Repository: d5/tengo (go)

Issue:
bug + panic in  for-loop (for k,v in dict syntax)
Bug: the key `k` is not visible inside the func `f` in the loop ( therefore: `Runtime Error: invalid index type: undefined`)
```
fmt := import(`fmt`)
bug := func(){
    map := {a:1.0,b:2.0}
    for k,v in map{
        f := func(){
            fmt.println(map[k])
        }
        f()
    }
}
bug()
```
While this is a proper workaround:
```
fmt := import(`fmt`)
workaround := func(){
    map := {a:1.0,b:2.0}
    for k,v in map{
        key := k
        f := func(){
            fmt.println(map[key])
        }
        f()
    }
}
workaround()
```

This segfaults:
```
fmt := import(`fmt`)

segfault := func(){
    map := {a:1.0,b:2.0}
    for k,v in map{
        k := k
        f := func(){
            fmt.println(map[k])
        }
        f()
    }
}
segfault()
```
```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x68 pc=0x529f12]

goroutine 1 [running]:
github.com/d5/tengo/v2.ToString(0x0, 0x0, 0xc00001a477, 0x7, 0xc0000c62e8)
    /go/src/github.com/d5/tegno/tengo.go:71 +0x62
github.com/d5/tengo/v2.(*Map).IndexGet(0xc00000e758, 0x0, 0x0, 0x63d5e0, 0xc0000da150, 0x0, 0x0)
    /go/src/github.com/d5/tegno/objects.go:1239 +0x39
github.com/d5/tengo/v2.(*VM).run(0xc0000f0000)
    /go/src/github.com/d5/tegno/vm.go:352 +0x394f
github.com/d5/tengo/v2.(*VM).Run(0xc0000f0000, 0xc0000f0000, 0x400)
    /go/src/github.com/d5/tegno/vm.go:77 +0xcf
main.CompileAndRun(0xc00000e6c0, 0xc0000ce000, 0xc4, 0x2c4, 0x7ffccbe0b94a, 0x29, 0x0, 0xc000062180)
    /go/src/github.com/d5/tegno/cmd/tengo/main.go:134 +0x1e8
main.main()
    /go/src/github.com/d5/tegno/cmd/tengo/main.go:73 +0x28b
```


Pull request description:
fix for in loop symbols
Closes #288 

Patch:
diff --git a/compiler.go b/compiler.go
index 1e2a494..757a810 100644
--- a/compiler.go
+++ b/compiler.go
@@ -847,8 +847,8 @@ func (c *Compiler) compileForInStmt(stmt *parser.ForInStmt) error {
 	//     ... body ...
 	//   }
 	//
-	// ":it" is a local variable but will be conflict with other user variables
-	// because character ":" is not allowed.
+	// ":it" is a local variable but it will not conflict with other user variables
+	// because character ":" is not allowed in the variable names.
 
 	// init
 	//   :it = iterator(iterable)
@@ -893,6 +893,7 @@ func (c *Compiler) compileForInStmt(stmt *parser.ForInStmt) error {
 		if keySymbol.Scope == ScopeGlobal {
 			c.emit(stmt, parser.OpSetGlobal, keySymbol.Index)
 		} else {
+			keySymbol.LocalAssigned = true
 			c.emit(stmt, parser.OpDefineLocal, keySymbol.Index)
 		}
 	}
@@ -909,6 +910,7 @@ func (c *Compiler) compileForInStmt(stmt *parser.ForInStmt) error {
 		if valueSymbol.Scope == ScopeGlobal {
 			c.emit(stmt, parser.OpSetGlobal, valueSymbol.Index)
 		} else {
+			valueSymbol.LocalAssigned = true
 			c.emit(stmt, parser.OpDefineLocal, valueSymbol.Index)
 		}
 	}


Test patch:
diff --git a/vm_test.go b/vm_test.go
index 4ffaed7..d451726 100644
--- a/vm_test.go
+++ b/vm_test.go
@@ -1531,7 +1531,23 @@ func TestFunction(t *testing.T) {
 		add2 := newAdder(2);
 		out = add2(5);
 		`, nil, 7)
+	expectRun(t, `
+		m := {a: 1}
+		for k,v in m {
+			func(){
+				out = k
+			}()
+		}
+		`, nil, "a")
 
+	expectRun(t, `
+		m := {a: 1}
+		for k,v in m {
+			func(){
+				out = v
+			}()
+		}
+		`, nil, 1)
 	// function as a argument
 	expectRun(t, `
 	add := func(a, b) { return a + b };