README

largefiles: update lfdirstate for unchanged largefiles during linear merging

Before this patch, linear merging of modified largefiles causes
an unexpected result, if (1) largefile collides with same-name normal one
in the target revision and (2) "local" largefile is chosen, even
though branch merging between such revisions works correctly.

Expected result of such linear merging is marking the largefile as
(re-)"added", but the actual result is marking it as "modified".

The standin of modified "local largefile" is not changed by linear
merging, and updating/merging update lfdirstate entries only for
largefiles of which standins are changed.

This patch adds the code path to update lfdirstate only for largefiles
of which standins are not changed.

In this case, "synclfdirstate" should be invoked with True as
"normallookup" argument always to force using "normallookup" on
dirstate for "n" files, because "normal" may mark target files as
"clean" unexpectedly.

To reduce cost of "lfile not in filelist", this patch converts
"filelist" to a "set" object: "filelist" is used only in (1) the newly
added code path and (2) the next line of "filelist = set(filelist)".

This is a temporary way to fix with less changes. For fundamental
resolution of this kind of problems in the future, "lfdirstate" should
be updated with "dirstate" simultaneously during "merge.update"
execution: maybe by hooking "recordupdates" (+ total refactoring
around lfdirstate handling)

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 $ make install    # do a system-wide install
 $ hg debuginstall # sanity-check setup
 $ hg              # see help

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