Bazel: add spack external find support (#18008)

var/spack/repos/builtin/packages/bazel/package.py

@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import re
+
 
 class Bazel(Package):
     """Bazel is an open-source build and test tool similar to Make, Maven, and
@@ -135,6 +137,14 @@ class Bazel(Package):
 
     phases = ['bootstrap', 'install']
 
+    executables = ['^bazel$']
+
+    @classmethod
+    def determine_version(cls, exe):
+        output = Executable(exe)('version', output=str, error=str)
+        match = re.search(r'Build label: ([\d.]+)', output)
+        return match.group(1) if match else None
+
     def url_for_version(self, version):
         if version >= Version('0.4.1'):
             url = 'https://github.com/bazelbuild/bazel/releases/download/{0}/bazel-{0}-dist.zip'