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.
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/62992
It would be valuable to either:
- Change the implementation of
If to traverse the full tree
- OR Add a separate function which does a tree traversal (not just the "causal chain") and use that from
HasType and HasInterface
- OR Add a cautionary warning to
HasType and HasInterface's docs which describe the behavior in the presence of multi-errors.
Both of these functions call
Ifwhich does a traversal of the causal chain, it does not traverse the full tree. Specifically,Ifinternally callsUnwrapOnceand doesn't handle the multi-error case, whereas functions likeIsandAsseparately handle the multi-error case.This leads to counter-intuitive behavior; you can have a value
xof 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
HasTypehere. https://github.com/sourcegraph/sourcegraph/pull/62992It would be valuable to either:
Ifto traverse the full treeHasTypeandHasInterfaceHasTypeandHasInterface's docs which describe the behavior in the presence of multi-errors.