As per
https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html
Before that, there were 91 separate integration tests binary.
(As discussed on Discord — I've done the `uv` crate, there's still a few
more commits coming before this is mergeable, and I want to see how it
performs in CI and locally).
It transpires that detecting the directory a script was sourced from is
non-trivial across `bash`, `ksh` and `zsh`.
The previous version was a one-liner and supported `bash` and `zsh` but
not `ksh`.
It is possible to keep the one-liner and add `ksh` support, but that is
mutually-exclusive with `zsh`.
Therefore, the only way to square this circle is to add an `if` block. A
silver lining here is that although longer, the script is probably
easier to follow as there is less code-golfing going on.
## Summary
Largely based on rustup's implementation (linked in the source).
Closes#5027.
## Test Plan
- Changed the executable directory to `uv/foo`.
- Ran script; verified that I could access executables in `foo`.
