tweak yihui#175 and add an example in the documentation

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: xaringan
 Type: Package
 Title: Presentation Ninja
-Version: 0.7.2
+Version: 0.7.3
 Authors@R: c(
     person("Yihui", "Xie", role = c("aut", "cre"), email = "[email protected]", comment = c(ORCID = "0000-0003-0645-5666")),
     person("Claus Thorn", "Ekstrøm", role = "ctb"),

NEWS.md

@@ -2,13 +2,13 @@
 
 ## NEW FEATURES
 
-- Added output highlighting using the chunk option `highlight.output`. (@malcolmbarrett, #175)
+- Added output highlighting using the chunk option `highlight.output` (thanks, @malcolmbarrett, #175).
 
-- Added a CSS theme `chocolate`. See [here](https://liao961120.github.io/slides/xaringan/) for an example slide. (@liao961120, #171)
+- Added a CSS theme `chocolate`. See [here](https://liao961120.github.io/slides/xaringan/) for an example slide (thanks, @liao961120, #171).
 
-- Added a set of CSS theme `kunoichi`, `shinobi` and `ninjutsu` - see [here for example](https://emitanaka.github.io/ninja-theme) (@emitanaka, #165)
+- Added a set of CSS theme `kunoichi`, `shinobi` and `ninjutsu` - see [here for example](https://emitanaka.github.io/ninja-theme) (thanks, @emitanaka, #165).
 
-- Added a CSS theme `lucy` (@LucyMcGowan, #163)
+- Added a CSS theme `lucy` (thanks, @LucyMcGowan, #163).
 
 # CHANGES IN xaringan VERSION 0.7
 

R/render.R

@@ -134,34 +134,31 @@ moon_reader = function(
 
   optk = list()
 
-  hooks = local({
-    ohooks = knitr::knit_hooks$get(); on.exit(knitr::knit_hooks$restore(ohooks))
-    knitr::render_markdown()
-    knitr::knit_hooks$get(c('source', 'output'))
-  })
-
-  hook_highlight = if (isTRUE(nature$highlightLines)) {
-    # an ugly way to access the `source` hook of markdown output in knitr
-    function(x, options) {
-      hook_source = hooks[['source']]
-      res = hook_source(x, options)
-      highlight_code(res)
-    }
+  highlight_hooks = NULL
+  if (isTRUE(nature$highlightLines)) {
+    # an ugly way to access hooks of markdown output in knitr
+    hooks = local({
+      ohooks = knitr::knit_hooks$get(); on.exit(knitr::knit_hooks$restore(ohooks))
+      knitr::render_markdown()
+      knitr::knit_hooks$get(c('source', 'output'))
+    })
+    highlight_hooks = list(
+      source = function(x, options) {
+        hook = hooks[['source']]
+        res = hook(x, options)
+        highlight_code(res)
+      },
+      output = function(x, options) {
+        hook = hooks[['output']]
+        res = highlight_output(x, options)
+        hook(res, options)
+      }
+    )
   }
 
-  hook_highlight_output = if (isTRUE(nature$highlightLines)) {
-    function(x, options) {
-      hook_output = hooks[['output']]
-      res = highlight_output(x, options)
-      hook_output(res, options)
-    }
-  }
 
   rmarkdown::output_format(
-    if (!is.null(hook_highlight)) {
-      rmarkdown::knitr_options(knit_hooks = list(source = hook_highlight,
-                                                 output = hook_highlight_output))
-    },
+    rmarkdown::knitr_options(knit_hooks = highlight_hooks),
     NULL, clean_supporting = self_contained,
     pre_knit = function(...) {
       optk <<- knitr::opts_knit$get()

R/utils.R

@@ -112,20 +112,9 @@ highlight_code = function(x) {
 }
 
 highlight_output = function(x, options) {
-  highlight.output = options$highlight.output
-  if (is.null(highlight.output)) return(x)
-  if (is.logical(highlight.output) & !highlight.output) return(x)
-  x = strsplit(x, '\n')[[1]]
-
-  if (isTRUE(highlight.output)) {
-     highlight.lines = seq_along(x)
-  } else if (is.numeric(highlight.output)) {
-    highlight.lines = highlight.output
-  } else {
-    stop("`highlight.output` must be numeric or logical")
-  }
-
-  x[highlight.lines] = paste0('*', x[highlight.lines])
+  if (is.null(i <- options$highlight.output) || isFALSE(i)) return(x)
+  x = split_lines(x)
+  x[i] = paste0('*', x[i])
   paste(x, collapse = '\n')
 }
 

inst/rmarkdown/templates/xaringan/skeleton/skeleton.Rmd

@@ -409,6 +409,24 @@ ggplot(mtcars) +
 
 # Some Tips
 
+When you enable line-highlighting, you can also use the chunk option `highlight.output` to highlight specific lines of the text output from a code chunk. For example, `highlight.output = TRUE` means highlighting all lines, and `highlight.output = c(1, 3)` means highlighting the first and third line.
+
+````md
+`r ''````{r, highlight.output=c(1, 3)}
+head(iris)
+```
+````
+
+```{r, highlight.output=c(1, 3), echo=FALSE}
+head(iris)
+```
+
+Question: what does `highlight.output = c(TRUE, FALSE)` mean? (Hint: think about R's recycling of vectors)
+
+---
+
+# Some Tips
+
 - To make slides work offline, you need to download a copy of remark.js in advance, because **xaringan** uses the online version by default (see the help page `?xaringan::moon_reader`).
 
 - You can use `xaringan::summon_remark()` to download the latest or a specified version of remark.js. By default, it is downloaded to `libs/remark-latest.min.js`.