Workspace "profile ignored" warning discounts the possibility of publishing binary crates which use profile settings

[daboross]

Problem

When a profile section is provided in the Cargo.toml for a crate in a workspace that isn't the workspace root, the following warning is generated:

warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/daboross/workspace/subcrate/Cargo.toml
workspace: /home/daboross/workspace/Cargo.toml

However, if subcrate is a binary crate published to crates.io, then the profile section will be used when someone cargo installs that crate. Moving the profile section to the workspace root would remove the settings when cargo installing the crate downloaded from crates.io.

Steps

1. Create a workspace & subcrate:

cargo new workspace && cd workspace && cargo new subcrate

2. Add workspace config:

echo "subcrate = { path = 'subcrate' }" >> Cargo.toml
echo "[workspace]" >> Cargo.toml

or copy whole Cargo.toml:

[package]
name = "workspace"
version = "0.1.0"
authors = ["David Ross <daboross@daboross.net>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
subcrate = { path = 'subcrate' }
[workspace]

3. Add profile to subcrate:

echo "[profile.release]" >> subcrate/Cargo.toml
echo "opt-level = 3" >> subcrate/Cargo.toml

Or copy whole Cargo.toml:

[package]
name = "subcrate"
version = "0.1.0"
authors = ["David Ross <daboross@daboross.net>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
[profile.release]
opt-level = 3

4. Build crates:

$ cargo build
warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   /home/daboross/workspace/subcrate/Cargo.toml
workspace: /home/daboross/workspace/Cargo.toml
   Compiling workspace v0.1.0 (/home/daboross/workspace)
    Finished dev [unoptimized + debuginfo] target(s) in 0.36s

Possible Solution(s)

Add a way to ignore this warning, and output a suggestion for that when outputting the error? Could be something like

[cargo-warnings]
ignored-profile = "ignore"

And when the error occurs, something like:

note: this profile will be used when publishing binary crates. To ignore warning, add the following to /home/dabross/workspace/subcrate/Cargo.toml:
  [cargo-warnings]
  ignored-profile = "ignore"

Another option could be to provide an option to copy configuration from workspace root when publishing the crate?

Notes

Output of cargo version: cargo 1.45.0-nightly (258c89644 2020-04-30)

I found this bug from this post on the users.rust-lang.org forum. The user in question decided to simply not have a workspace to avoid this error, but I don't think that's a good solution in general.

[ehuss]

The team discussed this a bit. We feel like it would probably be best if cargo publish would copy the profile from the workspace into the member package. Does that sound like it would resolve your use case?

I have definitely felt uneasy with that warning, since it cannot be silenced. However, I'm also a little uncomfortable with adding config and machinery for silencing it (just to avoid complexity).

[kornelski]

I get the same warning, but I'm not publishing anything. Copying of the profile would not be useful to me.

I combine a few standalone projects into a large workspace using git submodules. In my setup that is easier to work with than Cargo git dependencies and [patch].

The problem is that one of the subprojects pulled into the workspace is usable independently, and has its own profile. That one subproject supports WASM, so it has a profile with panic=abort; opt-level = 's', but I don't want that setting for the whole workspace. I would prefer that subproject to keep its profile when it's used outside of my workspace, but keep the workspace overriding that with its own profile.

So to me Cargo does the right thing. I'm aware the other profile is ignored, and that's exactly what I want. I just don't need to be reminded about this on every build.

[ehuss]

An alternate solution we discussed would be to have some kind of nested workspace support for the git submodule use case. Cargo and Rust have the same problem, since they use git submodules. But it sounds like @kornelski specifically wants to disable the profile. Hmm..

[kornelski]

To me it'd make sense if Cargo had a similar allow/deny mechanism that rustc has.

My problem is also related to lack of per-target profiles: #4897. I wouldn't need the other profile to be ignored in the workspace context if I could limit that profile to WASM targets.

[jrvanwhy]

The team discussed this a bit. We feel like it would probably be best if cargo publish would copy the profile from the workspace into the member package. Does that sound like it would resolve your use case?

Hi, I'm the poster from users.rust-lang.org. Yes, that would resolve my use case.

[DzenanJupic]

I just ran into the issue @kornelski described. I have a workspace, and one of the crates is a WASM application which should be compiled with panic = "abort" and opt-level = 's'. By creating a [profile.release.package.<PACKAGE>] section in the workspace Cargo.toml I can set opt-level = 's'.

For panic = "abort" there seems to be a bug, since when I place it in the [profile.release.package.<PACKAGE>], cargo says:

error: failed to parse manifest at `PATH\TO\WORKSPACE\Cargo.toml`

Caused by:
  `panic` may not be specified in a `package` profile

And when I place it in the crates Cargo.toml cargo says:

warning: profiles for the non root package will be ignored, specify profiles at the workspace root:
package:   PATH\TO\WORKSPACE\PACKAGE\Cargo.toml
workspace: PATH\TO\WORKSPACE\Cargo.toml

So there's no way of setting panic = "abort" while making cargo happy.

[nickgerace]

I ran into this as well. Same as @DzenanJupic with panic = "abort".

[JesusGuzmanJr]

I also ran into the same issue as @DzenanJupic. I was able to sidestep the issue by removing the cargo workspace from my project and instead use workspace emulation as provided by cargo-make.

Before
So instead of using a cargo workspace with a virtual manifest like this:

# Cargo.toml
[workspace]
members = ["crate1", "crate2"]

After
I now use Makefiles in all my crates. This is what the root Makefile looks like:

# Makefile.toml
[env]
# this tells cargo-make that this directory acts as a workspace root
CARGO_MAKE_WORKSPACE_EMULATION = true

# a list of crate members. since we do not have a Cargo.toml, we will need to specify this in here.
CARGO_MAKE_CRATE_WORKSPACE_MEMBERS = [
  "crate1",
  "crate2",
]

After setting up Makefiles in all my other crates I can now build my project like so:

Debug Build
cargo make build

Release Build
cargo make build --profile production

With cargo-make's workspace emulation, I no longer get the "profile ignored" warning and my WASM is optimized in release builds. 🎉

[JoshMcguigan]

I have the same issue with wanting to specify panic = "abort" for one package in a workspace.

I noticed the cargo docs mention this limitation:

[profile.<name>.package.<name>]  # Override profile for a package.
# Same keys for a normal profile (minus `panic`, `lto`, and `rpath`).

Is there a fundamental reason cargo can't support this? Or is it more a matter of requiring some additional work to implement?