simplify logic for when a #[loop_match] state type is valid

Author: folkertdev

compiler/rustc_mir_build/src/builder/expr/into.rs

@@ -254,25 +254,16 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // block available to the lowering of `#[const_continue]`.
 
                 fn is_supported_loop_match_type(ty: Ty<'_>) -> bool {
-                    if ty.is_integral() {
-                        return true;
-                    }
-
-                    if let Some(adt_def) = ty.ty_adt_def() {
-                        if adt_def.adt_kind() != ty::AdtKind::Enum {
-                            return false;
-                        }
-
-                        for variant in adt_def.variants() {
-                            if !variant.fields.is_empty() {
-                                return false;
+                    match ty.kind() {
+                        ty::Uint(_) | ty::Int(_) => true,
+                        ty::Adt(adt_def, _) => match adt_def.adt_kind() {
+                            ty::AdtKind::Struct | ty::AdtKind::Union => false,
+                            ty::AdtKind::Enum => {
+                                adt_def.variants().iter().all(|v| v.fields.is_empty())
                             }
-                        }
-
-                        return true;
+                        },
+                        _ => false,
                     }
-
-                    false
                 }
 
                 let state_ty = this.thir.exprs[state].ty;

tests/ui/feature-gates/feature-gate-loop-match.rs

@@ -1,3 +1,5 @@
+// A #[const_continue] to a labeled loop should error.
+
 enum State {
     A,
     B,

tests/ui/feature-gates/feature-gate-loop-match.stderr

@@ -1,5 +1,5 @@
 error[E0658]: the `#[loop_match]` attribute is an experimental feature
-  --> $DIR/feature-gate-loop-match.rs:9:5
+  --> $DIR/feature-gate-loop-match.rs:11:5
    |
 LL |     #[loop_match]
    |     ^^^^^^^^^^^^^
@@ -9,7 +9,7 @@ LL |     #[loop_match]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: the `#[const_continue]` attribute is an experimental feature
-  --> $DIR/feature-gate-loop-match.rs:14:21
+  --> $DIR/feature-gate-loop-match.rs:16:21
    |
 LL |                     #[const_continue]
    |                     ^^^^^^^^^^^^^^^^^
@@ -19,7 +19,7 @@ LL |                     #[const_continue]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0658]: the `#[const_continue]` attribute is an experimental feature
-  --> $DIR/feature-gate-loop-match.rs:19:21
+  --> $DIR/feature-gate-loop-match.rs:21:21
    |
 LL |                     #[const_continue]
    |                     ^^^^^^^^^^^^^^^^^

tests/ui/loop-match/const-continue-to-block.rs

@@ -1,3 +1,6 @@
+// A #[const_continue] to a normal labeled block (that does is not part of a #[loop_match]) should
+// error.
+
 #![allow(incomplete_features)]
 #![feature(loop_match)]
 #![crate_type = "lib"]

tests/ui/loop-match/const-continue-to-block.stderr

@@ -1,5 +1,5 @@
 error: `#[const_continue]` must break to a labeled block that participates in a `#[loop_match]`
-  --> $DIR/const-continue-to-block.rs:17:27
+  --> $DIR/const-continue-to-block.rs:20:27
    |
 LL |                     break 'b 2;
    |                           ^^

tests/ui/loop-match/invalid-attribute.rs

@@ -1,6 +1,6 @@
 // Checks that #[loop_match] and #[const_continue] attributes can be
 // placed on expressions only.
-//
+
 #![allow(incomplete_features)]
 #![feature(loop_match)]
 #![loop_match] //~ ERROR should be applied to a loop