Incorrect document regarding default value of `--target-dir` of `cargo install`

[seamlik]

Problem

In the manual, it says the default value of --target-dir is target in the root of the workspace. However when I install a crate, the build cache is actually somewhere else. Only if I add --target-dir target to the command would Cargo put the build cache there.

Motivation

When running the verification on a CI, I expected that we can cache the build of a cargo install as well which saves a lot of time. However I was misguided by the document.

Steps

1. cd into a workspace
2. cargo clean
3. cargo install cargo-audit
4. Observe that no target directory is created

Possible Solution(s)

• Let cargo install place the build cache at target
• Document the actual default place of the build cache

Output of cargo version:

cargo 1.51.0-nightly (783bc43c6 2021-01-20)
Linux 5.8.0-41-generic #46-Ubuntu SMP Mon Jan 18 16:48:44 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux