One of the fundamental rules of Subversion is that a “push” action does not cause a “pull,” nor the other way around. Just because you're ready to submit new changes to the repository doesn't mean you're ready to receive changes from other people. And if you have new changes still in progress, then svn update should gracefully merge repository changes into your own, rather than forcing you to publish them.
The main side effect of this rule is that it means a working copy has to do extra bookkeeping to track mixed revisions as well as be tolerant of the mixture. It's made more complicated by the fact that directories themselves are versioned.
For example, suppose you have a working copy entirely at
revision 10. You edit the
foo.html and then perform
an svn commit, which creates revision 15
in the repository. After the commit succeeds, many new
users would expect the working copy to be entirely at
revision 15, but that's not the case! Any number of changes
might have happened in the repository between revisions 10
and 15. The client knows nothing of those changes in the
repository, since you haven't yet run svn
update, and svn commit doesn't
pull down new changes. If, on the other hand,
svn commit were to automatically download
the newest changes, then it would be possible to set the
entire working copy to revision 15—but then we'd be
breaking the fundamental rule of “push”
and “pull” remaining separate actions.
Therefore, the only safe thing the Subversion client can do
is mark the one
foo.html—as being at
revision 15. The rest of the working copy remains at
revision 10. Only by running svn update
can the latest changes be downloaded and the whole working
copy be marked as revision 15.