style: require tag and revision for git urls

[Rylan12]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?
• Have you successfully run brew man locally and committed any changes?

---

Require a revision for git urls in homebrew/core

Require a tag as well if --strict is passed.

For example, this is always 👍:

url "https://github.com/foo/bar.git",
    tag:      "v1.0.0",
    revision: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"

This is 👍 unless --strict is passed and then 👎:

url "https://github.com/foo/bar.git",
    tag: "v1.0.0"

This is always 👎:

url "https://github.com/foo/bar.git"

[jonchang]

My quick thoughts on this:

has revision and tag: OK
has revision only: strict audit in core, fine everywhere else
has tag only: forbidden in core, fine everywhere else (??)

(I point this out only because I have a bunch of formulae in my personal tap that have only a revision because upstream doesn't believe in version tagging)

[Rylan12]

Yeah, I think that makes sense. There are a small number in homebrew/core that fall into the category of "not believing in tagging" so that would allow those to stay.

In terms of tag only, I don't have a preference as to whether to require it everywhere or only in core. It probably makes sense to only do it in core, though, because we don't need to be making decisions about what formulae are allowed for non-official taps.

[Rylan12]

Okay, I've updated the conditions a little bit:

• No requirements for non-core taps
• git urls must have a revision
• git urls must have a tag when passed with --strict

[jonchang]

Nice work. Let's try it out.

[MikeMcQuaid]

Nice work @Rylan12!