fix(gemini): normalize JSON Schema union types for Vertex compatibility#3150
fix(gemini): normalize JSON Schema union types for Vertex compatibility#3150Vaibhav701161 wants to merge 1 commit intomainfrom
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📝 WalkthroughSummary by CodeRabbit
WalkthroughAdds JSON Schema union-type handling to the Gemini provider by updating Changes
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~20 minutes Poem
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Confidence Score: 5/5Safe to merge — the change is well-scoped to the union-type normalization path with no impact on existing string-typed schemas. No P0/P1 findings. The type-switch pattern ( No files require special attention. Important Files Changed
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Actionable comments posted: 1
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Verify each finding against the current code and only fix it if needed.
Inline comments:
In `@core/providers/gemini/utils.go`:
- Around line 1265-1322: The union-type handling in the propType switch should
not assume propType is only []interface{} nor treat arrays of all-unparseable
elements as null; update the case to reuse extractTypesFromValue to parse both
[]interface{} and []string (or any slice of strings) into nonNullTypes and
hasNull, deduplicate properly, and only set schema.Type = TypeNULL when hasNull
is true (instead of when len(nonNullTypes)==0 regardless of hasNull); for
multiple non-null types set schema.AnyOf as before and preserve Nullable when
hasNull is true—modify the code around the propType branch that currently builds
nonNullTypes/hasNull (and references schema.Type, schema.Nullable, schema.AnyOf)
to call extractTypesFromValue and apply these rules.
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📒 Files selected for processing (2)
core/providers/gemini/uniontype_test.gocore/providers/gemini/utils.go
- Handle ["T", "null"] -> Type + Nullable
- Convert multi-type unions -> anyOf
- Deduplicate type arrays
- Prevent empty Type field causing Vertex 400 error
- Support both []interface{} and []string union type inputs
- Fix: only emit TypeNULL when "null" is explicitly present (not on all-invalid arrays)
- Refactor type extraction into reusable extractUnionTypes + applyUnionType helpers
- Add comprehensive unit tests + e2e validation
Addresses review feedback from Greptile and CodeRabbit.
Fixes issue: Vertex rejects tool schemas with union type arrays
Vaibhav701161
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Summary
This change fixes an incompatibility between Bifrost and Vertex AI when handling JSON Schema union types in tool and function parameters.
Previously, schemas containing union types such as:
"type": ["integer", "null"]
were not correctly normalized before being sent to the Gemini or Vertex provider. This resulted in invalid schemas where the
typefield was effectively missing, causing Vertex to reject requests with a 400 error.This PR introduces proper normalization of union types to ensure compatibility with Gemini and Vertex AI.
Previous Behavior
Bifrost assumed that the JSON Schema
typefield was always a string. When an array was provided:"type": ["integer", "null"]
the conversion logic failed silently because:
typefieldThis led to requests being rejected by Vertex with errors such as:
parameters. schema didn't specify the schema type field
As a result:
Current Behavior
The schema conversion logic now correctly handles JSON Schema union types.
Supported transformations:
"type": "integer"
-> unchanged
"type": ["integer", "null"]
-> type: "integer", nullable: true
"type": ["string", "null"]
-> type: "string", nullable: true
"type": ["integer", "string"]
-> anyOf: [{type: "integer"}, {type: "string"}]
"type": ["integer", "string", "null"]
-> anyOf: [...], nullable: true
"type": ["null"]
-> type: "null"
Additional improvements:
Validation
The fix has been validated through both unit tests and real end-to-end requests.
Unit Tests
End-to-End Verification
A real request using:
"type": ["integer", "null"]
was successfully processed through Bifrost and accepted by Gemini (gemini-2.5-flash), resulting in a valid tool call:
"tool_calls": [
{
"function": {
"name": "get_process",
"arguments": {
"pid": 42,
"timeout_secs": null
}
}
}
]
This confirms:
(See attached screenshot)
Impact
Type of change
Affected areas
How to test
execute:
curl -s -X POST http://localhost:9090/v1/chat/completions
-H "Content-Type: application/json"
-d '{
"model": "gemini/gemini-2.5-flash",
"messages": [
{
"role": "user",
"content": "Call get_process with pid 42 and timeout_secs null"
}
],
"tools": [
{
"type": "function",
"function": {
"name": "get_process",
"parameters": {
"type": "object",
"properties": {
"pid": { "type": "integer" },
"timeout_secs": { "type": ["integer", "null"] }
},
"required": ["pid"]
}
}
}
],
"tool_choice": "auto"
}'
Expected:
Breaking changes
Related issues
Fixes: #3141
Security considerations
No changes to authentication, data handling, or external interfaces. Schema normalization is internal.
Checklist