Add jinja is list filter (#201)

* Add is_list jinja filter

* Changie

* Add test

.changes/unreleased/Under the Hood-20241001-161733.yaml

@@ -0,0 +1,6 @@
+kind: Under the Hood
+body: Add a jinja "is_list" filter
+time: 2024-10-01T16:17:33.652809-04:00
+custom:
+  Author: gshank
+  Issue: "200"

dbt_common/clients/jinja.py

@@ -470,11 +470,16 @@ def __reduce__(self) -> NoReturn:
     return Undefined
 
 
+def is_list(value):
+    return isinstance(value, list)
+
+
 NATIVE_FILTERS: Dict[str, Callable[[Any], Any]] = {
     "as_text": TextMarker,
     "as_bool": BoolMarker,
     "as_native": NativeMarker,
     "as_number": NumberMarker,
+    "is_list": is_list,
 }
 
 
@@ -483,6 +488,7 @@ def __reduce__(self) -> NoReturn:
     "as_bool": lambda x: x,
     "as_native": lambda x: x,
     "as_number": lambda x: x,
+    "is_list": is_list,
 }
 
 

tests/unit/test_jinja.py

@@ -1,7 +1,7 @@
 import unittest
 
 from dbt_common.clients._jinja_blocks import BlockTag
-from dbt_common.clients.jinja import extract_toplevel_blocks
+from dbt_common.clients.jinja import extract_toplevel_blocks, get_template, render_template
 from dbt_common.exceptions import CompilationError
 
 
@@ -503,3 +503,24 @@ def test_if_endfor_newlines(self) -> None:
 hi
 {% endmaterialization %}
 """
+
+
+def test_if_list_filter():
+    jinja_string = """
+        {%- if my_var | is_list -%}
+            Found a list
+        {%- else -%}
+            Did not find a list
+        {%- endif -%}
+    """
+    # Check with list variable
+    ctx = {"my_var": ["one", "two"]}
+    template = get_template(jinja_string, ctx)
+    rendered = render_template(template, ctx)
+    assert "Found a list" in rendered
+
+    # Check with non-list variable
+    ctx = {"my_var": "one"}
+    template = get_template(jinja_string, ctx)
+    rendered = render_template(template, ctx)
+    assert "Did not find a list" in rendered