tests/failfilemerge.py

templater: pass opened file-like object to templatespec

I think I said earlier that I planned to create a special templatespec
variant for built-in templates. That was true (I planned that), but I
ended up (in this patch) just adding a file-like object to the
`mapfile_templatespec()` variant instead.

Differential Revision: https://phab.mercurial-scm.org/D8893

# extension to emulate interrupting filemerge._filemerge

from __future__ import absolute_import

from mercurial import (
    error,
    extensions,
    filemerge,
)


def failfilemerge(
    filemergefn, premerge, repo, wctx, mynode, orig, fcd, fco, fca, labels=None
):
    raise error.Abort("^C")
    return filemergefn(premerge, repo, mynode, orig, fcd, fco, fca, labels)


def extsetup(ui):
    extensions.wrapfunction(filemerge, '_filemerge', failfilemerge)