API: supply additional data for requirements

[EricFromCanada]

• 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?

---

Adds additional fields to the "requirements" section of the formula JSON API; specifically:

• for :maximum_macos, changes name to "maximum_macos"
• adds version which can have a value for "macos", "maximum_macos", "java", and "xcode" requirements, and is null for others
• adds contexts which is a list of one or both "build" and "test" and an empty list otherwise
• also adds an inspect method to macos_requirement.rb so it includes the comparator and version

Merging this will allow fixing the display of e.g. macOS requirements for pages like https://formulae.brew.sh/formula/valgrind which don't include any version information.

Example output

# macos run version
$ brew info --json go | jq ".[0].requirements"
[
  {
	"name": "macos",
	"cask": null,
	"download": null,
	"version": "10.11",
	"contexts": []
  }
]

# maximum_macos run version
$ brew info --json valgrind | jq ".[0].requirements"
[
  {
	"name": "maximum_macos",
	"cask": null,
	"download": null,
	"version": "10.13",
	"contexts": []
  }
]

# maximum_macos build version
$ brew info --json gcc@5 | jq ".[0].requirements"
[
  {
	"name": "maximum_macos",
	"cask": null,
	"download": null,
	"version": "10.13",
	"contexts": [
	  "build"
	]
  }
]

# xcode build
$ brew info --json llvm | jq ".[0].requirements"
[
  {
	"name": "xcode",
	"cask": null,
	"download": null,
	"version": null,
	"contexts": [
	  "build"
	]
  }
]

# xcode version
$ brew info --json rswift | jq ".[0].requirements"
[
  {
	"name": "xcode",
	"cask": null,
	"download": null,
	"version": "10.0",
	"contexts": []
  }
]

# xcode version build
$ brew info --json plank | jq ".[0].requirements"
[
  {
	"name": "xcode",
	"cask": null,
	"download": null,
	"version": "11.3",
	"contexts": [
	  "build"
	]
  }
]

# xcode versions for run & build
$ brew info --json needle | jq ".[0].requirements"
[
  {
	"name": "xcode",
	"cask": null,
	"download": null,
	"version": "10.0",
	"contexts": [
	  "build"
	]
  },
  {
	"name": "xcode",
	"cask": null,
	"download": null,
	"version": "6.0",
	"contexts": []
  }
]

# xcode version for build & test
$ brew info --json sourcedocs | jq ".[0].requirements"
[
  {
	"name": "xcode",
	"cask": null,
	"download": null,
	"version": "10.3",
	"contexts": [
	  "build",
	  "test"
	]
  }
]

# java version
$ brew info --json blazegraph | jq ".[0].requirements"
[
  {
	"name": "java",
	"cask": "adoptopenjdk",
	"download": null,
	"version": "1.7+",
	"contexts": []
  }
]

# java version for build & test
$ brew info --json infer | jq ".[0].requirements"
[
  {
	"name": "java",
	"cask": "homebrew/cask-versions/adoptopenjdk8",
	"download": null,
	"version": "1.8",
	"contexts": [
	  "build",
	  "test"
	]
  }
]

  

[MikeMcQuaid]

Good call! One tiny nit.

[MikeMcQuaid]

Much better ❤️

[MikeMcQuaid]

Nice work as usual @EricFromCanada!