fix(plugin-webpack): fix incorrect PRELOAD_WEBPACK_ENTRY.

[tgds]

BrowserWindow preload parameter should be an absolute path. Remove prepending 'file://' from prod
value of PRELOAD_WEBPACK_ENTRY.
Properly escape backslashes in the dev value of PRELOAD_WEBPACK_ENTRY to prevent failure on Windows.

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• [x ] I agree to follow the code of conduct that this project follows, as appropriate.
• [x ] The changes are appropriately documented (if applicable).
• [ x] The changes have sufficient test coverage (if applicable).
• [- ] The testsuite passes successfully on my local machine (if applicable).
  These tests are failing, but are unrelated:

1) electron-forge API (with installer=yarn)
       after init
         after package
           make
             throws an error when the specified maker doesn't support the current platform:
     AssertionError: expected promise to be rejected with an error matching /the maker declared that it cannot run/ but got 'Could not find module with name: /Users/tom/code/electron-forge/packages/api/core/test/fixture/maker-unsupported'

  2) electron-forge API (with installer=yarn)
       after init
         after package
           make
             throws an error when the specified maker doesn't implement isSupportedOnCurrentPlatform():
     AssertionError: expected promise to be rejected with an error matching /incompatible with this version/ but got 'Could not find module with name: /Users/tom/code/electron-forge/packages/api/core/test/fixture/maker-incompatible'

  3) rebuilder
       no config
         "before all" hook:
     Error: Exited with status 1

  4) rebuilder
       with config
         "before all" hook:
     Error: Exited with status 1

[malept]

Thanks, can you add a test for this?

[malept]

Why doesn't this part of the ternary expression need the escaping logic?

[tgds]

It doesn't need it, because the result is an expression. (Keep in mind, the webpackDefine plugin does not define the variable, it just replaces MAIN_WINDOW_PRELOAD_WEBPACK_ENTRY in the source with whatever string it's given)

In production

{
  preload: MAIN_WINDOW_PRELOAD_WEBPACK_ENTRY
}

will get transformed to

{
  preload: require('path').resolve(__dirname, '../renderer', 'MAIN_WINDOW', 'preload.js')
}

Whereas in development, the result is a string and needs to get properly escaped since

MAIN_WINDOW_PRELOAD_WEBPACK_ENTRY = `'${path.resolve(this.baseDir, 'renderer', entryPoint.name, 'preload.js')}'`

results in

{
  preload: '\basedir\renderer\main\preload.js'
}

However, it has to be

{
  preload: '\\basedir\\renderer\\main\\preload.js'
}

[tgds]

Sure, I'll try. A unit test, or E2E and actually spawn electron browserWindow with preload?

[malept]

A unit test, please.

[tgds]

@malept, a test added

[tgds]

Sorry, rebased and squashed, because I used my company email address by mistake in the original commit

[malept]

Perhaps use String.raw() anywhere where there's a string literal with backslashes.

Other than that, I defer to @MarshallOfSound.

[tgds]

@MarshallOfSound, any chance to merge this soon, please, as this bug is blocking the use of preload scripts on Windows?