EPUB: improve SVG image output, closes #2766

[mb21]

This is not ready to merge yet...

Can we use System.Directory.doesFileExist instead of P.fetchItem somehow? Also, fetchItem appears to make pandoc fail if the file is not found even though I'm checking for :: PandocError (which I copied from the ICML writer).

[jgm]

+++ Mauro Bieg [Jan 30 17 02:33 ]:

This is not ready to merge yet... Can we use System.Directory.doesFileExist instead of P.fetchItem somehow?

Since you're in PandocMonad you can only use things defined there. Of course, if it turns out we need something like doesFileExist there we could consider adding a function like that...

Also, fetchItem appears to make pandoc fail if the file is not found even though I'm checking for :: PandocError (which I copied from the ICML writer).

Is it failing with a PandocError?

[mb21]

Since you're in PandocMonad you can only use things defined there.

That's what I figured...

Of course, if it turns out we need something like doesFileExist there we could consider adding a function like that...

I'm not sure how smart the lazy evaluation of fetchItem is. But I suspect it will read the whole file into memory. So it feels cleaner to add a doesFileExist. Or should it be doesItemExist and try to fetch remote resources as well?

Is it failing with a PandocError?

I think it was, yes. Probably a PandocFileReadError (it was outputting problem reading media) The code that caused it was:

runExceptT $ lift $ P.fetchItem (writerSourceURL opts) src

I have now changed it to using catchError (do _ <- P.fetchItem ... but this seems somewhat of a hack... shouldn't the runExceptT change the exception to an either which can then be handled explicitly?

[jgm]

If we end up merging some form of #2211, then we could simply generate the png fallback from the svg and we wouldn't need to check for its existence...

[mb21]

Good point. Instead, we could also use rasterific in a filter that does the necessary transformations on all referenced SVG images. (Depending on the output format it would fallback to png or pdf.) Then again, from a user perspective it's always nice to have more stuff built in.

[mb21]

This doesn't seem to be the right approach anymore. See e.g. #4058 (comment)