Fix Gemini function-calling INVALID_ARGUMENT by relaxing Gemini tool validation and cleaning schema

internal/util/gemini_schema.go

@@ -16,6 +16,93 @@ var gjsonPathKeyReplacer = strings.NewReplacer(".", "\\.", "*", "\\*", "?", "\\?
 // It handles unsupported keywords, type flattening, and schema simplification while preserving
 // semantic information as description hints.
 func CleanJSONSchemaForAntigravity(jsonStr string) string {
+	return cleanJSONSchema(jsonStr, true)
+}
+
+func removeKeywords(jsonStr string, keywords []string) string {
+	for _, key := range keywords {
+		for _, p := range findPaths(jsonStr, key) {
+			if isPropertyDefinition(trimSuffix(p, "."+key)) {
+				continue
+			}
+			jsonStr, _ = sjson.Delete(jsonStr, p)
+		}
+	}
+	return jsonStr
+}
+
+// removePlaceholderFields removes placeholder-only properties ("_" and "reason") and their required entries.
+func removePlaceholderFields(jsonStr string) string {
+	// Remove "_" placeholder properties.
+	paths := findPaths(jsonStr, "_")
+	sortByDepth(paths)
+	for _, p := range paths {
+		if !strings.HasSuffix(p, ".properties._") {
+			continue
+		}
+		jsonStr, _ = sjson.Delete(jsonStr, p)
+		parentPath := trimSuffix(p, ".properties._")
+		reqPath := joinPath(parentPath, "required")
+		req := gjson.Get(jsonStr, reqPath)
+		if req.IsArray() {
+			var filtered []string
+			for _, r := range req.Array() {
+				if r.String() != "_" {
+					filtered = append(filtered, r.String())
+				}
+			}
+			if len(filtered) == 0 {
+				jsonStr, _ = sjson.Delete(jsonStr, reqPath)
+			} else {
+				jsonStr, _ = sjson.Set(jsonStr, reqPath, filtered)
+			}
+		}
+	}
+
+	// Remove placeholder-only "reason" objects.
+	reasonPaths := findPaths(jsonStr, "reason")
+	sortByDepth(reasonPaths)
+	for _, p := range reasonPaths {
+		if !strings.HasSuffix(p, ".properties.reason") {
+			continue
+		}
+		parentPath := trimSuffix(p, ".properties.reason")
+		props := gjson.Get(jsonStr, joinPath(parentPath, "properties"))
+		if !props.IsObject() || len(props.Map()) != 1 {
+			continue
+		}
+		desc := gjson.Get(jsonStr, p+".description").String()
+		if desc != "Brief explanation of why you are calling this tool" {
+			continue
+		}
+		jsonStr, _ = sjson.Delete(jsonStr, p)
+		reqPath := joinPath(parentPath, "required")
+		req := gjson.Get(jsonStr, reqPath)
+		if req.IsArray() {
+			var filtered []string
+			for _, r := range req.Array() {
+				if r.String() != "reason" {
+					filtered = append(filtered, r.String())
+				}
+			}
+			if len(filtered) == 0 {
+				jsonStr, _ = sjson.Delete(jsonStr, reqPath)
+			} else {
+				jsonStr, _ = sjson.Set(jsonStr, reqPath, filtered)
+			}
+		}
+	}
+
+	return jsonStr
+}
+
+// CleanJSONSchemaForGemini transforms a JSON schema to be compatible with Gemini tool calling.
+// It removes unsupported keywords and simplifies schemas, without adding empty-schema placeholders.
+func CleanJSONSchemaForGemini(jsonStr string) string {
+	return cleanJSONSchema(jsonStr, false)
+}
+
+func cleanJSONSchema(jsonStr string, addPlaceholder bool) string {
 	// Phase 1: Convert and add hints
 	jsonStr = convertRefsToHints(jsonStr)
 	jsonStr = convertConstToEnum(jsonStr)
@@ -31,10 +118,16 @@ func CleanJSONSchemaForAntigravity(jsonStr string) string {
 
 	// Phase 3: Cleanup
 	jsonStr = removeUnsupportedKeywords(jsonStr)
+	if !addPlaceholder {
+		// Gemini schema cleanup: remove nullable/title and placeholder-only fields.
+		jsonStr = removeKeywords(jsonStr, []string{"nullable", "title"})
+		jsonStr = removePlaceholderFields(jsonStr)
+	}
 	jsonStr = cleanupRequiredFields(jsonStr)
-
 	// Phase 4: Add placeholder for empty object schemas (Claude VALIDATED mode requirement)
-	jsonStr = addEmptySchemaPlaceholder(jsonStr)
+	if addPlaceholder {
+		jsonStr = addEmptySchemaPlaceholder(jsonStr)
+	}
 
 	return jsonStr
 }