Handle asset source being a buffer, not a string

[praxxis]

I am still trying to track down why this happens, but when doing a production build source() returns a Buffer instead of a string. It seems to be fine in development, so my intuition is that it's minification related, but I haven't been able to isolate exactly which option. Changing mode, disabling the Uglify plugin - nothing seems to alter how this works in a production build.

Example in production build (output of typeof compilation.assets[manifestPath].source()):

type of source: object

vs dev

type of source: string

[almothafar]

Thanks for this PR, for webpack 3 I see this is working correctly, so I'm not sure what this should fix, also in most webpack plugins that I saw and that is working with webpack 4, there are no problems that need this change, may you please provide me with any source that I can see the problem and the resolution? or at least a similar issue that fixed in this way on another plugin.

[praxxis]

I've tracked this down to imagemin-webpack-plugin. I have an example repo up at https://github.com/praxxis/manifest-plugin-bug that shows the problem. From my debugging it seems that including the imagemin plugin turns source assets into RawSource instances, instead of CachedSource or SourceMapSource. RawSource.source() doesn't seem to produce the same output, hence .replace() not being valid.

[praxxis]

webpack/webpack-sources#26 looks like a similar bug, and it points to Webpack's implementation being inconsistent

[praxxis]

a workaround for anyone else hitting this: change the test option of imagemin to only include image types

[almothafar]

I think extra .toString() does not hurt even if no issues here, but still I don't see it is necessary to merge this if it is another plugin issues, as you said it is imagemin and there is a workaround for it.

Also, Object.toString() will get the output like "[object Object]", isn't right?

Anyways, I really not have that much experience of webpack plugins development, I will look into your repo and try to figure out what the problem.