Confusing error when attempting to use alias from --config PATH

[ian-h-chamberlain]

Problem

Hopefully this isn't a duplicate, I haven't been able to find any similar issues so far.

Attempting to use an alias from a config file included with --config fails with an error message that doesn't really explain what went wrong:

$ cat ~/.config/cargo/custom.toml 
───────┬──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: /home/ian/.config/cargo/custom.toml
───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ [alias]
   2   │ p = "publish --dry-run"
───────┴──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

$ command cargo --config ~/.config/cargo/custom.toml p 
error: no such command: `p`

    Did you mean `p`?

    View all installed commands with `cargo --list`
    Find a package to install `p` with `cargo search cargo-p` 

The suggested cargo --list is doesn't help, since it still shows the alias from the included config file:

$ command cargo +nightly --config ~/.config/cargo/custom.toml --list | grep -C2 'alias: pub'
    override
    owner                Manage the owners of a crate on the registry
    p                    alias: publish --dry-run
    package              Assemble the local package into a distributable tarball
    pkgid                Print a fully qualified package specification

Steps

1. Create a config file with an alias (see above for example, e.g. p)
2. Attempt to use that alias by running cargo --config $PATH p
3. Observer error

Possible Solution(s)

What I would really like is for this to Just Work (i.e. treat the alias the same as if it was automatically picked up from ~/.config/cargo/config.toml; I wanted to use this as a workaround for #7723 not being implemented so I could add machine-specific aliases by including files from the command line.

At the very least, I think the error message Did you mean `p` message could be updated to include a message about this being unsupported or something like that.

Notes

A workaround is to create e.g. a custom cargo-p subcommand but I'd rather not have to do this for a lot of little convenience aliases and instead keep them all together in one config file.

Version

$ command cargo +nightly -vV
cargo 1.88.0-nightly (7918c7eb5 2025-04-27)
release: 1.88.0-nightly
commit-hash: 7918c7eb59614c39f1c4e27e99d557720976bdd7
commit-date: 2025-04-27
host: x86_64-unknown-linux-gnu
libgit2: 1.9.0 (sys:0.20.0 vendored)
libcurl: 8.12.1-DEV (sys:0.4.80+curl-8.12.1 vendored ssl:OpenSSL/3.4.1)
ssl: OpenSSL 3.4.1 11 Feb 2025
os: NixOS 25.5.0 [64-bit]

[ehuss]

Thanks for the report! I believe this is a duplicate of #10853, so closing in favor of that.

[ian-h-chamberlain]

Ah, I forgot to check if --config alias.foo had the same effect, maybe I would have found that issue if I thought to look for it. Good to know that CARGO_ALIAS_FOO also works, maybe I will be able to use that as a workaround in my case, thanks!