Always create elided lifetime parameters for functions by cjgillot · Pull Request #97720 · rust-lang/rust (original) (raw)
Anonymous and elided lifetimes in functions are sometimes (async fns) --and sometimes not (regular fns)-- desugared to implicit generic parameters.
This difference of treatment makes it some downstream analyses more complicated to handle. This step is a pre-requisite to perform lifetime elision resolution on AST.
There is currently an inconsistency in the treatment of argument-position impl-trait for functions and async fns:
trait Foo<'a> {} fn foo(t: impl Foo<'_>) {} //~ ERROR missing lifetime specifier async fn async_foo(t: impl Foo<'_>) {} //~ OK fn bar(t: impl Iterator<Item = &'_ u8>) {} //~ ERROR missing lifetime specifier async fn async_bar(t: impl Iterator<Item = &'_ u8>) {} //~ OK
The current implementation reports "missing lifetime specifier" on foo, but accepts it in async_foo.
This PR proposes to accept the anonymous lifetime in both cases as an extra generic lifetime parameter.
This change would be insta-stable, so let's ping t-lang.
Anonymous lifetimes in GAT bindings keep being forbidden:
fn foo(t: impl Foo<Assoc<'_> = Bar<'_>>) {} ^^ ^^ forbidden ok
I started a discussion here: https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/Anonymous.20lifetimes.20in.20universal.20impl-trait/near/284968606