Fixes #17849 (#18055) [backport:1.2]

* Fixes #17849
* Update compiler/closureiters.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
(cherry picked from commit a6bd6c7ed8)

compiler/closureiters.nim

@@ -604,6 +604,12 @@ proc lowerStmtListExprs(ctx: var Ctx, n: PNode, needsSplit: var bool): PNode =
             internalError(ctx.g.config, "lowerStmtListExpr(nkCaseStmt): " & $branch.kind)
         result.add(n)
         result.add(ctx.newEnvVarAccess(tmp))
+      elif n[0].kind == nkStmtListExpr:
+        result = newNodeI(nkStmtList, n.info)
+        let (st, ex) = exprToStmtList(n[0])
+        result.add(st)
+        n[0] = ex
+        result.add(n)
 
   of nkCallKinds, nkChckRange, nkChckRangeF, nkChckRange64:
     var ns = false

tests/iter/tyieldintry.nim

@@ -483,5 +483,19 @@ block: # nnkChckRange
 
   test(it, 1, 2, 3)
 
-echo "ok"
+block: #17849 - yield in case subject
+  template yieldInCase: int =
+    yield 2
+    3
 
+  iterator it(): int {.closure.} =
+    yield 1
+    case yieldInCase()
+    of 1: checkpoint(11)
+    of 3: checkpoint(13)
+    else: checkpoint(14)
+    yield 5
+
+  test(it, 1, 2, 13, 5)
+
+echo "ok"