DefinePlugin / add support for watch mode

[crazyx13th]

Feature request

What is the expected behavior?
For Example: I have a build nr, which increments each "runWatch" hook. But DefinePlugin only define variables at start, not on re-compile.

What is motivation or use case for adding/changing the behavior?
Now you can use a Function as a value (#6749). DefinePlugin only should update value with this defined function.

How should this be implemented in your opinion?
Only update values with the user defined function. Many other Plugins use a function for updates values on re-compile.

Are you willing to work on this yourself?
I will support this as good as I can :-)

[sokra]

The module need to marked as non-cacheable to support this behavior. The DefinePlugin.runtimeValue support a list of dependencies which cause a rebuild of the module. You can send a PR adding the ability to pass true as fileDependencies which flags the module as non-cacheable and reevaulate the expression every-build. This is bad for performance (because module is no longer cached), so avoid using the defined variable in too many modules.

[crazyx13th]

thx!
if someone need's it, here is an example:

this.plugins.push(new webpack.DefinePlugin({
	'app.env': {
		'appVersion': `"${this.settings.appVersion}"`,
		'appHash': `"${this.settings.appHash}"`,
		'buildNr': webpack.DefinePlugin.runtimeValue(() => `"${this.settings.buildNr}"`, []),
		'apiPath': `"${process.env.APP_APIPATH}"`,
		'stage': `"${this.configuration.mode}"`,
	}
}));

[ZuBB]

Thanks @crazyx13th it does work!

[kettanaito]

For anybody wondering, this is how you provide a runtime define variable:

// webpack.config.js
const webpack = require('webpack')

module.exports = {
  plugins: [
    new webpack.DefinePlugin({
      MY_VARIABLE_NAME: webpack.DefinePlugin.runtimeValue(
        () => JSON.stringify('ANY_VALUE'),
        // Passing the second argument as `true` reevaluates the defined expression.
        // Beware that this disables module caching and must be used with caution.
        true,
      ),
    })
  ]
}