Type check every argument of variadic functions (fixes #329)

CHANGELOG.rst

@@ -1,7 +1,10 @@
 Next Release (TBD)
 ==================
 
-* No changes yet.
+* Fix ``merge()`` and other variadic functions leaking a raw Python
+  ``TypeError``/``ValueError`` instead of a ``JMESPathTypeError`` when an
+  argument after the first had an invalid type
+  (`issue #329 <https://github.com/jmespath/jmespath.py/issues/329>`__)
 
 
 1.1.0

jmespath/functions.py

@@ -91,8 +91,14 @@ def _validate_arguments(self, args, signature, function_name):
         return self._type_check(args, signature, function_name)
 
     def _type_check(self, actual, signature, function_name):
-        for i in range(len(signature)):
-            allowed_types = signature[i]['types']
+        for i in range(len(actual)):
+            if i < len(signature):
+                allowed_types = signature[i]['types']
+            else:
+                # Variadic function: every trailing argument is described
+                # by the final signature entry, so keep validating against
+                # it instead of leaving the extra args unchecked.
+                allowed_types = signature[-1]['types']
             if allowed_types:
                 self._type_check_single(actual[i], allowed_types,
                                         function_name)

tests/compliance/functions.json

@@ -267,6 +267,23 @@
       "expression": "merge(`{\"a\": 1, \"b\": 2}`, `{\"a\": 2, \"c\": 3}`, `{\"d\": 4}`)",
       "result": {"a": 2, "b": 2, "c": 3, "d": 4}
     },
+    {
+      "comment": "variadic argument after the first must also be type checked",
+      "expression": "merge(`{\"a\": 1}`, `null`)",
+      "error": "invalid-type"
+    },
+    {
+      "expression": "merge(`{\"a\": 1}`, null_key)",
+      "error": "invalid-type"
+    },
+    {
+      "expression": "merge(`{\"a\": 1}`, `{\"b\": 2}`, `5`)",
+      "error": "invalid-type"
+    },
+    {
+      "expression": "merge(`{\"a\": 1}`, str)",
+      "error": "invalid-type"
+    },
     {
       "expression": "min(numbers)",
       "result": -1