Trigger pipeline only if certain files are changed

So I posted this on the Community Discussion site, but it's worth having here.

We need to restrict our pipeline steps to only run when commits contain changes in our client/*/ filepath glob.

Concourse.ci, Drone.ci, and I assume other CI servers provide the option to restrict steps to commits only containing certain file paths.

At the moment it seems we are limited to manually grepping "git log" and emitting an exit 1, which would cause the build to fail.

Ideally I'd want a branch build to not even start, so being able to specify branches and steps to only run when there are (or are not) matching files in the commit would look like:

- step:
  image: node:alpine-8
  script:
    - npm install
    - npm run prod
  filter:
    includes:
      - client/src/**/*
      - package.json
   
...

So that commits containing file changes matching:

• server/*/ and client/*/ would run the above step
• server/*/ would not run the above step
• client/*/ would run the above step
• package.json would run the above step

Other examples:

- step:
  filter:
    excludes:
      - server/**/*.cshtml

- step:
  filter:
    includes:
      - client/build/gulp/**/*
    excludes:
      - server/**/*.cshtml

excludes would prevent the step from running if any files in the commit match the patterns.

includes would ensure that the step only ran if at least one of the changed files matches the patterns.