Tracking issue to stabilize --print target-spec-json

[cardoe]

This issue is meant to track the stabilization of the rustc flag --print target-spec-json which will output the currently selected target as a valid target spec that can be loaded with --target for only the same version of the compiler that generated it. This explicitly avoids saying that target specs are stable but instead intends to assist target spec users to know that their configuration will work with the current version of the compiler.

ref #38061

[Mark-Simulacrum]

We currently don't even seem to know about this unless -Zunstable-options is passed, which make it incredibly hard to discover. I think there's a note somewhere about that, but I don't know quite where. Just noting here.

[zackmdavis]

don't even seem to know about this unless -Zunstable-options is passed, which make it incredibly hard to discover

(probably bug #41683, fixed in #43260)

[cardoe]

ping on possibly stabilizing this.

[nrc]

We discussed this at the dev-tools meeting today. The general feeling was that while this is a fine feature with no obvious problems, there is not a lot of pressure to stabilise, and that given that target specs are unstable, it is probably best not to rush into that.

@cardoe Is there motivation from your end to have this on stable, rather than nightly-only?