vscode extension: custom "check" using cargo alias is not fully implemented

[jmaargh]

Cargo has a neat aliasing feature which can use one of the two syntaxes in the .cargo/config.toml file (or equivalent):

[alias]
c1 = "clippy"
c2 = ["clippy", "--", "-W", "clippy::pedantic"]

Both of these work as expected in the terminal, but only c1 works when you set it as "rust-analyzer.checkOnSave.command": "c1" in vscode. With c2 I get the following in the extension logs (RA_LOG=warn):

[ERROR flycheck] Flycheck failed to run the following command: "cargo" "c2" "--workspace" "--message-format=json" "--manifest-path" "/home/john-mark/code/Rust/emugb/Cargo.toml" "--all-targets"
[ERROR rust_analyzer::main_loop] cargo check failed: Cargo watcher failed, the command produced no valid metadata (exit code: ExitStatus(ExitStatus(25856)))

[jonas-schievink]

I think this is working as expected. For commands that are not CLI-compatible with cargo check, you can set rust-analyzer.checkOnSave.overrideCommand instead.

[jmaargh]

That's a bit of a pain. I was hoping to have a single source-of-truth for preferred clippy flags, and I obviously don't want to have --message-format=json when running in the terminal.

[jmaargh]

As an aside, it would be lovely if malformed checkOnSave.commands didn't just silently fail: no error popup, not even a log message until I re-started with an environment variable set.

[lnicola]

I was hoping to have a single source-of-truth for preferred clippy flags

That's clippy.toml, right?

[jmaargh]

@lnicola I think it should, but the clippy people apparently disagree: rust-lang/rust-clippy#1313

[Veykril]

We now show an error pop up and proper information, otherwise this works as intended.