bazel: python executable required (#28286)

* bazel: python executable required

* python: add autodetection of +pythoncmd

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

@@ -110,7 +110,7 @@ class Bazel(Package):
     variant('nodepfail', default=True, description='Disable failing dependency checks due to injected absolute paths - required for most builds using bazel with spack')
 
     depends_on('java', type=('build', 'run'))
-    depends_on('python', type=('build', 'run'))
+    depends_on('python+pythoncmd', type=('build', 'run'))
     depends_on('zip', when='platform=linux', type=('build', 'run'))
 
     # make work on power9 (2x commits)

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

@@ -271,6 +271,13 @@ def determine_variants(cls, exes, version_str):
         python = Executable(exes[0])
 
         variants = ''
+        for exe in exes:
+            if os.path.basename(exe) == 'python':
+                variants += '+pythoncmd'
+                break
+        else:
+            variants += '~pythoncmd'
+
         for module in ['readline', 'sqlite3', 'dbm', 'nis',
                        'zlib', 'bz2', 'lzma', 'ctypes', 'uuid']:
             try: