Sequence query fix (#83758)

Co-authored-by: flowerysong <junk+github@flowerysong.com>

changelogs/fragments/fix-lookup-sequence-keyword-args-only.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - sequence lookup - sequence query/lookups without positional arguments now return a valid list if their kwargs comprise a valid sequence expression (https://github.com/ansible/ansible/issues/82921).

lib/ansible/plugins/lookup/sequence.py

@@ -171,6 +171,12 @@ class LookupModule(LookupBase):
             setattr(self, f, self.get_option(f))
 
     def sanity_check(self):
+        """
+        Returns True if options comprise a valid sequence expression
+        Raises AnsibleError if options are an invalid expression
+        Returns false if options are valid but result in an empty sequence - these cases do not raise exceptions
+        in order to maintain historic behavior
+        """
         if self.count is None and self.end is None:
             raise AnsibleError("must specify count or end in with_sequence")
         elif self.count is not None and self.end is not None:
@@ -180,17 +186,18 @@ class LookupModule(LookupBase):
             if self.count != 0:
                 self.end = self.start + self.count * self.stride - 1
             else:
-                self.start = 0
-                self.end = 0
-                self.stride = 0
-            del self.count
+                return False
         if self.stride > 0 and self.end < self.start:
             raise AnsibleError("to count backwards make stride negative")
         if self.stride < 0 and self.end > self.start:
             raise AnsibleError("to count forward don't make stride negative")
+        if self.stride == 0:
+            return False
         if self.format.count('%') != 1:
             raise AnsibleError("bad formatting string: %s" % self.format)
 
+        return True
+
     def generate_sequence(self):
         if self.stride >= 0:
             adjust = 1
@@ -210,6 +217,10 @@ class LookupModule(LookupBase):
     def run(self, terms, variables, **kwargs):
         results = []
 
+        if kwargs and not terms:
+            # All of the necessary arguments can be provided as keywords, but we still need something to loop over
+            terms = ['']
+
         for term in terms:
             try:
                 # set defaults/global
@@ -223,10 +234,9 @@ class LookupModule(LookupBase):
                     raise AnsibleError("unknown error parsing with_sequence arguments: %r. Error was: %s" % (term, e))
 
                 self.set_fields()
-                self.sanity_check()
-
-                if self.stride != 0:
+                if self.sanity_check():
                     results.extend(self.generate_sequence())
+
             except AnsibleError:
                 raise
             except Exception as e:

test/integration/targets/lookup_sequence/tasks/main.yml

@@ -196,3 +196,32 @@
           - ansible_failed_result.msg == expected
       vars:
         expected: "bad formatting string: d"
+
+# Tests for lookup()/plugin() jinja invocation:
+# Many of these tests check edge case behaviors that are only possible when invoking query/lookup sequence through jinja.
+# While they aren't particularly intuitive, these tests ensure playbooks that could be relying on these behaviors don't
+# break in future
+- name: Test lookup with keyword args only
+  assert:
+    that:
+      - query("ansible.builtin.sequence", count=5, start=10) == ["10", "11", "12", "13", "14"]
+
+- name: Test that multiple positional args produces concatenated sequence
+  assert:
+    that:
+      - query("ansible.builtin.sequence", "count=5 start=1", "count=3 start=10 stride=2") == ["1", "2", "3", "4", "5", "10", "12", "14"]
+
+- name: Test that keyword arguments are applied to all positional expressions
+  assert:
+    that:
+      - query("ansible.builtin.sequence", "count=5 start=0", "count=5 start=20", stride=2) == ["0", "2", "4", "6", "8", "20", "22", "24", "26", "28"]
+
+- name: Test that keyword arguments do not overwrite parameters present in positional expressions
+  assert:
+    that:
+      - query("ansible.builtin.sequence", "count=5 start=0", "count=5", start=20) == ["0", "1", "2", "3", "4", "20", "21", "22", "23", "24"]
+
+- name: Test that call with no arguments produces an empty list
+  assert:
+    that:
+      - query("ansible.builtin.sequence") == []