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Implement merge_incore_recursive(), mostly through the use of a new
helper function, merge_ort_internal(), which itself is based off
merge_recursive_internal() from merge-recursive.c.
This drops the number of failures in the testsuite when run under
GIT_TEST_MERGE_ALGORITHM=ort from around 1500 to 647.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In order to handle recursive merges, after merging merge-bases we need
to clear away most of the data we had built up but some of it needs to
be kept -- in particular the "output" field. Rename the function to
reflect its future change in use.
Further, since "reinitialize" means we'll be reusing the fields
immediately, take advantage of this to only partially clear maps,
leaving the hashtable allocated and pre-sized. (This may be slightly
out-of-order since the speedups aren't realized until there are far
more strmaps in use, but the patch submission process already went out
of order because of various questions and requests for strmap. Anyway,
see commit 6ccdfc2a20 ("strmap: enable faster clearing and reusing of
strmaps", 2020-11-05), for performance details about the use of
strmap_partial_clear().)
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In a subsequent commit, we will implement the traditional recursiveness
that gave merge-recursive its name, namely merging non-unique
merge-bases to come up with a single virtual merge base. Copy a few
helper functions from merge-recursive.c that we will use in the
implementation.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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The focus here is on adding a path_msg() which will queue up
warning/conflict/notice messages about the merge for later processing,
storing these in a pathname -> strbuf map. It might seem like a big
change, but it really just is:
* declaration of necessary map with some comments
* initialization and recording of data
* a bunch of code to iterate over the map at print/free time
* at least one caller in order to avoid an error about having an
unused function (which we provide in the form of implementing
modify/delete conflict handling).
At this stage, it is probably not clear why I am opting for delayed
output processing. There are multiple reasons:
1. Merges are supposed to abort if they would overwrite dirty changes
in the working tree. We cannot correctly determine whether changes
would be overwritten until both rename detection has occurred and
full processing of entries with the renames has finalized.
Warning/conflict/notice messages come up at intermediate codepaths
along the way, so unless we want spurious conflict/warning messages
being printed when the merge will be aborted anyway, we need to
save these messages and only print them when relevant.
2. There can be multiple messages for a single path, and we want all
messages for a give path to appear together instead of having them
grouped by conflict/warning type. This was a problem already with
merge-recursive.c but became even more important due to the
splitting apart of conflict types as discussed in the commit
message for 1f3c9ba707 ("t6425: be more flexible with rename/delete
conflict messages", 2020-08-10)
3. Some callers might want to avoid showing the output in certain
cases, such as if the end result is a clean merge. Rebases have
typically done this.
4. Some callers might not want the output to go to stdout or even
stderr, but might want to do something else with it entirely.
For example, a --remerge-diff option to `git show` or `git log
-p` that remerges on the fly and diffs merge commits against the
remerged version would benefit from stdout/stderr not being
written to in the standard form.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This simplistic and weird-looking patch is here to facilitate future
patch submissions. Adding this stub allows rename detection code to
reference it in one patch series, while a separate patch series can
define the implementation, and then both series can merge cleanly and
work nicely together at that point.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Commit b658536f59 ("merge-ort: add some high-level algorithm structure",
2020-10-27) added high-level structure of the ort merge algorithm. As
we have added more and more functions, that high-level structure has
been slightly obscured. Since functions are still grouped according to
this high-level structure, add comments denoting sections where all the
functions are specifically tied to a piece of the high-level structure.
This function groupings include a few sub-divisions of the original
high-level structure, including some sub-divisions that are yet to be
submitted. Each has (or will have) several functions all serving as
helpers to one or two main functions for each section.
As an added bonus, the comments will serve to provide a small textual
separation between nearby sections and allow the next three patch series
to be submitted independently and merge cleanly.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This field will be used in future patches to allow removal of paths from
opt->priv->paths.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This field is not yet used, but will be used by both the rename handling
code, and the conflict type handling code in process_entry().
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Move most of merge_finalize() into a new helper function,
clear_internal_opts(). This is a step to facilitate recursive merges,
as well as some future optimizations.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Include blob.h for definition of blob_type, and commit-reach.h for
declarations of get_merge_bases() and in_merge_bases(). While none of
these are used yet, we want to avoid cross-dependencies in the next
three series of patches for merge-ort and merge them at the end; adding
these "#include"s now avoids textual conflicts.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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After checkout(), the working tree has the appropriate contents, and the
index matches the working copy. That means that all unmodified and
cleanly merged files have correct index entries, but conflicted entries
need to be updated.
We do this by looping over the conflicted entries, marking the existing
index entry for the path with CE_REMOVE, adding new higher order staged
for the path at the end of the index (ignoring normal index sort order),
and then at the end of the loop removing the CE_REMOVED-marked cache
entries and sorting the index.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Since merge-ort creates a tree for its output, when there are no
conflicts, updating the working tree and index is as simple as using the
unpack_trees() machinery with a twoway_merge (i.e. doing the equivalent
of a "checkout" operation).
If there were conflicts in the merge, then since the tree we created
included all the conflict markers, then using the unpack_trees machinery
in this manner will still update the working tree correctly. Further,
all index entries corresponding to cleanly merged files will also be
updated correctly by this procedure. Index entries corresponding to
conflicted entries will appear as though the user had run "git add -u"
after the merge to accept all files as-is with conflict markers.
Thus, after running unpack_trees(), there needs to be a separate step
for updating the entries in the index corresponding to conflicted files.
This will be the job for the function record_conflicted_index_entris(),
which will be implemented in a subsequent commit.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This adds a basic implementation for merge_switch_to_result(), though
just in terms of a few new empty functions that will be defined in
subsequent commits.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Our order for processing of entries means that if we have a tree of
files that looks like
Makefile
src/moduleA/foo.c
src/moduleA/bar.c
src/moduleB/baz.c
src/moduleB/umm.c
tokens.txt
Then we will process paths in the order of the leftmost column below. I
have added two additional columns that help explain the algorithm that
follows; the 2nd column is there to remind us we have oid & mode info we
are tracking for each of these paths (which differs between the paths
which I'm not representing well here), and the third column annotates
the parent directory of the entry:
tokens.txt <version_info> ""
src/moduleB/umm.c <version_info> src/moduleB
src/moduleB/baz.c <version_info> src/moduleB
src/moduleB <version_info> src
src/moduleA/foo.c <version_info> src/moduleA
src/moduleA/bar.c <version_info> src/moduleA
src/moduleA <version_info> src
src <version_info> ""
Makefile <version_info> ""
When the parent directory changes, if it's a subdirectory of the previous
parent directory (e.g. "" -> src/moduleB) then we can just keep appending.
If the parent directory differs from the previous parent directory and is
not a subdirectory, then we should process that directory.
So, for example, when we get to this point:
tokens.txt <version_info> ""
src/moduleB/umm.c <version_info> src/moduleB
src/moduleB/baz.c <version_info> src/moduleB
and note that the next entry (src/moduleB) has a different parent than
the last one that isn't a subdirectory, we should write out a tree for it
100644 blob <HASH> umm.c
100644 blob <HASH> baz.c
then pop all the entries under that directory while recording the new
hash for that directory, leaving us with
tokens.txt <version_info> ""
src/moduleB <new version_info> src
This process repeats until at the end we get to
tokens.txt <version_info> ""
src <new version_info> ""
Makefile <version_info> ""
and then we can write out the toplevel tree. Since we potentially have
entries in our string_list corresponding to multiple different toplevel
directories, e.g. a slightly different repository might have:
whizbang.txt <version_info> ""
tokens.txt <version_info> ""
src/moduleD <new version_info> src
src/moduleC <new version_info> src
src/moduleB <new version_info> src
src/moduleA/foo.c <version_info> src/moduleA
src/moduleA/bar.c <version_info> src/moduleA
When src/moduleA is popped off, we need to know that the "last
directory" reverts back to src, and how many entries in our string_list
are associated with that parent directory. So I use an auxiliary
offsets string_list which would have (parent_directory,offset)
information of the form
"" 0
src 2
src/moduleA 5
Whenever I write out a tree for a subdirectory, I set versions.nr to
the final offset value and then decrement offsets.nr...and then add
an entry to versions with a hash for the new directory.
The idea is relatively simple, there's just a lot of accounting to
implement this.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Create a new function, write_tree(), which will take a list of
basenames, modes, and oids for a single directory and create a tree
object in the object-store. We do not yet have just basenames, modes,
and oids for just a single directory (we have a mixture of entries from
all directory levels in the hierarchy) so we still die() before the
current call to write_tree(), but the next patch will rectify that.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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As a step towards transforming the processed path->conflict_info entries
into an actual tree object, start recording basenames, modes, and oids
in a dir_metadata structure. Subsequent commits will make use of this
to actually write a tree.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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We want to handle paths below a directory before needing to handle the
directory itself. Also, we want to handle the directory immediately
after the paths below it, so we can't use simple lexicographic ordering
from strcmp (which would insert foo.txt between foo and foo/file.c).
Copy string_list_df_name_compare() from merge-recursive.c, and set up a
string list of paths sorted by that function so that we can iterate in
the desired order.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Add a process_entries() implementation that just loops over the paths
and processes each one individually with an auxiliary process_entry()
call. Add a basic process_entry() as well, which handles several cases
but leaves a few of the more involved ones with die-not-implemented
messages. Also, although process_entries() is supposed to create a
tree, it does not yet have code to do so -- except in the special case
of merging completely empty trees.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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When all three trees have the same oid, there is no need to recurse into
these trees to find that all files within them happen to match. We can
just record any one of the trees as the resolution of merging that
particular path.
Immediately resolving trees for other types of trivial tree merges (such
as one side matches the merge base, or the two sides match each other)
would prevent us from detecting renames for some paths, and thus prevent
us from doing three-way content merges for those paths whose renames we
did not detect.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Create a helper function, setup_path_info(), which can be used to record
all the information we want in a merged_info or conflict_info. While
there is currently only one caller of this new function, and some of its
particular parameters are fixed, future callers of this function will be
added later.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Three-way merges, by their nature, are going to often have two or more
trees match at a given subdirectory. We can avoid calling
fill_tree_descriptor() on the same tree by checking when these trees
match. Noting when various oids match will also be useful in other
calculations and optimizations as well.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This does not actually collect any necessary info other than the
pathnames involved, since it just allocates an all-zero conflict_info
and stuffs that into paths. However, it invokes the traverse_trees()
machinery to walk over all the paths and sets up the basic
infrastructure we need.
I have left out a few obvious optimizations to try to make this patch as
short and obvious as possible. A subsequent patch will add some of
those back in with some more useful data fields before we introduce a
patch that actually sets up the conflict_info fields.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Various places in merge-recursive used an err() function when it hit
some kind of unrecoverable error. That code was from the reusable bits
of merge-recursive.c that we liked, such as merge_3way, writing object
files to the object store, reading blobs from the object store, etc. So
create a similar function to allow us to port that code over, and use it
for when we detect problems returned from collect_merge_info()'s
traverse_trees() call, which we will be adding next.
While we are at it, also add more documentation for the "clean" field
from struct merge_result, particularly since the name suggests a boolean
but it is not quite one and this is our first non-boolean usage.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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In my cursory investigation, histogram diffs are about 2% slower than
Myers diffs. Others have probably done more detailed benchmarks. But,
in short, histogram diffs have been around for years and in a number of
cases provide obviously better looking diffs where Myers diffs are
unintelligible but the performance hit has kept them from becoming the
default.
However, there are real merge bugs we know about that have triggered on
git.git and linux.git, which I don't have a clue how to address without
the additional information that I believe is provided by histogram
diffs. See the following:
https://lore.kernel.org/git/20190816184051.GB13894@sigill.intra.peff.net/
https://lore.kernel.org/git/CABPp-BHvJHpSJT7sdFwfNcPn_sOXwJi3=o14qjZS3M8Rzcxe2A@mail.gmail.com/
https://lore.kernel.org/git/CABPp-BGtez4qjbtFT1hQoREfcJPmk9MzjhY5eEq1QhXT23tFOw@mail.gmail.com/
I don't like mismerges. I really don't like silent mismerges. While I
am sometimes willing to make performance and correctness tradeoff, I'm
much more interested in correctness in general. I want to fix the above
bugs. I have not yet started doing so, but I believe histogram diff at
least gives me an angle. Unfortunately, I can't rely on using the
information from histogram diff unless it's in use. And it hasn't been
used because of a few percentage performance hit.
In testcases I have looked at, merge-ort is _much_ faster than
merge-recursive for non-trivial merges/rebases/cherry-picks. As such,
this is a golden opportunity to switch out the underlying diff algorithm
(at least the one used by the merge machinery; git-diff and git-log are
separate questions); doing so will allow me to get additional data and
improved diffs, and I believe it will help me fix the above bugs at some
point in the future.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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merge_start() basically does a bunch of sanity checks, then allocates
and initializes opt->priv -- a struct merge_options_internal.
Most of the sanity checks are usable as-is. The
allocation/intialization is a bit different since merge-ort has a very
different merge_options_internal than merge-recursive, but the idea is
the same.
The weirdest part here is that merge-ort and merge-recursive use the
same struct merge_options, even though merge_options has a number of
fields that are oddly specific to merge-recursive's internal
implementation and don't even make sense with merge-ort's high-level
design (e.g. buffer_output, which merge-ort has to always do). I reused
the same data structure because:
* most the fields made sense to both merge algorithms
* making a new struct would have required making new enums or somehow
externalizing them, and that was getting messy.
* it simplifies converting the existing callers by not having to
have different code paths for merge_options setup.
I also marked detect_renames as ignored. We can revisit that later, but
in short: merge-recursive allowed turning off rename detection because
it was sometimes glacially slow. When you speed something up by a few
orders of magnitude, it's worth revisiting whether that justification is
still relevant. Besides, if folks find it's still too slow, perhaps
they have a better scaling case than I could find and maybe it turns up
some more optimizations we can add. If it still is needed as an option,
it is easy to add later.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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merge_ort_nonrecursive_internal() will be used by both
merge_inmemory_nonrecursive() and merge_inmemory_recursive(); let's
focus on it for now. It involves some setup -- merge_start() --
followed by the following chain of functions:
collect_merge_info()
This function will populate merge_options_internal's paths field,
via a call to traverse_trees() and a new callback that will be added
later.
detect_and_process_renames()
This function will detect renames, and then adjust entries in paths
to move conflict stages from old pathnames into those for new
pathnames, so that the next step doesn't have to think about renames
and just can do three-way content merging and such.
process_entries()
This function determines how to take the various stages (versions of
a file from the three different sides) and merge them, and whether
to mark the result as conflicted or cleanly merged. It also writes
out these merged file versions as it goes to create a tree.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Set up some basic internal data structures. The only carry-over from
merge-recursive.c is call_depth, though needed_rename_limit will be
added later.
The central piece of data will definitely be the strmap "paths", which
will map every relevant pathname under consideration to either a
merged_info or a conflict_info. ("conflicted" is a strmap that is a
subset of "paths".)
merged_info contains all relevant information for a non-conflicted
entry. conflict_info contains a merged_info, plus any additional
information about a conflict such as the higher orders stages involved
and the names of the paths those came from (handy once renames get
involved). If an entry remains conflicted, the merged_info portion of a
conflict_info will later be filled with whatever version of the file
should be placed in the working directory (e.g. an as-merged-as-possible
variation that contains conflict markers).
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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This is the beginning of a new merge strategy. While there are some API
differences, and the implementation has some differences in behavior, it
is essentially meant as an eventual drop-in replacement for
merge-recursive.c. However, it is being built to exist side-by-side
with merge-recursive so that we have plenty of time to find out how
those differences pan out in the real world while people can still fall
back to merge-recursive. (Also, I intend to avoid modifying
merge-recursive during this process, to keep it stable.)
The primary difference noticable here is that the updating of the
working tree and index is not done simultaneously with the merge
algorithm, but is a separate post-processing step. The new API is
designed so that one can do repeated merges (e.g. during a rebase or
cherry-pick) and only update the index and working tree one time at the
end instead of updating it with every intermediate result. Also, one
can perform a merge between two branches, neither of which match the
index or the working tree, without clobbering the index or working tree.
The next three commits will demonstrate various uses of this new API.
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Elijah Newren