cargo test shouldn't build crates that don't contain tests

[oriongonza]

Problem

If in my workspace I have the following crate graph:
A - B - C
But only A and B have tests, C will also build even when it has no reachable tests.

Proposed Solution

Don't build C if it doesn't have tests (or all are #[ignore]d, though this is a stretch).

Realistically this will require some basic level of compiling to check whether there are tests but noting past the macro expasion step.

Notes

No response

[ehuss]

Sorry, I'm not quite understanding what this is asking. Can you give a full, minimal reproduction?

In general, if you don't want C to be tested, then you will have to use test=false and doctest=false in its target definition.