Always use CreateParameter mode for function definitions.

Author: cjgillot

compiler/rustc_resolve/src/late.rs

@@ -758,7 +758,10 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
                 // We don't need to deal with patterns in parameters, because
                 // they are not possible for foreign or bodiless functions.
                 self.with_lifetime_rib(
-                    LifetimeRibKind::AnonymousPassThrough(fn_id, false),
+                    LifetimeRibKind::AnonymousCreateParameter {
+                        binder: fn_id,
+                        report_in_path: false,
+                    },
                     |this| walk_list!(this, visit_param, &sig.decl.inputs),
                 );
                 self.with_lifetime_rib(
@@ -792,18 +795,13 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
                         // generic parameters.  This is especially useful for `async fn`, where
                         // these fresh generic parameters can be applied to the opaque `impl Trait`
                         // return type.
-                        let rib = if async_node_id.is_some() {
-                            // Only emit a hard error for `async fn`, since this kind of
-                            // elision has always been allowed in regular `fn`s.
+                        this.with_lifetime_rib(
                             LifetimeRibKind::AnonymousCreateParameter {
                                 binder: fn_id,
-                                report_in_path: true,
-                            }
-                        } else {
-                            LifetimeRibKind::AnonymousPassThrough(fn_id, false)
-                        };
-                        this.with_lifetime_rib(
-                            rib,
+                                // Only emit a hard error for `async fn`, since this kind of
+                                // elision has always been allowed in regular `fn`s.
+                                report_in_path: async_node_id.is_some(),
+                            },
                             // Add each argument to the rib.
                             |this| this.resolve_params(&declaration.inputs),
                         );

src/test/ui/generic-associated-types/bugs/issue-87748.stderr

@@ -4,12 +4,12 @@ error[E0478]: lifetime bound not satisfied
 LL |     fn do_sth(_: u32) {}
    |     ^^^^^^^^^^^^^^^^^
    |
-note: lifetime parameter instantiated with the anonymous lifetime #2 defined here
+note: lifetime parameter instantiated with the anonymous lifetime as defined here
   --> $DIR/issue-87748.rs:18:5
    |
 LL |     fn do_sth(_: u32) {}
    |     ^^^^^^^^^^^^^^^^^
-note: but lifetime parameter must outlive the anonymous lifetime #1 defined here
+note: but lifetime parameter must outlive the anonymous lifetime as defined here
   --> $DIR/issue-87748.rs:18:5
    |
 LL |     fn do_sth(_: u32) {}

src/test/ui/generic-associated-types/issue-95305.rs

@@ -11,7 +11,10 @@ trait Foo {
 fn foo(x: &impl Foo<Item<'_> = u32>) { }
                        //~^ ERROR `'_` cannot be used here [E0637]
 
+// Ok: the anonymous lifetime is bound to the function.
 fn bar(x: &impl for<'a> Foo<Item<'a> = &'_ u32>) { }
-                                      //~^ ERROR missing lifetime specifier
+
+// Ok: the anonymous lifetime is bound to the function.
+fn baz(x: &impl for<'a> Foo<Item<'a> = &u32>) { }
 
 fn main() {}

src/test/ui/generic-associated-types/issue-95305.stderr

@@ -4,18 +4,6 @@ error[E0637]: `'_` cannot be used here
 LL | fn foo(x: &impl Foo<Item<'_> = u32>) { }
    |                          ^^ `'_` is a reserved lifetime name
 
-error[E0106]: missing lifetime specifier
-  --> $DIR/issue-95305.rs:14:41
-   |
-LL | fn bar(x: &impl for<'a> Foo<Item<'a> = &'_ u32>) { }
-   |                                         ^^ expected named lifetime parameter
-   |
-help: consider using the `'a` lifetime
-   |
-LL | fn bar(x: &impl for<'a> Foo<Item<'a> = &'a u32>) { }
-   |                                         ~~
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0106, E0637.
-For more information about an error, try `rustc --explain E0106`.
+For more information about this error, try `rustc --explain E0637`.

src/test/ui/issues/issue-37884.stderr

@@ -6,7 +6,7 @@ LL |     fn next(&'a mut self) -> Option<Self::Item>
    |
    = note: expected fn pointer `fn(&mut RepeatMut<'a, T>) -> Option<_>`
               found fn pointer `fn(&'a mut RepeatMut<'a, T>) -> Option<_>`
-note: the anonymous lifetime #1 defined here...
+note: the anonymous lifetime as defined here...
   --> $DIR/issue-37884.rs:6:5
    |
 LL |     fn next(&'a mut self) -> Option<Self::Item>

src/test/ui/nll/ty-outlives/impl-trait-captures.stderr

@@ -2,14 +2,14 @@ error[E0700]: hidden type for `impl Trait` captures lifetime that does not appea
   --> $DIR/impl-trait-captures.rs:11:5
    |
 LL | fn foo<'a, T>(x: &T) -> impl Foo<'a> {
-   |                  -- hidden type `&ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrAnon(0)) T` captures the anonymous lifetime defined here
+   |                  -- hidden type `&ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrNamed(DefId(0:13 ~ impl_trait_captures[1afc]::foo::'_), '_)) T` captures the anonymous lifetime defined here
 LL |     x
    |     ^
    |
-help: to declare that the `impl Trait` captures `ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrAnon(0))`, you can add an explicit `ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrAnon(0))` lifetime bound
+help: to declare that the `impl Trait` captures `ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrNamed(DefId(0:13 ~ impl_trait_captures[1afc]::foo::'_), '_))`, you can add an explicit `ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrNamed(DefId(0:13 ~ impl_trait_captures[1afc]::foo::'_), '_))` lifetime bound
    |
-LL | fn foo<'a, T>(x: &T) -> impl Foo<'a> + ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrAnon(0)) {
-   |                                      ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+LL | fn foo<'a, T>(x: &T) -> impl Foo<'a> + ReFree(DefId(0:8 ~ impl_trait_captures[1afc]::foo), BrNamed(DefId(0:13 ~ impl_trait_captures[1afc]::foo::'_), '_)) {
+   |                                      ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 
 error: aborting due to previous error
 

src/test/ui/suggestions/impl-trait-missing-lifetime.rs

@@ -1,2 +1,8 @@
-fn f(_: impl Iterator<Item = &'_ ()>) {} //~ ERROR missing lifetime specifier
+// This is understood as `fn foo<'_1>(_: impl Iterator<Item = &'_1 ()>) {}`.
+fn f(_: impl Iterator<Item = &'_ ()>) {}
+
+// But that lifetime does not participate in resolution.
+fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+//~^ ERROR missing lifetime specifier
+
 fn main() {}

src/test/ui/suggestions/impl-trait-missing-lifetime.stderr

@@ -1,13 +1,14 @@
 error[E0106]: missing lifetime specifier
-  --> $DIR/impl-trait-missing-lifetime.rs:1:31
+  --> $DIR/impl-trait-missing-lifetime.rs:5:50
    |
-LL | fn f(_: impl Iterator<Item = &'_ ()>) {}
-   |                               ^^ expected named lifetime parameter
+LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()> { x.next() }
+   |                                                  ^^ expected named lifetime parameter
    |
-help: consider introducing a 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: consider using the `'static` lifetime
    |
-LL | fn f<'a>(_: impl Iterator<Item = &'a ()>) {}
-   |     ++++                          ~~
+LL | fn g(x: impl Iterator<Item = &'_ ()>) -> Option<&'static ()> { x.next() }
+   |                                                  ~~~~~~~
 
 error: aborting due to previous error
 

src/test/ui/wf/wf-in-foreign-fn-decls-issue-80468.stderr

@@ -21,11 +21,11 @@ note: because this has an unmet lifetime requirement
    |
 LL | pub struct Wrapper<T: Trait>(T);
    |                       ^^^^^ introduces a `'static` lifetime requirement
-note: the anonymous lifetime #1 defined here...
-  --> $DIR/wf-in-foreign-fn-decls-issue-80468.rs:16:5
+note: the anonymous lifetime as defined here...
+  --> $DIR/wf-in-foreign-fn-decls-issue-80468.rs:16:29
    |
 LL |     pub fn repro(_: Wrapper<Ref>);
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                             ^^^
 note: ...does not necessarily outlive the static lifetime introduced by the compatible `impl`
   --> $DIR/wf-in-foreign-fn-decls-issue-80468.rs:13:1
    |