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Defer tail call ret ty equality to check_tail_calls #144915

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Defer tail call ret ty equality to check_tail_calls #144915

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2 changes: 1 addition & 1 deletion compiler/rustc_borrowck/src/type_check/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1931,7 +1931,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
self.tcx(),
self.infcx.typing_env(self.infcx.param_env),
) {
span_mirbug!(self, term, "call to converging function {:?} w/o dest", sig);
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isn't the point here that the function does not diverge (as its return type is not uninhabited), but we don't have a dest?

as in, the comment was correct

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hm... i think i see, but in that case i would call it non-diverging

span_mirbug!(self, term, "call to diverging function {:?} w/o dest", sig);
}
}
}
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18 changes: 2 additions & 16 deletions compiler/rustc_mir_build/src/check_tail_calls.rs
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Expand Up @@ -60,7 +60,7 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
let BodyTy::Fn(caller_sig) = self.thir.body_type else {
span_bug!(
call.span,
"`become` outside of functions should have been disallowed by hit_typeck"
"`become` outside of functions should have been disallowed by hir_typeck"
)
};

Expand Down Expand Up @@ -118,21 +118,7 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
}

if caller_sig.inputs_and_output != callee_sig.inputs_and_output {
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please also add a test that we anonymize bound vars: for<'a> fn(&'a ()) and for<'b> fn(&'b ())

if caller_sig.inputs() != callee_sig.inputs() {
self.report_arguments_mismatch(expr.span, caller_sig, callee_sig);
}

// FIXME(explicit_tail_calls): this currently fails for cases where opaques are used.
// e.g.
// ```
// fn a() -> impl Sized { become b() } // ICE
// fn b() -> u8 { 0 }
// ```
// we should think what is the expected behavior here.
// (we should probably just accept this by revealing opaques?)
Comment on lines -125 to -132
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Can you keep this fixme? (it doesn't ICE anymore, but doesn't work either...)

if caller_sig.output() != callee_sig.output() {
span_bug!(expr.span, "hir typeck should have checked the return type already");
}
self.report_arguments_mismatch(expr.span, caller_sig, callee_sig);
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nit: the function should probably be renamed to report_signature_mismatch

}

{
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15 changes: 15 additions & 0 deletions tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.rs
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@@ -0,0 +1,15 @@
#![feature(explicit_tail_calls)]
#![allow(incomplete_features)]

fn foo() -> for<'a> fn(&'a i32) {
become bar();
//~^ ERROR mismatched signatures
}

fn bar() -> fn(&'static i32) {
dummy
}

fn dummy(_: &i32) {}

fn main() {}
12 changes: 12 additions & 0 deletions tests/ui/explicit-tail-calls/ret-ty-hr-mismatch.stderr
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@@ -0,0 +1,12 @@
error: mismatched signatures
--> $DIR/ret-ty-hr-mismatch.rs:5:5
|
LL | become bar();
| ^^^^^^^^^^^^
|
= note: `become` requires caller and callee to have matching signatures
= note: caller signature: `fn() -> for<'a> fn(&'a i32)`
= note: callee signature: `fn() -> fn(&i32)`
Comment on lines +8 to +9
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Why are we not printing 'static? This looks so confusing 😵‍💫

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Because we erase regions. We could print the unerased signature, but this has nothing to do with static, and it is a preexisting issue with args.

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preexisting example:

#![feature(explicit_tail_calls)]
#![allow(incomplete_features)]

fn foo<'a>(_: fn(&'a ())) {
    become bar(dummy);
}

fn bar(_: fn(&())) {}

fn dummy(_: &()) {}

fn main() {}

error: mismatched signatures
 --> src/main.rs:5:5
  |
5 |     become bar(dummy);
  |     ^^^^^^^^^^^^^^^^^
  |
  = note: `become` requires caller and callee to have matching signatures
  = note: caller signature: `fn(fn(&()))`
  = note: callee signature: `fn(for<'a> fn(&'a ()))`

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I've opened #144957 so that we don't forget to return to this at some point


error: aborting due to 1 previous error

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