github.com/onsi/gomega@v1.32.0/matchers/with_transform.go (about)

     1  package matchers
     2  
     3  import (
     4  	"fmt"
     5  	"reflect"
     6  
     7  	"github.com/onsi/gomega/types"
     8  )
     9  
    10  type WithTransformMatcher struct {
    11  	// input
    12  	Transform interface{} // must be a function of one parameter that returns one value and an optional error
    13  	Matcher   types.GomegaMatcher
    14  
    15  	// cached value
    16  	transformArgType reflect.Type
    17  
    18  	// state
    19  	transformedValue interface{}
    20  }
    21  
    22  // reflect.Type for error
    23  var errorT = reflect.TypeOf((*error)(nil)).Elem()
    24  
    25  func NewWithTransformMatcher(transform interface{}, matcher types.GomegaMatcher) *WithTransformMatcher {
    26  	if transform == nil {
    27  		panic("transform function cannot be nil")
    28  	}
    29  	txType := reflect.TypeOf(transform)
    30  	if txType.NumIn() != 1 {
    31  		panic("transform function must have 1 argument")
    32  	}
    33  	if numout := txType.NumOut(); numout != 1 {
    34  		if numout != 2 || !txType.Out(1).AssignableTo(errorT) {
    35  			panic("transform function must either have 1 return value, or 1 return value plus 1 error value")
    36  		}
    37  	}
    38  
    39  	return &WithTransformMatcher{
    40  		Transform:        transform,
    41  		Matcher:          matcher,
    42  		transformArgType: reflect.TypeOf(transform).In(0),
    43  	}
    44  }
    45  
    46  func (m *WithTransformMatcher) Match(actual interface{}) (bool, error) {
    47  	// prepare a parameter to pass to the Transform function
    48  	var param reflect.Value
    49  	if actual != nil && reflect.TypeOf(actual).AssignableTo(m.transformArgType) {
    50  		// The dynamic type of actual is compatible with the transform argument.
    51  		param = reflect.ValueOf(actual)
    52  
    53  	} else if actual == nil && m.transformArgType.Kind() == reflect.Interface {
    54  		// The dynamic type of actual is unknown, so there's no way to make its
    55  		// reflect.Value. Create a nil of the transform argument, which is known.
    56  		param = reflect.Zero(m.transformArgType)
    57  
    58  	} else {
    59  		return false, fmt.Errorf("Transform function expects '%s' but we have '%T'", m.transformArgType, actual)
    60  	}
    61  
    62  	// call the Transform function with `actual`
    63  	fn := reflect.ValueOf(m.Transform)
    64  	result := fn.Call([]reflect.Value{param})
    65  	if len(result) == 2 {
    66  		if !result[1].IsNil() {
    67  			return false, fmt.Errorf("Transform function failed: %s", result[1].Interface().(error).Error())
    68  		}
    69  	}
    70  	m.transformedValue = result[0].Interface() // expect exactly one value
    71  
    72  	return m.Matcher.Match(m.transformedValue)
    73  }
    74  
    75  func (m *WithTransformMatcher) FailureMessage(_ interface{}) (message string) {
    76  	return m.Matcher.FailureMessage(m.transformedValue)
    77  }
    78  
    79  func (m *WithTransformMatcher) NegatedFailureMessage(_ interface{}) (message string) {
    80  	return m.Matcher.NegatedFailureMessage(m.transformedValue)
    81  }
    82  
    83  func (m *WithTransformMatcher) MatchMayChangeInTheFuture(_ interface{}) bool {
    84  	// TODO: Maybe this should always just return true? (Only an issue for non-deterministic transformers.)
    85  	//
    86  	// Querying the next matcher is fine if the transformer always will return the same value.
    87  	// But if the transformer is non-deterministic and returns a different value each time, then there
    88  	// is no point in querying the next matcher, since it can only comment on the last transformed value.
    89  	return types.MatchMayChangeInTheFuture(m.Matcher, m.transformedValue)
    90  }