the first step for #1864: warn if markdown is not a dependency of the…

… package containing vignettes based on the knitr::knitr engine

NEWS.md

@@ -26,6 +26,8 @@
 
 - For a non-matrix object passed to `kable()`, its columns are formatted individually via `format()`. Previously, the whole object is coerced via `as.matrix()` (thanks, @thebioengineer, #1827).
 
+- For packages that contain R Markdown vignettes using the vignette engines based on the **markdown** package (e.g., `knitr::knitr`), the **markdown** package should be declared in `Suggests` in the package `DESCRIPTION` unless it has already been declared as a dependency in other fields. For this version of **knitr**, you will see a warning in `R CMD check` in the CRAN incoming check. In the future, you may see a warning in a regular `R CMD check`, so please add **markdown** to `Suggests` at your earliest convenience. If it is not clear how to do it, please see #1864.
+
 ## MINOR CHANGES
 
 - `knitr::image_uri()` calls `xfun::base64_uri()` instead of `markdown:::.b64EncodeFile()` now.

R/utils-conversion.R

@@ -109,6 +109,21 @@ knit2pdf = function(
 #' unlink(c('test.Rmd', 'test.html', 'test.md'))
 knit2html = function(input, output = NULL, ..., envir = parent.frame(), text = NULL,
                      quiet = FALSE, encoding = 'UTF-8', force_v1 = FALSE) {
+  # packages containing vignettes using R Markdown v1 should declare dependency
+  # on 'markdown' in DESCRIPTION (typically in Suggests)
+  if (!is.na(pkg <- Sys.getenv('_R_CHECK_PACKAGE_NAME_', NA)) && pkg != 'markdown') {
+    info = packageDescription(pkg, fields = c('Depends', 'Imports', 'Suggests'))
+    if (!'markdown' %in% unlist(strsplit(unlist(info), '[[:space:],]+'))) {
+      if (is_CRAN_incoming()) stop2(
+        "The 'markdown' package should be declared as a dependency of the '", pkg,
+        "' package (e.g., in the  'Suggests' field of DESCRIPTION), because it ",
+        "contains vignette(s) built with the 'markdown' package. Please see ",
+        "https://github.com/yihui/knitr/issues/1864 for more information."
+      )
+    }
+  }
+  # TODO: remove the above hack in the future when no CRAN packages have the issue
+
   if (!force_v1 && is.null(text)) {
     signal = if (is_R_CMD_check()) warning2 else stop2
     if (length(grep('^---\\s*$', head(read_utf8(input), 1)))) signal(

R/utils.R

@@ -772,6 +772,10 @@ is_R_CMD_check = function() {
     any(c('_R_CHECK_TIMINGS_', '_R_CHECK_LICENSE_') %in% names(Sys.getenv()))
 }
 
+is_CRAN_incoming = function() {
+  isTRUE(as.logical(Sys.getenv('_R_CHECK_CRAN_INCOMING_REMOTE_')))
+}
+
 # is the inst dir under . or ..? differs in R CMD build/INSTALL and devtools/roxygen2
 inst_dir = function(...) {
   p = file.path(c('..', '.'), 'inst', ...)