Mergify Conditions

Conditions are an essential component of Mergify rules, as they define the criteria that must be met for a rule to be applied. By utilizing conditions, you can create highly customizable and flexible rules tailored to your specific workflow requirements. Conditions enable you to target pull requests based on various factors such as their status, properties, labels, and associated statuses or checks.

In this guide, we will explore the structure, syntax, and usage of conditions in Mergify rules. You will learn how to craft effective conditions that help you automate and streamline your pull request management process.

A condition in Mergify rules is composed of three key components: attributes, operators, and values, along with optional modifiers. These components work together to define the criteria that must be met for the condition to be considered true.

The grammar for a condition is as follows:

[ "-" ] [ "#" ] <attribute> [ <operator> <value> ]

• The optional minus (-) operator at the beginning of the condition negates the result of the condition, acting as a “not” operator.

• The optional hash (#) operator is used to evaluate the length of a list when the attribute is a list.

Attributes represent the properties or characteristics of a pull request that you want to evaluate in your condition. These can include elements such as the number of approvals, the presence of specific labels, or the status of CI checks.

Operators are used to compare the attribute to a specified value. Mergify supports various comparison operators (e.g., =, !=, <, >).

When the attribute is a list, comparison operators behave as if “any” is used on the list, meaning the condition will return true if any element of the list matches the given operator and value.

Values are the reference points used to evaluate the attribute. They can be strings, numbers, or booleans, depending on the attribute being evaluated.

For example, consider the following condition:

#approved-reviews-by >= 2

In this condition:

• The attribute is approved-reviews-by, which represents the list of approved reviewers for a pull request.

• The operator is >=, which means “greater than or equal to.”

• The value is 2, which indicates the minimum number of approved reviews required for the condition to be true.

• The hash (#) operator is used to evaluate the length of the list of approved reviewers.

Understanding the structure of a condition is crucial for creating effective Mergify rules that cater to your specific needs and requirements.

Attributes are properties of pull requests or events used to filter and evaluate the conditions within rules. They can be used to create more specific and targeted rules for your repository.

Operators allow you to compare attributes with specified values in order to determine if a condition is true or false. Mergify supports several types of operators that cater to different types of comparisons. Familiarizing yourself with these operators is essential for crafting effective conditions in your Mergify rules.

Here is a list of the available operators:

For example, let’s consider a condition that requires a pull request to have a specific label:

label = bugfix

In this condition:

• The attribute is label, which represents the labels associated with a pull request.

• The operator is =, which means “equal to.”

• The value is bugfix, which is the label we want the pull request to have.

Some attributes have a type of list. Most operators are able to match value against lists: they will iterate over all the values of the list and return true if any of the value matches.

For example, the label attribute is a list of string containing the names of the label attached to a pull request. With a pull request whose labels are (bug, work-in-progress), then:

• label = work-in-progress is true because there is a label named work-in-progress.

• label = enhancement is false because there is no label named enhancement.

• label != work-in-progress is false because there is a label named work-in-progress.

• label ~= ^work is true because there is a label matching the regular expression ^work.

• -label ~= ^work is false because there is a label matching the regular expression ^work but the condition is reversed with the - prefix.

The same applies for the files attribute — which contains the list of modified files:

• files = README is true if the file README is modified in the pull request.

• files != README is true if the file README is not modified in the pull request.

• files ~= ^src/ is true if any files in the src directory is modified in the pull request.

• -files ~= ^src/ is true if none of the files that are modified are in the src directory.

• files ~= ^(README.md|CONTRIBUTING.md)$ is true if the file README.md or CONTRIBUTING.md is modified in the pull requests.

In this example, we use the = operator to match a specific milestone for the pull request:

- name: Rule for milestone "v1.0"
  conditions:
    - milestone = v1.0
  actions:
    # Your actions here

In this example, we use the <= operator to check if the number of files modified in the pull request is less than or equal to 50:

- name: Rule for small changes
  conditions:
    - "#files <= 50"
  actions:
    # Your actions here

In this example, we use the != operator to check if the pull request does not have the specified labels:

- name: Rule when not a bug
  conditions:
    - label != bug
  actions:
    # Your actions here

Mergify allows you to combine multiple conditions using logical operators, making it possible to create more intricate rules that cater to your specific workflow requirements. You can use the and and or logical operators to join conditions together.

The and operator is used to join conditions such that all conditions must be true for the overall condition to be true. In Mergify rules, the and operator is represented by placing conditions on separate lines within the same rule.

Alternatively, you can use the and keyword to explicitly group conditions together.

Example:

pull_request_rules:
  - name: Merge when all conditions are met
    conditions:
      - and:
        - "#approved-reviews-by >= 2"
        - "check-success = test job"
    actions:
      merge:
        method: merge

In this example, the pull request will only be merged if it has at least 2 approved reviews and the test job check passes.

The or operator is used to join conditions such that if any one of the conditions is true, the overall condition is considered true. In Mergify rules, the or operator is represented by using the or keyword and specifying conditions as a list.

Example:

pull_request_rules:
  - name: Merge when either condition is met
    conditions:
      - or:
        - "#approved-reviews-by >= 2"
        - "check-success = test job"
    actions:
      merge:
        method: merge

In this example, the pull request will be merged if it has at least 2 approved reviews or if the test job check passes.

Combining conditions using logical operators can help you create more sophisticated rules tailored to your repository’s workflow and requirements.

When crafting conditions for your Mergify rules, it’s essential to test and debug them to ensure they are working as intended. This section will guide you through the process of testing and debugging conditions in your Mergify configuration.

The Mergify configuration editor is a useful tool to help you test your conditions and rules on existing pull requests without actually triggering the actions defined in your rules. To access the configuration editor, follow these steps:

1. Navigate to your Mergify dashboard.
2. Select the repository you want to test.
3. Click on the “Config Editor” tab.

In the configuration editor, you can enter your conditions and see how they would be evaluated on your pull requests. You can also test your entire Mergify configuration by copying and pasting it into the configuration editor.

Once you have created and committed your Mergify configuration file, Mergify will evaluate the conditions in your rules for each pull request. To debug your conditions and understand why a rule may not be working as expected, you can analyze the Mergify Checks on a pull request:

1. Navigate to the “Checks” tab of the pull request.
2. Look for the “Mergify” check in the list of checks.
3. Click on “Summary” to view the detailed Mergify report.

In the Mergify report, you can see which rules were evaluated and whether the conditions were met or not. This can help you identify any issues in your conditions and make adjustments as necessary.