Run rustdoc as part of CI process / resolve failure on docs.rs

[iliekturtles]

https://docs.rs/crate/uom/0.31.0/builds/332917

v0.31.0 failed to build documentation on docs.rs. Likely cause is time/memory limits based on the SIGKILL in the log. The log also highlights a warning that wasn't caught as part of the CI process.

Running rustdoc as part of CI is complicated because cargo doc doesn't provide a way to pass the -D warnings flag to rustdoc itself. rustdoc doesn't use RUSTFLAGS or a similar variable as far as I can tell and the cargo interface provides no escape to send parameters directly rust doc, e.g. cargo doc -- -D warnings.

Currently uom instructs docs.rs to compile with all features.

uom/Cargo.toml

Lines 19 to 20 in 8a4883b

	[package.metadata.docs.rs]
	all-features = true

How much time/memory is this taking? Reduce the number of features? Ask for a sandbox limit increase?

[iliekturtles]

Turns out RUSTDOCFLAGS works.

https://doc.rust-lang.org/cargo/reference/environment-variables.html

[iliekturtles]

Reduced features for docs.rs to drop max memory usage below 3 GB.

~/uom (master)$ /usr/bin/time cargo doc --all-features
    Finished dev [unoptimized + debuginfo] target(s) in 1m 49s
106.50user 43.56system 1:50.04elapsed 136%CPU (0avgtext+0avgdata 3246772maxresident)k
0inputs+0outputs (0major+2071424minor)pagefaults 0swaps

~/uom (master)$ /usr/bin/time -v cargo doc --features "usize u32 u64 isize i32 i64 bigint biguint rational rational32 rational64 bigrational try-from use_serde"
    Finished dev [unoptimized + debuginfo] target(s) in 54.93s
    Maximum resident set size (kbytes): 2536176