fix #3505 wrong var {.global.} initialization, asign variable to it (#20812)

* fix #3505 wrong var {.global.} initialization, asign variable to it

* fix #5132 as well

* follow suggestions

* handle all call kinds

* Update tests/global/t3505.nim

* Update compiler/semstmts.nim

* Update compiler/semstmts.nim

* Update compiler/semstmts.nim

* follow suggestion

* Update compiler/semstmts.nim

Co-authored-by: Andreas Rumpf <rumpf_a@web.de>
(cherry picked from commit 1410243d3b)

compiler/semstmts.nim

@@ -36,6 +36,7 @@ const
   errRecursiveDependencyX = "recursive dependency: '$1'"
   errRecursiveDependencyIteratorX = "recursion is not supported in iterators: '$1'"
   errPragmaOnlyInHeaderOfProcX = "pragmas are only allowed in the header of a proc; redefinition of $1"
+  errCannotAssignToGlobal = "cannot assign local to global variable"
 
 proc semDiscard(c: PContext, n: PNode): PNode =
   result = n
@@ -516,6 +517,24 @@ proc errorSymChoiceUseQualifier(c: PContext; n: PNode) =
     inc i
   localError(c.config, n.info, errGenerated, err)
 
+template isLocalVarSym(n: PNode): bool =
+  n.kind == nkSym and 
+    n.sym.kind in {skVar, skLet} and not 
+    ({sfGlobal, sfPure} <= n.sym.flags or
+      sfCompileTime in n.sym.flags)
+  
+proc usesLocalVar(n: PNode): bool =
+  for z in 1 ..< n.len:
+    if n[z].isLocalVarSym:
+      return true
+    elif n[z].kind in nkCallKinds:
+      if usesLocalVar(n[z]):
+        return true
+
+proc globalVarInitCheck(c: PContext, n: PNode) =
+  if n.isLocalVarSym or n.kind in nkCallKinds and usesLocalVar(n):
+    localError(c.config, n.info, errCannotAssignToGlobal)
+
 proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
   if n.len == 1:
     result = semLowerLetVarCustomPragma(c, n[0], n)
@@ -668,7 +687,8 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
         vm.setupCompileTimeVar(c.module, c.idgen, c.graph, x)
       if v.flags * {sfGlobal, sfThread} == {sfGlobal}:
         message(c.config, v.info, hintGlobalVar)
-
+      if {sfGlobal, sfPure} <= v.flags:
+        globalVarInitCheck(c, def)
       suggestSym(c.graph, v.info, v, c.graph.usageSym)
 
 proc semConst(c: PContext, n: PNode): PNode =