restructure R buildpack docs
@@ -19,15 +19,22 @@ class RBuildPack(PythonBuildPack):
date snapshot of https://mran.microsoft.com/timemachine
from which libraries are to be installed.
- 2. A `DESCRIPTION` file signaling an R package, or
- a Stencila document (*.jats.xml) with R code chunks (i.e. language="r")
- is found:
+ 2. A `DESCRIPTION` file signaling an R package
- MRAN snapshot is set to latest date that is guaranteed to exist
- across timezones.
+ 3. A Stencila document (*.jats.xml) with R code chunks (i.e. language="r")
- 3. (Optional) An `install.R` file that will be executed at build time,
- and can be used for installing packages from both MRAN and GitHub.
+ If there is no `runtime.txt`, then the MRAN snapshot is set to latest
+ date that is guaranteed to exist across timezones.
+
+ R packages are installed if specified either
+
+ - in a file `install.R`, that will be executed at build time,
+ and can be used for installing packages from both MRAN and GitHub
+
+ - as dependencies in a `DESCRIPTION` file
+
+ - are needed by a specific tool, for example the package `stencila` is
+ installed and configured if a Stencila document is given.
The `r-base` package from Ubuntu apt repositories is used to install
R itself, rather than any of the methods from https://cran.r-project.org/.
@@ -70,8 +77,6 @@ class RBuildPack(PythonBuildPack):
super().detect() is not called in this function - it would return false
unless a `requirements.txt` is present and we do not want to require the
presence of a `requirements.txt` to use R.
-
- Instead we check the options described in the class comment above.
"""
# If no date is found, then self.checkpoint_date will be False
# Otherwise, it'll be a date object, which will evaluate to True
