`remap-path-prefix` is not convenient to use in .cargo/config for privacy

[Boscop]

Let's say when building your executable for release, you have this goal: Maximum privacy, strip all paths associated with the build machine from the release executable. Requirements:

• it should be doable with no cmd line flags (just a fixed .cargo/config)
• it should work regardless of which machine the build is done on
• it should work regardless of what the path to the project is on the build machine
• it should not require mentioning paths from a specific build machine in any file in the repo (like .cargo/config)

remap-path-prefix-from requires specifying the path to the project. There are 2 problems with it:

1. It's very user-unfriendly, if all someone wants is to just maximum privacy when releasing a binary.
2. It requires specifying the absolute path that should be hidden from the exe, which depends on the folder structure of the build machine, thus it can't be done with a fixed .cargo/config.

It would be better to have an option that:

1. Is easier to use when the goal is maximum privacy.
2. Works independently of the path to the project folder on every build machine that it's run on, not requiring to specify the path. It should be inferred.

It could look like this: --strip-path-prefix and it behaves like remap-path-prefix-from set to the path to the project and remap-path-prefix-to set to the empty string.

If this is too much to ask, as an alternative, it should be possible to pass a placeholder to remap-path-prefix-from that always means "the project's path", so that it can be used inside .cargo/config, agnostic to the build machine / project path.

[joshtriplett]

Ideally, I'd like to see Rust defaulting to omitting full paths, and only including project-root-relative paths. That would make Rust builds more reproducible, as well as hiding potentially private information.

[Evrey]

When using log, I already get project-relative paths for my own code, like src/log.rs. However, for dependencies the full absolute path is logged, for example: /home/evrey/.cargo/registry/src/github.com-1ecc6299db9ec823/winit-0.20.0-alpha6/src/platform_impl/linux/x11/window.rs So… we're half-way there for privacy in paths. I think it may be good enough to start the latter path after .config, displaying it as $CARGO_HOME/registry/… instead.

rust-lang/rfcs#3127 is try for this but yes rust should be reproduce and private by default. they claim will be default but im not trust until i see so

[jyn514]

2. It requires specifying the absolute path that should be hidden from the exe, which depends on the folder structure of the build machine, thus it can't be done with a fixed .cargo/config.

This is tracked in #89434.

The other issues you mentioned look like they would also be solved by -Z remap-cwd-prefix.