typeck: catch continues pointing to blocks

compiler/rustc_hir_typeck/src/expr.rs

@@ -532,14 +532,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ExprKind::Break(destination, ref expr_opt) => {
                 self.check_expr_break(destination, expr_opt.as_deref(), expr)
             }
-            ExprKind::Continue(destination) => {
-                if destination.target_id.is_ok() {
-                    tcx.types.never
-                } else {
-                    // There was an error; make type-check fail.
-                    Ty::new_misc_error(tcx)
-                }
-            }
+            ExprKind::Continue(destination) => self.check_expr_continue(destination, expr),
             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
             ExprKind::Become(call) => self.check_expr_become(call, expr),
             ExprKind::Let(let_expr) => self.check_expr_let(let_expr, expr.hir_id),
@@ -989,6 +982,31 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    fn check_expr_continue(
+        &self,
+        destination: hir::Destination,
+        expr: &'tcx hir::Expr<'tcx>,
+    ) -> Ty<'tcx> {
+        if let Ok(target_id) = destination.target_id {
+            if let hir::Node::Expr(hir::Expr { kind: ExprKind::Loop(..), .. }) =
+                self.tcx.hir_node(target_id)
+            {
+                self.tcx.types.never
+            } else {
+                // Liveness linting assumes `continue`s all point to loops. We'll report an error
+                // in `check_mod_loops`, but make sure we don't run liveness (#113379, #121623).
+                let guar = self.dcx().span_delayed_bug(
+                    expr.span,
+                    "found `continue` not pointing to loop, but no error reported",
+                );
+                Ty::new_error(self.tcx, guar)
+            }
+        } else {
+            // There was an error; make type-check fail.
+            Ty::new_misc_error(self.tcx)
+        }
+    }
+
     fn check_expr_return(
         &self,
         expr_opt: Option<&'tcx hir::Expr<'tcx>>,

compiler/rustc_mir_build/src/builder/mod.rs

@@ -66,8 +66,7 @@ pub fn build_mir<'tcx>(tcx: TyCtxt<'tcx>, def: LocalDefId) -> Body<'tcx> {
                 }
             };
 
-            // this must run before MIR dump, because
-            // "not all control paths return a value" is reported here.
+            // Checking liveness after building the THIR ensures there were no typeck errors.
             //
             // maybe move the check to a MIR pass?
             tcx.ensure_ok().check_liveness(def);

compiler/rustc_passes/src/liveness.rs

@@ -122,7 +122,6 @@ enum LiveNodeKind {
     VarDefNode(Span, HirId),
     ClosureNode,
     ExitNode,
-    ErrNode,
 }
 
 fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
@@ -133,7 +132,6 @@ fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
         VarDefNode(s, _) => format!("Var def node [{}]", sm.span_to_diagnostic_string(s)),
         ClosureNode => "Closure node".to_owned(),
         ExitNode => "Exit node".to_owned(),
-        ErrNode => "Error node".to_owned(),
     }
 }
 
@@ -492,6 +490,9 @@ struct Liveness<'a, 'tcx> {
 impl<'a, 'tcx> Liveness<'a, 'tcx> {
     fn new(ir: &'a mut IrMaps<'tcx>, body_owner: LocalDefId) -> Liveness<'a, 'tcx> {
         let typeck_results = ir.tcx.typeck(body_owner);
+        // Liveness linting runs after building the THIR. We make several assumptions based on
+        // typeck succeeding, e.g. that breaks and continues are well-formed.
+        assert!(typeck_results.tainted_by_errors.is_none());
         // FIXME(#132279): we're in a body here.
         let typing_env = ty::TypingEnv::non_body_analysis(ir.tcx, body_owner);
         let closure_min_captures = typeck_results.closure_min_captures.get(&body_owner);
@@ -976,8 +977,9 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 // Now that we know the label we're going to,
                 // look it up in the continue loop nodes table
                 self.cont_ln.get(&sc).cloned().unwrap_or_else(|| {
-                    self.ir.tcx.dcx().span_delayed_bug(expr.span, "continue to unknown label");
-                    self.ir.add_live_node(ErrNode)
+                    // Liveness linting happens after building the THIR. Bad labels should already
+                    // have been caught.
+                    span_bug!(expr.span, "continue to unknown label");
                 })
             }
 

tests/ui/label/continue-pointing-to-block-ice-113379.rs

@@ -0,0 +1,12 @@
+//! Regression test for ICE #113379. Liveness linting assumes that `continue`s all point to loops.
+//! This tests that if a `continue` points to a block, we don't run liveness lints.
+
+async fn f999() -> Vec<usize> {
+    //~^ ERROR `async fn` is not permitted in Rust 2015
+    'b: {
+        //~^ ERROR mismatched types
+        continue 'b;
+        //~^ ERROR `continue` pointing to a labeled block
+    }
+}
+//~^ ERROR `main` function not found

tests/ui/label/continue-pointing-to-block-ice-113379.stderr

@@ -0,0 +1,43 @@
+error[E0670]: `async fn` is not permitted in Rust 2015
+  --> $DIR/continue-pointing-to-block-ice-113379.rs:4:1
+   |
+LL | async fn f999() -> Vec<usize> {
+   | ^^^^^ to use `async fn`, switch to Rust 2018 or later
+   |
+   = help: pass `--edition 2024` to `rustc`
+   = note: for more on editions, read https://doc.rust-lang.org/edition-guide
+
+error[E0601]: `main` function not found in crate `continue_pointing_to_block_ice_113379`
+  --> $DIR/continue-pointing-to-block-ice-113379.rs:11:2
+   |
+LL | }
+   |  ^ consider adding a `main` function to `$DIR/continue-pointing-to-block-ice-113379.rs`
+
+error[E0696]: `continue` pointing to a labeled block
+  --> $DIR/continue-pointing-to-block-ice-113379.rs:8:9
+   |
+LL | /     'b: {
+LL | |
+LL | |         continue 'b;
+   | |         ^^^^^^^^^^^ labeled blocks cannot be `continue`'d
+LL | |
+LL | |     }
+   | |_____- labeled block the `continue` points to
+
+error[E0308]: mismatched types
+  --> $DIR/continue-pointing-to-block-ice-113379.rs:6:5
+   |
+LL | /     'b: {
+LL | |
+LL | |         continue 'b;
+LL | |
+LL | |     }
+   | |_____^ expected `Vec<usize>`, found `()`
+   |
+   = note: expected struct `Vec<usize>`
+           found unit type `()`
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0308, E0601, E0670, E0696.
+For more information about an error, try `rustc --explain E0308`.

tests/ui/label/continue-pointing-to-block-ice-121623.rs

@@ -0,0 +1,11 @@
+//! Regression test for ICE #121623. Liveness linting assumes that `continue`s all point to loops.
+//! This tests that if a `continue` points to a block, we don't run liveness lints.
+
+fn main() {
+    match () {
+        _ => 'b: {
+            continue 'b;
+            //~^ ERROR `continue` pointing to a labeled block
+        }
+    }
+}

tests/ui/label/continue-pointing-to-block-ice-121623.stderr

@@ -0,0 +1,14 @@
+error[E0696]: `continue` pointing to a labeled block
+  --> $DIR/continue-pointing-to-block-ice-121623.rs:7:13
+   |
+LL |           _ => 'b: {
+   |  ______________-
+LL | |             continue 'b;
+   | |             ^^^^^^^^^^^ labeled blocks cannot be `continue`'d
+LL | |
+LL | |         }
+   | |_________- labeled block the `continue` points to
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0696`.