Rollup merge of #144851 - WaffleLapkin:instrinsic-deny, r=compiler-errors,scottmcm

Forbid tail calling intrinsics

There is only one intrinsic that can be called on stable, as far as I can find, (`transmute`). And in general tail calling intrinsics doesn't make much sense.

Alternative to rust-lang/rust#144815 (and thus closes rust-lang/rust#144815)
Fixes https://github.com/rust-lang/rust/issues/144806

r? ``@scottmcm``

2 files changed, 27 insertions, 0 deletions

diff --git a/tests/ui/explicit-tail-calls/intrinsics.rs b/tests/ui/explicit-tail-calls/intrinsics.rs
new file mode 100644
index 00000000000..6fc521fa27d
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/intrinsics.rs
@@ -0,0 +1,13 @@
+#![feature(explicit_tail_calls, core_intrinsics)]
+#![expect(incomplete_features, internal_features)]
+
+fn trans((): ()) {
+    unsafe { become std::mem::transmute(()) } //~ error: tail calling intrinsics is not allowed
+
+}
+
+fn cats(x: u64) -> u32 {
+    become std::intrinsics::ctlz(x) //~ error: tail calling intrinsics is not allowed
+}
+
+fn main() {}
diff --git a/tests/ui/explicit-tail-calls/intrinsics.stderr b/tests/ui/explicit-tail-calls/intrinsics.stderr
new file mode 100644
index 00000000000..b012e3629dd
--- /dev/null
+++ b/tests/ui/explicit-tail-calls/intrinsics.stderr
@@ -0,0 +1,14 @@
+error: tail calling intrinsics is not allowed
+  --> $DIR/intrinsics.rs:5:14
+   |
+LL |     unsafe { become std::mem::transmute(()) }
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: tail calling intrinsics is not allowed
+  --> $DIR/intrinsics.rs:10:5
+   |
+LL |     become std::intrinsics::ctlz(x)
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+