stdenv/setup: make substituteInPlace require actual files

I've often run into substituteInPlace doing nothing when I invoked it
wrong, like:

substituteInPlace --replace-fail from to file.txt

The substitute function would pass file.txt on to substituteStream,
which complain about the extraneous argument. However, if no files are
passed, substitute is never called and substituteInPlace silently does
nothing.

It would be more annoying to make substituteInPlace accept file
arguments anywhere (since it would need to understand the arguments to
substituteStream), so let's error on this incorrect usage instead.

Change-Id: Ib2daad6f49bbe516a273a35d7f2a31fc42fd053c

0 files changed, 0 insertions, 0 deletions