fix(vertex): fix CreateCachedContentRequest enum error (#16965)

* feat: add _fix_enum_types function to remove enums from non-string fields in schema

* test: add test for _fix_enum_types function to validate enum removal from non-string fields

Author: sdip15fa

litellm/llms/vertex_ai/common_utils.py

@@ -274,6 +274,57 @@ def _fix_enum_empty_strings(schema, depth=0):
         _fix_enum_empty_strings(items, depth=depth + 1)
 
 
+def _fix_enum_types(schema, depth=0):
+    """Remove `enum` fields when the schema type is not string.
+
+    Gemini / Vertex APIs only allow enums for string-typed fields. When an enum
+    is present on a non-string typed property (or when `anyOf` types do not
+    include a string type), remove the enum to avoid provider validation errors.
+    """
+    if depth > DEFAULT_MAX_RECURSE_DEPTH:
+        raise ValueError(
+            f"Max depth of {DEFAULT_MAX_RECURSE_DEPTH} exceeded while processing schema."
+        )
+
+    if not isinstance(schema, dict):
+        return
+
+    # If enum exists but type is not string (and anyOf doesn't include string), drop enum
+    if "enum" in schema and isinstance(schema["enum"], list):
+        schema_type = schema.get("type")
+        keep_enum = False
+        if isinstance(schema_type, str) and schema_type.lower() == "string":
+            keep_enum = True
+        else:
+            anyof = schema.get("anyOf")
+            if isinstance(anyof, list):
+                for item in anyof:
+                    if isinstance(item, dict):
+                        item_type = item.get("type")
+                        if isinstance(item_type, str) and item_type.lower() == "string":
+                            keep_enum = True
+                            break
+
+        if not keep_enum:
+            schema.pop("enum", None)
+
+    # Recurse into nested structures
+    properties = schema.get("properties", None)
+    if properties is not None:
+        for _, value in properties.items():
+            _fix_enum_types(value, depth=depth + 1)
+
+    items = schema.get("items", None)
+    if items is not None:
+        _fix_enum_types(items, depth=depth + 1)
+
+    anyof = schema.get("anyOf", None)
+    if anyof is not None and isinstance(anyof, list):
+        for item in anyof:
+            if isinstance(item, dict):
+                _fix_enum_types(item, depth=depth + 1)
+
+
 def _build_vertex_schema(parameters: dict, add_property_ordering: bool = False):
     """
     This is a modified version of https://github.com/google-gemini/generative-ai-python/blob/8f77cc6ac99937cd3a81299ecf79608b91b06bbb/google/generativeai/types/content_types.py#L419
@@ -307,6 +358,9 @@ def _build_vertex_schema(parameters: dict, add_property_ordering: bool = False):
     # Handle empty strings in enum values - Gemini doesn't accept empty strings in enums
     _fix_enum_empty_strings(parameters)
 
+    # Remove enums for non-string typed fields (Gemini requires enum only on strings)
+    _fix_enum_types(parameters)
+
     # Handle empty items objects
     process_items(parameters)
     add_object_type(parameters)

tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py

@@ -803,6 +803,124 @@ def test_fix_enum_empty_strings():
     assert input_schema["properties"]["user_agent_type"]["description"] == "Device type for user agent"
 
 
+def test_fix_enum_types():
+    """
+    Test _fix_enum_types function removes enum fields when type is not string.
+    
+    This test verifies the fix for the issue where Gemini rejects cached content
+    with function parameter enums on non-string types, causing API failures.
+
+    Relevant issue: Gemini only allows enums for string-typed fields
+    """
+    from litellm.llms.vertex_ai.common_utils import _fix_enum_types
+
+    # Input: Schema with enum on non-string type (the problematic case)
+    input_schema = {
+        "type": "object",
+        "properties": {
+            "truncateMode": {
+                "enum": ["auto", "none", "start", "end"],
+                "type": "string",  # This should keep the enum
+                "description": "How to truncate content"
+            },
+            "maxLength": {
+                "enum": [100, 200, 500],  # This should be removed
+                "type": "integer",
+                "description": "Maximum length"
+            },
+            "enabled": {
+                "enum": [True, False],  # This should be removed
+                "type": "boolean",
+                "description": "Whether feature is enabled"
+            },
+            "nested": {
+                "type": "object",
+                "properties": {
+                    "innerEnum": {
+                        "enum": ["a", "b", "c"],  # This should be kept
+                        "type": "string"
+                    },
+                    "innerNonStringEnum": {
+                        "enum": [1, 2, 3],  # This should be removed
+                        "type": "integer"
+                    }
+                }
+            },
+            "anyOfField": {
+                "anyOf": [
+                    {"type": "string", "enum": ["option1", "option2"]},  # This should be kept
+                    {"type": "integer", "enum": [1, 2, 3]}  # This should be removed
+                ]
+            }
+        }
+    }
+
+    # Expected output: Non-string enums removed, string enums kept
+    expected_output = {
+        "type": "object",
+        "properties": {
+            "truncateMode": {
+                "enum": ["auto", "none", "start", "end"],  # Kept - string type
+                "type": "string",
+                "description": "How to truncate content"
+            },
+            "maxLength": {  # enum removed
+                "type": "integer",
+                "description": "Maximum length"
+            },
+            "enabled": {  # enum removed
+                "type": "boolean",
+                "description": "Whether feature is enabled"
+            },
+            "nested": {
+                "type": "object",
+                "properties": {
+                    "innerEnum": {
+                        "enum": ["a", "b", "c"],  # Kept - string type
+                        "type": "string"
+                    },
+                    "innerNonStringEnum": {  # enum removed
+                        "type": "integer"
+                    }
+                }
+            },
+            "anyOfField": {
+                "anyOf": [
+                    {"type": "string", "enum": ["option1", "option2"]},  # Kept - has string type
+                    {"type": "integer"}  # enum removed
+                ]
+            }
+        }
+    }
+
+    # Apply the transformation
+    _fix_enum_types(input_schema)
+
+    # Verify the transformation
+    assert input_schema == expected_output
+
+    # Verify specific transformations:
+    # 1. String enums are preserved
+    assert "enum" in input_schema["properties"]["truncateMode"]
+    assert input_schema["properties"]["truncateMode"]["enum"] == ["auto", "none", "start", "end"]
+    
+    assert "enum" in input_schema["properties"]["nested"]["properties"]["innerEnum"]
+    assert input_schema["properties"]["nested"]["properties"]["innerEnum"]["enum"] == ["a", "b", "c"]
+
+    # 2. Non-string enums are removed
+    assert "enum" not in input_schema["properties"]["maxLength"]
+    assert "enum" not in input_schema["properties"]["enabled"]
+    assert "enum" not in input_schema["properties"]["nested"]["properties"]["innerNonStringEnum"]
+
+    # 3. anyOf with string type keeps enum, non-string removes it
+    assert "enum" in input_schema["properties"]["anyOfField"]["anyOf"][0]
+    assert "enum" not in input_schema["properties"]["anyOfField"]["anyOf"][1]
+
+    # 4. Other properties preserved
+    assert input_schema["properties"]["maxLength"]["type"] == "integer"
+    assert input_schema["properties"]["enabled"]["type"] == "boolean"
+
+
 def test_get_token_url():
     from litellm.llms.vertex_ai.gemini.vertex_and_google_ai_studio_gemini import (
         VertexLLM,