[RFC PATCH 2/2] gitlab-ci: Introduce allow_skipping_job_template

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

It might be overkill (and frustrating) to rerun all the jobs when
iterating over a single code unit. As some users are interested
in only rerunning a specific set of jobs, allow them to use a
"manual" profile, when jobs are created in the pipeline but not
started. It is up to the user to manually start the jobs of
interest.

To switch a repository to manual, set QEMU_DEFAULT_WORKFLOW_MANUAL
in the project UI, following [1].

Once a repository is using the manual workflow, the user can still
automatically start the jobs by explicitly set the
QEMU_IGNORE_DEFAULT_WORKFLOW which disable the manual mode.

Example while pushing a branch/tag from command line (see [2]):

  $ git push -o ci.variable="QEMU_IGNORE_DEFAULT_WORKFLOW=1" \
      myrepo mybranch

[1] https://docs.gitlab.com/ee/ci/variables/#create-a-custom-variable-in-the-ui
[2] https://docs.gitlab.com/ee/user/project/push_options.html#push-options-for-gitlab-cicd

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 .gitlab-ci.d/crossbuilds.yml |  4 ++++
 .gitlab-ci.yml               | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/.gitlab-ci.d/crossbuilds.yml b/.gitlab-ci.d/crossbuilds.yml
index 864cad7cec5..56b053cbb52 100644
--- a/.gitlab-ci.d/crossbuilds.yml
+++ b/.gitlab-ci.d/crossbuilds.yml
@@ -1,4 +1,5 @@
 .cross_system_build_job:
+  extends: .allow_skipping_job
   stage: build
   image: $CI_REGISTRY_IMAGE/qemu/$IMAGE:latest
   timeout: 80m
@@ -18,6 +19,7 @@
 # KVM), and set extra options (such disabling other accelerators) via the
 # $ACCEL_CONFIGURE_OPTS variable.
 .cross_accel_build_job:
+  extends: .allow_skipping_job
   stage: build
   image: $CI_REGISTRY_IMAGE/qemu/$IMAGE:latest
   timeout: 30m
@@ -30,6 +32,7 @@
     - make -j$(expr $(nproc) + 1) all check-build
 
 .cross_user_build_job:
+  extends: .allow_skipping_job
   stage: build
   image: $CI_REGISTRY_IMAGE/qemu/$IMAGE:latest
   script:
@@ -40,6 +43,7 @@
     - make -j$(expr $(nproc) + 1) all check-build
 
 .cross_sanity_check_job:
+  extends: .allow_skipping_job
   stage: build
   image: $CI_REGISTRY_IMAGE/qemu/$IMAGE:latest
   timeout: 3m
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 98bff03b47b..26b85f08f35 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -13,7 +13,21 @@ include:
   - local: '/.gitlab-ci.d/containers.yml'
   - local: '/.gitlab-ci.d/crossbuilds.yml'
 
+.allow_skipping_job_template: &allow_skipping_job_definition
+  rules:
+    # Skip if the user set the QEMU_DEFAULT_WORKFLOW_MANUAL variable for its
+    # project. Can be overridden by setting the QEMU_IGNORE_DEFAULT_WORKFLOW
+    # variable.
+    - if: $CI_PIPELINE_SOURCE == "push" && $QEMU_DEFAULT_WORKFLOW_MANUAL && $QEMU_IGNORE_DEFAULT_WORKFLOW == null
+      when: manual
+      allow_failure: true
+    - when: always
+
+.allow_skipping_job:
+  <<: *allow_skipping_job_definition
+
 .native_build_job_template: &native_build_job_definition
+  <<: *allow_skipping_job_definition
   stage: build
   image: $CI_REGISTRY_IMAGE/qemu/$IMAGE:latest
   before_script:
@@ -35,6 +49,7 @@ include:
       fi
 
 .native_test_job_template: &native_test_job_definition
+  <<: *allow_skipping_job_definition
   stage: test
   image: $CI_REGISTRY_IMAGE/qemu/$IMAGE:latest
   script:
@@ -43,6 +58,7 @@ include:
     - make $MAKE_CHECK_ARGS
 
 .acceptance_template: &acceptance_definition
+  <<: *allow_skipping_job_definition
   cache:
     key: "${CI_JOB_NAME}-cache"
     paths:
@@ -536,6 +552,7 @@ check-dco:
     GIT_DEPTH: 1000
 
 build-libvhost-user:
+  <<: *allow_skipping_job_definition
   stage: build
   image: $CI_REGISTRY_IMAGE/qemu/fedora:latest
   before_script:
@@ -547,6 +564,7 @@ build-libvhost-user:
     - ninja
 
 pages:
+  <<: *allow_skipping_job_definition
   image: $CI_REGISTRY_IMAGE/qemu/ubuntu2004:latest
   stage: test
   needs:
-- 
2.26.2