`find-tag' is an obsolete function (as of 25.1); use `xref-find-definitions' instead

[gracjan]

find-tag' is an obsolete function (as of 25.1); usexref-find-definitions' instead

[deviant-logic]

This was observed in a travis build failure at: https://travis-ci.org/haskell/haskell-mode/jobs/63166721#L237

See also: emacs-mirror/emacs@394ce95#diff-4ad57e26784306cc4489c7d1c246f71fR437