Fix cycle detection in internal/value.Format #87
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The cycle detection in value.Format uses a map of uintptrs, which is not correct as this assumes that the Go GC never uses a moving collector. Instead, we should be using unsafe.Pointer, which the GC knows how to scan. Also, push pointer checking of slices down to the level of individual elements. We do this because the slice pointer is not sufficient to determine equality. For example, v[:0] and v[:1] both have the same slice pointer, but are clearly different values. Since the purego environment forbids the use of unsafe, create a Pointer type that is an abstraction over an opaque pointer. The Pointer type can only be compared. In the purego, continue to use uintptr, which is the best we can do.
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The cycle detection in value.Format uses a map of uintptrs, which is not
correct as this assumes that the Go GC never uses a moving collector.
Instead, we should be using unsafe.Pointer, which the GC knows how to scan.
Also, push pointer checking of slices down to the level of individual elements.
We do this because the slice pointer is not sufficient to determine equality.
For example, v[:0] and v[:1] both have the same slice pointer, but are
clearly different values.
Since the purego environment forbids the use of unsafe, create a Pointer type
that is an abstraction over an opaque pointer. The Pointer type can only be
compared. In the purego, continue to use uintptr, which is the best we can do.