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text/template: panics on method on nil interface value [1.12 backport] #30464
…nterfaces Trying to call a method on a nil interface is a panic in Go. For example: var stringer fmt.Stringer println(stringer.String()) // nil pointer dereference In https://golang.org/cl/143097 we started recovering panics encountered during function and method calls. However, we didn't handle this case, as text/template panics before evalCall is ever run. In particular, reflect's MethodByName will panic if the receiver is of interface kind and nil: panic: reflect: Method on nil interface value Simply add a check for that edge case, and have Template.Execute return a helpful error. Note that Execute shouldn't just error if the interface contains a typed nil, since we're able to find a method to call in that case. Finally, add regression tests for both the nil and typed nil interface cases. Fixes #30464. Change-Id: Iffb21b40e14ba5fea0fcdd179cd80d1f23cabbab Reviewed-on: https://go-review.googlesource.com/c/161761 Run-TryBot: Daniel Martí <email@example.com> TryBot-Result: Gobot Gobot <firstname.lastname@example.org> Reviewed-by: Emmanuel Odeke <email@example.com> (cherry picked from commit 15b4c71) Reviewed-on: https://go-review.googlesource.com/c/go/+/164457 Reviewed-by: Brad Fitzpatrick <firstname.lastname@example.org>