Stabilize named profiles
This stabilizes the named profiles feature. As an overview of what this does, it allows specifying custom named profiles, such as:
```toml
[profile.release-lto]
inherits = "release"
lto = true
```
And enables the use of the `--profile` CLI option to choose a profile by name.
Another key change here is that cargo now only uses a single profile per command. Previously, some commands such as `cargo test` would use a mix of profiles based on which package and target were being built.
### Summary of new behavior
* Profiles can now have arbitrary names. New profiles require the `inherits` key.
* The `--profile` flag is now available on all build commands.
* The `CompileMode` is no longer considered for choosing the profile, only one profile will be used. Previously, building a test, benchmark, or doctest would use the test or bench profile, and all dependencies would use the dev/release profiles. This change is done to arguably make it easier to understand, and to possibly give more desired and intuitive behavior.
* The `test` profile now inherits settings from the `dev` profile (and `bench` from `release`).
### Deviations from the original RFC and implementation
* The original RFC indicated that `--all-targets` without `--profile` would retain the old behavior where it would use different profiles for different targets. However, the implementation uses a single profile, to avoid confusion and to keep things simple.
* The `dir-name` key is not exposed to the user. The implementation is retained to handle mapping of built-in profile names (test/dev→debug, bench→release). This can be exposed in the future if necessary.
### Notes about this PR
* Fixed an issue where the duplicate package override check would randomly return matches for inherited profiles like `test`.
* I left some of the old, vestigial code behind to possibly make it easier to revert this PR if necessary. If this does land, I think it can be eventually removed (code using `Feature::named_profiles` and various things using `named_profiles_enabled`).
* Added `target` to reserved list, just because.
* Adds a warning if `--release` is combined with `--profile` in `cargo rustc`, `check`, or `fix`. The `--release` flag was being ignored.
### Hazards and concerns
* This has had very little real-world testing.
* Custom profile directories may conflict with other things in the `target` directory. We have reserved profile names that currently conflict (such as `doc` or `package`). However, they can still collide with target names. This also presents a hazard if Cargo ever wants to add new things to that top directory. We decided to proceed with this because:
* We currently have no plans to add new built-in profiles.
* We have reserved several profile names (including anything starting with "cargo"), and the profile name syntax is deliberately limited (so cargo is still free to add `.` prefixed hidden directories).
* A user creating a profile that collides with a target name resides in the "don't do that" territory. Also, that shouldn't be catastrophic, as the directories are still somewhat organized differently.
* Artifacts may no longer be shared in some circumstances. This can lead to substantially increased `target` directory sizes (and build times), particularly if the `test` profile is not the same as the `dev` profile. Previously, dependencies would use the `dev` profile for both. If the user wants to retain the old behavior, they can use an override like `[profile.test.package."*"]` and set the same settings as `dev`.
* This may break existing workflows. It is possible, though unlikely, that changes to the profile settings will cause changes to how things build in such a way to break behavior.
* Another example is using something like `cargo build` to prime a cache that is used for `cargo test`, and there is a custom `test` profile, the cache will no longer be primed.
* The legacy behavior with `cargo rustc`, `cargo check`, and `cargo fix` may be confusing. We may in the future consider something like a `--mode` flag to formalize that behavior.
* The `PROFILE` environment variable in build scripts may cause confusion or cause problems since it only sets `release` or `debug`. Some people may be using that to determine if `--release` should be used for a recursive `cargo` invocation. Currently I noted in the documentation that it shouldn't be used. However, I think it could be reasonable to maybe add a separate environment variable (`PROFILE_NAME`?) that exposes the actual profile used. We felt that changing the existing value could cause too much breakage (and the mapping of debug→dev is a little awkward).
Closes #6988
projects / cargo.git / commitdiff