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Allow WithTransform()'s function to accept a nil value #422

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merged 1 commit into from Feb 26, 2021
Merged

Allow WithTransform()'s function to accept a nil value #422

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20 changes: 15 additions & 5 deletions matchers/with_transform.go
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Expand Up @@ -40,15 +40,25 @@ func NewWithTransformMatcher(transform interface{}, matcher types.GomegaMatcher)
}

func (m *WithTransformMatcher) Match(actual interface{}) (bool, error) {
// return error if actual's type is incompatible with Transform function's argument type
actualType := reflect.TypeOf(actual)
if !actualType.AssignableTo(m.transformArgType) {
return false, fmt.Errorf("Transform function expects '%s' but we have '%s'", m.transformArgType, actualType)
// prepare a parameter to pass to the Transform function
var param reflect.Value
{
if actual != nil {
// return error if actual's type is incompatible with Transform function's argument type
actualType := reflect.TypeOf(actual)
if !actualType.AssignableTo(m.transformArgType) {
return false, fmt.Errorf("Transform function expects '%s' but we have '%s'", m.transformArgType, actualType)
}
param = reflect.ValueOf(actual)
} else {
// make a nil value of the expected type
param = reflect.New(m.transformArgType).Elem()
}
Comment on lines +53 to +56
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@cbandy cbandy Feb 26, 2021 •
edited

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This is no longer checking that the actual = nil is appropriate for the transform function. This incorrectly succeeds:

gomega.WithTransform(
	func(int) bool { return true },
	gomega.BeTrue(),
).Match(nil)

I recommend the following:

	var param reflect.Value
	if actual != nil && reflect.TypeOf(actual).AssignableTo(m.transformArgType) {
		// The original type of actual is compatible with the transform argument.
		param = reflect.ValueOf(actual)

	} else if actual == nil && m.transformArgType.Kind() == reflect.Interface {
		// The original type of actual is unknown, so there's no way to make its
		// reflect.Value. Create a nil of the transform argument, which is known.
		param = reflect.Zero(m.transformArgType)

	} else {
		return false, fmt.Errorf("Transform function expects '%s' but we have '%T'", m.transformArgType, actual)
	}

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thanks @cbandy - are you up for submitting this as a PR?

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Yep, no problem. Submitted #423.

}

// call the Transform function with `actual`
fn := reflect.ValueOf(m.Transform)
result := fn.Call([]reflect.Value{reflect.ValueOf(actual)})
result := fn.Call([]reflect.Value{param})
m.transformedValue = result[0].Interface() // expect exactly one value

return m.Matcher.Match(m.transformedValue)
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8 changes: 7 additions & 1 deletion matchers/with_transform_test.go
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Expand Up @@ -51,7 +51,13 @@ var _ = Describe("WithTransformMatcher", func() {
Expect(S{1, "hi"}).To(WithTransform(transformer, Equal("hi")))

// transform expects interface
errString := func(e error) string { return e.Error() }
errString := func(e error) string {
if e == nil {
return "<nil>"
}
return e.Error()
}
Expect(nil).To(WithTransform(errString, Equal("<nil>")), "handles nil actual values")
Expect(errors.New("abc")).To(WithTransform(errString, Equal("abc")))
})

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