Crossreferenced GHC 8.0.2

[Robin Palotai]

Hello Matthew,

Please see inline

2017-06-30 11:57 GMT+02:00 Matthew Pickering <matthewtpickering at gmail.com>:

> Hi Robin,
>
> This looks really useful for developers.
>
> 1. Would it be possible to provide a script which allows developers to
> build this index for themselves easily?
>

First, build and install the `ghc_kythe_wrapper` (instructions at
https://github.com/google/haskell-indexer).

Then build GHC with `make`, and capture the build log. Here's the hacky
script I used:
https://gist.github.com/robinp/222cf3a39cc19178ec8691522056d7fe

It filters the log and replaces GHC calls to call the wrapper, which emits
Kythe entries.

Finally run `serve.sh` of the repo to postprocess and serve the entries
through HTTP.

This is all pretty new, so feedback or questions welcome. If the method
distills, could try to write a more formal guide.


> 2. Is it possible to use this tool to detect dead code? Functions
> which are not used anywhere in the compiler.
>

We'll get there eventually, but for now the emitted data is not
fine-grained enough. The main missing piece is recording what are exported
entities of a module (Kythe schema discussion in progress). Without this,
unused locals (which anyway surface with -Wall) would be presented and
noisy.

Also, one would probably need to postprocess the data a bit for this, like
loading into a graph database or other ways.

Did you see https://github.com/ndmitchell/weeder by the way? Might work.


> 3. How are you pretty printing the output whilst retaining the source
> formatting? I had a quick look at the source but I couldn't see where
> the output was being produced.
>
>
The haskell-indexer-frontend-kythe emits Kythe (http://kythe.io) schema
data. We just export the source offsets, and it's the Kythe postprocessing
/ serving pipeline that does all the formatting.


> Cheers,
>
> Matt
>
> On Fri, Jun 30, 2017 at 8:55 AM, Robin Palotai <palotai.robin at gmail.com>
> wrote:
> > Hello GHC devs,
> >
> > I ran haskell-indexer [1] on the GHC 8.0.2 tarball, partly because I find
> > myself reading GHC source from time to time while working on the indexer,
> > and partly since it's fun.
> >
> > First, here you can click around [2] and find where beloved functions are
> > called from:
> > http://stuff.codereview.me/#ghc/compiler/hsSyn/HsBinds.hs?
> corpus&signature
> > (scroll down a bit, imports are not linked yet).
> >
> > Second, the way I indexed was pretty simple. I took the output of `make`,
> > replaced the ghc used with the ghc_kythe_wrapper, and filtered the lines
> > which included '-c', since I noticed that those duplicate previous large
> > compile lines. This only indexes the stage1 compilation AFAIU.
> >
> > Feel free to suggest a better way to tap into the compilations to get
> > everything properly indexed (and possibly only once).
> >
> > Any comments welcome!
> > Robin
> >
> > [1]: https://github.com/google/haskell-indexer
> >
> > [2]: TLDR UI quirks:
> >   - Click the :: in top-left to navigate file tree
> >   - Ctrl-Click (on linux) to go directly to definition (otherwise click
> > stuff from bottom pane)
> >   - Bottom pane often hides content, close it if stuck.
> >
> > _______________________________________________
> > ghc-devs mailing list
> > ghc-devs at haskell.org
> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
> >
>
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