Code compiles on playground but fails when passed via stdin to rustc

MusicalNinjaDad:

My worry would be autocfg. If anyone has probes with a leading #[deny(warnings)] then that could break with rather nasty consequences

Unsure about T-compiler but T-cargo has decided to not support build probes, see Provide a way for build scripts to invoke rustc the way cargo would · Issue #11244 · rust-lang/cargo · GitHub

Without Cargo support, build probes have some gotchas.

Also, for fully general build probes, like autocfg, the edïtion should be set. The caller has to do this currently. We've approved telling build scripts the edition but it is unclear if that might get superseded by a compiler feature.