Workshop Overview Pages (without episodes) should be allowed

[zkamvar]

We have a situation where we have workshop overview pages for datacarpentry and library carpentry (e.g. https://datacarpentry.org/genomics-workshop/) that do not have any episodes.

Reprex

pegboard::get_lesson("datacarpentry/genomics-workshop")
#> Loading required namespace: gert
#> Error: The _episodes/ directory must have (R)markdown files

^{Created on 2023-08-08 with reprex v2.0.2}

Note: this works for one workshop overview page because it has episodes:

pegboard::get_lesson("LibraryCarpentry/lc-overview")
#> Loading required namespace: gert
#> <Lesson>
#>   Public:
#>     blocks: function (type = NULL, level = 0, path = FALSE) 
#>     built: NULL
#>     challenges: function (path = FALSE, graph = FALSE, recurse = TRUE) 
#>     clone: function (deep = FALSE) 
#>     episodes: list
#>     extra: NULL
#>     files: active binding
#>     get: function (element = NULL, collection = "episodes") 
#>     handout: function (path = NULL, solution = FALSE) 
#>     initialize: function (path = ".", rmd = FALSE, jekyll = TRUE, ...) 
#>     isolate_blocks: function () 
#>     load_built: function () 
#>     n_problems: active binding
#>     path: /tmp/Rtmpk8ln7F/LibraryCarpentry--lc-overview
#>     reset: function () 
#>     rmd: FALSE
#>     sandpaper: FALSE
#>     show_problems: active binding
#>     solutions: function (path = FALSE) 
#>     summary: function (collection = "episodes") 
#>     thin: function (verbose = TRUE) 
#>     validate_divs: function () 
#>     validate_headings: function (verbose = TRUE) 
#>     validate_links: function () 
#>   Private:
#>     deep_clone: function (name, value)

^{Created on 2023-08-08 with reprex v2.0.2}

Diagnosis

Currently, these fail here:

pegboard/R/read_jekyll_episodes.R

Lines 36 to 40 in d19ac71

	} else if (md_exists && md_n == 0L) {
	stop(glue::glue("The _episodes/ directory must have (R)markdown files"),
	call. = FALSE
	)
	} else {

If we can change this to a warning, then it should be okay.

This will help address carpentries/lesson-transition#83, carpentries/lesson-transition#84, carpentries/lesson-transition#85, carpentries/lesson-transition#86, and carpentries/lesson-transition#27

[zkamvar]

I'm going to think a bit more about this because {sandpaper} doesn't like lessons without episodes.

[zkamvar]

Note: Workbench-wide details can be found at carpentries/workbench#65