Auto merge of #100676 - lcnr:implied-bounds-yay, r=nikomatsakis

implied bounds: explicitly state which types are assumed to be wf

Adds a new query which maps each definition to the types which that definition assumes to be well formed. The intent is to make it easier to reason about implied bounds.

This change should not influence the user-facing behavior of rustc. Notably, `borrowck` still only assumes that the function signature of associated functions is well formed while `wfcheck` assumes that the both the function signature and the impl trait ref is well formed. Not sure if that by itself can trigger UB or whether it's just annoying.

As a next step, we can add `WellFormed` predicates to `predicates_of` of these items and can stop adding the wf bounds at each place which uses them. I also intend to move the computation from `assumed_wf_types` to `implied_bounds` into the `param_env` computation. This requires me to take a deeper look at `compare_predicate_entailment` which is currently somewhat weird wrt implied bounds so I am not touching this here.

r? `@nikomatsakis`

16 files changed, 95 insertions, 44 deletions

diff --git a/src/test/ui/associated-types/associated-types-for-unimpl-trait.stderr b/src/test/ui/associated-types/associated-types-for-unimpl-trait.stderr
index 6552c8be780..389cc7beddd 100644
--- a/src/test/ui/associated-types/associated-types-for-unimpl-trait.stderr
+++ b/src/test/ui/associated-types/associated-types-for-unimpl-trait.stderr
@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `Self: Get` is not satisfied
-  --> $DIR/associated-types-for-unimpl-trait.rs:10:40
+  --> $DIR/associated-types-for-unimpl-trait.rs:10:5
    |
 LL |     fn uhoh<U:Get>(&self, foo: U, bar: <Self as Get>::Value) {}
-   |                                        ^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
    |
 help: consider further restricting `Self`
    |
diff --git a/src/test/ui/associated-types/associated-types-no-suitable-bound.stderr b/src/test/ui/associated-types/associated-types-no-suitable-bound.stderr
index b2ee1b5e6d0..1feaa612ee6 100644
--- a/src/test/ui/associated-types/associated-types-no-suitable-bound.stderr
+++ b/src/test/ui/associated-types/associated-types-no-suitable-bound.stderr
@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `T: Get` is not satisfied
-  --> $DIR/associated-types-no-suitable-bound.rs:11:21
+  --> $DIR/associated-types-no-suitable-bound.rs:11:5
    |
 LL |     fn uhoh<T>(foo: <T as Get>::Value) {}
-   |                     ^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `T`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `T`
    |
 help: consider restricting type parameter `T`
    |
diff --git a/src/test/ui/associated-types/associated-types-no-suitable-supertrait-2.stderr b/src/test/ui/associated-types/associated-types-no-suitable-supertrait-2.stderr
index 2e40dbd065d..cc3ed556115 100644
--- a/src/test/ui/associated-types/associated-types-no-suitable-supertrait-2.stderr
+++ b/src/test/ui/associated-types/associated-types-no-suitable-supertrait-2.stderr
@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `Self: Get` is not satisfied
-  --> $DIR/associated-types-no-suitable-supertrait-2.rs:17:40
+  --> $DIR/associated-types-no-suitable-supertrait-2.rs:17:5
    |
 LL |     fn uhoh<U:Get>(&self, foo: U, bar: <Self as Get>::Value) {}
-   |                                        ^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
    |
 help: consider further restricting `Self`
    |
diff --git a/src/test/ui/associated-types/associated-types-no-suitable-supertrait.stderr b/src/test/ui/associated-types/associated-types-no-suitable-supertrait.stderr
index bd3ee2abd2c..18f2830d8b2 100644
--- a/src/test/ui/associated-types/associated-types-no-suitable-supertrait.stderr
+++ b/src/test/ui/associated-types/associated-types-no-suitable-supertrait.stderr
@@ -1,14 +1,14 @@
 error[E0277]: the trait bound `(T, U): Get` is not satisfied
-  --> $DIR/associated-types-no-suitable-supertrait.rs:22:40
+  --> $DIR/associated-types-no-suitable-supertrait.rs:22:5
    |
 LL |     fn uhoh<U:Get>(&self, foo: U, bar: <(T, U) as Get>::Value) {}
-   |                                        ^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `(T, U)`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `(T, U)`
 
 error[E0277]: the trait bound `Self: Get` is not satisfied
-  --> $DIR/associated-types-no-suitable-supertrait.rs:17:40
+  --> $DIR/associated-types-no-suitable-supertrait.rs:17:5
    |
 LL |     fn uhoh<U:Get>(&self, foo: U, bar: <Self as Get>::Value) {}
-   |                                        ^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
    |
 help: consider further restricting `Self`
    |
diff --git a/src/test/ui/associated-types/associated-types-projection-to-unrelated-trait-in-method-without-default.stderr b/src/test/ui/associated-types/associated-types-projection-to-unrelated-trait-in-method-without-default.stderr
index 2e67c21940f..66d59bccdbb 100644
--- a/src/test/ui/associated-types/associated-types-projection-to-unrelated-trait-in-method-without-default.stderr
+++ b/src/test/ui/associated-types/associated-types-projection-to-unrelated-trait-in-method-without-default.stderr
@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `Self: Get` is not satisfied
-  --> $DIR/associated-types-projection-to-unrelated-trait-in-method-without-default.rs:10:40
+  --> $DIR/associated-types-projection-to-unrelated-trait-in-method-without-default.rs:10:5
    |
 LL |     fn okay<U:Get>(&self, foo: U, bar: <Self as Get>::Value);
-   |                                        ^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Get` is not implemented for `Self`
    |
 help: consider further restricting `Self`
    |
diff --git a/src/test/ui/associated-types/issue-59324.stderr b/src/test/ui/associated-types/issue-59324.stderr
index dd5ec7175b5..62cf1f37a77 100644
--- a/src/test/ui/associated-types/issue-59324.stderr
+++ b/src/test/ui/associated-types/issue-59324.stderr
@@ -45,16 +45,20 @@ LL | pub trait ThriftService<Bug: NotFoo + Foo>:
    |                                     +++++
 
 error[E0277]: the trait bound `(): Foo` is not satisfied
-  --> $DIR/issue-59324.rs:23:29
+  --> $DIR/issue-59324.rs:23:1
    |
 LL | fn with_factory<H>(factory: dyn ThriftService<()>) {}
-   |                             ^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `()`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `()`
 
 error[E0277]: the trait bound `Bug: Foo` is not satisfied
-  --> $DIR/issue-59324.rs:16:8
+  --> $DIR/issue-59324.rs:16:5
    |
-LL |     fn get_service(
-   |        ^^^^^^^^^^^ the trait `Foo` is not implemented for `Bug`
+LL | /     fn get_service(
+LL | |
+LL | |
+LL | |         &self,
+LL | |     ) -> Self::AssocType;
+   | |_________________________^ the trait `Foo` is not implemented for `Bug`
    |
 help: consider further restricting this bound
    |
diff --git a/src/test/ui/issues/issue-18611.stderr b/src/test/ui/issues/issue-18611.stderr
index bd18d46223e..22c3470b61e 100644
--- a/src/test/ui/issues/issue-18611.stderr
+++ b/src/test/ui/issues/issue-18611.stderr
@@ -1,8 +1,10 @@
 error[E0277]: the trait bound `isize: HasState` is not satisfied
-  --> $DIR/issue-18611.rs:1:18
+  --> $DIR/issue-18611.rs:1:1
    |
-LL | fn add_state(op: <isize as HasState>::State) {
-   |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HasState` is not implemented for `isize`
+LL | / fn add_state(op: <isize as HasState>::State) {
+LL | |
+LL | | }
+   | |_^ the trait `HasState` is not implemented for `isize`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-20831-debruijn.stderr b/src/test/ui/issues/issue-20831-debruijn.stderr
index 57f9575bdbd..ef62dece836 100644
--- a/src/test/ui/issues/issue-20831-debruijn.stderr
+++ b/src/test/ui/issues/issue-20831-debruijn.stderr
@@ -1,8 +1,14 @@
 error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
-  --> $DIR/issue-20831-debruijn.rs:28:8
+  --> $DIR/issue-20831-debruijn.rs:28:5
    |
-LL |     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
-   |        ^^^^^^^^^
+LL | /     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
+LL | |         // Not obvious, but there is an implicit lifetime here -------^
+LL | |
+LL | |         //
+...  |
+LL | |         self.sub = t;
+LL | |     }
+   | |_____^
    |
 note: first, the lifetime cannot outlive the anonymous lifetime defined here...
   --> $DIR/issue-20831-debruijn.rs:28:58
@@ -15,10 +21,16 @@ note: ...but the lifetime must also be valid for the lifetime `'a` as defined he
 LL | impl<'a> Publisher<'a> for MyStruct<'a> {
    |      ^^
 note: ...so that the types are compatible
-  --> $DIR/issue-20831-debruijn.rs:28:8
+  --> $DIR/issue-20831-debruijn.rs:28:5
    |
-LL |     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
-   |        ^^^^^^^^^
+LL | /     fn subscribe(&mut self, t : Box<dyn Subscriber<Input=<Self as Publisher>::Output> + 'a>) {
+LL | |         // Not obvious, but there is an implicit lifetime here -------^
+LL | |
+LL | |         //
+...  |
+LL | |         self.sub = t;
+LL | |     }
+   | |_____^
    = note: expected `<MyStruct<'a> as Publisher<'_>>`
               found `<MyStruct<'_> as Publisher<'_>>`
 
diff --git a/src/test/ui/issues/issue-35570.rs b/src/test/ui/issues/issue-35570.rs
index 42cef9a47f2..a2b0222d4f3 100644
--- a/src/test/ui/issues/issue-35570.rs
+++ b/src/test/ui/issues/issue-35570.rs
@@ -6,7 +6,8 @@ trait Trait2<'a> {
 }
 
 fn _ice(param: Box<dyn for <'a> Trait1<<() as Trait2<'a>>::Ty>>) {
-//~^ the trait bound `for<'a> (): Trait2<'a>` is not satisfied
+    //~^ ERROR the trait bound `for<'a> (): Trait2<'a>` is not satisfied
+    //~| ERROR the trait bound `for<'a> (): Trait2<'a>` is not satisfied
     let _e: (usize, usize) = unsafe{mem::transmute(param)};
 }
 
diff --git a/src/test/ui/issues/issue-35570.stderr b/src/test/ui/issues/issue-35570.stderr
index 2697d46bdb2..ebc40f6786f 100644
--- a/src/test/ui/issues/issue-35570.stderr
+++ b/src/test/ui/issues/issue-35570.stderr
@@ -1,9 +1,19 @@
 error[E0277]: the trait bound `for<'a> (): Trait2<'a>` is not satisfied
+  --> $DIR/issue-35570.rs:8:1
+   |
+LL | / fn _ice(param: Box<dyn for <'a> Trait1<<() as Trait2<'a>>::Ty>>) {
+LL | |
+LL | |
+LL | |     let _e: (usize, usize) = unsafe{mem::transmute(param)};
+LL | | }
+   | |_^ the trait `for<'a> Trait2<'a>` is not implemented for `()`
+
+error[E0277]: the trait bound `for<'a> (): Trait2<'a>` is not satisfied
   --> $DIR/issue-35570.rs:8:40
    |
 LL | fn _ice(param: Box<dyn for <'a> Trait1<<() as Trait2<'a>>::Ty>>) {
    |                                        ^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'a> Trait2<'a>` is not implemented for `()`
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/nll/normalization-bounds-error.stderr b/src/test/ui/nll/normalization-bounds-error.stderr
index 6da3d5d9692..6abe53127c3 100644
--- a/src/test/ui/nll/normalization-bounds-error.stderr
+++ b/src/test/ui/nll/normalization-bounds-error.stderr
@@ -1,8 +1,8 @@
 error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'d` due to conflicting requirements
-  --> $DIR/normalization-bounds-error.rs:12:4
+  --> $DIR/normalization-bounds-error.rs:12:1
    |
 LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
-   |    ^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: first, the lifetime cannot outlive the lifetime `'d` as defined here...
   --> $DIR/normalization-bounds-error.rs:12:14
@@ -15,10 +15,10 @@ note: ...but the lifetime must also be valid for the lifetime `'a` as defined he
 LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
    |                  ^^
 note: ...so that the types are compatible
-  --> $DIR/normalization-bounds-error.rs:12:4
+  --> $DIR/normalization-bounds-error.rs:12:1
    |
 LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
-   |    ^^^^^^^^^
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: expected `Visitor<'d>`
               found `Visitor<'_>`
 
diff --git a/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.rs b/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.rs
index c1dab6086ef..1106352037a 100644
--- a/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.rs
+++ b/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.rs
@@ -19,7 +19,8 @@ trait Trait2<'a, 'b> {
 // since for it to be WF, we would need to know that `'y: 'x`, but we
 // do not infer that.
 fn callee<'x, 'y, T>(t: &'x dyn for<'z> Trait1< <T as Trait2<'y, 'z>>::Foo >)
-    //~^ the trait bound `for<'z> T: Trait2<'y, 'z>` is not satisfied
+    //~^ ERROR the trait bound `for<'z> T: Trait2<'y, 'z>` is not satisfied
+    //~| ERROR the trait bound `for<'z> T: Trait2<'y, 'z>` is not satisfied
 {
 }
 
diff --git a/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.stderr b/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.stderr
index 6844e866532..66f592c34dd 100644
--- a/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.stderr
+++ b/src/test/ui/regions/regions-implied-bounds-projection-gap-hr-1.stderr
@@ -1,4 +1,19 @@
 error[E0277]: the trait bound `for<'z> T: Trait2<'y, 'z>` is not satisfied
+  --> $DIR/regions-implied-bounds-projection-gap-hr-1.rs:21:1
+   |
+LL | / fn callee<'x, 'y, T>(t: &'x dyn for<'z> Trait1< <T as Trait2<'y, 'z>>::Foo >)
+LL | |
+LL | |
+LL | | {
+LL | | }
+   | |_^ the trait `for<'z> Trait2<'y, 'z>` is not implemented for `T`
+   |
+help: consider restricting type parameter `T`
+   |
+LL | fn callee<'x, 'y, T: for<'z> Trait2<'y, 'z>>(t: &'x dyn for<'z> Trait1< <T as Trait2<'y, 'z>>::Foo >)
+   |                    ++++++++++++++++++++++++
+
+error[E0277]: the trait bound `for<'z> T: Trait2<'y, 'z>` is not satisfied
   --> $DIR/regions-implied-bounds-projection-gap-hr-1.rs:21:49
    |
 LL | fn callee<'x, 'y, T>(t: &'x dyn for<'z> Trait1< <T as Trait2<'y, 'z>>::Foo >)
@@ -9,6 +24,6 @@ help: consider restricting type parameter `T`
 LL | fn callee<'x, 'y, T: for<'z> Trait2<'y, 'z>>(t: &'x dyn for<'z> Trait1< <T as Trait2<'y, 'z>>::Foo >)
    |                    ++++++++++++++++++++++++
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0277`.
diff --git a/src/test/ui/specialization/min_specialization/issue-79224.stderr b/src/test/ui/specialization/min_specialization/issue-79224.stderr
index 34da1dd12df..fd34a59d2bd 100644
--- a/src/test/ui/specialization/min_specialization/issue-79224.stderr
+++ b/src/test/ui/specialization/min_specialization/issue-79224.stderr
@@ -1,8 +1,12 @@
 error[E0277]: the trait bound `B: Clone` is not satisfied
-  --> $DIR/issue-79224.rs:18:17
+  --> $DIR/issue-79224.rs:18:1
    |
-LL | impl<B: ?Sized> Display for Cow<'_, B> {
-   |                 ^^^^^^^ the trait `Clone` is not implemented for `B`
+LL | / impl<B: ?Sized> Display for Cow<'_, B> {
+LL | |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+LL | |         write!(f, "foo")
+LL | |     }
+LL | | }
+   | |_^ the trait `Clone` is not implemented for `B`
    |
    = note: required for `B` to implement `ToOwned`
 help: consider further restricting this bound
@@ -11,10 +15,12 @@ LL | impl<B: ?Sized + std::clone::Clone> Display for Cow<'_, B> {
    |                +++++++++++++++++++
 
 error[E0277]: the trait bound `B: Clone` is not satisfied
-  --> $DIR/issue-79224.rs:19:12
+  --> $DIR/issue-79224.rs:19:5
    |
-LL |     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-   |            ^^^^^ the trait `Clone` is not implemented for `B`
+LL | /     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+LL | |         write!(f, "foo")
+LL | |     }
+   | |_____^ the trait `Clone` is not implemented for `B`
    |
    = note: required for `B` to implement `ToOwned`
 help: consider further restricting this bound
diff --git a/src/test/ui/traits/issue-91594.stderr b/src/test/ui/traits/issue-91594.stderr
index 9f9acf85113..5fcd090a834 100644
--- a/src/test/ui/traits/issue-91594.stderr
+++ b/src/test/ui/traits/issue-91594.stderr
@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `Foo: HasComponent<()>` is not satisfied
-  --> $DIR/issue-91594.rs:10:6
+  --> $DIR/issue-91594.rs:10:1
    |
 LL | impl HasComponent<<Foo as Component<Foo>>::Interface> for Foo {}
-   |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HasComponent<()>` is not implemented for `Foo`
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `HasComponent<()>` is not implemented for `Foo`
    |
    = help: the trait `HasComponent<<Foo as Component<Foo>>::Interface>` is implemented for `Foo`
 note: required for `Foo` to implement `Component<Foo>`
diff --git a/src/test/ui/wf/wf-foreign-fn-decl-ret.stderr b/src/test/ui/wf/wf-foreign-fn-decl-ret.stderr
index b03023b5fd1..78312a09105 100644
--- a/src/test/ui/wf/wf-foreign-fn-decl-ret.stderr
+++ b/src/test/ui/wf/wf-foreign-fn-decl-ret.stderr
@@ -1,8 +1,8 @@
 error[E0277]: the trait bound `(): Foo` is not satisfied
-  --> $DIR/wf-foreign-fn-decl-ret.rs:11:25
+  --> $DIR/wf-foreign-fn-decl-ret.rs:11:5
    |
 LL |     pub fn lint_me() -> <() as Foo>::Assoc;
-   |                         ^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `()`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `()`
 
 error[E0277]: the trait bound `u32: Unsatisfied` is not satisfied
   --> $DIR/wf-foreign-fn-decl-ret.rs:14:32