`bazel query` call to output groups or providers of a target

Description of the problem / feature request:

It would be handy to be able to use bazel query to list all of the output groups or providers that a target returns. This makes it easier for new users of bazel and for folks developing new rules or aspects to learn what you can rely on from a target and ease the API discovery process.

Feature requests: what underlying problem are you trying to solve with this feature?

There’s a lot of opacity on what a target will actually do and, even with pretty good documentation, you can end up reading a lot of code to figure out what it can give you. A bazel query call you can make to get the output groups or providers would shortcut this process.

[arxanas]

Here is a full example of the new invocation:

bazel cquery '//foo:bar' --output starlark --starlark:expr='providers(target)'

For example, to show just the names of the providers which are available, you can call .keys() on the resulting dict:

bazel cquery '//foo:bar' --output starlark --starlark:expr='providers(target).keys()'

[c-parsons]

Indeed, it does.

See the new documentation for this feature.

Particularly,

list all of the output groups or providers that a target returns

Use the new providers() function of this feature.