Support nested structs of the form A::B = Struct.new(...)

[marshall-lee]

Description

On my codebase, yard fails when it happens to meet Struct.new assigned to a nested constant e.g. this code:

A::B = Struct.new(:a, :b, :c)

fails with the following error:

[warn]: in YARD::Handlers::Ruby::ConstantHandler: Undocumentable Struct assignment to A::B

Completed Tasks

• I have read the Contributing Guide.
• The pull request is complete (implemented / written).
• Git commits have been cleaned up (squash WIP / revert commits).
• I wrote tests and ran bundle exec rake locally (if code is attached to PR).

[lsegal]

Thanks for getting this fixed!