Reject closures in patterns

Author: tmiasko

compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs

@@ -130,6 +130,9 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
                     traits::NonStructuralMatchTy::Opaque => {
                         "opaque types cannot be used in patterns".to_string()
                     }
+                    traits::NonStructuralMatchTy::Closure => {
+                        "closures cannot be used in patterns".to_string()
+                    }
                     traits::NonStructuralMatchTy::Generator => {
                         "generators cannot be used in patterns".to_string()
                     }

compiler/rustc_trait_selection/src/traits/structural_match.rs

@@ -17,6 +17,7 @@ pub enum NonStructuralMatchTy<'tcx> {
     Dynamic,
     Foreign,
     Opaque,
+    Closure,
     Generator,
     Projection,
 }
@@ -154,6 +155,9 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
             ty::Projection(..) => {
                 return ControlFlow::Break(NonStructuralMatchTy::Projection);
             }
+            ty::Closure(..) => {
+                return ControlFlow::Break(NonStructuralMatchTy::Closure);
+            }
             ty::Generator(..) | ty::GeneratorWitness(..) => {
                 return ControlFlow::Break(NonStructuralMatchTy::Generator);
             }
@@ -197,7 +201,7 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
                 // First check all contained types and then tell the caller to continue searching.
                 return ty.super_visit_with(self);
             }
-            ty::Closure(..) | ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => {
+            ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => {
                 bug!("unexpected type during structural-match checking: {:?}", ty);
             }
             ty::Error(_) => {

src/test/ui/consts/closure-structural-match-issue-90013.rs

@@ -0,0 +1,8 @@
+// Regression test for issue 90013.
+// check-pass
+#![allow(incomplete_features)]
+#![feature(inline_const)]
+
+fn main() {
+    const { || {} };
+}

src/test/ui/pattern/non-structural-match-types.rs

@@ -0,0 +1,14 @@
+// edition:2021
+#![allow(incomplete_features)]
+#![allow(unreachable_code)]
+#![feature(const_async_blocks)]
+#![feature(inline_const)]
+
+fn main() {
+    match loop {} {
+        const { || {} } => {}, //~ ERROR cannot be used in patterns
+    }
+    match loop {} {
+        const { async {} } => {}, //~ ERROR cannot be used in patterns
+    }
+}

src/test/ui/pattern/non-structural-match-types.stderr

@@ -0,0 +1,14 @@
+error: `[closure@$DIR/non-structural-match-types.rs:9:17: 9:22]` cannot be used in patterns
+  --> $DIR/non-structural-match-types.rs:9:9
+   |
+LL |         const { || {} } => {},
+   |         ^^^^^^^^^^^^^^^
+
+error: `impl Future` cannot be used in patterns
+  --> $DIR/non-structural-match-types.rs:12:9
+   |
+LL |         const { async {} } => {},
+   |         ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+