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Guidance on how to contribute
There are two primary ways to help:
- Using the issue tracker, and
- Changing the code-base.
Using the issue tracker
Use the issue tracker to suggest feature requests, report bugs, and ask questions. This is also a great way to connect with the developers of the project as well as others who are interested in this solution.
Use the issue tracker to find ways to contribute. Find a bug or a feature, mention in the issue that you will take on that effort, then follow the "Changing the code-base" guidance below.
Changing the code-base
Generally speaking, you should fork this repository, make changes in your own fork, and then submit a pull-request. All new code should have been thoroughly tested end-to-end in order to validate implemented features and the presence or lack of defects.
Working with forks
- Configure this repository as a remote for your own fork, and
- Sync your fork with this repository before beginning to work on a new pull-request.
Tests
All pipeline library coding must come with automated unit tests.
Documentation
The contract of functionality exposed by a library functionality needs to be documented, so it can be properly used. Implementation of a functionality and its documentation shall happen within the same commit(s).
Code Style
The code should follow any stylistic and architectural guidelines prescribed by the project. In the absence of guidelines, mimic the styles and patterns in the existing code-base.
Variables, methods, types and so on shall have meaningful self describing names. Doing so makes understanding code easier and requires less commenting. It helps people who did not write the code to understand it better.
Code shall contain comments to explain the intention of the code when it is unclear what the intention of the author was. In such cases, comments should describe the "why" and not the "what" (that is in the code already).
EditorConfig
To ensure a common file format, there is a .editorConfig file in place. To respect this file, check if your editor does support it natively or you need to download a plugin.
Commit Message Style
Write meaningful commit messages and adhere to standard formatting.
Good commit messages speed up the review process and help to keep this project maintainable in the long term.
Code Style
The intention of this section is to describe the code style for this project. As reference document, the Groovy's style guide was taken. For further reading about Groovy's syntax and examples, please refer to this guide.
This project is intended to run in Jenkins [2] as part of a Jenkins Pipeline [3]. It is composed by Jenkins Pipeline's syntax, Groovy's syntax and Java's syntax.
Some Groovy's syntax is not yet supported by Jenkins. It is also the intention of this section to remark which Groovy's syntax is not yet supported by Jenkins.
As Groovy supports 99% of Java’s syntax [1], many Java developers tend to write Groovy code using Java's syntax. Such a developer should also consider the following code style for this project.
Omit semicolons
Use the return keyword
In Groovy it is optional to use the return keyword. Use explicitly the return keyword for better readability.
Use def
When using def in Groovy, the type is Object. Using def simplifies the code, for example imports are not needed, and therefore the development is faster.
Do not use a visibility modifier for public classes and methods
By default, classes and methods are public, the use of the public modifier is not needed.
Do not omit parentheses for Groovy methods
In Groovy is possible to omit parentheses for top-level expressions, but Jenkins Pipeline's syntax use a block, specifically pipeline { } as top-level expression [4]. Do not omit parenthesis for Groovy methods because Jenkins will interpret the method as a Pipeline Step. Conversely, do omit parenthesis for Jenkins Pipeline's Steps.
Omit the .class suffix
In Groovy, the .class suffix is not needed. Omit the .class suffix for simplicity and better readability.
e.g. new ExpectedException().expect(AbortException.class)
--> new ExpectedException().expect(AbortException)
Omit getters and setters
When declaring a field without modifier inside a Groovy bean, the Groovy compiler generates a private field and a getter and setter.
Do not initialize beans with named parameters
Do not initialize beans with named parameters, because it is not supported by Jenkins:
e.g. Version javaVersion = new Version( major: 1, minor: 8)
Initialize beans using Java syntax:
e.g. Version javaVersion = new Version(1, 8)
Use named parameters for Jenkins Pipeline Steps:
e.g. sh returnStdout: true, script: command
Do not use with() operator
The with operator is not yet supported by Jenkins, and it must not be used or encapsulated in a @NonCPS method.
Use == operator
Use Groovy’s == instead of Java equals() to avoid NullPointerExceptions. To compare the references of objects, instead of ==, you should use a.is(b) [1].
Use GStrings
In Groovy, single quotes create Java Strings, and double quotes can create Java Strings or GStrings, depending if there is or not interpolation of variables [1]. Using GStrings variable and string concatenation is more simple.
Do not use curly braces {} for variables or variable.property
For variables, or variable.property, drop the curly braces:
e.g. echo "[INFO] ${name} version ${version.version} is installed."
--> echo "[INFO] $name version $version.version is installed."
Use 'single quotes' for Strings and constants.
Use "double quotes" for GStrings.
Use '''triple single quotes''' for multiline Strings.
Use """triple double quotes""" for multiline GStrings.
Use /slash/ for regular expresions.
This notation avoids to double escape backslashes, making easier working with regex.
Use native syntax for data structures
Use the native syntax for data structures provided by Groovy like lists, maps, regex, or ranges of values.
Use aditional Groovy methods
Use the additional methods provided by Groovy to manipulate String, Files, Streams, Collections, and other classes. For a complete description of all available methods, please read the GDK API [5].
Use Groovy's switch
Groovy’s switch accepts any kind of type, thereby is more powerful. In this case, the use of def instead of a type is necessary.
Use alias for import
In Groovy, it is possible to assign an alias to imported packages. Use alias for imported packages to avoid the use of fully-qualified names and increase readability.
Use Groovy syntax to check objects
In Groovy a null, void, equal to zero, or empty object evaluates to false, and if not, evaluates to true. Instead of writing null and size checks e.g. if (name != null && name.length > 0) {}, use just the object if (name) {}.
Use ?. operator
Use the safe dereference operator ?., to simplify the code for accessing objects and object members safely. Using this operator, the Groovy compiler checks null objects and null object members, and returns null if the object or the object member is null and never throws a NullPointerException.
Use ?: operator
Use Elvis operator ?: to simplify default value validations.
Use any keyword
If the type of the exception thrown inside a try block is not important, catch any exception using the any keyword.
Use assert
To check parameters, return values, and more, use the assert statement.
Reference
[1] Groovy's syntax: http://groovy-lang.org/style-guide.html
[2] Jenkins: https://jenkins.io/doc/book/getting-started/
[3] Jenkins Pipeline: https://jenkins.io/doc/book/pipeline/
[4] Jenkins Pipeline's syntax: https://jenkins.io/doc/book/pipeline/syntax/
[5] GDK: Groovy Development Kit: http://groovy-lang.org/groovy-dev-kit.html