👌 Fail and emit warning on filters that do not return a boolean result

docs/changelog.rst

@@ -91,6 +91,9 @@ Internal
 * 🧪 Add testing of JS scripts using Cypress integrated into PyTest (`#1051 <https://github.com/useblocks/sphinx-needs/pull/1051>`_)
 * 🧪 Add code coverage to CI testing (`#1067 <https://github.com/useblocks/sphinx-needs/pull/1067>`_)
 
+* Bugfix: Check filter strings for correctness.
+  (`#964 <https://github.com/useblocks/sphinx-needs/pull/964>`_)
+
 1.3.0
 -----
 Released: 16.08.2023

sphinx_needs/filter_common.py

@@ -296,6 +296,10 @@ def filter_needs(
     return found_needs
 
 
+def need_search(*args: Any, **kwargs: Any) -> bool:
+    return bool(re.search(*args, **kwargs))
+
+
 @measure_time("filtering")
 def filter_single_need(
     need: NeedsInfoType,
@@ -327,15 +331,17 @@ def filter_single_need(
     # Get needs external filter data and merge to filter_context
     filter_context.update(config.filter_data)
 
-    filter_context["search"] = re.search
+    filter_context["search"] = need_search
     result = False
     try:
         # Set filter_context as globals and not only locals in eval()!
         # Otherwise, the vars not be accessed in list comprehensions.
         if filter_compiled:
-            result = bool(eval(filter_compiled, filter_context))
+            result = eval(filter_compiled, filter_context)
         else:
-            result = bool(eval(filter_string, filter_context))
+            result = eval(filter_string, filter_context)
+        if not isinstance(result, bool):
+            raise NeedsInvalidFilter(f"Filter did not evaluate to a boolean, instead {type(result)}: {result}")
     except Exception as e:
         raise NeedsInvalidFilter(f"Filter {filter_string} not valid. Error: {e}.")
     return result