mergetools: add new conflict marker format with diffs in I use 3-way conflict markers. Often when I resolve them, I manually compare one the base with one side and apply the differences to the other side. That can be hard when the conflict marker is large. This patch introduces a new type of conflict marker, which I'm hoping will make it easier to resolve conflicts. The new format uses `<<<<<<<` and `>>>>>>>` to open and close the markers, just like our existing 2-way and 3-way conflict markers. Instead of having 2 or 3 snapshots (left+right or left+base+right), it has a sequence of diffs. A diff looks like this: ``` ------- base +++++++ left a -b +c d ``` A diff that adds one side ("diff from nothing") has a `=======` header instead and does not have have `+` prefixed on its lines. A regular 3-way merge can be viewed as adding one side plus a diff between the base and the other side. It thus has two ways of being represented, depending on which side is being diffed: ``` <<<<<<< ======= left contents on left ------- base +++++++ right contents on -left +right >>>>>>> ``` or ``` <<<<<<< ------- base +++++++ left contents on -right +left ======= right contents on right >>>>>>> ``` I've made it so the new merge tool tries to pick a version that has the most common lines (no difference in the example above). I've called the new tool "mergediff" to stick to the convention of starting with "merge" if the tool tries a regular 3-way merge. The idea came from my pet VCS (placeholder name `jj`), which has support for octopus merges and other ways of ending up with merges of more than 3 versions. I wanted to be able to represent such conflicts in the working copy and therefore thought of this format (although I have not yet implemented it in my VCS). I then attended a meeting with Larry McVoy, who said BitKeeper has an option (`bk smerge -g`) for showing a similar format, which reminded me to actually attempt this in Mercurial. Differential Revision: https://phab.mercurial-scm.org/D9551

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== New Features ==

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 * `hg mv -A` can now be used with `--at-rev`. It behaves just like

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   `hg cp -A --at-rev`, i.e. it marks the destination as a copy of the

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   source whether or not the source still exists (but the source must

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   exist in the parent revision).

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 * New revset predicate `diffcontains(pattern)` for filtering revisions

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   in the same way as `hg grep --diff pattern`.

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 * The memory footprint per changeset and per file during pull/unbundle

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   operations has been significantly reduced.

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== New Experimental Features ==

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== Bug Fixes ==

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== Backwards Compatibility Changes ==

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== Internal API Changes ==

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 * `merge.update()` is now private (renamed to `_update()`). Hopefully

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   the higher-level functions available in the same module cover your

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   use cases.

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 * `phases.registernew` now takes a set of revisions instead of a list

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   of nodes. `phases.advanceboundary` takes an optional set of revisions

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   in addition to the list of nodes. The corresponeding members of the

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   `phasecache` class follow this change.

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 * The `addgroup` member of `revlog` classes no longer keeps a list of

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   all found nodes. It now returns True iff a node was found in the group.

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   An optional callback for duplicated nodes can be used by callers to keep

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   track of all nodes themselve.

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 * The `_chaininfocache` of `revlog` classes has been changed from a dict

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   to a LRU cache.