Merges Without Mergeinfo
Subversion tries to generate merge metadata whenever it can, to
make future invocations of svn
merge smarter. There are still situations, however,
where svn:mergeinfo data is
not created or changed. Remember to be a bit wary of these
scenarios:
- Merging unrelated sources
If you ask svn merge to compare two URLs that aren’t related to each other, a patch will still be generated and applied to your working copy, but no merging metadata will be created. There’s no common history between the two sources, and future “smart” merges depend on that common history.
- Merging from foreign repositories
While it’s possible to run a command such as
svn merge -r 100:200, the resultant patch will also lack any historical merge metadata. At time of this writing, Subversion has no way of representing different repository URLs within thehttp://svn.foreignproject.com/repos/trunksvn:mergeinfoproperty.- Using
--ignore-ancestry If this option is passed to svn merge, it causes the merging logic to mindlessly generate differences the same way that svn diff does, ignoring any historical relationships. We discuss this later in the chapter in Noticing or Ignoring Ancestry.
- Applying reverse merges to a target’s natural history
Earlier in this chapter (Undoing Changes), we discussed how to use svn merge to apply a “reverse patch” as a way of rolling back changes. If this technique is used to undo a change to an object’s personal history (e.g., commit r5 to the trunk, then immediately roll back r5 using
svn merge . -c -5), this sort of merge doesn’t affect the recorded mergeinfo.[23]
[23] Interestingly, after rolling back a revision like this,
we wouldn’t be able to reapply the revision using svn
merge . -c 5, since the mergeinfo would already list
r5 as being applied. We would have to use the --ignore-ancestry option to make
the merge command ignore the existing mergeinfo!