[!IMPORTANT]
Syntax highlighting for HTML help pages was added to R v4.2 so there is now less of a use case for this package. Though you might still want to use it since it does look a bit nicer than the default provided by R. Advantages include more consistent font size, highlighting colors consistent with RStudio theme, highlighting all code snippets in the doc instead of just Usage and Examples.

Syntax highlighting for R HTML documentation

Overview

This package enables syntax highlighting for R HTML documentation.

Syntax highlighting follows RStudio theme when running RStudio. When running outside RStudio, theme customization is supported, with Textmate set as the default. See Themes for more details.

The syntax highlighter comes from Ace text editor, the same editor underlying RStudio.

Related rstudio/rstudio#2303

Installation

The package can be installed via R-universe (recommended)

install.packages("rdocsyntax", repos = "https://kiendang.r-universe.dev")

or Github

# install.packages("remotes")
remotes::install_github("kiendang/rdocsyntax")

Usage

Enable syntax highlighting

rdocsyntax::highlight_html_docs()

Code in HTML documents is now highlighted

?try

If help pages are not displayed in HTML mode by default, e.g. when R is not running inside RStudio, set help_type option to html:

help(try, help_type = "html")

or

options(help_type = "html")
?try

Disable syntax highlighting

rdocsyntax::unhighlight_html_docs()

Enable syntax highlighting automatically on startup

Append

rdocsyntax::highlight_html_docs()

to your .Rprofile

[!CAUTION]
This might cause failure when upgrading R packages. It is recommended to comment out that line in .Rprofile before you run update.packages().

Extras

Themes

When running inside RStudio, syntax highlighting always follows RStudio theme.

When running outside RStudio, theme can be changed by setting the rdocsyntax.theme option. Valid choices are:

• Light themes: chrome, clouds, cloud9_day, crimson_editor, dawn, dreamweaver, eclipse, github, iplastic, katzenmilch, kuroir, solarized_light, sqlserver, textmate, tomorrow, xcode
• Dark themes: ambiance, chaos, cloud9_night, cloud9_night_low_color, clouds_midnight, cobalt, dracula, gob, gruvbox, idle_fingers, kr_theme, merbivore, merbivore_soft, mono_industrial, monokai, nord_dark, one_dark, pastel_on_dark, solarized_dark, terminal, tomorrow_night, tomorrow_night_blue, tomorrow_night_bright, tomorrow_night_eighties, twilight, vibrant_ink

e.g. to switch to dracula:

options(rdocsyntax.theme = "dracula")

The default theme is textmate in case rdocsyntax.theme is not set or set to an invalid value.

Syntax highlighting for vignettes

Due to security reasons by default only code in ? help pages is syntax highlighted. Syntax highlighting for other pages served by the dynamic help server httpd including vignettes can be enabled by setting

options(rdocsyntax.extra = TRUE)

Code in most vignettes has already been highlighted by default without the need for rdocsyntax. However one might still want to enable rdocsyntax for them anyway so that the color scheme matches that of RStudio. This is particularly useful when RStudio is set to a dark theme since most vignettes highlight their code with the textmate color scheme, which is a light theme and not dark mode friendly.

Setting rdocsyntax.extra = TRUE does not affect user defined httpd endpoints under /custom/, only those under /doc/ and /library/.

Inline ## Not run

There are ## Not run code examples that are single line. e.g in ?rstudioapi::highlightUi

## Not run: rstudioapi::highlightUi("#rstudio_workbench_panel_git")

The code will not be syntax-highlighted because the whole line is treated as a comment.

The solution we use is to turn it into

## Not run:
rstudioapi::highlightUi("#rstudio_workbench_panel_git")

in the generated html.

Debug mode

To show errors from rdocsyntax httpd help server for development/debugging purpose:

options(rdocsyntax.dev = TRUE)

Implementation details

R HTML help pages are rendered and served by the internal help server httpd. The package works by replacing the built-in httpd with one that receives the original HTML doc, makes changes to the HTML so that parts of the doc that contains code would be highlighted, then serves the modified HTML.

Client side and server side highlighting

The code that does the highlighting is written in JavaScript since it depends on the Ace static highlighter. Previously, up to v0.5.x, highlighting was done server side, i.e. rdocsyntax used V8 to execute the JavaScript code and finished highlighting the HTML doc before returning it through httpd.

Starting from v0.6.0, highlighting has instead been done client side. The JavaScript highlighting code is injected into the original HTML doc in a script tag and then executed by whatever browser that eventually displays the doc, either RStudio or an external browser. Compared to server side highlighting, this is more efficient since rdocsyntax no longer has to run its own JavaScript engine. As a result, the heavy dependency on V8 has been dropped.

Legacy server side highlighting is still available on an opt-in basis.

options(rdocsyntax.server_side_highlighting = TRUE)

Of course V8 needs to be installed for this to work.

Sys.setenv(DOWNLOAD_STATIC_LIBV8 = 1)
install.packages("V8")

ctx <- V8::v8()
ctx
# <V8 engine 8.3.110.9>
#  $assign(name, value, auto_unbox = TRUE, ...)
#  $call(fun, ..., auto_unbox = TRUE)
#  $console()
#  $eval(src, serialize = FALSE)
#  $get(name, ...)
#  $reset()
#  $source(file)
#  $validate(src)

CRAN?

Due to rdocsyntax directly overriding tools:::httpd it is unlikely to be submitted to CRAN. Overwriting an object, especially an unexported one, in another package’s namespace, is considered an anti-pattern. An alternative implementation that does not involve replacing the internal httpd can be found at kiendang/rdocsyntax.ex (now unmaintained). rdocsyntax.ex does not integrate as nicely with RStudio: help pages are displayed in the Viewer instead of Helper pane and extra functionalities such as search, forward, backward are not available.

Development

requirements: yarn

clone the repo

git clone --recursive https://github.com/kiendang/rdocsyntax.git

install js dependencies

yarn install

rebuild the javascript files (only needed if the files in srcjs are updated)

yarn build

The built files are placed in inst/js.