Component ignores "i" and "s" props in debug mode

[michaelkryukov]

Do you want to request a feature or report a bug?
bug

What is the current behaviour?
Preact pops i and s from props, confusing them with __source and __self.

If the current behaviour is a bug, please provide the steps to reproduce.
Example application: https://codesandbox.io/s/focused-yalow-fiqpy.

I used the debugger to follow execution and got to part:

  preact__WEBPACK_IMPORTED_MODULE_0__["options"].vnode = function (e) {
    var n, t;
    e.props && e.props.i && (n = e.props.i, delete e.props.i), e.props && e.props.s && (t = e.props.s, delete e.props.s), e.s = t, e.i = n, Object.defineProperties(e, l), o && o(e);
  }, preact__WEBPACK_IMPORTED_MODULE_0__["options"].diffed = function (e) {
// ...

Here line e.props && e.props.i && (n = e.props.i, delete e.props.i), e.props && e.props.s && (t = e.props.s, delete e.props.s), e.s = t, e.i = n, Object.defineProperties(e, l), o && o(e); "pops" i and s from props and rewrites it to the component.

I checked sources from npm:

wget $(npm view preact@next dist.tarball)
tar -xvzf preact-10.0.0-rc.3.tgz
cat package/debug/dist/debug.js | grep "e.props&&e.props.i&&(n=e.props.i,delete e.props.i)"; echo $? 

You will see 0, as grep will find troubling part.

What is the expected behaviour?
Props __self and __source should not be mangled to i and s.

Please mention other relevant information.
I noticed this problem, while trying to use https://github.com/STRML/react-grid-layout, which uses a prop with the name "i". I was getting strange errors about missing required props.

Seems like this issue was present in all 10.0.0 versions, but for different prop names.

$ preact info

Environment Info:

  System:
    OS: Linux 5.0 Ubuntu 19.04 (Disco Dingo)
    CPU: (4) x64 Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz
  Binaries:
    Node: 12.10.0 - /usr/bin/node
    Yarn: 1.19.0 - /usr/bin/yarn
    npm: 6.11.3 - /usr/bin/npm
  Browsers:
    Chrome: 77.0.3865.90
    Firefox: 66.0.3
  npmGlobalPackages:
    preact-cli: 3.0.0-rc.5

[JoviDeCroock]

Hey, thank you so much for this issue report. The research has made it easy for me to file the appropriate fix and is now in pull request. Thank you for the effort!