ci: allow using custom interpreter for local manifest

Local manifests are mostly useful for various kinds of pipelines, e.g. for
merge requests and branch testing. They can use rules:if syntax to modify a
variable that is later used in shell. Due to the way variable interpolation
works in GitLab runners, the value itself cannot use further shell constructs,
like sub-shell substitution.

Introduce CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST_INTERPRETER variable, which
defaults to "echo" and allows using a custom interpreter. One possible use-case
is to use "eval" as interpreter and an arbitrary bash program, which is meant
to print the new local manifest, as value.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>

.gitlab-ci.yml

@@ -76,6 +76,16 @@ reuse:
     # GitLab cache system, and will be reused between pipelines of the same
     # project. Note that the .cache directory name is special.
     CI_ONIRO_MANIFEST_MIRROR_REPO_DIR: $CI_PROJECT_DIR/.cache/repo-mirror
+    # XML snippet to inject as a "local manifest" for repo. Those allow arbitrary
+    # modifications to the project structure to happen before "repo sync" is used
+    # to construct the workspace.
+    #
+    # The default interpreter for the local manifest is plain "echo". For some
+    # more complex cases, where inline shell is required, use "eval" instead
+    # and put "cat" echo into the local manifest, coupled with a here-doc
+    # value.
+    CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST: ""
+    CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST_INTERPRETER: echo
     # Directory where repo workspace is constructed.
     CI_ONIRO_REPO_WORKSPACE_DIR: $CI_PROJECT_DIR/.tmp/repo-workspace
     # Use fastest cache compression algorithm, as bulk of the cache is
@@ -169,7 +179,7 @@ reuse:
     - echo "Initializing repository workspace from $CI_ONIRO_MANIFEST_REPO_URL and $CI_ONIRO_MANIFEST_REPO_REV"
     - repo init --reference "$CI_ONIRO_MANIFEST_MIRROR_REPO_DIR" --manifest-url "$CI_ONIRO_MANIFEST_REPO_URL" --manifest-branch "$CI_ONIRO_MANIFEST_REPO_REV" --no-clone-bundle
     - mkdir -p "${CI_ONIRO_REPO_WORKSPACE_DIR}/.repo/local_manifests"
-    - test -n "${CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST:-}" && echo "$CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST" | tee "${CI_ONIRO_REPO_WORKSPACE_DIR}/.repo/local_manifests/local.xml"
+    - test -n "${CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST:-}" && "$CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST_INTERPRETER" "$CI_ONIRO_REPO_WORKSPACE_LOCAL_MANIFEST" | tee "${CI_ONIRO_REPO_WORKSPACE_DIR}/.repo/local_manifests/local.xml"
     - echo "Synchronizing repository workspace"
     - repo sync --force-sync
     - gl_section_close repo_workspace_setup