Presubmit checks

All changelists sent to Fuchsia undergo a series of static analysis checks in presubmit.

Types of checks

Language linters

Linters are run automatically for a variety of languages and will leave comments in the Checks tab of Gerrit.

Presubmit tools

Some of the presubmit checks are tools that are language-agnostic but provide stronger confidence in the quality of a changelist.

keep-sorted

keep-sorted is an opt-in linter that enforces that source code lines are kept in alphabetical order. It can be enabled by wrapping a code block in keep-sorted start and keep-sorted end comments.

For example, the following list's elements will be required to be in alphabetical order, enforced by presubmit checks:

a_list = [
    # keep-sorted start
    "bar",
    "baz",
    "foo",
    # keep-sorted end
]

keep-sorted is language-agnostic and supports "#" and "//" comments.

See the upstream documentation for all options.

keep-sorted is also enforced by fx format-code.

IfThisThenThat

IfThisThenThat is a check that can be used to ensure files that co-change with one another stay synchronized. If one file changes, a warning is given that the other file(s) should change too in the same changelist. Ideally, such a check should not be necessary, but can come up when executable code needs to be synchronized with configuration files.

IfThisThenThat leaves warnings and so does not block changelist submission.

Example

Unlike other presubmit checks which operate independently, IFTTT checks need to be manually implemented. To set up a new IFTTT check, insert the special comments // LINT.IfChange and // LINT.ThenChange(<other_file_path>) in each file that should be updated together.

In the following example, IFTTT checks are implemented for test.go and main.rs. If only one of the files change, a warning appears in Gerrit.

test.go

import fmt

// LINT.IfChange

fmt.Println("When this block changes, so must main.rs")

// LINT.ThenChange(main.rs)

main.rs

// LINT.IfChange

println!("When this block changes, so must test.go");

// LINT.ThenChange(test.go)

Note that for Markdown files, the structure must be wrapped in comments so that Markdown ignores the syntax.

<!--

// LINT.IfChange

-->

Block to be changed.

<!--

// LINT.ThenChange(test.go)

-->

IfThisThenThat supports absolute file paths (those that start with /), and relative paths (those that do not start with /).

If the text within the LINT.IfChange/ThenChange directives is altered, so too must the other file that is pointed to. Files should always have the LINT directives in each file that is joined. A one-way directive would mean that one file can lose synchronization from the other.

If an IfThisThenThat directive is violated, a comment is left on the CL:

The warning also appears on the Checks tab: