fixes #9839; fixes noReturn pragma doesn't work for non-simple templates (#21048)

compiler/semstmts.nim

@@ -2447,9 +2447,12 @@ proc semStmtList(c: PContext, n: PNode, flags: TExprFlags, expectedType: PType =
     else:
       n.typ = n[i].typ
       if not isEmptyType(n.typ): n.transitionSonsKind(nkStmtListExpr)
-    if n[i].kind in nkLastBlockStmts or
+    var m = n[i]
-        n[i].kind in nkCallKinds and n[i][0].kind == nkSym and
+    while m.kind in {nkStmtListExpr, nkStmtList} and m.len > 0: # from templates
-        sfNoReturn in n[i][0].sym.flags:
+      m = m.lastSon
+    if m.kind in nkLastBlockStmts or
+        m.kind in nkCallKinds and m[0].kind == nkSym and
+        sfNoReturn in m[0].sym.flags:
       for j in i + 1..<n.len:
         case n[j].kind
         of nkPragma, nkCommentStmt, nkNilLit, nkEmpty, nkState: discard

tests/controlflow/tunreachable.nim

@@ -0,0 +1,32 @@
+discard """
+  cmd: "nim check --warningAsError:UnreachableCode $file"
+  action: "reject"
+  nimout: '''
+tunreachable.nim(23, 3) Error: unreachable code after 'return' statement or '{.noReturn.}' proc [UnreachableCode]
+tunreachable.nim(30, 3) Error: unreachable code after 'return' statement or '{.noReturn.}' proc [UnreachableCode]
+'''
+"""
+  
+# bug #9839
+template myquit1():untyped=
+  ## foo
+  quit(1)
+template myquit2():untyped=
+  echo 123
+  myquit1()
+
+proc main1()=
+
+  # BUG: uncommenting this doesn't give `Error: unreachable statement`
+  myquit2()
+
+  echo "after"
+
+main1()
+
+proc main2() =
+  myquit1()
+
+  echo "after"
+
+main2()