Display alias target on 'cargo help <alias>`

[sstangl]

Previously, `cargo help <alias>` resolved the alias and displayed the
help for the targeted subcommand. For example, if `br` were aliased to
`build --release`, `cargo help br` would display the manpage for
cargo-build.

With this patch, it will print "'br' is aliased to 'build --release'".

Addresses issue #10138.

This is my first patch to Cargo. I attempted to follow the style of the surrounding code. Please let me know if any changes are required: happy to make them. In particular, I wasn't sure if any tests exist for this path.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

Please see the contribution instructions for more information.

[sstangl]

Aha, found the test location! I'll fix that up.

[sstangl]

One good UX option here may be to show the manpage if the alias is a simple command, e.g., b = build, but show the alias if it's a more complicated command, e.g., br = build --release. That would perhaps be the least surprising change, while still servicing the needs of users who define more complicated aliases. I'll wait for feedback on what direction you'd like to take.

[weihanglo]

Looks great!
Might need to update doc of handle_embedded_help as well? Since we don't display man for alias anymore

cargo/src/bin/cargo/commands/help.rs

Lines 18 to 20 in 6d75259

	/// Returns `true` if a man page was displayed. In this case, Cargo should
	/// exit.
	pub fn handle_embedded_help(config: &Config) -> bool {

[alexcrichton]

@bors: r+

Seems reasonable to me, thanks!

[bors]

📌 Commit 4c66d18 has been approved by alexcrichton

[bors]

⌛ Testing commit 4c66d18 with merge c689f55...

[bors]

☀️ Test successful - checks-actions
Approved by: alexcrichton
Pushing c689f55 to master...

[poliorcetics]

Thank you @sstangl !