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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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Fix an ICE when using become in a default trait method. 
The logic determining whether the relevant function is marked as `#[track_caller]`
only worked with functions that could be resolved to a concrete instance, which default
trait methods cannot. We need to check the codegen attribute on the default method itself.
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@jakubadamw
jakubadamw committed Aug 12, 2025
commit e409fd2df372aa5dae1a7886ce517179c535c499
23 changes: 16 additions & 7 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 @@ -3,6 +3,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::Applicability;
use rustc_hir::LangItem;
use rustc_hir::def::DefKind;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::span_bug;
use rustc_middle::thir::visit::{self, Visitor};
use rustc_middle::thir::{BodyTy, Expr, ExprId, ExprKind, Thir};
Expand Down Expand Up @@ -184,15 +185,23 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
}

/// Returns true if function of type `ty` needs location argument
/// (i.e. if a function is marked as `#[track_caller]`).
///
/// Panics if the function's instance can't be immediately resolved.
/// (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() {
let instance =
ty::Instance::expect_resolve(self.tcx, self.typing_env, did, substs, DUMMY_SP);

instance.def.requires_caller_location(self.tcx)
// 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
}
Expand Down