Register template filters on the fallback Jinja2 environment

When server.templates.path is configured, render_j2_template() creates a
custom Environment and registers the to_json filter on it. If a requested
template is not present in that directory, a second Environment is built
for the built-in templates, but no filters were registered on it, so any
built-in template using {{ ... | to_json }} (items.html, item.html,
stac_items.html) failed with TemplateAssertionError: No filter named
'to_json'.

Register the filter and global on the fallback environment as well, so a
partial custom templates directory transparently falls back to the
built-in templates.

Adds tests/unittests/test_ogc_api_util.py covering both the custom
template override and the fallback path.

Author: Sanjays2402

pycsw/ogc/api/util.py

@@ -219,6 +219,8 @@ def render_j2_template(config, template, data):
             LOGGER.debug(err)
             LOGGER.debug('Custom template not found; using default')
             env = Environment(loader=FileSystemLoader(TEMPLATES))
+            env.filters['to_json'] = to_json
+            env.globals.update(to_json=to_json)
             template = env.get_template(template)
         else:
             raise

tests/unittests/test_ogc_api_util.py

@@ -0,0 +1,70 @@
+# =================================================================
+#
+# Authors: Tom Kralidis
+#
+# Copyright (c) 2026 Tom Kralidis
+#
+# Permission is hereby granted, free of charge, to any person
+# obtaining a copy of this software and associated documentation
+# files (the "Software"), to deal in the Software without
+# restriction, including without limitation the rights to use,
+# copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the
+# Software is furnished to do so, subject to the following
+# conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+# OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+# HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+# WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+# FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+# OTHER DEALINGS IN THE SOFTWARE.
+#
+# =================================================================
+"""Unit tests for pycsw.ogc.api.util"""
+
+import pytest
+
+from pycsw.ogc.api import util
+
+pytestmark = pytest.mark.unit
+
+TEMPLATE_USING_TO_JSON = "{{ data | to_json }}"
+
+
+def test_render_j2_template_custom_templates_path(tmp_path, monkeypatch):
+    default_templates = tmp_path / 'default'
+    default_templates.mkdir()
+    (default_templates / 'items.html').write_text(TEMPLATE_USING_TO_JSON)
+    monkeypatch.setattr(util, 'TEMPLATES', str(default_templates))
+
+    custom_templates = tmp_path / 'custom'
+    custom_templates.mkdir()
+    (custom_templates / 'items.html').write_text('custom')
+
+    config = {'server': {'templates': {'path': str(custom_templates)}}}
+
+    assert util.render_j2_template(config, 'items.html', {}) == 'custom'
+
+
+def test_render_j2_template_fallback_keeps_filters(tmp_path, monkeypatch):
+    """a template missing from templates.path falls back to the default
+    templates, which must keep the to_json filter registered"""
+
+    default_templates = tmp_path / 'default'
+    default_templates.mkdir()
+    (default_templates / 'items.html').write_text(TEMPLATE_USING_TO_JSON)
+    monkeypatch.setattr(util, 'TEMPLATES', str(default_templates))
+
+    custom_templates = tmp_path / 'custom'
+    custom_templates.mkdir()
+    (custom_templates / 'item.html').write_text('custom')
+
+    config = {'server': {'templates': {'path': str(custom_templates)}}}
+
+    assert util.render_j2_template(config, 'items.html', {}) == '{}'