Add spec for brew package URLs

PURL-TYPES.rst

@@ -87,6 +87,32 @@ bitnami
       pkg:bitnami/[email protected]
       pkg:bitnami/[email protected]?arch=arm64
 
+brew
+----
+``brew`` for Homebrew-based packages:
+
+- There is no default package repository; this should be implied either from
+  the ``namespace`` or using a tap URL via the ``tap_url`` qualifier.
+- The ``namespace``, which is called a "Tap" in Homebrew terminology, defaults to ``homebrew/core``.
+
+  - When the ``tap_url`` qualifier is not specified, the Tap identifier corresponds to the URL
+    ``https://github.com/{org}/homebrew-{tap}``, such as
+    ``https://github.com/homebrew/homebrew-core`` for ``homebrew/core``.
+  - When the ``tap_url`` qualifier is specified, the Tap identifier is the local name of the Tap.
+
+- The ``name`` is the formula name. Formula names that contain ``@`` must be percent-encoded,
+  such as ``postgresql%4012`` for ``postgres@12``.
+- The ``version`` is the formula version.
+- Qualifier ``tap_url``: for taps that are not on GitHub or otherwise require an explicit URL,
+  this is the full ``git`` URL to the tap.
+- Examples::
+
+      pkg:brew/[email protected]
+      pkg:brew/postgresql%[email protected]
+      pkg:brew/homebrew/core/[email protected]
+      pkg:brew/some-org/some-tap/[email protected]
+      pkg:brew/some-org/some-tap/[email protected]?tap_url=https://git.example.com/some-org/some-tap.git
+
 cocoapods
 ---------
 ``cocoapods`` for CocoaPods:

test-suite-data.json

@@ -550,5 +550,113 @@
     "qualifiers": null,
     "subpath": null,
     "is_invalid": false
+  },
+  {
+    "description": "brew names may contain at signs",
+    "purl": "pkg:brew/postgres%4016",
+    "canonical_purl": "pkg:brew/postgres%4016",
+    "type": "brew",
+    "namespace": null,
+    "name": "postgres@16",
+    "version": null,
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": false
+  },
+  {
+    "description": "brew may contain multiple at signs",
+    "purl": "pkg:brew/postgres@[email protected]",
+    "canonical_purl": "pkg:brew/postgres%[email protected]",
+    "type": "brew",
+    "namespace": null,
+    "name": "postgres@16",
+    "version": "16.1",
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": false
+  },
+  {
+    "description": "brew may specify a namespace that uses the Homebrew default tap lookup mechanism",
+    "purl": "pkg:brew/some-org/some-tap/[email protected]?tap_url=https://git.example.com/some-org/some-tap.git",
+    "canonical_purl": "pkg:brew/some-org/some-tap/[email protected]?tap_url=https://git.example.com/some-org/some-tap.git",
+    "type": "brew",
+    "namespace": "https://git.example.com/some-org/some-tap.git",
+    "name": "sqlite",
+    "version": "3.43.2",
+    "qualifiers": { "tap_url": "https://git.example.com/some-org/some-tap.git"},
+    "subpath": null,
+    "is_invalid": false
+  },
+  {
+    "description": "brew may specify a namespace that uses the Homebrew default tap lookup mechanism",
+    "purl": "pkg:brew/some-org/some-tap/[email protected]",
+    "canonical_purl": "pkg:brew/some-org/some-tap/[email protected]",
+    "type": "brew",
+    "namespace": "some-org/some-tap",
+    "name": "sqlite",
+    "version": "3.43.2",
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": false
+  },
+  {
+    "description": "brew may specify a namespace that is its default repository",
+    "purl": "pkg:brew/homebrew/core/[email protected]",
+    "canonical_purl": "pkg:brew/homebrew/core/[email protected]",
+    "type": "brew",
+    "namespace": "homebrew/core",
+    "name": "sqlite",
+    "version": "3.43.2",
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": false
+  },
+  {
+    "description": "brew typical formula",
+    "purl": "pkg:brew/[email protected]",
+    "canonical_purl": "pkg:brew/[email protected]",
+    "type": "brew",
+    "namespace": null,
+    "name": "sqlite",
+    "version": "3.43.2",
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": false
+  },
+  {
+    "description": "invalid brew purl without name",
+    "purl": "pkg:brew/@0.9.1",
+    "canonical_purl": "pkg:brew/@0.9.1",
+    "type": "brew",
+    "namespace": null,
+    "name": null,
+    "version": "0.9.1",
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": true
+  },
+  {
+    "description": "invalid brew purl without version",
+    "purl": "pkg:brew/A3",
+    "canonical_purl": "pkg:brew/A3",
+    "type": "brew",
+    "namespace": null,
+    "name": "A3",
+    "version": null,
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": true
+  },
+  {
+    "description": "brew requires name and version at minimum",
+    "purl": "pkg:brew",
+    "canonical_purl": "pkg:brew",
+    "type": "brew",
+    "namespace": null,
+    "name": null,
+    "version": null,
+    "qualifiers": null,
+    "subpath": null,
+    "is_invalid": true
   }
 ]