executus/tool/argcoerce.go

package tool

import (
	"encoding/json"
	"reflect"
	"strconv"
	"strings"
)

// unmarshalArgsLenient decodes the raw JSON arguments the model supplied
// into the tool's typed Args struct, tolerating the classic LLM tool-call
// bug of emitting numbers and booleans as strings ("3" where the schema
// said integer, "true" where it said boolean).
//
// Why mort-side (vs relying on the library): legacy gollm's Define performed
// this coercion internally (tool_coerce.go), and several years of tool
// traffic depend on the tolerance. majordomo's DefineTool decodes
// strictly by design, so the gated wrappers re-create the leniency here
// — the strict path is tried first and coercion only runs on failure,
// which makes the happy path zero-cost.
func unmarshalArgsLenient(raw json.RawMessage, target any) error {
	if len(raw) == 0 {
		return nil
	}
	strictErr := json.Unmarshal(raw, target)
	if strictErr == nil {
		return nil
	}
	coerced, err := coerceArgsToType(raw, reflect.TypeOf(target).Elem())
	if err != nil {
		// Malformed JSON: surface the original strict error, which
		// names the real problem.
		return strictErr
	}
	if err := json.Unmarshal(coerced, target); err != nil {
		return strictErr
	}
	return nil
}

// coerceArgsToType reparses argsJSON with leniency: where the target
// struct expects a numeric or boolean field but the JSON value is a
// string, it converts the string to the target kind. Recurses into
// nested structs, slices, maps, and pointer fields. Returns a freshly
// marshaled JSON byte slice that unmarshals strictly into the target.
func coerceArgsToType(argsJSON []byte, target reflect.Type) ([]byte, error) {
	var raw any
	if err := json.Unmarshal(argsJSON, &raw); err != nil {
		return nil, err
	}
	raw = coerceValue(raw, target)
	return json.Marshal(raw)
}

func coerceValue(v any, t reflect.Type) any {
	if t == nil {
		return v
	}
	for t.Kind() == reflect.Pointer {
		t = t.Elem()
	}

	switch t.Kind() {
	case reflect.Struct:
		m, ok := v.(map[string]any)
		if !ok {
			return v
		}
		for i := 0; i < t.NumField(); i++ {
			f := t.Field(i)
			if !f.IsExported() {
				continue
			}
			name := jsonFieldName(f)
			if name == "-" {
				continue
			}
			if val, present := m[name]; present {
				m[name] = coerceValue(val, f.Type)
			}
		}
		return m

	case reflect.Slice, reflect.Array:
		arr, ok := v.([]any)
		if !ok {
			return v
		}
		elemType := t.Elem()
		for i := range arr {
			arr[i] = coerceValue(arr[i], elemType)
		}
		return arr

	case reflect.Map:
		m, ok := v.(map[string]any)
		if !ok {
			return v
		}
		valType := t.Elem()
		for k := range m {
			m[k] = coerceValue(m[k], valType)
		}
		return m

	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		if s, ok := v.(string); ok {
			s = strings.TrimSpace(s)
			s = strings.TrimPrefix(s, "+")
			if n, err := strconv.ParseInt(s, 10, 64); err == nil {
				return n
			}
			if f, err := strconv.ParseFloat(s, 64); err == nil {
				return int64(f)
			}
		}

	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
		if s, ok := v.(string); ok {
			s = strings.TrimSpace(s)
			s = strings.TrimPrefix(s, "+")
			if n, err := strconv.ParseUint(s, 10, 64); err == nil {
				return n
			}
			if f, err := strconv.ParseFloat(s, 64); err == nil && f >= 0 {
				return uint64(f)
			}
		}

	case reflect.Float32, reflect.Float64:
		if s, ok := v.(string); ok {
			s = strings.TrimSpace(s)
			if f, err := strconv.ParseFloat(s, 64); err == nil {
				return f
			}
		}

	case reflect.Bool:
		if s, ok := v.(string); ok {
			if b, err := strconv.ParseBool(strings.TrimSpace(s)); err == nil {
				return b
			}
		}
	}
	return v
}

// jsonFieldName returns the effective JSON key for a struct field:
// the json tag's name part when present, the Go field name otherwise,
// or "-" when the field is excluded.
func jsonFieldName(f reflect.StructField) string {
	tag, ok := f.Tag.Lookup("json")
	if !ok {
		return f.Name
	}
	name, _, _ := strings.Cut(tag, ",")
	if name == "" {
		return f.Name
	}
	return name
}