ENH: Add CircleCI skip [skip circle] [skip azp] [skip appveyor] [skip actions]

Author: larsoner

.circleci/config.yml

@@ -24,6 +24,19 @@ commands:
               git pull --ff-only upstream "refs/pull/$(cat merge.txt)/merge";
             fi
 
+  check-skip:
+    steps:
+      - run:
+          name: Check-skip
+          command: |
+            export COMMIT_MESSAGE=$(git log --max-count=1 --skip=1 --pretty=format:"%B" | tr "\n" " ")
+            echo "Got commit message:"
+            echo "${COMMIT_MESSAGE}"
+            if [[ -v CIRCLE_PULL_REQUEST ]] && ([[ "$COMMIT_MESSAGE" == *"[skip circle]"* ]] || [[ "$COMMIT_MESSAGE" == *"[circle skip]"* ]]); then
+              echo "Skip detected, exiting job ${CIRCLE_JOB} for PR ${CIRCLE_PULL_REQUEST}."
+              circleci-agent step halt;
+            fi
+
   apt-install:
     steps:
       - run:
@@ -139,6 +152,7 @@ jobs:
       - image: circleci/python:3.8
     steps:
       - checkout
+      - check-skip
       - merge
 
       - apt-install

doc/devel/coding_guide.rst

@@ -219,6 +219,17 @@ will run on all supported platforms and versions of Python.
 
   .. _tox: https://tox.readthedocs.io/
 
+* If you know your changes do not need to be tested (this is very rare!), all
+  CIs can be skipped by including ``[ci skip]`` or ``[skip ci]`` in your
+  commit message. If you know only a subset of CIs need to be run (e.g.,
+  if you are changing some block of plain reStructuredText and only want
+  only CircleCI to run to render the result), individual CIs can be skipped
+  to save bandwidth using:
+
+  - GitHub Actions: ``[skip actions]``
+  - AppVeyor: ``[skip appveyor]``
+  - Azure Pipelines: ``[skip azp]``
+  - CircleCI: ``[skip circle]``
 
 .. _pr-squashing: