Raise exception for unsupported R versions

repo2docker/buildpacks/r.py

@@ -65,6 +65,7 @@ class RBuildPack(PythonBuildPack):
         version.
         """
         version_map = {
+            "3.4": "3.4",
             "3.5": "3.5.3-1bionic",
             "3.5.0": "3.5.0-1bionic",
             "3.5.1": "3.5.1-2bionic",
@@ -81,10 +82,13 @@ class RBuildPack(PythonBuildPack):
             parts = self.runtime.split("-")
             if len(parts) == 5:
                 r_version = parts[1]
+                if r_version not in version_map:
+                    raise ValueError(
+                        "Version '{}' of R is not supported.".format(r_version)
+                    )
 
-            # see if we need to translate the specified version into a
-            # "full" version string
-            self._r_version = version_map.get(r_version, r_version)
+            # translate to the full version string
+            self._r_version = version_map.get(r_version)
 
         return self._r_version
 

tests/unit/test_r.py

@@ -5,6 +5,20 @@ import pytest
 from repo2docker import buildpacks
 
 
+def test_unsupported_version(tmpdir):
+    tmpdir.chdir()
+
+    with open("runtime.txt", "w") as f:
+        f.write("r-3.8-2019-01-01")
+
+    r = buildpacks.RBuildPack()
+    with pytest.raises(ValueError) as excinfo:
+        # access the property to trigger the exception
+        _ = r.r_version
+        # check the version is mentioned in the exception
+        assert "'3.8'" in str(excinfo.value)
+
+
 @pytest.mark.parametrize(
     "runtime_version, expected", [("", "3.6"), ("3.6", "3.6"), ("3.5.1", "3.5")]
 )