[LorrensP-2158466]

Attempts to implement #69268. related zulip discussion: #t-types/call-for-participation > looking for help with generalizing coroutine trait

PR makes the Yield assoc item of Coroutine a GAT by using a lifetime, making it possible to return borrows from inside of the coroutine:

pub trait Coroutine<R = ()> {
  type Yield<'a>
  where
      Self: 'a;
  type Return;
  
fn resume<'a>(self: Pin<&'a mut Self>, arg: R) -> CoroutineState<Self::Yield<'a>, Self::Return>;

Work in progress of course.

r? @oli-obk

[rustbot]

Some changes occurred in compiler/rustc_attr_ir

cc @jdonszelmann, @JonathanBrouwer

[LorrensP-2158466]

I have absolutely no idea if this is how I insert that lifetime. but its the only way i could make it work.

if its correct, there is probably a nicer way :D

View changes since the review

[LorrensP-2158466]

So with the tests, i mostly got away with usign HRTBs for the yield lifetimes. but some use stucts that borrow from self and return a coroutine, some of these i could not handle...

and ofcourse the dyn Coroutine<...> thing not working.

[rust-log-analyzer]

The job test-x86_64-gnu-llvm-22 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [mir-opt] tests/mir-opt/inline/inline_coroutine.rs stdout ----
------rustc stdout------------------------------

------rustc stderr------------------------------
error[E0716]: temporary value dropped while borrowed
##[error]  --> /checkout/tests/mir-opt/inline/inline_coroutine.rs:13:28
   |
13 |     let _r = Pin::new(&mut g()).resume(false);
   |                            ^^^               - temporary value is freed at the end of this statement
   |                            |
   |                            creates a temporary value which is freed while still in use
14 | }
   | - borrow might be used here, when `_r` is dropped and runs the destructor for type `CoroutineState<<impl Coroutine<bool> as Coroutine<bool>>::Yield<'_>, <impl Coroutine<bool> as Coroutine<bool>>::Return>`
   |
help: consider using a `let` binding to create a longer lived value
   |
13 ~     let mut binding = g();
14 ~     let _r = Pin::new(&mut binding).resume(false);
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0716`.

------------------------------------------

error: compilation failed!
status: exit status: 1
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/mir-opt/inline/inline_coroutine.rs" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage2" "--target=i686-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "-O" "-Copt-level=1" "-Zdump-mir=Inline" "-Zvalidate-mir" "-Zlint-mir" "-Zdump-mir-exclude-pass-number" "-Zmir-include-spans=false" "--crate-type=rlib" "-Zmir-opt-level=4" "-Zmir-enable-passes=+ReorderBasicBlocks,+ReorderLocals" "-Zdump-mir-dir=/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt/inline/inline_coroutine" "--emit" "mir" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/mir-opt/inline/inline_coroutine" "-Znext-solver=coherence" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "--edition=2015" "-Zinline-mir-hint-threshold=1000" "-C" "debuginfo=full"
stdout: none
--- stderr -------------------------------
error[E0716]: temporary value dropped while borrowed
##[error]  --> /checkout/tests/mir-opt/inline/inline_coroutine.rs:13:28
   |
13 |     let _r = Pin::new(&mut g()).resume(false);
   |                            ^^^               - temporary value is freed at the end of this statement
   |                            |
   |                            creates a temporary value which is freed while still in use
14 | }
   | - borrow might be used here, when `_r` is dropped and runs the destructor for type `CoroutineState<<impl Coroutine<bool> as Coroutine<bool>>::Yield<'_>, <impl Coroutine<bool> as Coroutine<bool>>::Return>`
   |
help: consider using a `let` binding to create a longer lived value
   |
13 ~     let mut binding = g();
14 ~     let _r = Pin::new(&mut binding).resume(false);
   |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0716`.

[oli-obk]

as discussed on zulip, let's add the lifetime to the trait instead of the GAT while GATs are still a bit undersupported

[rust-bors]

☔ The latest upstream changes (presumably #165493) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.