WHEN library

Purpose of this library is to evaluate conditional expressions written in domain specific language defined in Conditions DSL section bellow for given set of parameters.

Each condition will be evaluated either as true or false for given set of parameters if it is valid expression in Conditions DSL, otherwise error is returned.

Usage

Just add it to your mix.exs file:

{:when, github: "renderedtext/when"}

and then you can evaluate string condition written in Conditions DSL with:

When.evaluate(condition, parameters)

where parameters is map containing {keyword, value} pairs for each keyword that appears in condition string.

Conditions DSL

Formal language definition in extended Backus-Naur Form (EBNF) notation:

expression = expression bool_operator term
           | term

term = "(" expression ")"      
     | keyword operator string
     | string operator keyword
     | string                  
     | boolean

bool_operator = "and" | "AND" | "or" | "OR"

keyword = "branch" | "BRANCH" | "tag" | "TAG" | "pull_request" | "PULL_REQUEST" |
 "result" | "RESULT" | "result_reason" | "RESULT_REASON"

operator = "=" | "!=" | "=~" | "!~"

boolean = "true" | "TRUE" | "false" | "FALSE"

string = ? all characters between two single quotes, e.g. 'master' ?

Each keyword in passed expression is replaced with passed value from parameters map when expression is evaluated, and then operations identified with one of the operators from above are executed with those values.

KEYWORD	MEANING
branch	Name of the GitHub branch from which originated the pipeline that is being executed.
tag	Name of the GitHub tag from which originated the pipeline that is being executed.
pull_request	Number (as string) of GitHub pull request from which originated the pipeline that is being executed.
result	Execution result of pipeline, block, or job. Possible values are: passed, stopped, canceled and failed.
result_reason	The reason for given result of execution. Possible values are: test, malformed, stuck, deleted, internal and user.

OPERATOR	OPERATION RESULT
=	True if keyword value and given string are equal
!=	True if keyword value and given string are not equal
=~	True if keyword value and given PCRE* string match
!~	True if keyword value and given PCRE* string do not match
and	True if expressions on both sides are true
or	True if at least one of two expressions is true

* PCRE = Perl Compatible Regular Expression

YAML usage examples

Promotions

Promote automatically always

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "true"

Promote automatically on any branch and any result

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch =~ '.*' AND result =~ '.*'"

Promote automatically on any branch and result is passed

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch =~ '.*' AND result = 'passed'"

Promote automatically only when master result is passed

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch = 'master' AND result = 'passed'"

Promote automatically only master branch

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch = 'master'"

Promote automatically all branches that start with “df/”

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch =~ '^df\/'"

Promote automatically on staging or master branches

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch = 'staging' OR branch = 'master'"

Promote automatically on any tag

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "tag =~ '.*'"

Promote automatically if tag starts with “v1.”

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "tag =~ '^v1\.'"

Promote automatically if tag starts with "v1." and result is passed

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "tag =~ '^v1\.' AND result = 'passed'"

Promote automatically on master branch and tags

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "branch = 'master' OR tag =~ '.*'"

Promote automatically on master branch and tags when the result is passed

promotions:
  - name: Deploy to production
    pipeline_file: prod.yml
    auto:
      when: "(branch = 'master' OR tag =~ '.*') AND result = 'passed'"

Skip block exection

Skip always

blocks:
  - name: Unit tests
    skip:
      when: "true"

Skip on any branch

blocks:
  - name: Unit tests
    skip:
      when: "branch = '.*'"

Skip when master

blocks:
  - name: Unit tests
    skip:
      when: "branch = 'master'"

Skip when branch starts with “df/”

blocks:
  - name: Unit tests
    skip:
      when: "branch =~ '^df\/'"

Skip when branch is staging or master

blocks:
  - name: Unit tests
    skip:
      when: "branch = 'staging' OR branch = 'master'"

Skip on any tag

blocks:
  - name: Unit tests
    skip:
      when: "tag =~ '.*'"

Skip when tag start with “v1.”

blocks:
  - name: Unit tests
    skip:
      when: "tag =~ '^v1\.'"

Skip on master branch and any tags

blocks:
  - name: Unit tests
    skip:
      when: "branch = 'master' OR tag =~ '.*'"

Execute when branch starts with “dev/” == Skip when branch doesn’t start with dev/

blocks:
  - name: Unit tests
    skip:
      when: "branch !~ '^dev\/'"

Fail-fast

Stop running blocks *

Cancel pending blocks when a block fails

fail_fast:
  cancel:
    when: "true"

Cancel pending blocks when a block fails and on master branch

fail_fast:
  cancel:
    when: "branch = 'master'"

Cancel pending blocks when a block fails and branch starts with “df/”

fail_fast:
  cancel:
    when: "branch =~ '^df\/'"

Cancel pending blocks when a block fails and branch is staging or master

fail_fast:
  cancel:
    when: "branch = 'staging' OR branch = 'master'"

Cancel pending blocks when a block fails and on any tag

fail_fast:
  cancel:
    when: "tag =~ '.*'"

Cancel pending blocks when a block fails and tag starts with “v1.”

fail_fast:
  cancel:
    when: "tag =~ '^v1\.'"

Cancel pending blocks when a block fails and branch is master or any tag

fail_fast:
  cancel:
    when: "branch = 'master' OR tag =~ '.*'"

Cancel pending blocks when a block fails and branch doesn’t start with “dev/”

fail_fast:
  cancel:
    when: "tag !~ '^dev\/'"

Scheduling strategies

queue:
  mode:
    stop:
      when: "branch = 'master' OR tag =~ '.*'"
    cancel:
      when: "tag =~ '.*'"