detect infinite recursion with tail calls in ctfe

Author: WaffleLapkin

compiler/rustc_mir_transform/src/ctfe_limit.rs

@@ -18,7 +18,7 @@ impl<'tcx> crate::MirPass<'tcx> for CtfeLimit {
             .basic_blocks
             .iter_enumerated()
             .filter_map(|(node, node_data)| {
-                if matches!(node_data.terminator().kind, TerminatorKind::Call { .. })
+                if matches!(node_data.terminator().kind, TerminatorKind::Call { .. } | TerminatorKind::TailCall { .. })
                     // Back edges in a CFG indicate loops
                     || has_back_edge(doms, node, node_data)
                 {

tests/ui/explicit-tail-calls/infinite-recursion-in-ctfe.rs

@@ -0,0 +1,10 @@
+#![feature(explicit_tail_calls)]
+#![expect(incomplete_features)]
+
+const _: () = f();
+
+const fn f() {
+    become f(); //~ error: constant evaluation is taking a long time
+}
+
+fn main() {}

tests/ui/explicit-tail-calls/infinite-recursion-in-ctfe.stderr

@@ -0,0 +1,17 @@
+error: constant evaluation is taking a long time
+  --> $DIR/infinite-recursion-in-ctfe.rs:7:5
+   |
+LL |     become f();
+   |     ^^^^^^^^^^
+   |
+   = note: this lint makes sure the compiler doesn't get stuck due to infinite loops in const eval.
+           If your compilation actually takes a long time, you can safely allow the lint.
+help: the constant being evaluated
+  --> $DIR/infinite-recursion-in-ctfe.rs:4:1
+   |
+LL | const _: () = f();
+   | ^^^^^^^^^^^
+   = note: `#[deny(long_running_const_eval)]` on by default
+
+error: aborting due to 1 previous error
+