allow runner configuration to use feature flags

[BartMassey]

Problem

In the embedded space, I have several chips with the same target triple, but which require a different runner. My Cargo.toml contains features that are sufficient to know which runner to use. However, my .cargo/config.toml cannot choose a runner based on those features. Error-prone manual editing is required.

(Specifically, target is thumbv7em-none-eabihf, runner is probe-rs run --chip=nrf52833-xxAA or probe-rs run --chip=nrf52840-xxAA depending on board feature flags.)

Proposed Solution

It would be great to be able to have the full Cargo cfg() available in cargo.toml. Specifically, it would be nice to be able to write something like

[target.'cfg(feature = "myfeature")']

I'm not wedded to the particulars: anything that lets me pick the correct runner automagically would be fine.

Notes

No response

[weihanglo]

Thanks for providing your use case. This seems like a duplicate of #8170. In the meanwhile custom --cfg is an alternative. Close in favor of #8170.

See also #14306.