Fix unwanted rebuilds in xtask commands

[nicholasbishop]

Recently, cargo xtask test started doing a lot of rebuilding. Possibly this started with cargo 1.85, but I'm not sure.

The behavior was: cargo xtask test builds xtask and all of its dependencies in order to launch xtask. Then it would rebuild everything again to run the test command. If you then ran cargo xtask test a second time, everything would again be rebuilt. In other words, the build cache essentially wasn't working.

Fix by clearing all CARGO env vars in fix_nested_cargo_env.

Also update command_to_string to exclude cleared env vars, otherwise the command logging gets quite verbose.

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)

[phip1611]

I ran this with rust 1.82 und 1.85. The following env vars are deleted

1.82

Deleting cargo env CARGO=/nix/store/9dp7c0afzkkqalj5035ycz7pgb7p9m39-cargo-1.82.0-x86_64-unknown-linux-gnu/bin/cargo
Deleting cargo env CARGO_MANIFEST_DIR=/home/pschuster/dev/other/uefi-rs/xtask
Deleting cargo env CARGO_PKG_AUTHORS=
Deleting cargo env CARGO_PKG_DESCRIPTION=
Deleting cargo env CARGO_PKG_HOMEPAGE=
Deleting cargo env CARGO_PKG_LICENSE=
Deleting cargo env CARGO_PKG_LICENSE_FILE=
Deleting cargo env CARGO_PKG_NAME=xtask
Deleting cargo env CARGO_PKG_README=
Deleting cargo env CARGO_PKG_REPOSITORY=
Deleting cargo env CARGO_PKG_RUST_VERSION=
Deleting cargo env CARGO_PKG_VERSION=0.0.0
Deleting cargo env CARGO_PKG_VERSION_MAJOR=0
Deleting cargo env CARGO_PKG_VERSION_MINOR=0
Deleting cargo env CARGO_PKG_VERSION_PATCH=0
Deleting cargo env CARGO_PKG_VERSION_PRE=

1.85

Deleting cargo env CARGO=/home/pschuster/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/cargo
Deleting cargo env CARGO_HOME=/home/pschuster/.cargo
Deleting cargo env CARGO_MANIFEST_DIR=/home/pschuster/dev/other/uefi-rs/xtask
Deleting cargo env CARGO_MANIFEST_PATH=/home/pschuster/dev/other/uefi-rs/xtask/Cargo.toml
Deleting cargo env CARGO_PKG_AUTHORS=
Deleting cargo env CARGO_PKG_DESCRIPTION=
Deleting cargo env CARGO_PKG_HOMEPAGE=
Deleting cargo env CARGO_PKG_LICENSE=
Deleting cargo env CARGO_PKG_LICENSE_FILE=
Deleting cargo env CARGO_PKG_NAME=xtask
Deleting cargo env CARGO_PKG_README=
Deleting cargo env CARGO_PKG_REPOSITORY=
Deleting cargo env CARGO_PKG_RUST_VERSION=
Deleting cargo env CARGO_PKG_VERSION=0.0.0
Deleting cargo env CARGO_PKG_VERSION_MAJOR=0
Deleting cargo env CARGO_PKG_VERSION_MINOR=0
Deleting cargo env CARGO_PKG_VERSION_PATCH=0
Deleting cargo env CARGO_PKG_VERSION_PRE=

The effective difference is that CARGO_HOME and CARGO_MANIFEST_PATH have been added.

Given these facts, I don't exactly understand the cause of the rebuilds. But thank you for fixing it.