[SR-539] Cascading documentation comments

[gribozavr]

Previous ID	SR-539
Radar	rdar://problem/16512247
Original Reporter	@gribozavr
Type	Bug

Additional Detail from JIRA

Votes	1
Component/s	Source Tooling
Labels	Bug, StarterBug
Assignee	None
Priority	Medium

md5: b8301471acb7f784c7f605035b40a5eb

Issue Description:

Swift should be able to find comments on 'related' decls: we should look at overridden superclass and protocol methods and properties, getters/setters should get comments from the property or subscript, etc.

[swift-ci]

Comment by Dave Addey (JIRA)

Conversely, I suggest that we shouldn't do this kind of substitution for comments on inherited types. For example, if a subclass doesn't have a doc comment, the superclass's doc comment is not a valid substitute.

(I completely agree that this would be useful for members, however.)