support Rollup [hash] placeholder

[alexdilley]

Breaking change

Utilize emitFile({ type: 'asset' }) plugin context utility function to allow extracted file to respect Rollup's assetFileNames name pattern, and thus support unique/cache-busting file naming based on the content of the asset.

Requires users who specify the plugin option, extract: true (explicit string paths are unaffected), to configure Rollup's output.assetFileNames setting (to '[name][extname]'), since this defaults to placing the generated .css/.css.map files under an assets directory relative to output.dir (as well as adding the [hash] placeholder to the file name), which hence doesn't mirror present functionality.

[codecov[bot]]

Codecov Report

Merging #226 into master will increase coverage by 0.02%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #226      +/-   ##
==========================================
+ Coverage   91.69%   91.72%   +0.02%     
==========================================
  Files           9        9              
  Lines         289      290       +1     
  Branches      100       98       -2     
==========================================
+ Hits          265      266       +1     
  Misses         24       24

Impacted Files	Coverage Δ
src/index.js	96.34% <100%> (+0.04%)	:arrow_up:

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[dagda1]

It would be really great to have hashing behaviour. I'd love to know why it was not progressed to live

[pspeter3]

+1! Can we add support for this?

[benmccann]

I haven't tested the latest code in master, but is this PR still necessary? I see additional usage of emitFile in master now, so perhaps this has already been implemented?

https://github.com/egoist/rollup-plugin-postcss/blob/ceee1bc87d91d6c2692e2f44ae2753fa83a0b535/src/index.js#L244