🐛 Fix TerminalError(nil).Error() panic

[sheidkamp]

Fixes #2430 by checking it err is nil before calling Error() on it.

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[vincepri]

Is this a common pattern? We're at this point creating an error with a nil cause/inner error which might throw off the reconciliation loop.

[sheidkamp]

I only see it used here:

controller-runtime/pkg/internal/controller/controller.go

Line 319 in 7f0c6dc

if errors.Is(err, reconcile.TerminalError(nil)) {

which doesn't totally make sense because the previous line checks for err==nil (<- strikethrough because checking for err==nil does not mean that the unwrapped error is not nil)

An alternate solution would be to modify the controller to create that error with a non-nil value (empty string?) and maybe add protection in the TerminalError() function to not allow nil values.

[vincepri]

cc @alvaroaleman

[alvaroaleman]

The nil terminal error there is only used for the errors.Is comparison, in that context, the Error() method will never be called.

It isn't really expected to construct a terminal error with a nil inner error when returning it, as that means logging will not be able to tell you what the issue was. When did you run into this panicing?

[sheidkamp]

We run into this error when using the Eris error handling library. Example here:
https://go.dev/play/p/4N0EmuNcPHJ

errors.Is calls the 1st argument's Is method here: https://cs.opensource.google/go/go/+/master:src/errors/wrap.go;l=54?q=wrap.go&ss=go%2Fgo
And then Eris' Is function does call target.Error()
https://github.com/rotisserie/eris/blob/d0c56b6433ca96eedf3c9482ec51456aa80dd772/eris.go#L212
leading to the panic.

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This pull-request has been approved by: alvaroaleman, sheidkamp

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