typeck: remove redundant diverges code

src/librustc_typeck/check/_match.rs

@@ -53,25 +53,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // Otherwise, we have to union together the types that the arms produce and so forth.
         let scrut_diverges = self.diverges.replace(Diverges::Maybe);
 
-        // rust-lang/rust#55810: Typecheck patterns first (via eager
-        // collection into `Vec`), so we get types for all bindings.
-        let all_arm_pats_diverge: Vec<_> = arms
-            .iter()
-            .map(|arm| {
-                let mut all_pats_diverge = Diverges::WarnedAlways;
-                self.diverges.set(Diverges::Maybe);
-                self.check_pat_top(&arm.pat, scrut_ty, Some(scrut.span), true);
-                all_pats_diverge &= self.diverges.get();
-
-                // As discussed with @eddyb, this is for disabling unreachable_code
-                // warnings on patterns (they're now subsumed by unreachable_patterns
-                // warnings).
-                match all_pats_diverge {
-                    Diverges::Maybe => Diverges::Maybe,
-                    Diverges::Always { .. } | Diverges::WarnedAlways => Diverges::WarnedAlways,
-                }
-            })
-            .collect();
+        // #55810: Type check patterns first so we get types for all bindings.
+        for arm in arms {
+            self.check_pat_top(&arm.pat, scrut_ty, Some(scrut.span), true);
+        }
 
         // Now typecheck the blocks.
         //
@@ -102,19 +87,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             CoerceMany::with_coercion_sites(coerce_first, arms)
         };
 
-        let mut other_arms = vec![]; // used only for diagnostics
+        let mut other_arms = vec![]; // Used only for diagnostics.
         let mut prior_arm_ty = None;
-        for (i, (arm, pats_diverge)) in arms.iter().zip(all_arm_pats_diverge).enumerate() {
+        for (i, arm) in arms.iter().enumerate() {
             if let Some(g) = &arm.guard {
-                self.diverges.set(pats_diverge);
+                self.diverges.set(Diverges::Maybe);
                 match g {
                     hir::Guard::If(e) => {
                         self.check_expr_has_type_or_error(e, tcx.types.bool, |_| {})
                     }
                 };
             }
 
-            self.diverges.set(pats_diverge);
+            self.diverges.set(Diverges::Maybe);
             let arm_ty = if source_if
                 && if_no_else
                 && i != 0