Merge #20658: ci: Move linter task to cirrus

4045a6722c ci: Use cpu=1 for linter (Dhruv Mehta)
739d39022d ci: Move linter task to cirrus (Dhruv Mehta)

Pull request description:

  Solves #20467: Move linter to Cirrus-CI as Travis-CI.org is shutting down

ACKs for top commit:
  MarcoFalke:
    ACK 4045a6722c

Tree-SHA512: 9aa7487ac86c91fc68bb584d29134e304dbd46702514a5d47d1ef0de6b877d96d42b7589870fc67ad9a31f5d3a789728446da4418688f336111a9ba0f8de5feb

.cirrus.yml

@@ -1,12 +1,5 @@
 ### Global defaults
 
-timeout_in: 120m  # https://cirrus-ci.org/faq/#instance-timed-out
-container:
-  # https://cirrus-ci.org/faq/#are-there-any-limits
-  # Each project has 16 CPU in total, assign 2 to each container, so that 8 tasks run in parallel
-  cpu: 2
-  memory: 8G  # Set to 8GB to avoid OOM. https://cirrus-ci.org/guide/linux/#linux-containers
-  kvm: true  # Use kvm to avoid spurious CI failures in the default virtualization cluster, see https://github.com/bitcoin/bitcoin/issues/20093
 env:
   PACKAGE_MANAGER_INSTALL: "apt-get update && apt-get install -y"
   MAKEJOBS: "-j4"
@@ -15,11 +8,28 @@ env:
   CCACHE_SIZE: "200M"
   CCACHE_DIR: "/tmp/ccache_dir"
 
-### Global task template
-
+### Base template
 # https://cirrus-ci.org/guide/tips-and-tricks/#sharing-configuration-between-tasks
+base_template: &BASE_TEMPLATE
+  skip: $CIRRUS_REPO_FULL_NAME == "bitcoin-core/gui" && $CIRRUS_PR == "" # No need to run on the read-only mirror, unless it is a PR. https://cirrus-ci.org/guide/writing-tasks/#conditional-task-execution
+  merge_base_script:
+    - if [ "$CIRRUS_PR" = "" ]; then exit 0; fi
+    - bash -c "$PACKAGE_MANAGER_INSTALL git"
+    - git fetch $CIRRUS_REPO_CLONE_URL $CIRRUS_BASE_BRANCH
+    - git config --global user.email "ci@ci.ci"
+    - git config --global user.name "ci"
+    - git merge FETCH_HEAD  # Merge base to detect silent merge conflicts
+
+### Global task template
 global_task_template: &GLOBAL_TASK_TEMPLATE
-  skip: $CIRRUS_REPO_FULL_NAME == "bitcoin-core/gui" && $CIRRUS_PR == ""  # No need to run on the read-only mirror, unless it is a PR. https://cirrus-ci.org/guide/writing-tasks/#conditional-task-execution
+  << : *BASE_TEMPLATE
+  timeout_in: 120m  # https://cirrus-ci.org/faq/#instance-timed-out
+  container:
+    # https://cirrus-ci.org/faq/#are-there-any-limits
+    # Each project has 16 CPU in total, assign 2 to each container, so that 8 tasks run in parallel
+    cpu: 2
+    memory: 8G  # Set to 8GB to avoid OOM. https://cirrus-ci.org/guide/linux/#linux-containers
+    kvm: true  # Use kvm to avoid spurious CI failures in the default virtualization cluster, see https://github.com/bitcoin/bitcoin/issues/20093
   ccache_cache:
     folder: "/tmp/ccache_dir"
   depends_built_cache:
@@ -28,13 +38,6 @@ global_task_template: &GLOBAL_TASK_TEMPLATE
     folder: "/tmp/cirrus-ci-build/depends/sdk-sources"
   depends_releases_cache:
     folder: "/tmp/cirrus-ci-build/releases"
-  merge_base_script:
-    - if [ "$CIRRUS_PR" = "" ]; then exit 0; fi
-    - bash -c "$PACKAGE_MANAGER_INSTALL git"
-    - git fetch $CIRRUS_REPO_CLONE_URL $CIRRUS_BASE_BRANCH
-    - git config --global user.email "ci@ci.ci"
-    - git config --global user.name "ci"
-    - git merge FETCH_HEAD  # Merge base to detect silent merge conflicts
   ci_script:
     - ./ci/test_run_all.sh
 
@@ -54,6 +57,25 @@ global_task_template: &GLOBAL_TASK_TEMPLATE
 #  install_script:
 #    - choco install python --version=3.7.7 -y
 
+task:
+  name: 'lint'
+  << : *BASE_TEMPLATE
+  container:
+    image: ubuntu:bionic # For python 3.6, oldest supported version according to doc/dependencies.md
+    cpu: 1 # Cut bill in half for linting
+  # For faster CI feedback, immediately schedule the linters. https://cirrus-ci.org/pricing/#compute-credits
+  use_compute_credits: $CIRRUS_REPO_FULL_NAME == 'bitcoin/bitcoin'
+  setup_script:
+    - set -o errexit; source ./ci/test/00_setup_env.sh
+  before_install_script:
+    - set -o errexit; source ./ci/test/03_before_install.sh
+  install_script:
+    - set -o errexit; source ./ci/lint/04_install.sh
+  before_script:
+    - set -o errexit; source ./ci/lint/05_before_script.sh
+  lint_script:
+    - set -o errexit; source ./ci/lint/06_script.sh
+
 task:
   name: 'ARM [unit tests, no functional tests] [buster]'
   << : *GLOBAL_TASK_TEMPLATE