func()

in internal/backport/text/template/exec.go [608:684]

• 66 lines of code
• 25 McCabe index (conditional complexity)

func (s *state) evalField(dot reflect.Value, fieldName string, node parse.Node, args []parse.Node, final, receiver reflect.Value) reflect.Value {
	if !receiver.IsValid() {
		if s.tmpl.option.missingKey == mapError { // Treat invalid value as missing map key.
			s.errorf("nil data; no entry for key %q", fieldName)
		}
		return zero
	}
	typ := receiver.Type()
	receiver, isNil := indirect(receiver)
	if receiver.Kind() == reflect.Interface && isNil {
		// Calling a method on a nil interface can't work. The
		// MethodByName method call below would panic.
		s.errorf("nil pointer evaluating %s.%s", typ, fieldName)
		return zero
	}

	// Unless it's an interface, need to get to a value of type *T to guarantee
	// we see all methods of T and *T.
	ptr := receiver
	if ptr.Kind() != reflect.Interface && ptr.Kind() != reflect.Ptr && ptr.CanAddr() {
		ptr = ptr.Addr()
	}
	if method := ptr.MethodByName(fieldName); method.IsValid() {
		return s.evalCall(dot, method, false, node, fieldName, args, final)
	}
	hasArgs := len(args) > 1 || final != missingVal
	// It's not a method; must be a field of a struct or an element of a map.
	switch receiver.Kind() {
	case reflect.Struct:
		tField, ok := receiver.Type().FieldByName(fieldName)
		if ok {
			field := receiver.FieldByIndex(tField.Index)
			if tField.PkgPath != "" {
				s.errorf("%s is an unexported field of struct type %s", fieldName, typ)
			}
			// If it's a function, we must call it.
			if hasArgs {
				s.errorf("%s has arguments but cannot be invoked as function", fieldName)
			}
			return field
		}
	case reflect.Map:
		// If it's a map, attempt to use the field name as a key.
		nameVal := reflect.ValueOf(fieldName)
		if nameVal.Type().AssignableTo(receiver.Type().Key()) {
			if hasArgs {
				s.errorf("%s is not a method but has arguments", fieldName)
			}
			result := receiver.MapIndex(nameVal)
			if !result.IsValid() {
				switch s.tmpl.option.missingKey {
				case mapInvalid:
					// Just use the invalid value.
				case mapZeroValue:
					result = reflect.Zero(receiver.Type().Elem())
				case mapError:
					s.errorf("map has no entry for key %q", fieldName)
				}
			}
			return result
		}
	case reflect.Ptr:
		etyp := receiver.Type().Elem()
		if etyp.Kind() == reflect.Struct {
			if _, ok := etyp.FieldByName(fieldName); !ok {
				// If there's no such field, say "can't evaluate"
				// instead of "nil pointer evaluating".
				break
			}
		}
		if isNil {
			s.errorf("nil pointer evaluating %s.%s", typ, fieldName)
		}
	}
	s.errorf("can't evaluate field %s in type %s", fieldName, typ)
	panic("not reached")
}