Test opt-level not behaving as expected

[giarc3]

In ironoxide, we currently have 3 profile sections: [profile.dev], [profile.test], and [profile.release]. We have changed the default opt-level for dev and test to be 2.
I would advocate for setting dev back to 0 in order to allow for fast compilation by RLS while writing new code.

The problem with this is that I believe that [profile.test] is not working as documented. It appears that tests takes the optimization from [profile.dev] instead.

Running time cargo t after already compiling with cargo t --no-run, I get the following:

dev opt-level	test opt-level	test time
2	2	25s
0	2	90s

This suggests that test's opt-level is not respected.

I have seen threads (from years ago) where people suggest that [profile.test] and [profile.bench] be deprecated, as they argue that it should simply inherit from [profile.dev] and [profile.release], respectively, but I haven't seen mention of that happening, and the current docs still mention those sections.

In spite of all this, I would suggest the following:

• Set dev's opt-level to its default (0)
• Remove the [profile.test] section as I find it misleading
• Use cargo t for general testing, and cargo t --release when speed is a factor

[giarc3]

I found some additional information regarding profile optimizations: rust-lang/cargo#7591 (comment)

In particular:

There is some possibly confusing interaction with the test/bench profile. Because dependencies are always built with the dev/release profiles, overridding test/bench usually does not have an effect (unless specifying a workspace member that is being tested/benched). Overriding test/bench was previously prohibited, but was relaxed when named profiles were added.

Stabilizing in Rust 1.41, we will be able to add a section to our Cargo.toml that looks like:

# Set the default for dependencies
[profile.dev.package."*"]
opt-level = 3

which should allow us to optimize our dependencies while lowering the opt-level for dev.