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stack new is very slow at compiling Mustache templates #4133

snoyberg opened this Issue Jul 5, 2018 · 3 comments


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snoyberg commented Jul 5, 2018


  • Install a recent HEAD version of Stack. I'm using d5b5f77
  • Run stack new foo yesodweb/simple

Expect: it will generate the output in under 5 seconds

Actual: it takes a full minute to compile the Mustache template

I'm guessing the move over to mustache from hastache triggered this. The Yesod templates may be an extreme case because they include large base64-encoded binary blobs for images. I'll try applying the templates to one file at a time instead and see if it speeds things up.

CC @borsboom @JustusAdam

@snoyberg snoyberg added this to the P0: Blocking release milestone Jul 5, 2018

@snoyberg snoyberg self-assigned this Jul 5, 2018


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snoyberg commented Jul 5, 2018

I've determined that this can be triggered by trying to compile the bootstrap.css file, which weighs in at 149kb. Proposed workaround: I'm going to add an arbitrary limit to Stack.New to only apply mustache to files smaller than 50kb.


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JustusAdam commented Jul 5, 2018

Hmm ... I wouldn't be surprised if that's the parser. Perhaps someone with more experience in writing parsers can take a look at it?

mihaimaruseac added a commit that referenced this issue Jul 8, 2018

Merge pull request #4134 from commercialhaskell/4133-slow-stack-new
Do not apply Mustache to large files (fixes #4133)

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snoyberg commented Jul 9, 2018

@JustusAdam I'd love to do so, but unfortunately I likely won't have time for that in the next few weeks at least, I've got a bunch of major things on my plate I'm going to have to focus on, sorry.

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