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Fix an ICE observed with an explicit tail-call in a default trait method #145270

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Fix an ICE observed with an explicit tail-call in a default trait method #145270

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e409fd2
Fix an ICE when using `become` in a default trait method.
jakubadamw Aug 11, 2025
801a69c
Add a regression test for an ICE when using an explicit tail call in …
jakubadamw Aug 11, 2025
9cff6c7
Update the tests/ui/explicit-tail-calls/caller_is_track_caller.rs tes…
jakubadamw Aug 11, 2025
f41a618
Address review feedback.
jakubadamw Aug 12, 2025
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Address review feedback.
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@jakubadamw
jakubadamw committed Aug 12, 2025
commit f41a6182a9a14b0cc77ad01ddfcd478ac380db68
39 changes: 12 additions & 27 deletions 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 @@ -9,7 +9,7 @@ use rustc_middle::thir::visit::{self, Visitor};
use rustc_middle::thir::{BodyTy, Expr, ExprId, ExprKind, Thir};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_span::def_id::{DefId, LocalDefId};
use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
use rustc_span::{ErrorGuaranteed, Span};

pub(crate) fn check_tail_calls(tcx: TyCtxt<'_>, def: LocalDefId) -> Result<(), ErrorGuaranteed> {
let (thir, expr) = tcx.thir_body(def)?;
Expand All @@ -21,7 +21,6 @@ pub(crate) fn check_tail_calls(tcx: TyCtxt<'_>, def: LocalDefId) -> Result<(), E
}

let is_closure = matches!(tcx.def_kind(def), DefKind::Closure);
let caller_ty = tcx.type_of(def).skip_binder();

let mut visitor = TailCallCkVisitor {
tcx,
Expand All @@ -30,7 +29,7 @@ pub(crate) fn check_tail_calls(tcx: TyCtxt<'_>, def: LocalDefId) -> Result<(), E
// FIXME(#132279): we're clearly in a body here.
typing_env: ty::TypingEnv::non_body_analysis(tcx, def),
is_closure,
caller_ty,
caller_def_id: def,
};

visitor.visit_expr(&thir[expr]);
Expand All @@ -47,8 +46,8 @@ struct TailCallCkVisitor<'a, 'tcx> {
/// The result of the checks, `Err(_)` if there was a problem with some
/// tail call, `Ok(())` if all of them were fine.
found_errors: Result<(), ErrorGuaranteed>,
/// Type of the caller function.
caller_ty: Ty<'tcx>,
/// `LocalDefId` of the caller function.
caller_def_id: LocalDefId,
}

impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
Expand Down Expand Up @@ -168,7 +167,7 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
// coercing the function to an `fn()` pointer. (although in that case the tailcall is
// basically useless -- the shim calls the actual function, so tailcalling the shim is
// equivalent to calling the function)
let caller_needs_location = self.needs_location(self.caller_ty);
let caller_needs_location = self.caller_needs_location();

if caller_needs_location {
self.report_track_caller_caller(expr.span);
Expand All @@ -184,27 +183,13 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
}
}

/// Returns true if function of type `ty` needs location argument
/// (i.e. if a function is marked as `#[track_caller]`,
/// is an override of a default trait method marked as `#[track_caller]`
/// or an implementation of a prototype method marked as `#[track_caller]`)
fn needs_location(&self, ty: Ty<'tcx>) -> bool {
if let &ty::FnDef(did, substs) = ty.kind() {
// If this is a default trait method, it won't be resolved to a concrete instance.
if self
.tcx
.opt_associated_item(did)
.is_some_and(|impl_item| impl_item.container == ty::AssocItemContainer::Trait)
{
self.tcx.codegen_fn_attrs(did).flags.intersects(CodegenFnAttrFlags::TRACK_CALLER)
} else {
let instance =
ty::Instance::expect_resolve(self.tcx, self.typing_env, did, substs, DUMMY_SP);
instance.def.requires_caller_location(self.tcx)
}
} else {
false
}
/// Returns true if the caller function needs location argument
/// (i.e. if a function is marked as `#[track_caller]`)
fn caller_needs_location(&self) -> bool {
self.tcx
.codegen_fn_attrs(self.caller_def_id)
.flags
.contains(CodegenFnAttrFlags::TRACK_CALLER)
}

fn report_in_closure(&mut self, expr: &Expr<'_>) {
Expand Down
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