file_scope is now correctly merged when creating output_format

[atusy]

Currently, new output format ignores the file scope of the base format.
It is totally lost.

In this PR I fix the above behavior and add merge_file_scope().

To achieve merging, file_scope function needs two arguments, and the latter is new

• input_files which already exists
• current_file_scope which is determined by the base file_scope function

In this way, overlay can take into account of file scope determined by the base.

This is an API change, so I added some warnings and fallback mechanisms.

[atusy]

Note that I noticed this when adding tests on #2462, which should be able to extend file_scope from within chunks.

[yihui]

Looks good to me. Thanks!

[cderv]

Sorry for the delay on this @atusy.

it looks good to me. I think it won't break current behavior. Only place that we use it in in bookdown. It is even deactivated by default, and could be completely broken in fact ... :(

I am just curious: do we have a use case where we think merging file_scope requires applying overlay on base results ?

To me this would mean that we want to define a format that would for example extend gitbook() but would split again each of the splitted file, instead of providing an overwrite of the split function. Is that right ?

Just trying to understand correctly. I guess someone can do a function that ignores current_scope to completely ignore the base splitted content.

I was thinking maybe the latter would be the desired behavior when extending the base format. So I was curious if this change was driven by a use case. Thanks.

Other than this question I have, the implementation looks very good ! thanks a lot !

[CLAassistant]

All committers have signed the CLA.

[cderv]

In fact it is all good. Both usage can be done. Let's go with this default. Thanks a lot !

[atusy]

Actually I'm not sure if there would be any practical usecases...

One exception is test.
We can easily wrap testing output format and test if file_scope is working as expected.

test_that("file_scope replaces base format", {
  out_fmt <- output_format(
    knitr = NULL, pandoc = NULL, keep_md = NULL, clean_supporting = NULL,
    file_scope = function(input_file, file_scope, ...) {
      # do some tests here!
      testthat::expect_snapshot(cat(file_scope))
      return(file_scope)
    },
    base_format = bookdown::git_book
  )
  rmarkdown::render("example.Rmd", output_format = out_fmt)
})

[cderv]

Good use case ! I had not thought of that 😆