Set custom env vars required for RStudio to work

repo2docker/buildpacks/r.py

@@ -133,6 +133,19 @@ class RBuildPack(PythonBuildPack):
                 self._runtime = "r-{}".format(str(self._checkpoint_date))
             return True
 
+    def get_env(self):
+        """
+        Set custom env vars needed for RStudio to load
+        """
+        return super().get_env() + [
+            # rstudio (rsession) can't seem to find R unless we explicitly tell it where
+            # it is - just $PATH isn't enough. I discovered these are the env vars it
+            # looks for by digging through RStudio source and finding https://github.com/rstudio/rstudio/blob/main/src/cpp/r/session/RDiscovery.cpp
+            ("R_HOME", f"/opt/R/{self.r_version}/lib/R"),
+            ("R_DOC_DIR", "${R_HOME}/doc"),
+            ("LD_LIBRARY_PATH", "${R_HOME}/lib:${LD_LIBRARY_PATH}"),
+        ]
+
     def get_path(self):
         """
         Return paths to be added to the PATH environment variable.