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Native Image Code Style

To ensure the quality of code and that all contributors follow the same standards, we established a ruleset that grew over time and proved to be useful. Note that the rules are open for discussion!

Source Code Formatting #

The IDE projects generated with mx ideinit are configured with strict formatting rules. In Eclipse, when a file is saved, it is automatically formatted according to these rules. The configuration includes special comments which can be used to relax checks in particular regions of code.

Source code formatting can be disabled with special comments:

//@formatter:off

//@formatter:on

Comment reformatting can be disabled like this:

/*-
 *
 */

Checks with Checkstyle #

Checkstyle is used to verify adherence to the style rules. It can be run manually with mx checkstyle.

The default Checkstyle rules are defined in src/com.oracle.svm.core/.checkstyle_checks.xml and define various special comments, including

//Checkstyle: stop method name check

//Checkstyle: resume method name check

and similar commands for other checks that can be disabled (including general stop and resume commands). Of course, ensuring a reasonable use of these comments is a matter for code review.

If a project requires a different set of Checkstyle rules, this can be specified in mx.substratevm/suite.py by changing the value of the project’s checkstyle attribute (which, by default, references com.oracle.svm.core). Specific code files can be excluded from checkstyle on a directory granularity with a file src/<project name>/.checkstyle.exclude. Such an exclusion file must contain one directory per line, with paths relative to the project root. The file must be explicitly added with git add because git will ignore it by default.

When pulling a changeset which adds or removes Checkstyle XML files, the IDE might show inappropriate style warnings or errors. This is resolved by running mx ideinit and cleaning the affected projects.

IDE Integration #

IDE plugins can be helpful in adhering to style rules. Some examples are:

• Eclipse Checkstyle Plugin: reports Checkstyle violations in Eclipse, making it unnecessary to run mx checkstyle manually.
• IntelliJ Eclipse Code Formatter: formats source files in IntelliJ according to Eclipse IntelliJ rules. This plugin is automatically configured by mx ideinit.
• IntelliJ Save Actions to automatically format files before saving them.

See the documentation on IDE integration for further suggestions.

Further Reading #

• Native Image Hosted and Runtime Options