating `Value` with `#[derive(Eq, Hash, PartialEq)]`
    |
@@ -22,7 +20,7 @@ error[E0599]: the method `use_eq` exists for struct `Object<NoDerives>`, but its
   --> $DIR/issue-91550.rs:26:9
    |
 LL | pub struct NoDerives;
-   | -------------------- doesn't satisfy `NoDerives: Eq` or `NoDerives: PartialEq`
+   | -------------------- doesn't satisfy `NoDerives: Eq`
 LL |
 LL | struct Object<T>(T);
    | ---------------- method `use_eq` not found for this struct
@@ -37,9 +35,6 @@ LL | impl<T: Eq> Object<T> {
    |         ^^  ---------
    |         |
    |         unsatisfied trait bound introduced here
-   = note: the following trait bounds were not satisfied:
-           `NoDerives: PartialEq`
-           which is required by `NoDerives: Eq`
 help: consider annotating `NoDerives` with `#[derive(Eq, PartialEq)]`
    |
 LL + #[derive(Eq, PartialEq)]
@@ -50,7 +45,7 @@ error[E0599]: the method `use_ord` exists for struct `Object<NoDerives>`, but it
   --> $DIR/issue-91550.rs:27:9
    |
 LL | pub struct NoDerives;
-   | -------------------- doesn't satisfy `NoDerives: Eq`, `NoDerives: Ord`, `NoDerives: PartialEq` or `NoDerives: PartialOrd`
+   | -------------------- doesn't satisfy `NoDerives: Ord`
 LL |
 LL | struct Object<T>(T);
    | ---------------- method `use_ord` not found for this struct
@@ -65,13 +60,6 @@ LL | impl<T: Ord> Object<T> {
    |         ^^^  ---------
    |         |
    |         unsatisfied trait bound introduced here
-   = note: the following trait bounds were not satisfied:
-           `NoDerives: PartialOrd`
-           which is required by `NoDerives: Ord`
-           `NoDerives: PartialEq`
-           which is required by `NoDerives: Ord`
-           `NoDerives: Eq`
-           which is required by `NoDerives: Ord`
 help: consider annotating `NoDerives` with `#[derive(Eq, Ord, PartialEq, PartialOrd)]`
    |
 LL + #[derive(Eq, Ord, PartialEq, PartialOrd)]
@@ -82,7 +70,7 @@ error[E0599]: the method `use_ord_and_partial_ord` exists for struct `Object<NoD
   --> $DIR/issue-91550.rs:28:9
    |
 LL | pub struct NoDerives;
-   | -------------------- doesn't satisfy `NoDerives: Eq`, `NoDerives: Ord`, `NoDerives: PartialEq` or `NoDerives: PartialOrd`
+   | -------------------- doesn't satisfy `NoDerives: Ord` or `NoDerives: PartialOrd`
 LL |
 LL | struct Object<T>(T);
    | ---------------- method `use_ord_and_partial_ord` not found for this struct
@@ -100,13 +88,6 @@ LL | impl<T: Ord + PartialOrd> Object<T> {
    |         |     |
    |         |     unsatisfied trait bound introduced here
    |         unsatisfied trait bound introduced here
-   = note: the following trait bounds were not satisfied:
-           `NoDerives: PartialEq`
-           which is required by `NoDerives: Ord`
-           `NoDerives: Eq`
-           which is required by `NoDerives: Ord`
-           `NoDerives: PartialEq`
-           which is required by `NoDerives: PartialOrd`
 help: consider annotating `NoDerives` with `#[derive(Eq, Ord, PartialEq, PartialOrd)]`
    |
 LL + #[derive(Eq, Ord, PartialEq, PartialOrd)]

tests/ui/generic-associated-types/issue-119942-unsatisified-gat-bound-during-assoc-ty-selection.rs

@@ -29,5 +29,5 @@ where
 
 fn main() {
     let mut list = RcNode::<i32>::new();
-    //~^ ERROR the size for values of type `Node<i32, RcFamily>` cannot be known at compilation time
+    //~^ ERROR the variant or associated item `new` exists for enum `Node<i32, RcFamily>`, but its trait bounds were not satisfied
 }

tests/ui/generic-associated-types/issue-119942-unsatisified-gat-bound-during-assoc-ty-selection.stderr

@@ -15,20 +15,15 @@ help: consider relaxing the implicit `Sized` restriction
 LL |     type Pointer<T>: Deref<Target = T> + ?Sized;
    |                                        ++++++++
 
-error[E0599]: the size for values of type `Node<i32, RcFamily>` cannot be known at compilation time
+error[E0599]: the variant or associated item `new` exists for enum `Node<i32, RcFamily>`, but its trait bounds were not satisfied
   --> $DIR/issue-119942-unsatisified-gat-bound-during-assoc-ty-selection.rs:31:35
    |
 LL | enum Node<T, P: PointerFamily> {
-   | ------------------------------ variant or associated item `new` not found for this enum because it doesn't satisfy `Node<i32, RcFamily>: Sized`
+   | ------------------------------ variant or associated item `new` not found for this enum
 ...
 LL |     let mut list = RcNode::<i32>::new();
-   |                                   ^^^ doesn't have a size known at compile-time
+   |                                   ^^^ variant or associated item cannot be called on `Node<i32, RcFamily>` due to unsatisfied trait bounds
    |
-note: trait bound `Node<i32, RcFamily>: Sized` was not satisfied
-  --> $DIR/issue-119942-unsatisified-gat-bound-during-assoc-ty-selection.rs:4:18
-   |
-LL |     type Pointer<T>: Deref<Target = T>;
-   |          ------- ^ unsatisfied trait bound introduced here
 note: trait bound `(dyn Deref<Target = Node<i32, RcFamily>> + 'static): Sized` was not satisfied
   --> $DIR/issue-119942-unsatisified-gat-bound-during-assoc-ty-selection.rs:23:29
    |
@@ -37,8 +32,6 @@ LL | impl<T, P: PointerFamily> Node<T, P>
 LL | where
 LL |     P::Pointer<Node<T, P>>: Sized,
    |                             ^^^^^ unsatisfied trait bound introduced here
-note: the trait `Sized` must be implemented
-  --> $SRC_DIR/core/src/marker.rs:LL:COL
 
 error: aborting due to 2 previous errors
 

tests/ui/higher-ranked/trait-bounds/issue-30786.stderr

@@ -2,15 +2,14 @@ error[E0599]: the method `filterx` exists for struct `Map<Repeat, {closure@issue
   --> $DIR/issue-30786.rs:120:22
    |
 LL | pub struct Map<S, F> {
-   | -------------------- method `filterx` not found for this struct because it doesn't satisfy `_: StreamExt`
+   | -------------------- method `filterx` not found for this struct
 ...
 LL |     let filter = map.filterx(|x: &_| true);
    |                      ^^^^^^^ method cannot be called on `Map<Repeat, {closure@issue-30786.rs:119:27}>` due to unsatisfied trait bounds
    |
 note: the following trait bounds were not satisfied:
       `&'a mut &Map<Repeat, {closure@$DIR/issue-30786.rs:119:27: 119:34}>: Stream`
       `&'a mut &mut Map<Repeat, {closure@$DIR/issue-30786.rs:119:27: 119:34}>: Stream`
-      `&'a mut Map<Repeat, {closure@$DIR/issue-30786.rs:119:27: 119:34}>: Stream`
   --> $DIR/issue-30786.rs:98:50
    |
 LL | impl<T> StreamExt for T where for<'a> &'a mut T: Stream {}
@@ -26,15 +25,14 @@ error[E0599]: the method `countx` exists for struct `Filter<Map<Repeat, fn(&u64)
   --> $DIR/issue-30786.rs:132:24
    |
 LL | pub struct Filter<S, F> {
-   | ----------------------- method `countx` not found for this struct because it doesn't satisfy `_: StreamExt`
+   | ----------------------- method `countx` not found for this struct
 ...
 LL |     let count = filter.countx();
    |                        ^^^^^^ method cannot be called due to unsatisfied trait bounds
    |
 note: the following trait bounds were not satisfied:
       `&'a mut &Filter<Map<Repeat, for<'a> fn(&'a u64) -> &'a u64 {identity::<u64>}>, {closure@$DIR/issue-30786.rs:131:30: 131:37}>: Stream`
       `&'a mut &mut Filter<Map<Repeat, for<'a> fn(&'a u64) -> &'a u64 {identity::<u64>}>, {closure@$DIR/issue-30786.rs:131:30: 131:37}>: Stream`
-      `&'a mut Filter<Map<Repeat, for<'a> fn(&'a u64) -> &'a u64 {identity::<u64>}>, {closure@$DIR/issue-30786.rs:131:30: 131:37}>: Stream`
   --> $DIR/issue-30786.rs:98:50
    |
 LL | impl<T> StreamExt for T where for<'a> &'a mut T: Stream {}

tests/ui/impl-trait/issues/issue-62742.rs

@@ -3,7 +3,7 @@ use std::marker::PhantomData;
 fn _alias_check() {
     WrongImpl::foo(0i32);
     //~^ ERROR the trait bound `RawImpl<_>: Raw<_>` is not satisfied
-    //~| ERROR the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+    //~| ERROR the function or associated item `foo` exists for struct `SafeImpl<_, RawImpl<_>>`, but its trait bounds were not satisfied
     WrongImpl::<()>::foo(0i32);
     //~^ ERROR the trait bound `RawImpl<()>: Raw<()>` is not satisfied
     //~| ERROR trait bounds were not satisfied

tests/ui/impl-trait/issues/issue-62742.stderr

@@ -1,30 +1,27 @@
-error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
-  --> $DIR/issue-62742.rs:4:5
+error[E0599]: the function or associated item `foo` exists for struct `SafeImpl<_, RawImpl<_>>`, but its trait bounds were not satisfied
+  --> $DIR/issue-62742.rs:4:16
    |
 LL |     WrongImpl::foo(0i32);
-   |     ^^^^^^^^^^^^^^^^^^^^ the trait `Raw<_>` is not implemented for `RawImpl<_>`
+   |                ^^^ function or associated item cannot be called on `SafeImpl<_, RawImpl<_>>` due to unsatisfied trait bounds
+...
+LL | pub struct RawImpl<T>(PhantomData<T>);
+   | --------------------- doesn't satisfy `RawImpl<_>: Raw<_>`
+...
+LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
+   | ----------------------------------------- function or associated item `foo` not found for this struct
    |
-   = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
-note: required by a bound in `SafeImpl::<T, A>::foo`
+note: trait bound `RawImpl<_>: Raw<_>` was not satisfied
   --> $DIR/issue-62742.rs:29:20
    |
 LL | impl<T: ?Sized, A: Raw<T>> SafeImpl<T, A> {
-   |                    ^^^^^^ required by this bound in `SafeImpl::<T, A>::foo`
-LL |     pub fn foo(value: A::Value) {}
-   |            --- required by a bound in this associated function
-
-error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
-  --> $DIR/issue-62742.rs:4:5
-   |
-LL |     WrongImpl::foo(0i32);
-   |     ^^^^^^^^^ the trait `Raw<_>` is not implemented for `RawImpl<_>`
-   |
-   = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
-note: required by a bound in `SafeImpl`
-  --> $DIR/issue-62742.rs:27:35
+   |                    ^^^^^^  --------------
+   |                    |
+   |                    unsatisfied trait bound introduced here
+note: the trait `Raw` must be implemented
+  --> $DIR/issue-62742.rs:13:1
    |
-LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
-   |                                   ^^^^^^ required by this bound in `SafeImpl`
+LL | pub trait Raw<T: ?Sized> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0599]: the function or associated item `foo` exists for struct `SafeImpl<(), RawImpl<()>>`, but its trait bounds were not satisfied
   --> $DIR/issue-62742.rs:7:22
@@ -51,6 +48,19 @@ note: the trait `Raw` must be implemented
 LL | pub trait Raw<T: ?Sized> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
+error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+  --> $DIR/issue-62742.rs:4:5
+   |
+LL |     WrongImpl::foo(0i32);
+   |     ^^^^^^^^^ the trait `Raw<_>` is not implemented for `RawImpl<_>`
+   |
+   = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
+note: required by a bound in `SafeImpl`
+  --> $DIR/issue-62742.rs:27:35
+   |
+LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
+   |                                   ^^^^^^ required by this bound in `SafeImpl`
+
 error[E0277]: the trait bound `RawImpl<()>: Raw<()>` is not satisfied
   --> $DIR/issue-62742.rs:7:5
    |

tests/ui/impl-trait/issues/issue-84073.rs

@@ -29,5 +29,6 @@ where
 }
 
 fn main() {
-    Race::new(|race| race.when()); //~ ERROR overflow assigning `_` to `Option<_>`
+    Race::new(|race| race.when());
+    //~^ ERROR the method `when` exists for struct `RaceBuilder<_, Never<_>>`, but its trait bounds were not satisfied
 }

tests/ui/impl-trait/issues/issue-84073.stderr

@@ -1,9 +1,29 @@
-error[E0275]: overflow assigning `_` to `Option<_>`
-  --> $DIR/issue-84073.rs:32:22
+error[E0599]: the method `when` exists for struct `RaceBuilder<_, Never<_>>`, but its trait bounds were not satisfied
+  --> $DIR/issue-84073.rs:32:27
    |
+LL | pub struct Never<T>(PhantomData<T>);
+   | ------------------- doesn't satisfy `Never<_>: StatefulFuture<Option<_>>`
+...
+LL | pub struct RaceBuilder<F, S> {
+   | ---------------------------- method `when` not found for this struct
+...
 LL |     Race::new(|race| race.when());
-   |                      ^^^^
+   |                           ^^^^ method cannot be called on `RaceBuilder<_, Never<_>>` due to unsatisfied trait bounds
+   |
+note: trait bound `Never<_>: StatefulFuture<Option<_>>` was not satisfied
+  --> $DIR/issue-84073.rs:14:8
+   |
+LL | impl<T, F> RaceBuilder<T, F>
+   |            -----------------
+LL | where
+LL |     F: StatefulFuture<Option<T>>,
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^ unsatisfied trait bound introduced here
+note: the trait `StatefulFuture` must be implemented
+  --> $DIR/issue-84073.rs:3:1
+   |
+LL | pub trait StatefulFuture<S> {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0275`.
+For more information about this error, try `rustc --explain E0599`.

tests/ui/issues/issue-57362-2.rs

@@ -18,8 +18,10 @@ impl<'a> X for fn(&'a ()) {
     }
 }
 
+// FIXME(@compiler-errors): This error message is less than helpful.
 fn g() {
-    let x = <fn (&())>::make_g(); //~ ERROR the function
+    let x = <fn (&())>::make_g();
+    //~^ ERROR no function or associated item named `make_g` found for fn pointer `for<'a> fn(&'a ())` in the current scope
 }
 
 fn main() {}

tests/ui/issues/issue-57362-2.stderr

@@ -1,11 +1,9 @@
-error[E0599]: the function or associated item `make_g` exists for fn pointer `fn(&())`, but its trait bounds were not satisfied
-  --> $DIR/issue-57362-2.rs:22:25
+error[E0599]: no function or associated item named `make_g` found for fn pointer `for<'a> fn(&'a ())` in the current scope
+  --> $DIR/issue-57362-2.rs:23:25
    |
 LL |     let x = <fn (&())>::make_g();
-   |                         ^^^^^^ function or associated item cannot be called on `fn(&())` due to unsatisfied trait bounds
+   |                         ^^^^^^ function or associated item not found in `fn(&())`
    |
-   = note: the following trait bounds were not satisfied:
-           `for<'a> fn(&'a ()): X`
    = help: items from traits can only be used if the trait is implemented and in scope
 note: `X` defines an item `make_g`, perhaps you need to implement it
   --> $DIR/issue-57362-2.rs:8:1

tests/ui/mismatched_types/issue-36053-2.stderr

@@ -21,14 +21,16 @@ error[E0599]: the method `count` exists for struct `Filter<Fuse<Once<&str>>, {cl
 LL |     once::<&str>("str").fuse().filter(|a: &str| true).count();
    |                                       ---------       ^^^^^ method cannot be called due to unsatisfied trait bounds
    |                                       |
-   |                                       doesn't satisfy `<_ as FnOnce<(&&str,)>>::Output = bool` or `_: FnMut<(&&str,)>`
+   |                                       doesn't satisfy `_: FnMut<(&&str,)>` or `_: FnOnce<(&&str,)>`
    |
    = note: the following trait bounds were not satisfied:
-           `<{closure@$DIR/issue-36053-2.rs:7:39: 7:48} as FnOnce<(&&str,)>>::Output = bool`
-           which is required by `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
            `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnMut<(&&str,)>`
            which is required by `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
-           `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
+           `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnOnce<(&&str,)>`
+           which is required by `Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
+           `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnMut<(&&str,)>`
+           which is required by `&mut Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
+           `{closure@$DIR/issue-36053-2.rs:7:39: 7:48}: FnOnce<(&&str,)>`
            which is required by `&mut Filter<Fuse<std::iter::Once<&str>>, {closure@$DIR/issue-36053-2.rs:7:39: 7:48}>: Iterator`
 
 error: aborting due to 2 previous errors

tests/ui/missing-trait-bounds/issue-35677.stderr

@@ -6,8 +6,6 @@ LL |     this.is_subset(other)
    |
    = note: the following trait bounds were not satisfied:
            `T: Eq`
-           `T: PartialEq`
-           which is required by `T: Eq`
            `T: Hash`
 help: consider restricting the type parameters to satisfy the trait bounds
    |

tests/ui/nll/issue-57642-higher-ranked-subtype.rs

@@ -28,7 +28,8 @@ impl<T> Y for fn(T) {
 }
 
 fn higher_ranked_region_has_lost_its_binder() {
-    let x = <fn (&())>::make_g(); //~ ERROR the function
+    let x = <fn (&())>::make_g();
+    //~^ ERROR no function or associated item named `make_g` found for fn pointer `for<'a> fn(&'a ())` in the current scope
 }
 
 fn magical() {

tests/ui/nll/issue-57642-higher-ranked-subtype.stderr

@@ -1,11 +1,9 @@
-error[E0599]: the function or associated item `make_g` exists for fn pointer `fn(&())`, but its trait bounds were not satisfied
+error[E0599]: no function or associated item named `make_g` found for fn pointer `for<'a> fn(&'a ())` in the current scope
   --> $DIR/issue-57642-higher-ranked-subtype.rs:31:25
    |
 LL |     let x = <fn (&())>::make_g();
-   |                         ^^^^^^ function or associated item cannot be called on `fn(&())` due to unsatisfied trait bounds
+   |                         ^^^^^^ function or associated item not found in `fn(&())`
    |
-   = note: the following trait bounds were not satisfied:
-           `for<'a> fn(&'a ()): X`
    = help: items from traits can only be used if the trait is implemented and in scope
 note: `X` defines an item `make_g`, perhaps you need to implement it
   --> $DIR/issue-57642-higher-ranked-subtype.rs:4:1
@@ -14,7 +12,7 @@ LL | trait X {
    | ^^^^^^^
 
 error[E0599]: no function or associated item named `make_f` found for fn pointer `for<'a> fn(&'a ())` in the current scope
-  --> $DIR/issue-57642-higher-ranked-subtype.rs:35:25
+  --> $DIR/issue-57642-higher-ranked-subtype.rs:36:25
    |
 LL |     let x = <fn (&())>::make_f();
    |                         ^^^^^^ function or associated item not found in `fn(&())`