type_annotate_public_apis

Type annotate public APIs.

This rule is available as of Dart 2.0.0.

This rule has a quick fix available.

From Effective Dart:

PREFER type annotating public APIs.

Type annotations are important documentation for how a library should be used. Annotating the parameter and return types of public methods and functions helps users understand what the API expects and what it provides.

Note that if a public API accepts a range of values that Dart's type system cannot express, then it is acceptable to leave that untyped. In that case, the implicit dynamic is the correct type for the API.

For code internal to a library (either private, or things like nested functions) annotate where you feel it helps, but don't feel that you must provide them.

BAD:

install(id, destination) {
  // ...
}

Here, it's unclear what id is. A string? And what is destination? A string or a File object? Is this method synchronous or asynchronous?

GOOD:

Future<bool> install(PackageId id, String destination) {
  // ...
}

With types, all of this is clarified.

To enable the type_annotate_public_apis rule, add type_annotate_public_apis under linter > rules in your analysis_options.yaml file:

linter:
  rules:
    - type_annotate_public_apis