| Resolving Tree Conflicts |
| ======================== |
| |
| ############################################################################ |
| ### NOTE: This file describes what I'd like, not what Subversion does. ### |
| ### - Julian Foad, 2008 ### |
| ############################################################################ |
| |
| Resolution of tree conflicts includes: |
| |
| (i) A known state of the WC after the conflict is raised. |
| |
| (ii) Constructing the desired result from the conflicted state. |
| |
| (iii) Marking as resolved (both "svn resolve" and interactive). |
| |
| |
| I. STATE OF THE WC AFTER CONFLICT IS RAISED |
| =========================================== |
| |
| When a tree conflict is raised, the "old" and "theirs" and "mine" versions |
| should be stored locally in the WC in such a way that |
| |
| (a) Subversion can turn one of them into a final outcome when told |
| svn resolve --accept=theirs TARGET |
| |
| (b) the user can examine them and combine them to create a final outcome, |
| using commands like |
| svn proplist TARGET.theirs |
| svn merge TARGET.theirs OTHERFILE TARGET |
| |
| WC State is defined in terms of what file content and what scheduling is |
| stored for each of ".working" (the active WC file/dir during resolving), |
| ".mine" (the previous working file/dir, as preserved for reference), and |
| ".theirs" (the type and resulting content of the incoming change). |
| |
| The expected state for each case is defined in the "WC State" sections inside |
| the "Resolution Recipes" section. |
| |
| Principles |
| ---------- |
| |
| * When "svn update" or "svn switch" raises a tree conflict, it shall update |
| the victim's "base" version from OLD to THEIRS, and leave the "working" |
| version in a state that would be committable (but for the explicit check |
| that prevents committing an item marked as in conflict) and that, if |
| committed, would restore the item to how it looked in "mine". This may |
| involve changing the scheduling of the item, e.g. to be re-added if "update" |
| applied a delete. |
| |
| When "svn merge" raises a tree conflict, it shall not change the working |
| content or scheduling of the victim. |
| |
| * An update from rX to rY followed by an update back to rX should have no |
| overall effect on the local modifications scheduled in the WC. Likewise a |
| switch to a different URL@REV and a switch back to the original one. |
| Likewise a merge followed by a merge of the reverse change. |
| |
| Q. How do we store the "theirs" tree in the WC, especially in the case where |
| it's a tree and needs to be constructed anew because it comes (as an Add or |
| Mod) onto a WC item that's Del or not present? What I mean is to persuade |
| the normal "update" or "merge" code paths to construct a new WC directory |
| named "TARGET.theirs" on the fly and then recurse into it applying the |
| incoming mods. |
| |
| (Need to list the cases where constructing such a new WC tree will be |
| necessary.) |
| |
| |
| II. CONSTRUCTING THE DESIRED RESULT |
| =================================== |
| |
| For cases where the user needs to merge the two conflicting changes (as |
| opposed to choosing just one and ignoring the other), we need: |
| |
| * Recipes for the user to follow |
| - see the "Tree Conflict Resolution Recipes" section. |
| |
| * Enhanced facilities for merging changes from conflicting partial results |
| into the desired result. |
| - see the "Arbitrary Merge Facility Required" section. |
| |
| |
| Tree Conflict Resolution Recipes |
| ================================ |
| |
| This section sets out, for each type of tree conflict, the resolutions that I |
| expect would be commonly wanted, either giving a useful result directly or as |
| building blocks for more complex resolutions. |
| |
| The aim is to provide in each of the selected cases a sufficiently clear |
| recipe for a user to resolve most tree conflicts that they encounter. Such a |
| user is expected to be fairly proficient in using Subversion but not to have |
| any knowledge of the way tree conflicts are handled internally. |
| |
| Under each type of conflict are the following subsections: |
| |
| "WC State" describes the state in which the WC should be left when the |
| conflict is raised, according to the principles set out in section I. |
| |
| "Some use cases" lists some likely use cases by which a user might encounter |
| such a conflict, concentrating on cases that want a resolution other than |
| "THEIRS" or "MINE". |
| |
| "Options" lists resolution options that ought to be available. The |
| resolution options "THEIRS" and "MINE" should be available in every case (so |
| that a user can resolve a whole tree at once with one of those options) and |
| should be implemented internally. Any other options listed here may be |
| recipes for the user to apply manually. These recipes are starting from the |
| state in which the WC should be left by Subversion after raising a conflict. |
| |
| The "WC State" subsection is intended as design requirements, not for the end |
| user. I have not yet attempted to implement this as part of tree-conflict |
| detection, and have no idea to what extent this is currently achieved in the |
| tree-conflicts branch. |
| |
| The other two subsections are intended as the basis of material for end users |
| to read. |
| |
| Principles |
| ---------- |
| |
| * We shall assume the ability to examine the source-left ("old") and source- |
| right ("theirs") and target ("mine") tree states as well as the source |
| diffs. |
| |
| In a merge, we shall not assume or attempt to make use of any ancestral |
| relationship between the target and the source. |
| |
| Renames and Replacements |
| ------------------------ |
| |
| Incoming rename: |
| |
| An incoming rename is treated here as its two constituent actions - an |
| incoming delete and an incoming add - separately. |
| |
| Incoming replacement: |
| |
| In an incoming replacement, the delete is assumed to come before the add. |
| (Currently, they may sometimes come the wrong way around. I have not |
| analyzed the cases in which this can happen, nor the consequences.) |
| |
| Scheduled rename: |
| |
| With a scheduled rename, each of the names (the old and the new) will be |
| treated separately as a potential victim of a tree conflict. |
| |
| Scheduled replacement: |
| |
| A scheduled replacement is treated mainly the same as a scheduled deletion, |
| because any incoming change is assumed to apply to the old object that was |
| deleted rather than to the new object that replaced it. |
| |
| Where the ability to schedule a replacement of one node kind with another is |
| implied, this ability may not be supported (and currently is not supported) |
| by the working copy library. Such cases will therefore be unsupported. This |
| is not seen as a deficiency inherent in tree conflict handling, but as a |
| separate deficiency that restricts tree conflict handling in certain cases. |
| |
| Meaning of "Choose Theirs" and "Choose Mine" |
| -------------------------------------------- |
| |
| There is a subtle difference between the meanings of "Choose Theirs" and |
| "Choose Mine" as applied to an update or switch compared with when |
| the terms are applied to a merge. |
| |
| For update and switch, the final state resulting from the incoming change is |
| already existing in the history of the branch we're working on, and is going |
| to be our WC's new "base" version, so we can't choose to "ignore" this |
| incoming change. The request to "Choose Mine" means "Schedule the item to be |
| changed from its new base state back to how my version of it looked before |
| this operation". This may involve changing the scheduling of the item. The |
| request to "Choose Theirs" simply means "Discard my pending changes so as to |
| keep their version of it". |
| |
| For a merge, however, the final state of the incoming change is not going to |
| be the new base state of the branch we're working on, and so we _can_ choose |
| to ignore it if we so wish. Also, "my" version is a combination of historical |
| and working-copy changes, so we cannot in general choose to ignore this, we |
| can only schedule changes that reverse it. In a merge, then, "Choose Mine" |
| means "Leave my version of the item as it is" (which does not involve any |
| change of scheduling), while "Choose Theirs" means "Overwrite my version with |
| a copy of Their version of the item" (which may involve scheduling an add or |
| delete). The potential alternative meaning, "Make Their change", is not |
| viable: it is what Subversion already tried to do, and it resulted in the very |
| conflict we're now trying to resolve. |
| |
| |
| Recipes |
| ======= |
| |
| up/sw: Add onto Add |
| ------------------- |
| |
| WC State: |
| .working: sched=Normal/Replace, content=.mine |
| .mine: sched=Add[w/hist], content=Something |
| .theirs: action=Add[w/hist], content=Something |
| |
| Some use cases: |
| - I have already applied the patch - their item is identical to mine. |
| -> want to do it just once -> THEIRS. |
| - Two different new items happened to be given the same name. |
| -> accept theirs & rename mine -> RENAME-MINE. |
| - I was doing roughly the same thing but the item is a bit different. |
| -> merge the two items -> manual 2-way merge (or 3-way if both are w/hist |
| and it's the same copy-from source). |
| |
| Options: |
| THEIRS: As usual, like "svn revert TARGET". |
| MINE: My content as a scheduled modification, or as a scheduled replace* |
| if "my" node-kind (or copy-from?) differs. |
| RENAME-MINE: Add "my" content under a different name, and then accept |
| "their" add: |
| - Choose a new name for mine. |
| - svn rename TARGET NEWNAME |
| - svn revert TARGET |
| |
| If identical (node-kind, content, props, copyfrom-info?): |
| Recommend choosing THEIRS. |
| |
| |
| up/sw: Del onto Del |
| ------------------- |
| |
| WC State: |
| .working: sched=unversioned, content=None |
| .mine: sched=Del, content=None |
| .theirs: action=Del, content=None |
| |
| Some use cases: |
| - Already applied the patch |
| -> want to do it just once -> THEIRS. |
| - Renamed to two different names |
| -> want to undo Their renaming and make it like Mine, as if we had a |
| "Choose Mine" option that worked on whole rename operations. -> RENAME. |
| |
| Options: |
| THEIRS: As usual (but has no effect in this case) |
| MINE: As usual (but has no effect in this case) |
| RENAME: |
| - svn rename THEIR-NEW-NAME MY-NEW-NAME |
| And take care to notice if there were any modifications made at the same |
| time as the renames; if so, these might need merging. |
| |
| Note: In an update or switch, THEIRS and MINE are from the same OLD base, so |
| there is no possibility that the item we are deleting locally is different |
| from the item the incoming change is deleting. |
| |
| |
| up/sw: Mod onto Del |
| ------------------- |
| |
| WC State: |
| .working: sched=Del, content=None |
| .mine: sched=Del, content=None |
| .theirs: action=Mod, content=Something |
| |
| Some use cases: |
| - Locally renamed |
| -> want to apply the incoming mod to a different item -> ELSEWHERE. |
| |
| Options: |
| THEIRS: As usual. |
| MINE: Leave it deleted. |
| ELSEWHERE1: Apply their mod onto my renamed item. (Mine is the master.) |
| - Determine a way to obtain the incoming diff and apply it to the new |
| name, e.g. one of these: |
| - svn merge -r OLDREV:NEWREV TARGET(URL?) NEWNAME |
| (should be possible for "up" always, "sw" never, "merge" sometimes) |
| - svn merge -r old:theirs TARGET NEWNAME [*1] |
| ELSEWHERE2: Reapply my Rename [+mod] onto theirs. (Theirs is the master.) |
| - mv NEWNAME TMP |
| - svn revert NEWNAME / rm -rf NEWNAME |
| - Move TARGET.theirs to NEWNAME. Here's one way to do that: |
| - svn resolve --accept=theirs TARGET |
| - svn rename TARGET NEWNAME |
| - svn resolve --accept=mine TARGET |
| - svn merge TARGET@old TMP@working NEWNAME [*1] |
| |
| |
| up/sw: Del onto Mod |
| ------------------- |
| |
| WC State: |
| .working: sched=Add, content=.mine |
| .mine: sched=Normal, content=Something |
| .theirs: action=Del, content=None |
| |
| Some use cases: |
| - The incoming change is (part of) a rename |
| -> want to transfer my local mod to the renamed item -> MOVE-MY-MODS. |
| |
| Options: |
| THEIRS: As usual. |
| MINE: Schedule for Add. |
| MOVE-MY-MODS: Reapply my mod onto their renamed item. (Theirs is the master.) |
| - Determine their new name. |
| - Wait till up/sw has processed the new-named item. |
| - svn merge -r OLD:MINE TARGET THEIRNEWNAME [*1] |
| - svn revert TARGET |
| MOVE-MY-MODS2: Apply their rename[+mod] onto my item. (Mine is the master.) |
| - svn merge TARGET@old THEIRNEWNAME TARGET [*1] |
| - svn revert THEIRNEWNAME |
| - svn rename TARGET THEIRNEWNAME |
| |
| |
| merge: Add onto Something (Identical or Different-Content or Different-Kind) |
| ------------------------- |
| |
| WC State: |
| .working: =.mine |
| .mine: sched=(not Del), content=Something |
| .theirs: action=Add[w/hist?], content=Something |
| |
| Some use cases: |
| Same as for "up/sw: Add onto Add", plus one more: |
| - Two different new items happened to be given the same name. |
| -> keep mine & rename theirs -> RENAME-THEIRS. |
| |
| Options: |
| THEIRS: Schedule local mods (if any change needed) to replace mine |
| with theirs. (If copyfrom differs, should we schedule Replace or not?) |
| MINE: (Nothing to do.) |
| RENAME-MINE: Add "my" content under a new name, and accept "their" add under |
| the original name. (Theirs is the master.) |
| - Choose a new name for mine. |
| - svn rename TARGET NEWNAME |
| - svn resolve --accept=theirs TARGET |
| RENAME-THEIRS: Add theirs under a new name. (Mine is the master.) |
| - Choose a new name for theirs. |
| - svn rename TARGET.theirs NEWNAME [*1] |
| - svn resolve --accept=mine TARGET |
| |
| If identical (node-kind, content, props, copyfrom-info?): |
| Recommend choosing THEIRS. |
| |
| |
| merge: Del onto Nothing Here |
| ---------------------------- |
| |
| WC State: |
| .working: =.mine |
| .mine: sched=(Del/unversioned), content=None |
| .theirs: action=Del, content=None |
| |
| Some use cases: |
| - User's process is wrong: maybe something else needed to be merged first. |
| -> want to revert this whole merge. |
| - Already applied the patch or merged the change without recording the fact. |
| -> want to do it once -> MINE. |
| - The item being deleted (or renamed) in the source has been renamed in the |
| target branch. |
| -> want to delete/rename something else -> ELSEWHERE. |
| |
| Options: |
| THEIRS: Nothing to do - same result as MINE. |
| MINE: (Nothing to do.) |
| ELSEWHERE: Leave TARGET as it is, and |
| - Find the new name(s). |
| - svn delete MYNEWNAME |
| or |
| svn rename MYNEWNAME THEIRNEWNAME |
| |
| |
| merge: Del onto Not Same Kind |
| ----------------------------- |
| |
| WC State: |
| .working: =.mine |
| .mine: sched=(not Del), content=TheOtherKind |
| .theirs: action=Del, content=None |
| |
| Some use cases: |
| - User's process is wrong: maybe something else needed to be merged first. |
| -> want to revert this whole merge. |
| |
| Options: |
| THEIRS: |
| - svn delete TARGET |
| MINE: (Nothing to do.) |
| |
| |
| merge: Del onto Not Same Content |
| -------------------------------- |
| |
| WC State: |
| .working: =.mine |
| .mine: sched=(not Del), content=SameKind |
| .theirs: action=Del, content=None |
| |
| Some use cases: |
| - The content was intentionally divergent, and we still want to delete it. |
| -> THEIRS. |
| - The content was intentionally divergent, and the source node is being |
| renamed (and possibly modified at the same time). |
| -> Apply the incoming rename (possibly +mod) onto mine -> RENAME. |
| |
| Options: |
| THEIRS: |
| - svn delete TARGET |
| MINE: (Nothing to do.) |
| RENAME1: Apply their rename [+mod] onto mine. (Mine is the master.) |
| - Find the incoming new name. |
| - Wait till the new name has been processed (added). |
| - svn merge TARGET.old THEIRNEWNAME TARGET [*1] |
| - svn revert THEIRNEWNAME |
| - svn rename TARGET THEIRNEWNAME |
| RENAME2: Reapply my mods onto their renamed item. (Theirs is the master.) |
| - Find the incoming new name. |
| - Wait till the new name has been processed (added). |
| - svn merge -r old:mine TARGET THEIRNEWNAME [*1] |
| - svn resolve --accept=theirs TARGET |
| |
| |
| merge: Mod onto Nothing Here |
| ---------------------------- |
| |
| WC State: |
| .working: =.mine |
| .mine: sched=(Del/unversioned), content=None |
| .theirs: action=Mod, content=Something |
| |
| Some use cases: |
| - The item was renamed locally |
| -> apply the incoming mod elsewhere -> ELSEWHERE. |
| |
| Options: |
| THEIRS: Re-schedule the target to come back. |
| - copy TARGET.theirs TARGET |
| - svn add TARGET |
| MINE: (Nothing to do.) |
| ELSEWHERE1: Apply their mod onto mine. (Mine is the master.) |
| - Find the new name. |
| - Wait till the new name has been processed (added). |
| - svn merge -r OLD:THEIRS TARGET NEWNAME [*1] |
| ELSEWHERE2: Apply my rename[+mod] onto Theirs. (Theirs is the master.) |
| - svn merge -r BASE:WC NEWNAME TARGET.theirs [*1] |
| - mv TARGET.theirs NEWNAME |
| |
| |
| merge: Mod onto Not Same Kind |
| ----------------------------- |
| |
| WC State: |
| .working: =.mine |
| .mine: sched=(not Del), content=TheOtherKind |
| .theirs: action=Mod, content=Something |
| |
| Options: |
| THEIRS: Not supported. Throw an error. (Want to schedule the target to |
| replace with theirs, but WC doesn't support this.) |
| MINE: (Nothing to do.) |
| |
| |
| Note [*1]: These commands are not yet supported. |
| |
| |
| Arbitrary Merge Facility Required |
| ================================= |
| |
| To enable the user to resolve a "Rename onto Mod" or "Mod onto Rename" |
| conflict efficiently and flexible, we need the ability to merge the difference |
| between two arbitrary WC items into another WC item. The two source items: |
| - may have different names; |
| - may be related by copyfrom info in one that in some way refers to the |
| other; |
| - may be pre-resolution conflict results like TARGET.mine or TARGET@mine. |
| |
| Two ways this could be achieved: |
| |
| 1. Make use of history-sensitive merging by referring to the two items through |
| special revision kinds "old" "theirs" "mine": |
| |
| svn merge -r old:theirs TARGET NEWNAME |
| |
| 2. Use non-history-sensitive merging on arbitrary files |
| "<TARGET>.old" "<TARGET>.theirs" "<TARGET>.mine": |
| |
| svn merge TARGET.old TARGET.theirs NEWNAME |
| |
| Q. How can we most easily implement an extension of "svn merge" that achieves |
| a copyfrom-history-sensitive diff (between WC items) rather than an unaware |
| diff? |
| |
| |
| III. MARKING AS RESOLVED |
| ======================== |
| |
| Primary APIs: |
| |
| libsvn_wc/adm_ops.c:resolve_conflict_on_entry() |
| |
| Pre-tree-conflicts, the "resolve" functions in client through to WC layers all |
| end up calling resolve_conflict_on_entry() on each item. It marks all text |
| conflicts and property conflicts on the item as resolved. It also can select |
| and copy into place one of the available file-text choices, but doesn't appear |
| to have any such support for property conflicts. |
| |
| On the tree conflicts branch, (till branch@{2008-05-29} at least) this |
| function assumes it will be passed the path to the parent dir of some conflict |
| victims, and it simply clears tree conflict data about all victims from the |
| entries file. |
| |
| Plan |
| ---- |
| |
| Separate the different functions that resolve_conflict_on_entry() performs, |
| making it more modular and "orthogonal". |
| |
| Make the tree conflict functions operate on one victim rather than on a whole |
| parent directory having conflicts on any number of victims. |
| |
| Make these new functions public so that the caller can compose the various |
| actions (copying, marking as resolved, notifying, and recursing) in whatever |
| order it wants. |
| |
| Create the following new functions: |
| |
| * Copy one of the simple outcomes (old, mine, theirs) onto the target. |
| |
| select_conflict_outcome(path, svn_wc_conflict_choice_t, ...); |
| select_tree_conflict_outcome(victim_path, svn_wc_conflict_choice_t, ...); |
| |
| - Copies the user's choice onto the "working" version of the item. |
| - For tree conflicts, also includes changing the scheduling of the item. |
| - This operation, and certainly the choice part of it, is logically above |
| the WC layer, except for knowledge of where the files to choose from are |
| stored. |
| |
| |
| * Mark conflicts as resolved on a (victim) path. |
| |
| svn_wc_mark_conflict_resolved(path, ...); |
| |
| - Mark text and property conflicts on one item as resolved. |
| |
| svn_wc_mark_tree_conflict_resolved(victim_path, ...); |
| |
| - Mark the tree conflict on one victim as resolved. |
| |
| |
| * Support for resolver callback? - where/how? |
| |
| |