Account for empty strings when splitting the host pattern (#62442)

Improve tests
- add more unit test cases
- add specific integration test with more cases

Testing shows no major downside to calling .strip() twice in a comprehension vs. using a regular for loop and only calling .strip() once. Going with the comprehension for ease of maintenance and because comprehensions are optimized in CPython.

changelogs/fragments/split-host-pattern-empty-strings.yaml

@@ -0,0 +1,2 @@
+bugfixes:
+  - account for empty strings in when splitting the host pattern (https://github.com/ansible/ansible/issues/61964)

lib/ansible/inventory/manager.py

@@ -130,7 +130,7 @@ def split_host_pattern(pattern):
                 '''), pattern, re.X
             )
 
-    return [p.strip() for p in patterns]
+    return [p.strip() for p in patterns if p.strip()]
 
 
 class InventoryManager(object):

test/integration/targets/inventory_limit/aliases

@@ -0,0 +1 @@
+shippable/posix/group4

test/integration/targets/inventory_limit/hosts.yml

@@ -0,0 +1,5 @@
+all:
+  hosts:
+    host1:
+    host2:
+    host3:

test/integration/targets/inventory_limit/runme.sh

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+
+set -eux
+
+trap 'echo "Host pattern limit test failed"' ERR
+
+# https://github.com/ansible/ansible/issues/61964
+
+# These tests should return all hosts
+ansible -i hosts.yml all --limit ,, --list-hosts | tee out ; grep -q 'hosts (3)' out
+ansible -i hosts.yml ,, --list-hosts | tee out ; grep -q 'hosts (3)' out
+ansible -i hosts.yml , --list-hosts | tee out ; grep -q 'hosts (3)' out
+ansible -i hosts.yml all --limit , --list-hosts | tee out ; grep -q 'hosts (3)' out
+ansible -i hosts.yml all --limit '' --list-hosts | tee out ; grep -q 'hosts (3)' out
+
+
+# Only one host
+ansible -i hosts.yml all --limit ,,host1 --list-hosts | tee out ; grep -q 'hosts (1)' out
+ansible -i hosts.yml ,,host1 --list-hosts | tee out ; grep -q 'hosts (1)' out
+
+ansible -i hosts.yml all --limit host1,, --list-hosts | tee out ; grep -q 'hosts (1)' out
+ansible -i hosts.yml host1,, --list-hosts | tee out ; grep -q 'hosts (1)' out
+
+
+# Only two hosts
+ansible -i hosts.yml all --limit host1,,host3 --list-hosts | tee out ; grep -q 'hosts (2)' out
+ansible -i hosts.yml host1,,host3 --list-hosts | tee out ; grep -q 'hosts (2)' out
+
+ansible -i hosts.yml all --limit 'host1, ,    ,host3' --list-hosts | tee out ; grep -q 'hosts (2)' out
+ansible -i hosts.yml 'host1, ,    ,host3' --list-hosts | tee out ; grep -q 'hosts (2)' out
+

test/units/plugins/inventory/test_inventory.py

@@ -49,6 +49,10 @@ class TestInventory(unittest.TestCase):
         'a:b': ['a', 'b'],
         ' a : b ': ['a', 'b'],
         'foo:bar:baz[1:2]': ['foo', 'bar', 'baz[1:2]'],
+        'a,,b': ['a', 'b'],
+        'a,  ,b,,c, ,': ['a', 'b', 'c'],
+        ',': [],
+        '': [],
     }
 
     pattern_lists = [