Enabling symmetric merge, and UI details

Hi, merge fans. It's time to lose the temporary '--symmetric' option and make it the default mode in 'svn'. Some people have been kind enough to try using the 'symmetric' mode and report back, mainly Paul to whom I am most grateful.  I am aware of two current issues ([1],[2]) which I am investigating and they are looking simple enough to be resolved soon.  Please help me flag up any other issues. Before we consider the details of the UI changes, I thought back to how the user base would see 'symmetric merge' in the context of the history of Subversion's merge tracking, and wrote a brief overview at <http://wiki.apache.org/subversion/SymmetricMerge#The_User.27s_Perspective>. UI CHANGES I think, and please tell me if you disagree, that we will make the best progression with a UI like this, which the attached patch [6] roughly implements for illustration:   * Use the 'symmetric'/'auto'[3] mode for any merge that was previously a reintegrate or a non-reintegrate 'sync' merge.  That is, when there is:     - just one source;     - no start revision;     - (an end revision may be specified, which can be done without a start rev by specifying peg-rev syntax: SOURCE@END_REV);     - no incompatible options (such as --ignore-ancestry).   * If the code chooses a reintegrate-like merge, it will apply the strict WC checks like reintegrate does in 1.7.   * Make the '--reintegrate' option mean the user believes a reintegrate-style merge is needed, so check that the previous merge is as expected (that it, in the opposite direction) and bail out if not.   * Mark the '--reintegrate' option as deprecated, as the reason for its existence has gone.   * Delete the '--symmetric' option; it was only there for testing and has not been released. WHAT WILL NOT CHANGE Two specific things to call out:   * A merge specifying '--reintegrate' merge will not change in any scenario where 'merge --reintegrate' is the user's best option today.   * A merge specifying '-r X:Y' will not change.  This requests a cherry-pick merge, using merge tracking to avoid re-merging any revs in the range that are already merged.  Currently, if 'X' is 1 or a low enough number such that there are no unmerged revisions before 'X', then Subversion performs exactly the same kind of merge as when 'X' is not specified, which we call a 'sync' merge.  I believe we could make a later enhancement to automatically use 'reintegrate' mode if that would be the correct thing to do for merging the requested range. OPTIONS NOT ALLOWED WITH --REINTEGRATE The following options are not allowed with '--reintegrate' in 1.7 but are allowed for non-reintegrate merge-tracking merges:   --record-only   --depth   --force   --allow-mixed-revisions My recommendation for these options is that if we choose a reintegrate-style merge then we error out, saying "the required merge is reintegrate-like[4], and option --X is not supported for this kind of merge".  Otherwise we handle the option just like in 1.7. Please let me know if this seems good, while I go and adjust the help text. - Julian [1] Unexpected revision number in the "Merging r6 through r9" notification, <http://svn.haxx.se/dev/archive-2012-08/0005.shtml>. [2] Behaviour when the root has not been merged, a subtree has, and now we merge the root in the other direction, <http://svn.haxx.se/dev/archive-2012-08/0008.shtml>. [3] Every time I say 'symmetric', I try to think of a better name.  It's not symmetric, it's just based on a symmetric model.  'automatic'?  'bidirectional'? [4] Need to choose terminology for a reintegrate-style merge, for the UI.  "reversing direction"? [5] Wiki page, <http://wiki.apache.org/subversion/SymmetricMerge>. [6] Attachment, 'enable-symmetric-merge-1.patch'. [7] GUIs and other clients can switch to the new svn_client API when they are ready to do so; here I'm just talking about our 'svn' client. -- Subversion Live 2012 - 2 Days: training, networking, demos & more! http://bit.ly/NgUaRi Certified & Supported Apache Subversion Downloads: http://www.wandisco.com/subversion/download