Allow passing Electron launch CLI flags

[bahmutov]

Currently we allow passing Chrome browser CLI switches via https://on.cypress.io/browser-launch-api The user specifies these flags in the plugins file.

We should allow passing Electron CLI flags, but because we launch Electron FIRST way before the plugins file gets processed, then we need to somehow pipe it through CLI to the https://github.com/cypress-io/cypress/blob/develop/packages/server/lib/environment.coffee

Probable an environment variable would be ok to achieve this

ELECTRON_EXTRA_LAUNCH_ARGS=disable-dev-shm-usage 

that would be equivalent to running chrome --disable-dev-shm-usage

Note: only some Chrome CLI switches are supported though, see Electron Documentation Supported Chrome Command Line Switches

The parsed args will be fed to https://electronjs.org/docs/api/command-line#commandlineappendswitchswitch-value so we need to support both presence and value flags like

ELECTRON_EXTRA_LAUNCH_ARGS=foo bar=baz disable-renderer-backgrounding=true

that would be like (note that boolean flag "true" has been converted)

const { app } = require('electron')
app.commandLine.appendSwitch('foo')
app.commandLine.appendSwitch('bar', 'baz')
app.commandLine.appendSwitch('disable-renderer-backgrounding', true)

Related issues

• Make sending browser flags to the electron browser more intuitive #1519 (probably can mark as duplicate and close by same PR)

Related links

• Electron Documentation Supported Chrome Command Line Switches

[cypress-bot]

The code for this is done in cypress-io/cypress#5891, but has yet to be released.
We'll update this issue and reference the changelog when it's released.

[cypress-bot]

Released in 3.8.0.