Rollup merge of #94143 - est31:let_else_const_eval, r=lcnr

rustc_const_eval: adopt let else in more places

Continuation of #89933, #91018, #91481, #93046, #93590, #94011.

I have extended my clippy lint to also recognize tuple passing and match statements. The diff caused by fixing it is way above 1 thousand lines. Thus, I split it up into multiple pull requests to make reviewing easier. This PR handles rustc_const_eval.

2 files changed, 8 insertions, 14 deletions

diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
index 095c8f84f41..652f1c94a61 100644
--- a/compiler/rustc_const_eval/src/transform/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -134,11 +134,8 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
             .find(|(_, block)| matches!(block.terminator().kind, TerminatorKind::Return))
             .map(|(bb, _)| bb);
 
-        let return_block = match return_block {
-            None => {
-                return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), tainted_by_errors);
-            }
-            Some(bb) => bb,
+        let Some(return_block) = return_block else {
+            return qualifs::in_any_value_of_ty(ccx, ccx.body.return_ty(), tainted_by_errors);
         };
 
         let return_loc = ccx.body.terminator_loc(return_block);
diff --git a/compiler/rustc_const_eval/src/transform/promote_consts.rs b/compiler/rustc_const_eval/src/transform/promote_consts.rs
index cacc0018fe9..30764f689c9 100644
--- a/compiler/rustc_const_eval/src/transform/promote_consts.rs
+++ b/compiler/rustc_const_eval/src/transform/promote_consts.rs
@@ -747,15 +747,12 @@ impl<'a, 'tcx> Promoter<'a, 'tcx> {
         if loc.statement_index < num_stmts {
             let (mut rvalue, source_info) = {
                 let statement = &mut self.source[loc.block].statements[loc.statement_index];
-                let rhs = match statement.kind {
-                    StatementKind::Assign(box (_, ref mut rhs)) => rhs,
-                    _ => {
-                        span_bug!(
-                            statement.source_info.span,
-                            "{:?} is not an assignment",
-                            statement
-                        );
-                    }
+                let StatementKind::Assign(box (_, ref mut rhs)) = statement.kind else {
+                    span_bug!(
+                        statement.source_info.span,
+                        "{:?} is not an assignment",
+                        statement
+                    );
                 };
 
                 (