Stack overflow when calling toString on cyclic values

[folkertdev]

Someone ran into this in the elm slack channel.

Trying to print a Json.Decode.Value object that is generated by Html.Events' on function results
in a RangeError, originating in the addSlashes function (called by toString).

The weird thing is that when a Json.Value value
is generated with decoders in elm, everything works fine. #539 seems to suggest that the problem is with values that are generated by native modules. Here is an example that gives a RangeError on
elm-lang.org/try (in Chrome, v50 on linux mint)

import Html exposing (div, input)
import Html.App exposing (beginnerProgram)
import Html.Events exposing (onClick, on)

import Json.Decode as Json exposing (..)

import Debug

test : Json.Value
test =
    case Json.decodeString Json.value "{\"a\":\"1\"}" of 
        Ok v -> v
        Err e -> Debug.crash e


main =
  beginnerProgram { model = 0, view = view, update = update }


view model =
  div []
    [ input [ on "focus" (Json.map ValueMsg Json.value) ] []  
    ]


type Msg = ValueMsg Json.Value


update msg model =
  case msg of

    ValueMsg val -> 
        -- works just fine
        --Debug.log (toString test) model
        -- RangeError
        Debug.log (toString val) model

      -- RangeError: Maximum call stack size exceeded[Symbol.replace] @ 
        -- in the function addSlashes

[jinjor]

I ran into the same problem when I tried Debug.log on a Json.Value object which includes AudioNode.

The infinite loop is occurring at here in Native/Utils.js.

function toString(v)
{

        ...

        if (type === 'object')
            {
                var output = [];
                for (var k in v)
                {
                    output.push(k + ' = ' + toString(v[k])); // this is called many times
                }

This is caused by circular reference. AudioContext.destination returns AudioDestinationNode and AudioDestinationNode.context returns AudioContext.destination.

[jinjor]

I ran into the same problem when I tried Debug.log on a Json.Value object which includes AudioNode.

The infinite loop is occurring at here in Native/Utils.js.

function toString(v)
{

        ...

        if (type === 'object')
            {
                var output = [];
                for (var k in v)
                {
                    output.push(k + ' = ' + toString(v[k])); // this is called many times
                }

This is caused by circular reference. AudioContext.destination returns AudioDestinationNode and AudioDestinationNode.context returns AudioContext.destination.

[lukewestby]

@folkertdev could you rename this to something like "Stack overflow when calling toString on cyclic values"?

[lukewestby]

@folkertdev could you rename this to something like "Stack overflow when calling toString on cyclic values"?

[evancz]

Follow along in the #723 meta issue.

[evancz]

Follow along in the #723 meta issue.