bundler: Pinning bundler version to the system one

When there is a version mismatch between a lockfile and bundler
used to build a package, bundler might try to install a version
specified in the lockfile. This will result in a build failure
in a hermetic environment. This change forces bundler to
always use whichever version is present in the system by overriding
BUNDLE_VERSION variable and setting it to 'system'. See
  https://bundler.io/v2.5/man/bundle-config.1.html#LIST-OF-AVAILABLE-KEYS
for details.

Signed-off-by: Alexey Ovchinnikov <[email protected]>

cachi2/core/package_managers/bundler/main.py

@@ -159,6 +159,7 @@ def _prepare_for_hermetic_build(source_dir: RootedPath, output_dir: RootedPath)
         BUNDLE_CACHE_PATH: "${output_dir}/deps/bundler"
         BUNDLE_DEPLOYMENT: "true"
         BUNDLE_NO_PRUNE: "true"
+        BUNDLE_VERSION: "system"
     """
     )
     if potential_bundle_config.is_file():

tests/unit/package_managers/bundler/test_main.py

@@ -127,6 +127,7 @@ def test__prepare_for_hermetic_build_injects_necessary_variable_into_empty_confi
         BUNDLE_CACHE_PATH: "${output_dir}/deps/bundler"
         BUNDLE_DEPLOYMENT: "true"
         BUNDLE_NO_PRUNE: "true"
+        BUNDLE_VERSION: "system"
         """
     )
 
@@ -146,6 +147,7 @@ def test__prepare_for_hermetic_build_injects_necessary_variable_into_existing_co
         BUNDLE_CACHE_PATH: "${output_dir}/deps/bundler"
         BUNDLE_DEPLOYMENT: "true"
         BUNDLE_NO_PRUNE: "true"
+        BUNDLE_VERSION: "system"
         """
     )
     existing_preamble = dedent(
@@ -175,6 +177,7 @@ def test__prepare_for_hermetic_build_injects_necessary_variable_into_existing_al
         BUNDLE_CACHE_PATH: "${output_dir}/deps/bundler"
         BUNDLE_DEPLOYMENT: "true"
         BUNDLE_NO_PRUNE: "true"
+        BUNDLE_VERSION: "system"
         """
     )
     existing_preamble = dedent(
@@ -209,6 +212,7 @@ def test__prepare_for_hermetic_build_ignores_a_directory_in_place_of_config(
         BUNDLE_CACHE_PATH: "${output_dir}/deps/bundler"
         BUNDLE_DEPLOYMENT: "true"
         BUNDLE_NO_PRUNE: "true"
+        BUNDLE_VERSION: "system"
         """
     )