Rollup merge of rust-lang#103414 - compiler-errors:rpit-print-lt, r=cjgillot

Pretty print lifetimes captured by RPIT

This specifically makes the output in rust-lang#103409 change from:

```diff
  error: `impl` item signature doesn't match `trait` item signature
    --> $DIR/signature-mismatch.rs:15:5
     |
  LL |     fn async_fn(&self, buff: &[u8]) -> impl Future<Output = Vec<u8>>;
     |     ----------------------------------------------------------------- expected `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>>`
  ...
  LL |     fn async_fn<'a>(&self, buff: &'a [u8]) -> impl Future<Output = Vec<u8>> + 'a {
-  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>>`
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '2`
     |
     = note: expected `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>>`
-               found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>>`
+               found `fn(&'1 Struct, &'2 [u8]) -> impl Future<Output = Vec<u8>> + '2`
     = help: the lifetime requirements from the `impl` do not correspond to the requirements in the `trait`
     = help: verify the lifetime relationships in the `trait` and `impl` between the `self` argument, the other inputs and its output

  error: aborting due to previous error
```

Along with the UI tests in this PR, which I think are all improvements!

r? `@oli-obk` though feel free to re-roll

Author: notriddle

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -16,6 +16,7 @@ use rustc_session::cstore::{ExternCrate, ExternCrateSource};
 use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_target::abi::Size;
 use rustc_target::spec::abi::Abi;
+use smallvec::SmallVec;
 
 use std::cell::Cell;
 use std::char;
@@ -794,6 +795,7 @@ pub trait PrettyPrinter<'tcx>:
         let mut traits = FxIndexMap::default();
         let mut fn_traits = FxIndexMap::default();
         let mut is_sized = false;
+        let mut lifetimes = SmallVec::<[ty::Region<'tcx>; 1]>::new();
 
         for (predicate, _) in bounds.subst_iter_copied(tcx, substs) {
             let bound_predicate = predicate.kind();
@@ -824,6 +826,9 @@ pub trait PrettyPrinter<'tcx>:
                         &mut fn_traits,
                     );
                 }
+                ty::PredicateKind::TypeOutlives(outlives) => {
+                    lifetimes.push(outlives.1);
+                }
                 _ => {}
             }
         }
@@ -977,6 +982,11 @@ pub trait PrettyPrinter<'tcx>:
             write!(self, "Sized")?;
         }
 
+        for re in lifetimes {
+            write!(self, " + ")?;
+            self = self.print_region(re)?;
+        }
+
         Ok(self)
     }
 

src/test/ui/associated-type-bounds/inside-adt.rs

@@ -16,7 +16,7 @@ enum E2 { V(Box<dyn Iterator<Item: Copy>>) }
 //~^ ERROR associated type bounds are not allowed within structs, enums, or unions
 enum E3 { V(dyn Iterator<Item: 'static>) }
 //~^ ERROR associated type bounds are not allowed within structs, enums, or unions
-//~| ERROR the size for values of type `(dyn Iterator<Item = impl Sized> + 'static)`
+//~| ERROR the size for values of type `(dyn Iterator<Item = impl Sized + 'static> + 'static)`
 
 union U1 { f: ManuallyDrop<dyn Iterator<Item: Copy>> }
 //~^ ERROR associated type bounds are not allowed within structs, enums, or unions
@@ -25,6 +25,6 @@ union U2 { f: ManuallyDrop<Box<dyn Iterator<Item: Copy>>> }
 //~^ ERROR associated type bounds are not allowed within structs, enums, or unions
 union U3 { f: ManuallyDrop<dyn Iterator<Item: 'static>> }
 //~^ ERROR associated type bounds are not allowed within structs, enums, or unions
-//~| ERROR the size for values of type `(dyn Iterator<Item = impl Sized> + 'static)`
+//~| ERROR the size for values of type `(dyn Iterator<Item = impl Sized + 'static> + 'static)`
 
 fn main() {}

src/test/ui/associated-type-bounds/inside-adt.stderr

@@ -70,13 +70,13 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL | enum E1 { V(Box<dyn Iterator<Item: Copy>>) }
    |             ++++                        +
 
-error[E0277]: the size for values of type `(dyn Iterator<Item = impl Sized> + 'static)` cannot be known at compilation time
+error[E0277]: the size for values of type `(dyn Iterator<Item = impl Sized + 'static> + 'static)` cannot be known at compilation time
   --> $DIR/inside-adt.rs:17:13
    |
 LL | enum E3 { V(dyn Iterator<Item: 'static>) }
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = help: the trait `Sized` is not implemented for `(dyn Iterator<Item = impl Sized> + 'static)`
+   = help: the trait `Sized` is not implemented for `(dyn Iterator<Item = impl Sized + 'static> + 'static)`
    = note: no field of an enum variant may have a dynamically sized type
    = help: change the field's type to have a statically known size
 help: borrowed types always have a statically known size
@@ -107,14 +107,14 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL | union U1 { f: Box<ManuallyDrop<dyn Iterator<Item: Copy>>> }
    |               ++++                                      +
 
-error[E0277]: the size for values of type `(dyn Iterator<Item = impl Sized> + 'static)` cannot be known at compilation time
+error[E0277]: the size for values of type `(dyn Iterator<Item = impl Sized + 'static> + 'static)` cannot be known at compilation time
   --> $DIR/inside-adt.rs:26:15
    |
 LL | union U3 { f: ManuallyDrop<dyn Iterator<Item: 'static>> }
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
    |
-   = help: within `ManuallyDrop<(dyn Iterator<Item = impl Sized> + 'static)>`, the trait `Sized` is not implemented for `(dyn Iterator<Item = impl Sized> + 'static)`
-   = note: required because it appears within the type `ManuallyDrop<(dyn Iterator<Item = impl Sized> + 'static)>`
+   = help: within `ManuallyDrop<(dyn Iterator<Item = impl Sized + 'static> + 'static)>`, the trait `Sized` is not implemented for `(dyn Iterator<Item = impl Sized + 'static> + 'static)`
+   = note: required because it appears within the type `ManuallyDrop<(dyn Iterator<Item = impl Sized + 'static> + 'static)>`
    = note: no field of a union may have a dynamically sized type
    = help: change the field's type to have a statically known size
 help: borrowed types always have a statically known size

src/test/ui/associated-types/issue-87261.rs

@@ -77,10 +77,10 @@ where
 
 fn main() {
     accepts_trait(returns_opaque());
-    //~^ ERROR type mismatch resolving `<impl Trait as Trait>::Associated == ()`
+    //~^ ERROR type mismatch resolving `<impl Trait + 'static as Trait>::Associated == ()`
 
     accepts_trait(returns_opaque_derived());
-    //~^ ERROR type mismatch resolving `<impl DerivedTrait as Trait>::Associated == ()`
+    //~^ ERROR type mismatch resolving `<impl DerivedTrait + 'static as Trait>::Associated == ()`
 
     accepts_trait(returns_opaque_foo());
     //~^ ERROR type mismatch resolving `<impl Trait + Foo as Trait>::Associated == ()`
@@ -89,7 +89,7 @@ fn main() {
     //~^ ERROR type mismatch resolving `<impl DerivedTrait + Foo as Trait>::Associated == ()`
 
     accepts_generic_trait(returns_opaque_generic());
-    //~^ ERROR type mismatch resolving `<impl GenericTrait<()> as GenericTrait<()>>::Associated == ()`
+    //~^ ERROR type mismatch resolving `<impl GenericTrait<()> + 'static as GenericTrait<()>>::Associated == ()`
 
     accepts_generic_trait(returns_opaque_generic_foo());
     //~^ ERROR type mismatch resolving `<impl GenericTrait<()> + Foo as GenericTrait<()>>::Associated == ()`

src/test/ui/associated-types/issue-87261.stderr

@@ -132,7 +132,7 @@ note: required by a bound in `accepts_generic_trait`
 LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
    |                                              ^^^^^^^^^^^^^^^ required by this bound in `accepts_generic_trait`
 
-error[E0271]: type mismatch resolving `<impl Trait as Trait>::Associated == ()`
+error[E0271]: type mismatch resolving `<impl Trait + 'static as Trait>::Associated == ()`
   --> $DIR/issue-87261.rs:79:19
    |
 LL | fn returns_opaque() -> impl Trait + 'static {
@@ -144,18 +144,18 @@ LL |     accepts_trait(returns_opaque());
    |     required by a bound introduced by this call
    |
    = note:    expected unit type `()`
-           found associated type `<impl Trait as Trait>::Associated`
+           found associated type `<impl Trait + 'static as Trait>::Associated`
 note: required by a bound in `accepts_trait`
   --> $DIR/issue-87261.rs:43:27
    |
 LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
    |                           ^^^^^^^^^^^^^^^ required by this bound in `accepts_trait`
-help: consider constraining the associated type `<impl Trait as Trait>::Associated` to `()`
+help: consider constraining the associated type `<impl Trait + 'static as Trait>::Associated` to `()`
    |
 LL | fn returns_opaque() -> impl Trait<Associated = ()> + 'static {
    |                                  +++++++++++++++++
 
-error[E0271]: type mismatch resolving `<impl DerivedTrait as Trait>::Associated == ()`
+error[E0271]: type mismatch resolving `<impl DerivedTrait + 'static as Trait>::Associated == ()`
   --> $DIR/issue-87261.rs:82:19
    |
 LL | fn returns_opaque_derived() -> impl DerivedTrait + 'static {
@@ -167,13 +167,13 @@ LL |     accepts_trait(returns_opaque_derived());
    |     required by a bound introduced by this call
    |
    = note:    expected unit type `()`
-           found associated type `<impl DerivedTrait as Trait>::Associated`
+           found associated type `<impl DerivedTrait + 'static as Trait>::Associated`
 note: required by a bound in `accepts_trait`
   --> $DIR/issue-87261.rs:43:27
    |
 LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
    |                           ^^^^^^^^^^^^^^^ required by this bound in `accepts_trait`
-help: consider constraining the associated type `<impl DerivedTrait as Trait>::Associated` to `()`
+help: consider constraining the associated type `<impl DerivedTrait + 'static as Trait>::Associated` to `()`
    |
 LL | fn returns_opaque_derived() -> impl DerivedTrait<Associated = ()> + 'static {
    |                                                 +++++++++++++++++
@@ -222,7 +222,7 @@ note: required by a bound in `accepts_trait`
 LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
    |                           ^^^^^^^^^^^^^^^ required by this bound in `accepts_trait`
 
-error[E0271]: type mismatch resolving `<impl GenericTrait<()> as GenericTrait<()>>::Associated == ()`
+error[E0271]: type mismatch resolving `<impl GenericTrait<()> + 'static as GenericTrait<()>>::Associated == ()`
   --> $DIR/issue-87261.rs:91:27
    |
 LL | fn returns_opaque_generic() -> impl GenericTrait<()> + 'static {
@@ -234,13 +234,13 @@ LL |     accepts_generic_trait(returns_opaque_generic());
    |     required by a bound introduced by this call
    |
    = note:    expected unit type `()`
-           found associated type `<impl GenericTrait<()> as GenericTrait<()>>::Associated`
+           found associated type `<impl GenericTrait<()> + 'static as GenericTrait<()>>::Associated`
 note: required by a bound in `accepts_generic_trait`
   --> $DIR/issue-87261.rs:44:46
    |
 LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
    |                                              ^^^^^^^^^^^^^^^ required by this bound in `accepts_generic_trait`
-help: consider constraining the associated type `<impl GenericTrait<()> as GenericTrait<()>>::Associated` to `()`
+help: consider constraining the associated type `<impl GenericTrait<()> + 'static as GenericTrait<()>>::Associated` to `()`
    |
 LL | fn returns_opaque_generic() -> impl GenericTrait<(), Associated = ()> + 'static {
    |                                                    +++++++++++++++++

src/test/ui/impl-trait/hidden-lifetimes.stderr

@@ -1,4 +1,4 @@
-error[E0700]: hidden type for `impl Swap` captures lifetime that does not appear in bounds
+error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
   --> $DIR/hidden-lifetimes.rs:29:5
    |
 LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a {
@@ -11,7 +11,7 @@ help: to declare that the `impl Trait` captures `'b`, you can add an explicit `'
 LL | fn hide_ref<'a, 'b, T: 'static>(x: &'a mut &'b T) -> impl Swap + 'a + 'b {
    |                                                                     ++++
 
-error[E0700]: hidden type for `impl Swap` captures lifetime that does not appear in bounds
+error[E0700]: hidden type for `impl Swap + 'a` captures lifetime that does not appear in bounds
   --> $DIR/hidden-lifetimes.rs:46:5
    |
 LL | fn hide_rc_refcell<'a, 'b: 'a, T: 'static>(x: Rc<RefCell<&'b T>>) -> impl Swap + 'a {