Config env snapshot doesn't handle case-insensitive env vars correctly on windows

[sokra]

Problem

Some recent changes introduce snapshotting of env variables:

cargo/src/cargo/util/config/mod.rs

Lines 209 to 210 in a5d47a7

	/// Environment variables, separated to assist testing.
	env: HashMap<String, String>,

e. g. this PR #11727 by @kylematsuda

That introduces a little bug on windows where env vars are case-insensitive. env::var_os would handle that correctly, but config.get_env_os does a HashMap lookup which is case-sensitive.

e. g. the mentioned PR breaks the lookup of cargo subcommands on windows (where the env var is called Path instead of PATH).

Steps

1. On windows install a cargo subcommand into a different directory
2. Add the directory to your PATH
3. Run cargo
4. Cargo says: no such command: <subcommand>

Workaround:

set PATH2=%PATH%
set PATH=
set PATH=%PATH2%
set PATH2=

This changes the casing of the env variable.

Possible Solution(s)

Wrap the keys in the env snapshot HashMap with some case-insenstive NewType struct.

Notes

No response

Version

nightly-2023-03-01

[kylematsuda]

Hi, thanks for the detailed explanation. Sorry about this, I didn't know that env vars are case-insensitive on Windows until now.

The Config has another hashmap (upper_case_env) that contains the environment variables converted to upper case. @ehuss, do you think it might be an acceptable workaround to (1) convert the variable name to upper case, then (2) check in upper_case_env if the variable is not found in env (on Windows only)?

[ehuss]

Hm, I don't think that will work perfectly since upper_case_env modifies - to _ also. I can't offhand think of way to do this without having two separate maps (one with - converted, and one without).

I believe Windows does case conversion a little differently from how Rust does it (and it depends on the version of Windows), but I think for our purposes, to_uppercase() should be ok.

[ChrisDenton]

Btw, I wrote a detailed comment on a similar issue elsewhere.