Maintain chain of derived obligations

When evaluating the derived obligations from super traits, maintain a
reference to the original obligation in order to give more actionable
context in the output.

Author: estebank

src/librustc_trait_selection/traits/wf.rs

@@ -8,6 +8,7 @@ use rustc_middle::ty::subst::{GenericArgKind, SubstsRef};
 use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
 use rustc_span::symbol::{kw, Ident};
 use rustc_span::Span;
+use std::rc::Rc;
 
 /// Returns the set of obligations needed to make `ty` well-formed.
 /// If `ty` contains unresolved inference variables, this may include
@@ -315,6 +316,15 @@ impl<'a, 'tcx> WfPredicates<'a, 'tcx> {
             let implied_obligations = traits::util::elaborate_obligations(tcx, obligations.clone());
             let implied_obligations = implied_obligations.map(|obligation| {
                 let mut cause = cause.clone();
+                let parent_trait_ref = obligation
+                    .predicate
+                    .to_opt_poly_trait_ref()
+                    .unwrap_or_else(|| ty::Binder::dummy(*trait_ref));
+                let derived_cause = traits::DerivedObligationCause {
+                    parent_trait_ref,
+                    parent_code: Rc::new(obligation.cause.code.clone()),
+                };
+                cause.code = traits::ObligationCauseCode::ImplDerivedObligation(derived_cause);
                 extend_cause_with_original_assoc_item_obligation(
                     tcx,
                     trait_ref,

src/test/ui/associated-type-bounds/bad-bounds-on-assoc-in-trait.stderr

@@ -1,10 +1,17 @@
 error[E0277]: `<L1 as Lam<&'a u8>>::App` doesn't implement `std::fmt::Debug`
   --> $DIR/bad-bounds-on-assoc-in-trait.rs:31:6
    |
+LL | trait Case1 {
+   |       -----
+...
+LL |                 Debug
+   |                 ----- required by this bound in `Case1`
+...
 LL | impl Case1 for S1 {
    |      ^^^^^ `<L1 as Lam<&'a u8>>::App` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
    |
    = help: the trait `for<'a> std::fmt::Debug` is not implemented for `<L1 as Lam<&'a u8>>::App`
+   = note: required because of the requirements on the impl of `for<'a> std::fmt::Debug` for `<<<<S1 as Case1>::C as std::iter::Iterator>::Item as std::iter::Iterator>::Item as Lam<&'a u8>>::App`
 
 error[E0277]: `<<T as Case1>::C as std::iter::Iterator>::Item` is not an iterator
   --> $DIR/bad-bounds-on-assoc-in-trait.rs:36:20

src/test/ui/associated-types/defaults-unsound-62211-1.stderr

@@ -42,11 +42,18 @@ LL |     + Display = Self;
 error[E0277]: `T` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     + Display = Self;
+   |       ------- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ `T` cannot be formatted with the default formatter
    |
    = help: the trait `std::fmt::Display` is not implemented for `T`
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+   = note: required because of the requirements on the impl of `std::fmt::Display` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::fmt::Display> UncheckedCopy for T {}
@@ -55,9 +62,16 @@ LL | impl<T: std::fmt::Display> UncheckedCopy for T {}
 error[E0277]: the trait bound `T: std::ops::Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     + Deref<Target = str>
+   |       ------------------- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ the trait `std::ops::Deref` is not implemented for `T`
    |
+   = note: required because of the requirements on the impl of `std::ops::Deref` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::ops::Deref> UncheckedCopy for T {}
@@ -66,10 +80,17 @@ LL | impl<T: std::ops::Deref> UncheckedCopy for T {}
 error[E0277]: cannot add-assign `&'static str` to `T`
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     + AddAssign<&'static str>
+   |       ----------------------- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ no implementation for `T += &'static str`
    |
    = help: the trait `std::ops::AddAssign<&'static str>` is not implemented for `T`
+   = note: required because of the requirements on the impl of `std::ops::AddAssign<&'static str>` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::ops::AddAssign<&'static str>> UncheckedCopy for T {}
@@ -78,9 +99,16 @@ LL | impl<T: std::ops::AddAssign<&'static str>> UncheckedCopy for T {}
 error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-1.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     type Output: Copy
+   |                  ---- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `T`
    |
+   = note: required because of the requirements on the impl of `std::marker::Copy` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::marker::Copy> UncheckedCopy for T {}

src/test/ui/associated-types/defaults-unsound-62211-2.stderr

@@ -42,11 +42,18 @@ LL |     + Display = Self;
 error[E0277]: `T` doesn't implement `std::fmt::Display`
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     + Display = Self;
+   |       ------- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ `T` cannot be formatted with the default formatter
    |
    = help: the trait `std::fmt::Display` is not implemented for `T`
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+   = note: required because of the requirements on the impl of `std::fmt::Display` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::fmt::Display> UncheckedCopy for T {}
@@ -55,9 +62,16 @@ LL | impl<T: std::fmt::Display> UncheckedCopy for T {}
 error[E0277]: the trait bound `T: std::ops::Deref` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     + Deref<Target = str>
+   |       ------------------- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ the trait `std::ops::Deref` is not implemented for `T`
    |
+   = note: required because of the requirements on the impl of `std::ops::Deref` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::ops::Deref> UncheckedCopy for T {}
@@ -66,10 +80,17 @@ LL | impl<T: std::ops::Deref> UncheckedCopy for T {}
 error[E0277]: cannot add-assign `&'static str` to `T`
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     + AddAssign<&'static str>
+   |       ----------------------- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ no implementation for `T += &'static str`
    |
    = help: the trait `std::ops::AddAssign<&'static str>` is not implemented for `T`
+   = note: required because of the requirements on the impl of `std::ops::AddAssign<&'static str>` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::ops::AddAssign<&'static str>> UncheckedCopy for T {}
@@ -78,9 +99,16 @@ LL | impl<T: std::ops::AddAssign<&'static str>> UncheckedCopy for T {}
 error[E0277]: the trait bound `T: std::marker::Copy` is not satisfied
   --> $DIR/defaults-unsound-62211-2.rs:41:9
    |
+LL | trait UncheckedCopy: Sized {
+   |       -------------
+...
+LL |     type Output: Copy
+   |                  ---- required by this bound in `UncheckedCopy`
+...
 LL | impl<T> UncheckedCopy for T {}
    |         ^^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `T`
    |
+   = note: required because of the requirements on the impl of `std::marker::Copy` for `<T as UncheckedCopy>::Output`
 help: consider restricting type parameter `T`
    |
 LL | impl<T: std::marker::Copy> UncheckedCopy for T {}

src/test/ui/associated-types/issue-43924.stderr

@@ -9,14 +9,28 @@ LL |     type Out: Default + ToString + ?Sized = dyn ToString;
 error[E0277]: the trait bound `(dyn std::string::ToString + 'static): std::default::Default` is not satisfied
   --> $DIR/issue-43924.rs:10:6
    |
+LL | trait Foo<T: Default + ToString> {
+   |       ---
+LL |     type Out: Default + ToString + ?Sized = dyn ToString;
+   |               ------- required by this bound in `Foo`
+...
 LL | impl Foo<u32> for () {}
    |      ^^^^^^^^ the trait `std::default::Default` is not implemented for `(dyn std::string::ToString + 'static)`
+   |
+   = note: required because of the requirements on the impl of `std::default::Default` for `<() as Foo<u32>>::Out`
 
 error[E0277]: the trait bound `(dyn std::string::ToString + 'static): std::default::Default` is not satisfied
   --> $DIR/issue-43924.rs:11:6
    |
+LL | trait Foo<T: Default + ToString> {
+   |       ---
+LL |     type Out: Default + ToString + ?Sized = dyn ToString;
+   |               ------- required by this bound in `Foo`
+...
 LL | impl Foo<u64> for () {}
    |      ^^^^^^^^ the trait `std::default::Default` is not implemented for `(dyn std::string::ToString + 'static)`
+   |
+   = note: required because of the requirements on the impl of `std::default::Default` for `<() as Foo<u64>>::Out`
 
 error: aborting due to 3 previous errors
 

src/test/ui/associated-types/issue-65774-1.stderr

@@ -9,8 +9,15 @@ LL |     type MpuConfig: MyDisplay = T;
 error[E0277]: the trait bound `T: MyDisplay` is not satisfied
   --> $DIR/issue-65774-1.rs:16:6
    |
+LL | trait MPU {
+   |       ---
+LL |     type MpuConfig: MyDisplay = T;
+   |                     --------- required by this bound in `MPU`
+...
 LL | impl MPU for S { }
    |      ^^^ the trait `MyDisplay` is not implemented for `T`
+   |
+   = note: required because of the requirements on the impl of `MyDisplay` for `<S as MPU>::MpuConfig`
 
 error: aborting due to 2 previous errors
 

src/test/ui/associated-types/issue-65774-2.stderr

@@ -9,8 +9,15 @@ LL |     type MpuConfig: MyDisplay = T;
 error[E0277]: the trait bound `T: MyDisplay` is not satisfied
   --> $DIR/issue-65774-2.rs:16:6
    |
+LL | trait MPU {
+   |       ---
+LL |     type MpuConfig: MyDisplay = T;
+   |                     --------- required by this bound in `MPU`
+...
 LL | impl MPU for S { }
    |      ^^^ the trait `MyDisplay` is not implemented for `T`
+   |
+   = note: required because of the requirements on the impl of `MyDisplay` for `<S as MPU>::MpuConfig`
 
 error: aborting due to 2 previous errors
 

src/test/ui/builtin-superkinds/builtin-superkinds-double-superkind.stderr

@@ -1,11 +1,15 @@
 error[E0277]: `T` cannot be sent between threads safely
   --> $DIR/builtin-superkinds-double-superkind.rs:6:24
    |
+LL | trait Foo : Send+Sync { }
+   |             ---- required by this bound in `Foo`
+LL | 
 LL | impl <T: Sync+'static> Foo for (T,) { }
    |                        ^^^ `T` cannot be sent between threads safely
    |
    = help: within `(T,)`, the trait `std::marker::Send` is not implemented for `T`
    = note: required because it appears within the type `(T,)`
+   = note: required because of the requirements on the impl of `std::marker::Send` for `(T,)`
 help: consider further restricting this bound
    |
 LL | impl <T: Sync+'static + std::marker::Send> Foo for (T,) { }
@@ -14,11 +18,15 @@ LL | impl <T: Sync+'static + std::marker::Send> Foo for (T,) { }
 error[E0277]: `T` cannot be shared between threads safely
   --> $DIR/builtin-superkinds-double-superkind.rs:9:16
    |
+LL | trait Foo : Send+Sync { }
+   |                  ---- required by this bound in `Foo`
+...
 LL | impl <T: Send> Foo for (T,T) { }
    |                ^^^ `T` cannot be shared between threads safely
    |
    = help: within `(T, T)`, the trait `std::marker::Sync` is not implemented for `T`
    = note: required because it appears within the type `(T, T)`
+   = note: required because of the requirements on the impl of `std::marker::Sync` for `(T, T)`
 help: consider further restricting this bound
    |
 LL | impl <T: Send + std::marker::Sync> Foo for (T,T) { }

src/test/ui/builtin-superkinds/builtin-superkinds-in-metadata.stderr

@@ -3,9 +3,15 @@ error[E0277]: `T` cannot be sent between threads safely
    |
 LL | impl <T:Sync+'static> RequiresRequiresShareAndSend for X<T> { }
    |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `T` cannot be sent between threads safely
+   | 
+  ::: $DIR/auxiliary/trait_superkinds_in_metadata.rs:7:58
+   |
+LL | pub trait RequiresRequiresShareAndSend : RequiresShare + Send { }
+   |                                                          ---- required by this bound in `trait_superkinds_in_metadata::RequiresRequiresShareAndSend`
    |
    = help: within `X<T>`, the trait `std::marker::Send` is not implemented for `T`
    = note: required because it appears within the type `X<T>`
+   = note: required because of the requirements on the impl of `std::marker::Send` for `X<T>`
 help: consider further restricting this bound
    |
 LL | impl <T:Sync+'static + std::marker::Send> RequiresRequiresShareAndSend for X<T> { }

src/test/ui/builtin-superkinds/builtin-superkinds-simple.stderr

@@ -1,10 +1,14 @@
 error[E0277]: `std::rc::Rc<i8>` cannot be sent between threads safely
   --> $DIR/builtin-superkinds-simple.rs:6:6
    |
+LL | trait Foo : Send { }
+   |             ---- required by this bound in `Foo`
+LL | 
 LL | impl Foo for std::rc::Rc<i8> { }
    |      ^^^ `std::rc::Rc<i8>` cannot be sent between threads safely
    |
    = help: the trait `std::marker::Send` is not implemented for `std::rc::Rc<i8>`
+   = note: required because of the requirements on the impl of `std::marker::Send` for `std::rc::Rc<i8>`
 
 error: aborting due to previous error
 

src/test/ui/builtin-superkinds/builtin-superkinds-typaram-not-send.stderr

@@ -1,10 +1,14 @@
 error[E0277]: `T` cannot be sent between threads safely
   --> $DIR/builtin-superkinds-typaram-not-send.rs:5:24
    |
+LL | trait Foo : Send { }
+   |             ---- required by this bound in `Foo`
+LL | 
 LL | impl <T: Sync+'static> Foo for T { }
    |                        ^^^ `T` cannot be sent between threads safely
    |
    = help: the trait `std::marker::Send` is not implemented for `T`
+   = note: required because of the requirements on the impl of `std::marker::Send` for `T`
 help: consider further restricting this bound
    |
 LL | impl <T: Sync+'static + std::marker::Send> Foo for T { }

src/test/ui/dst/dst-sized-trait-param.stderr

@@ -1,20 +1,28 @@
 error[E0277]: the size for values of type `[isize]` cannot be known at compilation time
   --> $DIR/dst-sized-trait-param.rs:7:6
    |
+LL | trait Foo<T> : Sized { fn take(self, x: &T) { } } // Note: T is sized
+   |           - required by this bound in `Foo`
+LL | 
 LL | impl Foo<[isize]> for usize { }
    |      ^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `[isize]`
    = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: required because of the requirements on the impl of `std::marker::Sized` for `[isize]`
 
 error[E0277]: the size for values of type `[usize]` cannot be known at compilation time
   --> $DIR/dst-sized-trait-param.rs:10:6
    |
+LL | trait Foo<T> : Sized { fn take(self, x: &T) { } } // Note: T is sized
+   |                ----- required by this bound in `Foo`
+...
 LL | impl Foo<isize> for [usize] { }
    |      ^^^^^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `[usize]`
    = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: required because of the requirements on the impl of `std::marker::Sized` for `[usize]`
 
 error: aborting due to 2 previous errors
 

src/test/ui/generic-associated-types/construct_with_other_type.stderr

@@ -1,12 +1,19 @@
 error[E0271]: type mismatch resolving `for<'a> <<T as Baz>::Baa<'a> as std::ops::Deref>::Target == <<T as Baz>::Quux<'a> as Foo>::Bar<'a, 'static>`
   --> $DIR/construct_with_other_type.rs:19:9
    |
+LL | trait Baz {
+   |       ---
+...
+LL |     type Baa<'a>: Deref<Target = <Self::Quux<'a> as Foo>::Bar<'a, 'static>>  where Self: 'a;
+   |                         -------------------------------------------------- required by this bound in `Baz`
+...
 LL | impl<T> Baz for T where T: Foo {
    |         ^^^ expected type parameter `T`, found associated type
    |
    = note: expected associated type `<T as Foo>::Bar<'_, 'static>`
               found associated type `<<T as Baz>::Quux<'_> as Foo>::Bar<'_, 'static>`
    = note: you might be missing a type parameter or trait bound
+   = note: required because of the requirements on the impl of `Baz` for `T`
 
 error: aborting due to previous error
 

src/test/ui/generics/issue-61631-default-type-param-can-reference-self-in-trait.stderr

@@ -1,11 +1,15 @@
 error[E0277]: the size for values of type `[()]` cannot be known at compilation time
   --> $DIR/issue-61631-default-type-param-can-reference-self-in-trait.rs:19:6
    |
+LL | trait Tsized<P: Sized = [Self]> {}
+   |              - required by this bound in `Tsized`
+LL | 
 LL | impl Tsized for () {}
    |      ^^^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `std::marker::Sized` is not implemented for `[()]`
    = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
+   = note: required because of the requirements on the impl of `std::marker::Sized` for `[()]`
 
 error: aborting due to previous error