The scenario is:
On other machine (same working copy, but no changes):
How can I make svn diff produce patch-appliable patch, or cleanly apply patch produced by svn diff in this case? I can't commit. I would like to preserve mergeinfo (because the obvious workaround is to add the file as totally new, without connection to the previous one).
With subversion, you can specify which diff binary to use, and parameters to pass to it. See the manual on svn diff.
You'd want to produce a regular patch file from a svn diff, so you'd want the svn diff to look like a normal diff. Try this:
svn diff --diff-cmd /usr/bin/diff -x "-i -b" > mypatch
...
patch -p0 < mypatch
Proof of concept:
echo "newline" >> README.txt
svn diff --diff-cmd /usr/bin/diff -x "-i -b" > mypatch
cp README.txt README.txt.patched
svn revert README.txt
patch -p0 < mypatch
diff README.txt README.txt.patched
No difference in the two files after patching.