fix #12274 (#19180)

compiler/parser.nim

@@ -1146,7 +1146,7 @@ proc isExprStart(p: Parser): bool =
   of tkSymbol, tkAccent, tkOpr, tkNot, tkNil, tkCast, tkIf, tkFor,
      tkProc, tkFunc, tkIterator, tkBind, tkBuiltInMagics,
      tkParLe, tkBracketLe, tkCurlyLe, tkIntLit..tkCustomLit, tkVar, tkRef, tkPtr,
-     tkTuple, tkObject, tkWhen, tkCase, tkOut:
+     tkTuple, tkObject, tkWhen, tkCase, tkOut, tkTry, tkBlock:
     result = true
   else: result = false
 

tests/parser/t12274.nim

@@ -0,0 +1,9 @@
+var s: seq[int]
+s.add block:
+  let i = 1
+  i
+s.add try:
+  2
+except:
+  3
+doAssert s == @[1, 2]