rustc man page does not match `rustc --help` output

[h3fang]

Location (URL)

https://github.com/rust-lang/rust/blob/main/src/doc/man/rustc.1#L65

Summary

The rustc man page shows

-O
    Equivalent to -C opt-level=2.

that's different from rustc output

❯ /usr/bin/rustc --help | grep -- "-O"
    -O                  Equivalent to -C opt-level=3
❯ rustc -V
rustc 1.91.1 (ed61e7d7e 2025-11-07) (Arch Linux rust 1:1.91.1-2)

More information from https://bbs.archlinux.org/viewtopic.php?pid=2277265#p2277265

[bjorn3]

The man page was last updated 3 years ago to match the rustc --help output, but the -Copt-level default was changed less than a year ago. Maybe we should write something to automatically generate the man page from the rustc --help output?

[h3fang]

Yes, there is a issue tracking that #98977, but it hasn't updated for years as well.