fixes #784: also provide vignette engines with tangle disabled

NEWS.md

@@ -1,5 +1,9 @@
 # CHANGES IN knitr VERSION 1.7
 
+## NEW FEATURES
+
+- added vignette engines with the suffix `_notangle`, which have the same weave functions as those engines without this suffix but have disabled the tangle function, meaning there will not be R scripts generated from the vignettes during `R CMD build` or `R CMD check` (thanks, Carl Boettiger and Michael Koohafkan, #784)
+
 ## BUG FIXES
 
 - fixed #779: when the chunk options `tidy=FALSE` and `eval=FALSE`, `prompt=TRUE` did not work for R expressions of multiple lines (thanks, Qijie Zhao)

R/utils-vignettes.R

@@ -1,4 +1,17 @@
-# Wrappers to use in vignette building for R 3.0.0
+#' Package vignette engines
+#'
+#' Since R 3.0.0, package vignettes can use non-Sweave engines, and \pkg{knitr}
+#' has provided a few engines to compile vignettes via \code{\link{knit}()} with
+#' different templates. See \url{http://yihui.name/knitr/demo/vignette/} for
+#' more information.
+#' @name vignette_engines
+#' @examples library(knitr)
+#' vig_list = if (getRversion() > '3.0.0') tools::vignetteEngine(package = 'knitr')
+#' str(vig_list)
+#' vig_list[['knitr::knitr']][c('weave', 'tangle')]
+#' vig_list[['knitr::knitr_notangle']][c('weave', 'tangle')]
+#' vig_list[['knitr::docco_classic']][c('weave', 'tangle')]
+NULL
 
 vweave = vtangle = function(file, driver, syntax, encoding = '', quiet = FALSE, ...) {
   opts_chunk$set(error = FALSE)  # should not hide errors
@@ -27,6 +40,16 @@ body(vweave_rmarkdown)[5L] = expression(getFromNamespace('render', 'rmarkdown')(
   file, encoding = encoding, quiet = quiet, envir = globalenv()
 ))
 
+# do not tangle R code from vignettes
+untangle_weave = function(weave) {
+  body(weave)[3L] = expression({})
+  weave
+}
+vtangle_empty = function(file, ...) {
+  unlink(sub_ext(file, 'R'))
+  return()
+}
+
 Rversion = getRversion()
 
 register_vignette_engines = function(pkg) {
@@ -38,8 +61,17 @@ register_vignette_engines = function(pkg) {
   vig_engine('rmarkdown', if (has_package('rmarkdown')) {
     vweave_rmarkdown
   } else vweave, '[.][Rr](md|markdown)$')
+  # vignette engines that disable tangle
+  vig_list = tools::vignetteEngine(package = 'knitr')
+  engines  = grep('_notangle$', names(vig_list), value = TRUE, invert = TRUE)
+  for (eng in engines) vig_engine(
+    paste(sub('^knitr::', '', eng), 'notangle', sep = '_'),
+    untangle_weave(vig_list[[c(eng, 'weave')]]),
+    tangle = vtangle_empty,
+    pattern = vig_list[[c(eng, 'pattern')]]
+  )
 }
 # all engines use the same tangle and package arguments, so factor them out
-vig_engine = function(...) {
-  tools::vignetteEngine(..., tangle = vtangle, package = 'knitr')
+vig_engine = function(..., tangle = vtangle) {
+  tools::vignetteEngine(..., tangle = tangle, package = 'knitr')
 }