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Tail call diagnostics to include lifetime info #145012

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6 changes: 5 additions & 1 deletion compiler/rustc_mir_build/src/check_tail_calls.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -132,7 +132,11 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {

if caller_sig.inputs_and_output != callee_sig.inputs_and_output {
if caller_sig.inputs() != callee_sig.inputs() {
self.report_arguments_mismatch(expr.span, caller_sig, callee_sig);
self.report_arguments_mismatch(
expr.span,
self.caller_ty.fn_sig(self.tcx).skip_binder(),
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Suggested change
self.caller_ty.fn_sig(self.tcx).skip_binder(),
self.caller_ty.fn_sig(self.tcx).instantiate_identity(),

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It does not work for me

error[E0599]: no method named `instantiate_identity` found for struct `Binder` in the current scope
   --> compiler/rustc_mir_build/src/check_tail_calls.rs:137:53
    |
137 |                     self.caller_ty.fn_sig(self.tcx).instantiate_identity(),
    |                                                     ^^^^^^^^^^^^^^^^^^^^ method not found in `Binder<TyCtxt<'_>, FnSig<TyCtxt<'_>>>`

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oh, it's a binder, not an early binder. that should be liberated then probably, use tcx.liberate_late_bound_regions instead.

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I'd love to hear why current approach is not best just to learn things

Also about 'static yes it shows, should I include this in test?

4 |     become bar(dummy);
  |     ^^^^^^^^^^^^^^^^^
  |
  = note: -Ztrack-diagnostics: created at compiler/rustc_mir_build/src/check_tail_calls.rs:368:14
  = note: `become` requires caller and callee to have matching signatures
  = note: caller signature: `fn(for<'a> fn(&'a ()))`
  = note: callee signature: `fn(fn(&'static ()))`

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@Kivooeo Kivooeo Aug 6, 2025 •
edited
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I did tcx.liberate_late_bound_regions it works but I did not found a better way to obtain DefId rather than do this

Update TailCallCkVisitor with adding a field that will contain def id

struct TailCallCkVisitor<'a, 'tcx> {
    ... // existed fields
    def: DefId,
}

And create it like this

    let mut visitor = TailCallCkVisitor {
        ... // eixsted fields
        def: def.to_def_id(),
    };

This might be a bad solution to pass DefId like this?

    self.report_arguments_mismatch(
        expr.span,
        self.tcx.liberate_late_bound_regions(self.def, self.caller_ty.fn_sig(self.tcx)),
        self.tcx.liberate_late_bound_regions(self.def, ty.fn_sig(self.tcx)),
    );

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Hey @compiler-errors, when you have a moment, could you take another look and let me know which approach you think works better?

ty.fn_sig(self.tcx).skip_binder(),
);
}

// FIXME(explicit_tail_calls): this currently fails for cases where opaques are used.
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39 changes: 39 additions & 0 deletions tests/ui/explicit-tail-calls/caller-lifetime-presence.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,39 @@
//! Regression test for: https://github.com/rust-lang/rust/issues/144957
//!
//! This test ensures that lifetime information is included in diagnostics.
//!
//! Specifically, it checks that the `become` call produces an error with lifetimes shown
//! in both caller and callee signatures.
//!
//! If the test fails:
//! - Lifetimes may be missing (fix the diagnostic), or
//! - The message format changed (update the test).

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

fn foo<'a>(_: fn(&'a ())) {
become bar(dummy);
//~^ ERROR mismatched signatures
//~| NOTE `become` requires caller and callee to have matching signatures
//~| NOTE caller signature: `fn(fn(&'a ()))`
//~| NOTE callee signature: `fn(for<'a> fn(&'a ()))`
}

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

fn dummy(_: &()) {}

fn foo_(_: fn(&())) {
become bar1(dummy2);
//~^ ERROR mismatched signatures
//~| NOTE `become` requires caller and callee to have matching signatures
//~| NOTE caller signature: `fn(for<'a> fn(&'a ()))`
//~| NOTE callee signature: `fn(fn(&'a ()))`
}

fn bar1<'a>(_: fn(&'a ())) {}

fn dummy2(_: &()) {}

fn main() {}
22 changes: 22 additions & 0 deletions tests/ui/explicit-tail-calls/caller-lifetime-presence.stderr
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@@ -0,0 +1,22 @@
error: mismatched signatures
--> $DIR/caller-lifetime-presence.rs:16:5
|
LL | become bar(dummy);
| ^^^^^^^^^^^^^^^^^
|
= note: `become` requires caller and callee to have matching signatures
= note: caller signature: `fn(fn(&'a ()))`
= note: callee signature: `fn(for<'a> fn(&'a ()))`

error: mismatched signatures
--> $DIR/caller-lifetime-presence.rs:28:5
|
LL | become bar1(dummy2);
| ^^^^^^^^^^^^^^^^^^^
|
= note: `become` requires caller and callee to have matching signatures
= note: caller signature: `fn(for<'a> fn(&'a ()))`
= note: callee signature: `fn(fn(&'a ()))`

error: aborting due to 2 previous errors

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