jule: make error variable isolated from mutation and sharing

Author: mertcandav

std/jule/sema/eval.jule

@@ -3920,6 +3920,15 @@ impl unaryEval {
 		|:
 			match {
 			| canGetPtr(self.v):
+				// If the value is error, complain.
+				var, _ := self.v.Model.(&Var)
+				if var != nil && var.Name == "error" {
+					self.e.pushErr(self.u.X.Token, "cannot take pointer of the error value")
+					self.e.pushSuggestion("use an intermediary variable: myerr := error; &myerr")
+					self.v.Decl = true
+					ret
+				}
+
 				self.v.Type = &Type{
 					Kind: &Ptr{Value: self.v.Type},
 				}

std/jule/sema/scope.jule

@@ -2834,6 +2834,13 @@ fn checkAssign(mut s: &sema, mut left: &Value, mut right: &Value, op: &token::To
 		ret false
 	}
 
+	// If the value is error, complain.
+	var, _ := left.Model.(&Var)
+	if var != nil && var.Name == "error" {
+		s.pushErr(op, "cannot assign to the error value")
+		ret false
+	}
+
 	f := left.Type.Func()
 	if f != nil && f.Decl != nil && f.Decl.Global {
 		// Make sure function is indeed a global function.