Fix defer not not-working at top level (#10191)

compiler/sem.nim

@@ -556,8 +556,6 @@ proc isEmptyTree(n: PNode): bool =
   else: result = false
 
 proc semStmtAndGenerateGenerics(c: PContext, n: PNode): PNode =
-  if n.kind == nkDefer:
-    localError(c.config, n.info, "defer statement not supported at top level")
   if c.topStmts == 0 and not isImportSystemStmt(c.graph, n):
     if sfSystemModule notin c.module.flags and not isEmptyTree(n):
       c.importTable.addSym c.graph.systemModule # import the "System" identifier

compiler/semexprs.nim

@@ -2624,6 +2624,8 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   of nkStaticStmt:
     result = semStaticStmt(c, n)
   of nkDefer:
+    if c.currentScope == c.topLevelScope:
+      localError(c.config, n.info, "defer statement not supported at top level")
     n.sons[0] = semExpr(c, n.sons[0])
     if not n.sons[0].typ.isEmptyType and not implicitlyDiscardable(n.sons[0]):
       localError(c.config, n.info, "'defer' takes a 'void' expression")

tests/async/tasyncfilewrite.nim

@@ -9,7 +9,6 @@ import os, asyncfile, asyncdispatch
 const F = "test_async.txt"
 
 removeFile(F)
-defer: removeFile(F)
 let f = openAsync(F, fmWrite)
 var futs = newSeq[Future[void]]()
 for i in 1..3:
@@ -17,4 +16,4 @@ for i in 1..3:
 waitFor(all(futs))
 f.close()
 echo readFile(F)
-
+removeFile(F)

tests/exception/tdefer1.nim

@@ -1,6 +1,5 @@
 discard """
   output: '''hi
-hi
 1
 hi
 2
@@ -10,13 +9,6 @@ A'''
 
 # bug #1742
 
-template test(): untyped =
-    let a = 0
-    defer: echo "hi"
-    a
-
-let i = test()
-
 import strutils
 let x = try: parseInt("133a")
         except: -1
@@ -31,7 +23,7 @@ template atFuncEnd =
 
 template testB(): untyped =
     let a = 0
-    defer: echo "hi" # Delete this line to make it work
+    defer: echo "hi"
     a
 
 proc main =