note why --no-install-recommends is important for r packages

Author: minrk

repo2docker/buildpacks/_r_base.py

@@ -31,6 +31,9 @@ def rstudio_base_scripts(r_version):
     return [
         (
             "root",
+            # we should have --no-install-recommends on all our apt-get install commands,
+            # but here it's important because these recommend r-base,
+            # which will upgrade the installed version of R, undoing our pinned version
             r"""
             curl --silent --location --fail {rstudio_url} > /tmp/rstudio.deb && \
             curl --silent --location --fail {shiny_server_url} > /tmp/shiny.deb && \

repo2docker/buildpacks/r.py

@@ -292,6 +292,9 @@ def get_build_scripts(self):
             ),
             (
                 "root",
+                # we should have --no-install-recommends on all our apt-get install commands,
+                # but here it's important because it will pull in CRAN packages
+                # via r-recommends, which is only guaranteed to be compatible with the latest r-base-core
                 r"""
                 apt-get update > /dev/null && \
                 apt-get install --yes --no-install-recommends \