Rollup merge of #96385 - marmeladema:nll-fix-trait-lifetime-bound-suggestions, r=jackh726

Recover most `impl Trait` and `dyn Trait` lifetime bound suggestions under NLL

This is done by replacing the duplicated (and very partial) implementation from borrowck with one inspsired from `NiceRegionError::try_report_static_impl_trait` and by re-using `suggest_new_region_bound`.

Fixes #96277

r? ```@jackh726```

11 files changed, 128 insertions, 6 deletions

diff --git a/src/test/ui/impl-trait/issues/issue-88236-2.nll.stderr b/src/test/ui/impl-trait/issues/issue-88236-2.nll.stderr
index 9cf8ff76c87..66cffa9e36c 100644
--- a/src/test/ui/impl-trait/issues/issue-88236-2.nll.stderr
+++ b/src/test/ui/impl-trait/issues/issue-88236-2.nll.stderr
@@ -24,10 +24,14 @@ LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send
 LL |     x
    |     ^ returning this value requires that `'b` must outlive `'static`
    |
-help: to allow this `impl Trait` to capture borrowed data with lifetime `'b`, add `'b` as a bound
+help: to declare that the `impl Trait` captures data from argument `x`, you can add an explicit `'b` lifetime bound
    |
 LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a> + 'b {
    |                                                                                  ++++
+help: to declare that the `impl Trait` captures data from argument `x`, you can add an explicit `'b` lifetime bound
+   |
+LL | fn make_bad_impl<'b>(x: &'b ()) -> impl for<'a> Hrtb<'a, Assoc = impl Send + 'a + 'b> {
+   |                                                                                 ++++
 
 error: implementation of `Hrtb` is not general enough
   --> $DIR/issue-88236-2.rs:20:5
diff --git a/src/test/ui/impl-trait/must_outlive_least_region_or_bound.nll.stderr b/src/test/ui/impl-trait/must_outlive_least_region_or_bound.nll.stderr
index 0059f729bae..5a190649b63 100644
--- a/src/test/ui/impl-trait/must_outlive_least_region_or_bound.nll.stderr
+++ b/src/test/ui/impl-trait/must_outlive_least_region_or_bound.nll.stderr
@@ -32,7 +32,14 @@ LL | fn elided2(x: &i32) -> impl Copy + 'static { x }
    |               |
    |               let's call the lifetime of this reference `'1`
    |
-   = help: consider replacing `'1` with `'static`
+help: consider changing the `impl Trait`'s explicit `'static` bound to the lifetime of argument `x`
+   |
+LL | fn elided2(x: &i32) -> impl Copy + '_ { x }
+   |                                    ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn elided2(x: &'static i32) -> impl Copy + 'static { x }
+   |               ~~~~~~~~~~~~
 
 error: lifetime may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:11:55
@@ -40,7 +47,14 @@ error: lifetime may not live long enough
 LL | fn explicit2<'a>(x: &'a i32) -> impl Copy + 'static { x }
    |              -- lifetime `'a` defined here            ^ returning this value requires that `'a` must outlive `'static`
    |
-   = help: consider replacing `'a` with `'static`
+help: consider changing the `impl Trait`'s explicit `'static` bound to the lifetime of argument `x`
+   |
+LL | fn explicit2<'a>(x: &'a i32) -> impl Copy + 'a { x }
+   |                                             ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn explicit2<'a>(x: &'static i32) -> impl Copy + 'static { x }
+   |                     ~~~~~~~~~~~~
 
 error[E0621]: explicit lifetime required in the type of `x`
   --> $DIR/must_outlive_least_region_or_bound.rs:13:41
@@ -57,6 +71,15 @@ LL | fn elided5(x: &i32) -> (Box<dyn Debug>, impl Debug) { (Box::new(x), x) }
    |               -                                       ^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
    |               |
    |               let's call the lifetime of this reference `'1`
+   |
+help: to declare that the trait object captures data from argument `x`, you can add an explicit `'_` lifetime bound
+   |
+LL | fn elided5(x: &i32) -> (Box<dyn Debug + '_>, impl Debug) { (Box::new(x), x) }
+   |                                       ++++
+help: to declare that the `impl Trait` captures data from argument `x`, you can add an explicit `'_` lifetime bound
+   |
+LL | fn elided5(x: &i32) -> (Box<dyn Debug>, impl Debug + '_) { (Box::new(x), x) }
+   |                                                    ++++
 
 error: lifetime may not live long enough
   --> $DIR/must_outlive_least_region_or_bound.rs:29:69
@@ -64,7 +87,14 @@ error: lifetime may not live long enough
 LL | fn with_bound<'a>(x: &'a i32) -> impl LifetimeTrait<'a> + 'static { x }
    |               -- lifetime `'a` defined here                         ^ returning this value requires that `'a` must outlive `'static`
    |
-   = help: consider replacing `'a` with `'static`
+help: consider changing the `impl Trait`'s explicit `'static` bound to the lifetime of argument `x`
+   |
+LL | fn with_bound<'a>(x: &'a i32) -> impl LifetimeTrait<'a> + 'a { x }
+   |                                                           ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn with_bound<'a>(x: &'static i32) -> impl LifetimeTrait<'a> + 'static { x }
+   |                      ~~~~~~~~~~~~
 
 error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
   --> $DIR/must_outlive_least_region_or_bound.rs:34:5
diff --git a/src/test/ui/issues/issue-16922.nll.stderr b/src/test/ui/issues/issue-16922.nll.stderr
index 7f4f5b22eb3..9d9f32a97c0 100644
--- a/src/test/ui/issues/issue-16922.nll.stderr
+++ b/src/test/ui/issues/issue-16922.nll.stderr
@@ -5,6 +5,11 @@ LL | fn foo<T: Any>(value: &T) -> Box<dyn Any> {
    |                       - let's call the lifetime of this reference `'1`
 LL |     Box::new(value) as Box<dyn Any>
    |     ^^^^^^^^^^^^^^^ cast requires that `'1` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `value`, you can add an explicit `'_` lifetime bound
+   |
+LL | fn foo<T: Any>(value: &T) -> Box<dyn Any + '_> {
+   |                                          ++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/nll/mir_check_cast_unsize.stderr b/src/test/ui/nll/mir_check_cast_unsize.stderr
index 364d6c17ea7..8d02ef71d1b 100644
--- a/src/test/ui/nll/mir_check_cast_unsize.stderr
+++ b/src/test/ui/nll/mir_check_cast_unsize.stderr
@@ -5,6 +5,11 @@ LL | fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
    |        -- lifetime `'a` defined here
 LL |     x
    |     ^ returning this value requires that `'a` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `x`, you can add an explicit `'a` lifetime bound
+   |
+LL | fn bar<'a>(x: &'a u32) -> &'static dyn Debug + 'a {
+   |                                              ++++
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/object-lifetime/object-lifetime-default-from-box-error.nll.stderr b/src/test/ui/object-lifetime/object-lifetime-default-from-box-error.nll.stderr
index ae02c58d080..43695a7511d 100644
--- a/src/test/ui/object-lifetime/object-lifetime-default-from-box-error.nll.stderr
+++ b/src/test/ui/object-lifetime/object-lifetime-default-from-box-error.nll.stderr
@@ -6,6 +6,11 @@ LL | fn load(ss: &mut SomeStruct) -> Box<dyn SomeTrait> {
 ...
 LL |     ss.r
    |     ^^^^ returning this value requires that `'1` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `ss`, you can add an explicit `'_` lifetime bound
+   |
+LL | fn load(ss: &mut SomeStruct) -> Box<dyn SomeTrait + '_> {
+   |                                                   ++++
 
 error[E0507]: cannot move out of `ss.r` which is behind a mutable reference
   --> $DIR/object-lifetime-default-from-box-error.rs:18:5
diff --git a/src/test/ui/regions/region-object-lifetime-in-coercion.nll.stderr b/src/test/ui/regions/region-object-lifetime-in-coercion.nll.stderr
index 4d72724586e..724b06ce8b1 100644
--- a/src/test/ui/regions/region-object-lifetime-in-coercion.nll.stderr
+++ b/src/test/ui/regions/region-object-lifetime-in-coercion.nll.stderr
@@ -5,6 +5,15 @@ LL | fn a(v: &[u8]) -> Box<dyn Foo + 'static> {
    |         - let's call the lifetime of this reference `'1`
 LL |     let x: Box<dyn Foo + 'static> = Box::new(v);
    |            ^^^^^^^^^^^^^^^^^^^^^^ type annotation requires that `'1` must outlive `'static`
+   |
+help: consider changing the trait object's explicit `'static` bound to the lifetime of argument `v`
+   |
+LL | fn a(v: &[u8]) -> Box<dyn Foo + '_> {
+   |                                 ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn a(v: &'static [u8]) -> Box<dyn Foo + 'static> {
+   |         ~~~~~~~~~~~~~
 
 error: lifetime may not live long enough
   --> $DIR/region-object-lifetime-in-coercion.rs:19:5
@@ -13,6 +22,15 @@ LL | fn b(v: &[u8]) -> Box<dyn Foo + 'static> {
    |         - let's call the lifetime of this reference `'1`
 LL |     Box::new(v)
    |     ^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
+   |
+help: consider changing the trait object's explicit `'static` bound to the lifetime of argument `v`
+   |
+LL | fn b(v: &[u8]) -> Box<dyn Foo + '_> {
+   |                                 ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn b(v: &'static [u8]) -> Box<dyn Foo + 'static> {
+   |         ~~~~~~~~~~~~~
 
 error: lifetime may not live long enough
   --> $DIR/region-object-lifetime-in-coercion.rs:27:5
@@ -22,6 +40,11 @@ LL | fn c(v: &[u8]) -> Box<dyn Foo> {
 ...
 LL |     Box::new(v)
    |     ^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `v`, you can add an explicit `'_` lifetime bound
+   |
+LL | fn c(v: &[u8]) -> Box<dyn Foo + '_> {
+   |                               ++++
 
 error: lifetime may not live long enough
   --> $DIR/region-object-lifetime-in-coercion.rs:33:5
diff --git a/src/test/ui/regions/regions-close-object-into-object-2.nll.stderr b/src/test/ui/regions/regions-close-object-into-object-2.nll.stderr
index 1a79da2776b..473c99b672f 100644
--- a/src/test/ui/regions/regions-close-object-into-object-2.nll.stderr
+++ b/src/test/ui/regions/regions-close-object-into-object-2.nll.stderr
@@ -5,6 +5,15 @@ LL | fn g<'a, T: 'static>(v: Box<dyn A<T> + 'a>) -> Box<dyn X + 'static> {
    |      -- lifetime `'a` defined here
 LL |     Box::new(B(&*v)) as Box<dyn X>
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+   |
+help: consider changing the trait object's explicit `'static` bound to the lifetime of argument `v`
+   |
+LL | fn g<'a, T: 'static>(v: Box<dyn A<T> + 'a>) -> Box<dyn X + 'a> {
+   |                                                            ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn g<'a, T: 'static>(v: Box<(dyn A<T> + 'static)>) -> Box<dyn X + 'static> {
+   |                         ~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0515]: cannot return value referencing local data `*v`
   --> $DIR/regions-close-object-into-object-2.rs:13:5
diff --git a/src/test/ui/regions/regions-close-object-into-object-4.nll.stderr b/src/test/ui/regions/regions-close-object-into-object-4.nll.stderr
index 993b13ddbf8..05ddc09b2d0 100644
--- a/src/test/ui/regions/regions-close-object-into-object-4.nll.stderr
+++ b/src/test/ui/regions/regions-close-object-into-object-4.nll.stderr
@@ -29,6 +29,15 @@ LL | fn i<'a, T, U>(v: Box<dyn A<U>+'a>) -> Box<dyn X + 'static> {
    |      -- lifetime `'a` defined here
 LL |     Box::new(B(&*v)) as Box<dyn X>
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+   |
+help: consider changing the trait object's explicit `'static` bound to the lifetime of argument `v`
+   |
+LL | fn i<'a, T, U>(v: Box<dyn A<U>+'a>) -> Box<dyn X + 'a> {
+   |                                                    ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn i<'a, T, U>(v: Box<(dyn A<U> + 'static)>) -> Box<dyn X + 'static> {
+   |                   ~~~~~~~~~~~~~~~~~~~~~~~~~
 
 error[E0515]: cannot return value referencing local data `*v`
   --> $DIR/regions-close-object-into-object-4.rs:13:5
diff --git a/src/test/ui/regions/regions-proc-bound-capture.nll.stderr b/src/test/ui/regions/regions-proc-bound-capture.nll.stderr
index 6120a53eb09..ce4d2d4d111 100644
--- a/src/test/ui/regions/regions-proc-bound-capture.nll.stderr
+++ b/src/test/ui/regions/regions-proc-bound-capture.nll.stderr
@@ -6,6 +6,15 @@ LL | fn static_proc(x: &isize) -> Box<dyn FnMut() -> (isize) + 'static> {
 LL |     // This is illegal, because the region bound on `proc` is 'static.
 LL |     Box::new(move || { *x })
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
+   |
+help: consider changing the trait object's explicit `'static` bound to the lifetime of argument `x`
+   |
+LL | fn static_proc(x: &isize) -> Box<dyn FnMut() -> (isize) + '_> {
+   |                                                           ~~
+help: alternatively, add an explicit `'static` bound to this reference
+   |
+LL | fn static_proc(x: &'static isize) -> Box<dyn FnMut() -> (isize) + 'static> {
+   |                   ~~~~~~~~~~~~~~
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/lifetimes/trait-object-nested-in-impl-trait.nll.stderr b/src/test/ui/suggestions/lifetimes/trait-object-nested-in-impl-trait.nll.stderr
index 3ed3827b97d..6c65e4f0175 100644
--- a/src/test/ui/suggestions/lifetimes/trait-object-nested-in-impl-trait.nll.stderr
+++ b/src/test/ui/suggestions/lifetimes/trait-object-nested-in-impl-trait.nll.stderr
@@ -9,10 +9,14 @@ LL | |             remaining: self.0.iter(),
 LL | |         }
    | |_________^ returning this value requires that `'1` must outlive `'static`
    |
-help: to allow this `impl Trait` to capture borrowed data with lifetime `'1`, add `'_` as a bound
+help: to declare that the `impl Trait` captures data from argument `self`, you can add an explicit `'_` lifetime bound
    |
 LL |     fn iter(&self) -> impl Iterator<Item = Box<dyn Foo>> + '_ {
    |                                                          ++++
+help: to declare that the trait object captures data from argument `self`, you can add an explicit `'_` lifetime bound
+   |
+LL |     fn iter(&self) -> impl Iterator<Item = Box<dyn Foo + '_>> {
+   |                                                        ++++
 
 error: lifetime may not live long enough
   --> $DIR/trait-object-nested-in-impl-trait.rs:39:9
@@ -24,6 +28,11 @@ LL | |             current: None,
 LL | |             remaining: self.0.iter(),
 LL | |         }
    | |_________^ returning this value requires that `'1` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `self`, you can add an explicit `'_` lifetime bound
+   |
+LL |     fn iter(&self) -> impl Iterator<Item = Box<dyn Foo + '_>> + '_ {
+   |                                                        ++++
 
 error: lifetime may not live long enough
   --> $DIR/trait-object-nested-in-impl-trait.rs:50:9
@@ -35,6 +44,11 @@ LL | |             current: None,
 LL | |             remaining: self.0.iter(),
 LL | |         }
    | |_________^ returning this value requires that `'a` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `self`, you can add an explicit `'a` lifetime bound
+   |
+LL |     fn iter<'a>(&'a self) -> impl Iterator<Item = Box<dyn Foo + 'a>> + 'a {
+   |                                                               ++++
 
 error: lifetime may not live long enough
   --> $DIR/trait-object-nested-in-impl-trait.rs:61:9
@@ -47,10 +61,14 @@ LL | |             remaining: self.0.iter(),
 LL | |         }
    | |_________^ returning this value requires that `'a` must outlive `'static`
    |
-help: to allow this `impl Trait` to capture borrowed data with lifetime `'a`, add `'a` as a bound
+help: to declare that the `impl Trait` captures data from argument `self`, you can add an explicit `'a` lifetime bound
    |
 LL |     fn iter<'a>(&'a self) -> impl Iterator<Item = Box<dyn Foo>> + 'a {
    |                                                                 ++++
+help: to declare that the trait object captures data from argument `self`, you can add an explicit `'a` lifetime bound
+   |
+LL |     fn iter<'a>(&'a self) -> impl Iterator<Item = Box<dyn Foo + 'a>> {
+   |                                                               ++++
 
 error: aborting due to 4 previous errors
 
diff --git a/src/test/ui/underscore-lifetime/dyn-trait-underscore.nll.stderr b/src/test/ui/underscore-lifetime/dyn-trait-underscore.nll.stderr
index 53d45f6a8f2..0ffb77cf021 100644
--- a/src/test/ui/underscore-lifetime/dyn-trait-underscore.nll.stderr
+++ b/src/test/ui/underscore-lifetime/dyn-trait-underscore.nll.stderr
@@ -6,6 +6,11 @@ LL | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item=&T>> {
 LL |     //                      ^^^^^^^^^^^^^^^^^^^^^ bound *here* defaults to `'static`
 LL |     Box::new(items.iter())
    |     ^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`
+   |
+help: to declare that the trait object captures data from argument `items`, you can add an explicit `'_` lifetime bound
+   |
+LL | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item=&T> + '_> {
+   |                                                   ++++
 
 error: aborting due to previous error