[WIP] Diagnose elision failure on the AST

compiler/rustc_resolve/src/lib.rs

@@ -12,6 +12,7 @@
 #![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
 #![feature(if_let_guard)]
+#![feature(iter_intersperse)]
 #![feature(let_chains)]
 #![feature(let_else)]
 #![feature(never_type)]

src/test/ui/abi/numbers-arithmetic/i128-ffi.rs

@@ -12,7 +12,7 @@
 extern "C" {
     fn identity(f: u128) -> u128;
     fn square(f: i128) -> i128;
-    fn sub(f: i128, f: i128) -> i128;
+    fn sub(f: i128, g: i128) -> i128;
 }
 
 fn main() {

src/test/ui/associated-types/bound-lifetime-in-binding-only.elision.stderr

@@ -5,15 +5,10 @@ LL | fn elision<T: Fn() -> &i32>() {
    |                       ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
-help: consider making the bound lifetime-generic with a new `'a` lifetime
-   |
-LL | fn elision<T: for<'a> Fn() -> &'a i32>() {
-   |               +++++++         ~~~
 help: consider using the `'static` lifetime
    |
 LL | fn elision<T: Fn() -> &'static i32>() {
-   |                       ~~~~~~~~
+   |                        +++++++
 
 error: aborting due to previous error
 

src/test/ui/associated-types/bound-lifetime-in-return-only.elision.stderr

@@ -5,15 +5,10 @@ LL | fn elision(_: fn() -> &i32) {
    |                       ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
-   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
-help: consider making the type lifetime-generic with a new `'a` lifetime
-   |
-LL | fn elision(_: for<'a> fn() -> &'a i32) {
-   |               +++++++         ~~~
 help: consider using the `'static` lifetime
    |
 LL | fn elision(_: fn() -> &'static i32) {
-   |                       ~~~~~~~~
+   |                        +++++++
 
 error: aborting due to previous error
 

src/test/ui/async-await/issues/issue-63388-2.rs

@@ -9,6 +9,7 @@ trait Foo {}
 impl Xyz {
     async fn do_sth<'a>(
         foo: &dyn Foo, bar: &'a dyn Foo
+        //~^ ERROR `foo` has an anonymous lifetime `'_` but it needs to satisfy a `'static`
     ) -> &dyn Foo //~ ERROR missing lifetime specifier
     {
         foo

src/test/ui/async-await/issues/issue-63388-2.stderr

@@ -1,17 +1,43 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/issue-63388-2.rs:12:10
+  --> $DIR/issue-63388-2.rs:13:10
    |
 LL |         foo: &dyn Foo, bar: &'a dyn Foo
    |              --------       -----------
+LL |
 LL |     ) -> &dyn Foo
    |          ^ expected named lifetime parameter
    |
    = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `foo` or `bar`
 help: consider using the `'a` lifetime
    |
 LL |     ) -> &'a dyn Foo
-   |          ~~~
+   |           ++
 
-error: aborting due to previous error
+error[E0759]: `foo` has an anonymous lifetime `'_` but it needs to satisfy a `'static` lifetime requirement
+  --> $DIR/issue-63388-2.rs:11:9
+   |
+LL |         foo: &dyn Foo, bar: &'a dyn Foo
+   |         ^^^  -------- this data with an anonymous lifetime `'_`...
+   |         |
+   |         ...is used here...
+...
+LL |         foo
+   |         --- ...and is required to live as long as `'static` here
+   |
+note: `'static` lifetime requirement introduced by the return type
+  --> $DIR/issue-63388-2.rs:13:10
+   |
+LL |     ) -> &dyn Foo
+   |          ^^^^^^^^ requirement introduced by this return type
+LL |     {
+LL |         foo
+   |         --- because of this returned expression
+help: to declare that the trait object captures data from argument `foo`, you can add an explicit `'_` lifetime bound
+   |
+LL |     ) -> &dyn Foo + '_
+   |                   ++++
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0106`.
+Some errors have detailed explanations: E0106, E0759.
+For more information about an error, try `rustc --explain E0106`.

src/test/ui/c-variadic/variadic-ffi-6.stderr

@@ -4,11 +4,11 @@ error[E0106]: missing lifetime specifier
 LL | ) -> &usize {
    |      ^ expected named lifetime parameter
    |
-   = help: this function's return type contains a borrowed value with an elided lifetime, but the lifetime cannot be derived from the arguments
+   = help: this function's return type contains a borrowed value, but there is no value for it to be borrowed from
 help: consider using the `'static` lifetime
    |
 LL | ) -> &'static usize {
-   |      ~~~~~~~~
+   |       +++++++
 
 error: aborting due to previous error