Note: the test actually does not pass with the current diff, but it does if I make the feature optional:

  def install
    system "cargo", "install",
      *("--features starship-prompt" if build.with? "starship"),
      "--locked",
      "--root", prefix,
      "--path", "."
  end

Should I do that, or update the test to expect the starship prompt?

Edit: I fixed the test to match the output with the stable features enabled, which include the starship prompt.

I am also wondering if we should default to the stable features instead of singling out the starship prompt feature (which is included in the stable features set).

However, I was unable to get it to work with a similar syntax to the one currently in this PR (i.e. --features=stable), based on the instructions from the official README:

 def install
-    system "cargo", "install", "--locked", "--root", prefix, "--path", "."
+    system "cargo", "install", "--features", "stable", "--locked", "--root", prefix, "--path", "."
 end

Any thoughts about whether this is a better approach, and if so, how to make it work?

Ah, I just now read the release notes for 0.7.0. Turns out the stable features set is a new addition, so it should be available if we update the version in this PR. I'll do so tomorrow.

PR now updated to perform the 0.7.0 update as well as enable the stable features during build.

@BrewTestBot test this please.

lgtm, thanks @waldyrious!!