Both of these functions call If which does a traversal of the causal chain, it does not traverse the full tree. Specifically, If internally calls UnwrapOnce and doesn't handle the multi-error case, whereas functions like Is and As separately handle the multi-error case.
This leads to counter-intuitive behavior; you can have a value x of type T, and errors.Is(err, x) may be true, but errors.HasType(err, T{}) may fail.
Both of these functions call
If
which does a traversal of the causal chain, it does not traverse the full tree. Specifically,If
internally callsUnwrapOnce
and doesn't handle the multi-error case, whereas functions likeIs
andAs
separately handle the multi-error case.This leads to counter-intuitive behavior; you can have a value
x
of typeT
, anderrors.Is(err, x)
may be true, buterrors.HasType(err, T{})
may fail.I noticed this behavior while trying to add property-based tests to better understand the behavior of
HasType
here. https://github.com/sourcegraph/sourcegraph/pull/62992It would be valuable to either:
If
to traverse the full treeHasType
andHasInterface
HasType
andHasInterface
's docs which describe the behavior in the presence of multi-errors.