Tracking Issue for RFC 3013: Checking conditional compilation at compile time

[ehuss]

This is a tracking issue for the RFC 3013: Checking conditional compilation at compile time (rust-lang/rfcs#3013).

Issues: F-check-cfg --check-cfg
Documentation: https://doc.rust-lang.org/nightly/unstable-book/compiler-flags/check-cfg.html

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Implement the RFC (cc @rust-lang/compiler -- can anyone write up mentoring instructions?)
• Adjust documentation (check_cfg - Unstable book)
• Stabilization PR (FCP: Tracking Issue for RFC 3013: Checking conditional compilation at compile time #82450 (comment))

Unresolved Questions

• Which cfgs should be implicitly included? See this list in bootstrap for an example of some values that need "adding in" atop compiler defaults. (Try to go to master in the link above; the list may have been updated since then).

Implementation history

• Implement --check-cfg option (RFC 3013), take 2 #93915
• Add -Z check-cfg-features to enable compile-time checking of features cargo#10408
• Add -Z check-cfg-features support for rustdoc cargo#10428
• Add support for rustc --check-cfg well known names and values cargo#10486
• and many more