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reflect: regression in Type.ConvertibleTo #17952

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dsnet opened this issue Nov 16, 2016 · 2 comments
Closed

reflect: regression in Type.ConvertibleTo #17952

dsnet opened this issue Nov 16, 2016 · 2 comments
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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.8

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@dsnet
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dsnet commented Nov 16, 2016

8d0c105 caused a regression in functionality of ConvertibleTo.

The following test passes on Go 1.6 and 1.7, but fails on tip:

type timeTime time.Time

func Test(t *testing.T) {
	t1 := reflect.TypeOf((*time.Time)(nil))
	t2 := reflect.TypeOf((*timeTime)(nil))
	if !t1.ConvertibleTo(t2) || !t2.ConvertibleTo(t1) {
		t.Error("pointers not convertible")
	}

	t1 = reflect.TypeOf(time.Time{})
	t2 = reflect.TypeOf(timeTime{})
	if !t1.ConvertibleTo(t2) || !t2.ConvertibleTo(t1) {
		t.Error("values not convertible")
	}
}

/cc @rsc, @crawshaw, @ianlancetaylor
@dsnet dsnet added this to the Go1.8 milestone Nov 16, 2016
@dsnet dsnet added the NeedsFix The path to resolution is known, but the work has not been done. label Nov 16, 2016
@ianlancetaylor
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The problem is that for a definition like type timeTime time.Time the pkgPath of the struct is the package in which it is defined (in this case, main) and we use that pkgPath for the pkgPath of all the fields. But of course the fields are defined in package time.

Similarly, printing Field(i).PkgPath of reflect.TypeOf(timeTime) also prints the wrong value.

dnameField in cmd/compile/internal/gc/reflect.go assumes that it never needs to set the pkgPath of a field, but as far as I can tell that simply isn't true.

@gopherbot
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CL https://golang.org/cl/33333 mentions this issue.

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FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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@crawshaw @ianlancetaylor @dsnet @gopherbot