make jinja rendering in blocks more strict (#3827)

skyvern/utils/templating.py

@@ -0,0 +1,38 @@
+import re
+
+from jinja2 import Environment, StrictUndefined, UndefinedError, meta
+
+
+class Constants:
+    MissingVariablePattern = var_pattern = r"\{\{\s*([a-zA-Z_][a-zA-Z0-9_.\[\]'\"]*)\s*\}\}"
+
+
+def get_missing_variables(template_source: str, template_data: dict) -> set[str]:
+    # quick check - catch top-level undefineds
+    env = Environment(undefined=StrictUndefined)
+    ast = env.parse(template_source)
+    undeclared_vars = meta.find_undeclared_variables(ast)
+    missing_vars = undeclared_vars - set(template_data.keys())
+
+    # nested undefined won't be caught; let's check for those
+    if not missing_vars:
+        # try rendering to catch nested undefineds (dotted attributes, list/dict access)
+        try:
+            template = env.from_string(template_source)
+            template.render(template_data)
+        except UndefinedError:
+            # matches: {{ var }}, {{ var.attr }}, {{ var[0] }}, {{ var['key'] }}, {{ var.attr[0] }}
+            matches = re.findall(Constants.MissingVariablePattern, template_source)
+
+            for match in matches:
+                root = match.split("[")[0].split(".")[0]
+
+                # just check if the 'root' of the variable exists in the provided data
+                # if it does, add the whole match as missing
+                if root in template_data:
+                    missing_vars.add(match)
+
+            if not missing_vars:
+                raise  # re-raise if we couldn't determine missing vars
+
+    return missing_vars