Rollup merge of #86011 - tlyu:correct-sized-bound-spans, r=estebank

move implicit `Sized` predicate to end of list

In `Bounds::predicates()`, move the implicit `Sized` predicate to the
end of the generated list. This means that if there is an explicit
`Sized` bound, it will be checked first, and any resulting
diagnostics will have a more useful span.

Fixes #85998, at least partially. ~~Based on #85979, but only the last 2 commits are new for this pull request.~~ (edit: rebased) A full fix would need to deal with where-clauses, and that seems difficult. Basically, predicates are being collected in multiple stages, and there are two places where implicit `Sized` predicates can be inserted: once for generic parameters, and once for where-clauses. I think this insertion is happening too early, and we should actually do it only at points where we collect all of the relevant trait bounds for a type parameter.

I could use some help interpreting the changes to the stderr output. It looks like reordering the predicates changed some diagnostics that don't obviously have anything to do with `Sized` bounds. Possibly some error reporting code is making assumptions about ordering of predicates? The diagnostics for src/test/ui/derives/derives-span-Hash-*.rs seem to have improved, no longer pointing at the type parameter identifier, but src/test/ui/type-alias-impl-trait/generic_duplicate_param_use9.rs became less verbose for some reason.

I also ran into an instance of #84970 while working on this, but I kind of expected that could happen, because I'm reordering predicates. I can open a separate issue on that if it would be helpful.

``@estebank`` this seems likely to conflict (slightly?) with your work on #85947; how would you like to resolve that?

Author: matthiaskrgr

compiler/rustc_typeck/src/bounds.rs

@@ -64,16 +64,16 @@ impl<'tcx> Bounds<'tcx> {
             })
         });
 
-        sized_predicate
-            .into_iter()
-            .chain(self.region_bounds.iter().map(|&(region_bound, span)| {
+        self.region_bounds
+            .iter()
+            .map(|&(region_bound, span)| {
                 (
                     region_bound
                         .map_bound(|region_bound| ty::OutlivesPredicate(param_ty, region_bound))
                         .to_predicate(tcx),
                     span,
                 )
-            }))
+            })
             .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
                 let predicate = bound_trait_ref.with_constness(constness).to_predicate(tcx);
                 (predicate, span)
@@ -83,6 +83,7 @@ impl<'tcx> Bounds<'tcx> {
                     .iter()
                     .map(|&(projection, span)| (projection.to_predicate(tcx), span)),
             )
+            .chain(sized_predicate.into_iter())
             .collect()
     }
 }

src/test/ui/derives/derives-span-Hash-enum-struct-variant.stderr

@@ -11,7 +11,7 @@ note: required by a bound in `std::hash::Hash::hash`
   --> $SRC_DIR/core/src/hash/mod.rs:LL:COL
    |
 LL |     fn hash<H: Hasher>(&self, state: &mut H);
-   |             ^ required by this bound in `std::hash::Hash::hash`
+   |                ^^^^^^ required by this bound in `std::hash::Hash::hash`
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/derives/derives-span-Hash-enum.stderr

@@ -11,7 +11,7 @@ note: required by a bound in `std::hash::Hash::hash`
   --> $SRC_DIR/core/src/hash/mod.rs:LL:COL
    |
 LL |     fn hash<H: Hasher>(&self, state: &mut H);
-   |             ^ required by this bound in `std::hash::Hash::hash`
+   |                ^^^^^^ required by this bound in `std::hash::Hash::hash`
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/derives/derives-span-Hash-struct.stderr

@@ -11,7 +11,7 @@ note: required by a bound in `std::hash::Hash::hash`
   --> $SRC_DIR/core/src/hash/mod.rs:LL:COL
    |
 LL |     fn hash<H: Hasher>(&self, state: &mut H);
-   |             ^ required by this bound in `std::hash::Hash::hash`
+   |                ^^^^^^ required by this bound in `std::hash::Hash::hash`
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/derives/derives-span-Hash-tuple-struct.stderr

@@ -11,7 +11,7 @@ note: required by a bound in `std::hash::Hash::hash`
   --> $SRC_DIR/core/src/hash/mod.rs:LL:COL
    |
 LL |     fn hash<H: Hasher>(&self, state: &mut H);
-   |             ^ required by this bound in `std::hash::Hash::hash`
+   |                ^^^^^^ required by this bound in `std::hash::Hash::hash`
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error

src/test/ui/generic-associated-types/issue-74816.stderr

@@ -1,34 +1,34 @@
-error[E0277]: the trait bound `Self: Trait1` is not satisfied
+error[E0277]: the size for values of type `Self` cannot be known at compilation time
   --> $DIR/issue-74816.rs:9:5
    |
 LL |     type Associated: Trait1 = Self;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait1` is not implemented for `Self`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
 note: required by a bound in `Trait2::Associated`
-  --> $DIR/issue-74816.rs:9:22
+  --> $DIR/issue-74816.rs:9:5
    |
 LL |     type Associated: Trait1 = Self;
-   |                      ^^^^^^ required by this bound in `Trait2::Associated`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Trait2::Associated`
 help: consider further restricting `Self`
    |
-LL | trait Trait2: Trait1 {
-   |             ++++++++
+LL | trait Trait2: Sized {
+   |             +++++++
 
-error[E0277]: the size for values of type `Self` cannot be known at compilation time
+error[E0277]: the trait bound `Self: Trait1` is not satisfied
   --> $DIR/issue-74816.rs:9:5
    |
 LL |     type Associated: Trait1 = Self;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait1` is not implemented for `Self`
    |
 note: required by a bound in `Trait2::Associated`
-  --> $DIR/issue-74816.rs:9:5
+  --> $DIR/issue-74816.rs:9:22
    |
 LL |     type Associated: Trait1 = Self;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Trait2::Associated`
+   |                      ^^^^^^ required by this bound in `Trait2::Associated`
 help: consider further restricting `Self`
    |
-LL | trait Trait2: Sized {
-   |             +++++++
+LL | trait Trait2: Trait1 {
+   |             ++++++++
 
 error: aborting due to 2 previous errors
 

src/test/ui/generic-associated-types/issue-86483.stderr

@@ -20,13 +20,13 @@ LL |     for<'a> T: 'a,
    |                ^^
 
 error[E0311]: the parameter type `T` may not live long enough
-  --> $DIR/issue-86483.rs:9:5
+  --> $DIR/issue-86483.rs:9:19
    |
 LL | pub trait IceIce<T>
    |                  - help: consider adding an explicit lifetime bound...: `T: 'a`
 ...
 LL |     type Ice<'v>: IntoIterator<Item = &'v T>;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds...
+   |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds...
    |
 note: ...that is required by this bound
   --> $DIR/issue-86483.rs:7:16

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

@@ -6,10 +6,10 @@ LL | impl Tsized for () {}
    |
    = help: the trait `Sized` is not implemented for `[()]`
 note: required by a bound in `Tsized`
-  --> $DIR/issue-61631-default-type-param-can-reference-self-in-trait.rs:17:14
+  --> $DIR/issue-61631-default-type-param-can-reference-self-in-trait.rs:17:17
    |
 LL | trait Tsized<P: Sized = [Self]> {}
-   |              ^ required by this bound in `Tsized`
+   |                 ^^^^^ required by this bound in `Tsized`
 
 error: aborting due to previous error
 

src/test/ui/issues/issue-16966.stderr

@@ -1,11 +1,21 @@
-error[E0282]: type annotations needed
+error[E0283]: type annotations needed
   --> $DIR/issue-16966.rs:2:5
    |
 LL |     panic!(std::default::Default::default());
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `M` declared on the function `begin_panic`
    |
+   = note: cannot satisfy `_: Any`
+note: required by a bound in `begin_panic`
+  --> $SRC_DIR/std/src/panicking.rs:LL:COL
+   |
+LL | pub fn begin_panic<M: Any + Send>(msg: M) -> ! {
+   |                       ^^^ required by this bound in `begin_panic`
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider specifying the type argument in the function call
+   |
+LL |         $crate::rt::begin_panic::<M>($msg)
+   |                                +++++
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0283`.

src/test/ui/issues/issue-21160.stderr

@@ -10,7 +10,7 @@ note: required by a bound in `std::hash::Hash::hash`
   --> $SRC_DIR/core/src/hash/mod.rs:LL:COL
    |
 LL |     fn hash<H: Hasher>(&self, state: &mut H);
-   |             ^ required by this bound in `std::hash::Hash::hash`
+   |                ^^^^^^ required by this bound in `std::hash::Hash::hash`
    = note: this error originates in the derive macro `Hash` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error