Should cargo config get print warning if proxy config found in git/libcurl ?

[Carreau]

Problem

In #12566 it was slightly challenging to diagnose the issue as cargo +nightly -Zunstable-options config get http.proxy would say error: config value http.proxy is not set while proxy value was read from git configuration.

Proposed Solution

cargo config get already have logic and maybe_env utils function to print things like:

The following environment variables may affect the loaded values

pub fn http_proxy_exists(http: &CargoHttpConfig, config: &Config) -> bool also exists and has a more reliable logic as to wether a proxy is set.

In pub fn get I suggest to peak at the requested key and if it is either http or http.proxy do something similar at maybe_env, and print a warning like:

http.proxy may be affected by your git configuration or one of "http_proxy", "HTTP_PROXY", "https_proxy", "HTTPS_PROXY" env variable.

Notes

We can even likely modify proxy.rs, with crate-private functions to tell us where the proxy is set and have --show-origin works as well.

[weihanglo]

Thanks for the proposal. It is indeed a great idea to have a custom message for each key. Since cargo config get is still unstable, I lean towards not adding ad-hoc message at this moment.

#12087 is a relevant issue that a config value is intertwined with other environment variables. I wonder if we can revise the way we document environment variable for all config values. Like, only show the CARGO_* environment variable that is part of Cargo's configuration system. For config values that may be affected by other environments, just document the precedence explicitly and clearly.

---

Let's focus on documentation first!

triage:

@rustbot label -S-triage +S-documenting-cargo-itself +A-configuration +S-needs-design +E-medium

[Carreau]

For config values that may be affected by other environments, just document the precedence explicitly and clearly.

I think this is already clearly documented:

Sets an HTTP and HTTPS proxy to use. The format is in [libcurl format] as in
`[protocol://]host[:port]`. If not set, Cargo will also check the `http.proxy`
setting in your global git configuration. If none of those are set, the
`HTTPS_PROXY` or `https_proxy` environment variables set the proxy for HTTPS
requests, and `http_proxy` sets it for HTTP requests.

With one caveat, it says global configuration while I believe it also looks at local/.git/config

The precedence of CARGO_* is also quite explicit:

[...] the environment variable `CARGO_FOO_BAR` [...] 

Environment variables will take precedence over TOML configuration files. [...]

Since cargo config get is still unstable, I lean towards not adding ad-hoc message at this moment.

... Or do you mean "documenting in the output of cargo config get ?

[weihanglo]

I am thinking of making changes to configuration.md in general. But you're right, this issue be scoped in proxies itself. For general doc enhancements I should have opened a new issue.

Okay. I'll let this remain open for ad-hoc warning message.

@rustbot label -A-documenting-cargo-itself +Z-cargo-config