From 992e3b4f03e0bd348699337317091cc34268684b Mon Sep 17 00:00:00 2001
From: Waffle Lapkin <waffle.lapkin@gmail.com>
Date: Fri, 24 Jan 2025 04:19:10 +0100
Subject: [PATCH] fix tail call checks wrt `#[track_caller]`
only check the caller + disallow caller having the attr.
---
.../rustc_mir_build/src/check_tail_calls.rs | 51 ++++++++++---------
tests/crashes/134336.rs | 11 ----
.../ui/explicit-tail-calls/become-trait-fn.rs | 19 +++++++
.../callee_is_track_caller.rs | 15 ++++++
.../caller_is_track_caller.rs | 16 ++++++
.../caller_is_track_caller.stderr | 14 +++++
6 files changed, 92 insertions(+), 34 deletions(-)
delete mode 100644 tests/crashes/134336.rs
create mode 100644 tests/ui/explicit-tail-calls/become-trait-fn.rs
create mode 100644 tests/ui/explicit-tail-calls/callee_is_track_caller.rs
create mode 100644 tests/ui/explicit-tail-calls/caller_is_track_caller.rs
create mode 100644 tests/ui/explicit-tail-calls/caller_is_track_caller.stderr
diff --git a/compiler/rustc_mir_build/src/check_tail_calls.rs b/compiler/rustc_mir_build/src/check_tail_calls.rs
index 0659e3ea314..73f8bc4e901 100644
--- a/compiler/rustc_mir_build/src/check_tail_calls.rs
+++ b/compiler/rustc_mir_build/src/check_tail_calls.rs
@@ -131,11 +131,24 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
}
{
+ // `#[track_caller]` affects the ABI of a function (by adding a location argument),
+ // so a `track_caller` can only tail call other `track_caller` functions.
+ //
+ // The issue is however that we can't know if a function is `track_caller` or not at
+ // this point (THIR can be polymorphic, we may have an unresolved trait function).
+ // We could only allow functions that we *can* resolve and *are* `track_caller`,
+ // but that would turn changing `track_caller`-ness into a breaking change,
+ // which is probably undesirable.
+ //
+ // Also note that we don't check callee's `track_caller`-ness at all, mostly for the
+ // reasons above, but also because we can always tailcall the shim we'd generate for
+ // 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 callee_needs_location = self.needs_location(ty);
- if caller_needs_location != callee_needs_location {
- self.report_track_caller_mismatch(expr.span, caller_needs_location);
+ if caller_needs_location {
+ self.report_track_caller_caller(expr.span);
}
}
@@ -149,7 +162,9 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
}
/// Returns true if function of type `ty` needs location argument
- /// (i.e. if a function is marked as `#[track_caller]`)
+ /// (i.e. if a function is marked as `#[track_caller]`).
+ ///
+ /// Panics if the function's instance can't be immediately resolved.
fn needs_location(&self, ty: Ty<'tcx>) -> bool {
if let &ty::FnDef(did, substs) = ty.kind() {
let instance =
@@ -292,25 +307,15 @@ impl<'tcx> TailCallCkVisitor<'_, 'tcx> {
self.found_errors = Err(err);
}
- fn report_track_caller_mismatch(&mut self, sp: Span, caller_needs_location: bool) {
- let err = match caller_needs_location {
- true => self
- .tcx
- .dcx()
- .struct_span_err(
- sp,
- "a function marked with `#[track_caller]` cannot tail-call one that is not",
- )
- .emit(),
- false => self
- .tcx
- .dcx()
- .struct_span_err(
- sp,
- "a function mot marked with `#[track_caller]` cannot tail-call one that is",
- )
- .emit(),
- };
+ fn report_track_caller_caller(&mut self, sp: Span) {
+ let err = self
+ .tcx
+ .dcx()
+ .struct_span_err(
+ sp,
+ "a function marked with `#[track_caller]` cannot perform a tail-call",
+ )
+ .emit();
self.found_errors = Err(err);
}
diff --git a/tests/crashes/134336.rs b/tests/crashes/134336.rs
deleted file mode 100644
index 14b88e14f04..00000000000
--- a/tests/crashes/134336.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-//@ known-bug: #134336
-#![expect(incomplete_features)]
-#![feature(explicit_tail_calls)]
-
-trait Tr {
- fn f();
-}
-
-fn g<T: Tr>() {
- become T::f();
-}
diff --git a/tests/ui/explicit-tail-calls/become-trait-fn.rs b/tests/ui/explicit-tail-calls/become-trait-fn.rs
new file mode 100644
index 00000000000..03255f15dd0
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/become-trait-fn.rs
@@ -0,0 +1,19 @@
+// regression test for <https://github.com/rust-lang/rust/issues/134336>
+// this previously caused an ICE, because we would compare `#[track_caller]` of
+// the callee and the caller (in tailcalls specifically), leading to a problem
+// since `T::f`'s instance can't be resolved (we do not know if the function is
+// or isn't marked with `#[track_caller]`!)
+//
+//@ check-pass
+#![expect(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+trait Tr {
+ fn f();
+}
+
+fn g<T: Tr>() {
+ become T::f();
+}
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/callee_is_track_caller.rs b/tests/ui/explicit-tail-calls/callee_is_track_caller.rs
new file mode 100644
index 00000000000..bcb93fda8c8
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/callee_is_track_caller.rs
@@ -0,0 +1,15 @@
+//@ check-pass
+// FIXME(explicit_tail_calls): make this run-pass, once tail calls are properly implemented
+#![expect(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+fn a(x: u32) -> u32 {
+ become b(x);
+}
+
+#[track_caller]
+fn b(x: u32) -> u32 { x + 42 }
+
+fn main() {
+ assert_eq!(a(12), 54);
+}
diff --git a/tests/ui/explicit-tail-calls/caller_is_track_caller.rs b/tests/ui/explicit-tail-calls/caller_is_track_caller.rs
new file mode 100644
index 00000000000..4e5f3f12f83
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/caller_is_track_caller.rs
@@ -0,0 +1,16 @@
+#![expect(incomplete_features)]
+#![feature(explicit_tail_calls)]
+
+#[track_caller]
+fn a() {
+ become b(); //~ error: a function marked with `#[track_caller]` cannot perform a tail-call
+}
+
+fn b() {}
+
+#[track_caller]
+fn c() {
+ become a(); //~ error: a function marked with `#[track_caller]` cannot perform a tail-call
+}
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/caller_is_track_caller.stderr b/tests/ui/explicit-tail-calls/caller_is_track_caller.stderr
new file mode 100644
index 00000000000..79b9b45986c
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/caller_is_track_caller.stderr
@@ -0,0 +1,14 @@
+error: a function marked with `#[track_caller]` cannot perform a tail-call
+ --> $DIR/caller_is_track_caller.rs:6:5
+ |
+LL | become b();
+ | ^^^^^^^^^^
+
+error: a function marked with `#[track_caller]` cannot perform a tail-call
+ --> $DIR/caller_is_track_caller.rs:13:5
+ |
+LL | become a();
+ | ^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+