Regression: `Object.fromFoldable` causes stack overflow in Google Chrome

[gasi]

First of all, thanks for all your work on keeping the PureScript ecosystem up and running!

---

We recently upgraded from PS 0.11 to 0.12 and ran into the following regression Foreign.Object.fromFoldable (vs the old Data.StrMap.fromFoldable) causes a stack overflow for large inputs in Google Chrome (Safari and FF seemed to have higher limits):

❌ Repro: PureScript 0.12

module Main where

import Prelude

import Effect (Effect)
import Effect.Console (log)
import Data.Array ((..))
import Data.Tuple (Tuple(..))
import Foreign.Object as Object

main :: Effect Unit
main = do
  let m = Object.fromFoldable $ do
            x <- 1 .. 10000
            pure $ Tuple (show x) x
  log $ show m

Error

foreign.js:22 Uncaught RangeError: Maximum call stack size exceeded
    at foreign.js:22
    at foreign.js:6
    at foreign.js:20
    at foreign.js:20
    at foreign.js:20
    at foreign.js:20
    at foreign.js:20
    at foreign.js:20
    at foreign.js:20
    at foreign.js:20

✅ PureScript 0.11

Paste this into Try PureScript and observe that there is no stack overflow:

module Main where

import Prelude

import Control.Monad.Eff (Eff)
import Data.Array ((..))
import Data.Tuple (Tuple(..))
import Data.Foldable (fold)
import TryPureScript (DOM, h1, h2, p, text, list, indent, link, render, code)
import Data.StrMap as SM

main :: Eff (dom :: DOM) Unit
main = do
    let m = SM.fromFoldable $ do
              x <- 1 .. 10000
              pure $ Tuple (show x) x
    render $ fold
      [ p (text $ show m) ]

Observations

Superficially the two implementations look the same except the addition of Array.fromFoldable, but I confirmed removing it doesn’t change the outcome:

• PS 0.11: https://github.com/purescript-deprecated/purescript-maps/blob/c1a826b13ae681f523dcd0f93c5ee422b1e49072/src/Data/StrMap.purs#L195-L200
• PS 0.12:

  purescript-foreign-object/src/Foreign/Object.purs

  Lines 212 to 217 in 6c5c386

  	-- | Create a map from a foldable collection of key/value pairs
  	fromFoldable :: forall f a. Foldable f => f (Tuple String a) -> Object a
  	fromFoldable l = runST do
  	s <- OST.new
  	for_ (A.fromFoldable l) \(Tuple k v) -> OST.poke k v s
  	pure s

[justinwoo]

Related afaict purescript/purescript#3100

[natefaubion]

for_ is never stack safe with ST/Effect, but it was probably consuming less stack before with ST optimizations.