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2018-11-02xdiff: provide a separate emit callback for hunksLibravatar Jeff King2-5/+22
The xdiff library always emits hunk header lines to our callbacks as formatted strings like "@@ -a,b +c,d @@\n". This is convenient if we're going to output a diff, but less so if we actually need to compute using those numbers, which requires re-parsing the line. In preparation for moving away from this, let's teach xdiff a new callback function which gets the broken-out hunk information. To help callers that don't want to use this new callback, if it's NULL we'll continue to format the hunk header into a string. Note that this function renames the "outf" callback to "out_line", as well. This isn't strictly necessary, but helps in two ways: 1. Now that there are two callbacks, it's nice to use more descriptive names. 2. Many callers did not zero the emit_callback_data struct, and needed to be modified to set ecb.out_hunk to NULL. By changing the name of the existing struct member, that guarantees that any new callers from in-flight topics will break the build and be examined manually. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-08-17Merge branch 'sb/indent-heuristic-optim'Libravatar Junio C Hamano1-1/+11
"git diff --indent-heuristic" had a bad corner case performance. * sb/indent-heuristic-optim: xdiff: reduce indent heuristic overhead
2018-08-15Merge branch 'sb/histogram-less-memory'Libravatar Junio C Hamano1-55/+78
"git diff --histogram" had a bad memory usage pattern, which has been rearranged to reduce the peak usage. * sb/histogram-less-memory: xdiff/histogram: remove tail recursion xdiff/xhistogram: move index allocation into find_lcs xdiff/xhistogram: factor out memory cleanup into free_index() xdiff/xhistogram: pass arguments directly to fall_back_to_classic_diff
2018-08-01xdiff: reduce indent heuristic overheadLibravatar Stefan Beller1-1/+11
Skip searching for better indentation heuristics if we'd slide a hunk more than its size. This is the easiest fix proposed in the analysis[1] in response to a patch that mercurial took for xdiff to limit searching by a constant. Using a performance test as: #!python open('a', 'w').write(" \n" * 1000000) open('b', 'w').write(" \n" * 1000001) This patch reduces the execution of "git diff --no-index a b" from 0.70s to 0.31s. However limiting the sliding to the size of the diff hunk, which was proposed as a solution (that I found easiest to implement for now) is not optimal for cases like open('a', 'w').write(" \n" * 1000000) open('b', 'w').write(" \n" * 2000000) as then we'd still slide 1000000 times. In addition to limiting the sliding to size of the hunk, also limit by a constant. Choose 100 lines as the constant as that fits more than a screen, which really means that the diff sliding is probably not providing a lot of benefit anyway. [1] https://public-inbox.org/git/72ac1ac2-f567-f241-41d6-d0f83072e0b3@alum.mit.edu/ Reported-by: Jun Wu <quark@fb.com> Analysis-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-07-23xdiff/histogram: remove tail recursionLibravatar Stefan Beller1-6/+14
When running the same reproduction script as the previous patch, it turns out the stack is too small, which can be easily avoided. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-07-19xdiff/xhistogram: move index allocation into find_lcsLibravatar Stefan Beller1-43/+53
This fixes a memory issue when recursing a lot, which can be reproduced as seq 1 100000 >one seq 1 4 100000 >two git diff --no-index --histogram one two Before this patch, histogram_diff would call itself recursively before calling free_index, which would mean a lot of memory is allocated during the recursion and only freed afterwards. By moving the memory allocation (and its free call) into find_lcs, the memory is free'd before we recurse, such that memory is reused in the next step of the recursion instead of using new memory. This addresses only the memory pressure, not the run time complexity, that is also awful for the corner case outlined above. Helpful in understanding the code (in addition to the sparse history of this file), was https://stackoverflow.com/a/32367597 which reproduces most of the code comments of the JGit implementation. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-07-19xdiff/xhistogram: factor out memory cleanup into free_index()Libravatar Stefan Beller1-4/+9
This will be useful in the next patch as we'll introduce multiple callers. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-07-19xdiff/xhistogram: pass arguments directly to fall_back_to_classic_diffLibravatar Stefan Beller1-11/+11
By passing the 'xpp' and 'env' argument directly to the function 'fall_back_to_classic_diff', we eliminate an occurrence of the 'index' in histogram_diff, which will prove useful in a bit. While at it, move it up in the file. This will make the diff of one of the next patches more legible. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-07-17xdiff/xdiffi.c: remove unneeded function declarationsLibravatar Stefan Beller1-17/+0
There is no need to forward-declare these functions, as they are used after their implementation only. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-07-17xdiff/xdiff.h: remove unused flagsLibravatar Stefan Beller1-8/+0
These flags were there since the beginning (3443546f6e (Use a *real* built-in diff generator, 2006-03-24), but were never used. Remove them. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-12-19Merge branch 'jt/diff-anchored-patience'Libravatar Junio C Hamano2-5/+41
"git diff" learned a variant of the "--patience" algorithm, to which the user can specify which 'unique' line to be used as anchoring points. * jt/diff-anchored-patience: diff: support anchoring line(s)
2017-11-28Merge branch 'rs/include-comments-before-the-function-header'Libravatar Junio C Hamano1-3/+10
"git grep -W", "git diff -W" and their friends learned a heuristic to extend a pre-context beyond the line that matches the "function pattern" (aka "diff.*.xfuncname") to include a comment block, if exists, that immediately precedes it. * rs/include-comments-before-the-function-header: grep: show non-empty lines before functions with -W grep: update boundary variable for pre-context t7810: improve check of -W with user-defined function lines xdiff: show non-empty lines before functions with -W xdiff: factor out is_func_rec() t4051: add test for comments preceding function lines
2017-11-28diff: support anchoring line(s)Libravatar Jonathan Tan2-5/+41
Teach diff a new algorithm, one that attempts to prevent user-specified lines from appearing as a deletion or addition in the end result. The end user can use this by specifying "--anchored=<text>" one or more times when using Git commands like "diff" and "show". Signed-off-by: Jonathan Tan <jonathantanmy@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-11-27Merge branch 'jc/ignore-cr-at-eol'Libravatar Junio C Hamano2-12/+52
The "diff" family of commands learned to ignore differences in carriage return at the end of line. * jc/ignore-cr-at-eol: diff: --ignore-cr-at-eol xdiff: reassign xpparm_t.flags bits
2017-11-21xdiff: show non-empty lines before functions with -WLibravatar René Scharfe1-0/+3
Non-empty lines before a function definition are most likely comments for that function and thus relevant. Include them in function context. Such a non-empty line might also belong to the preceeding function if there is no separating blank line. Stop extending the context upwards also at the next function line to make sure only one extra function body is shown at most. Original-patch-by: Vegard Nossum <vegard.nossum@oracle.com> Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-11-21xdiff: factor out is_func_rec()Libravatar René Scharfe1-3/+7
Add a helper for checking if a given record is a function line. It frees callers from having to deal with the buffer arguments of match_func_rec(). Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-11-09Replace Free Software Foundation address in license noticesLibravatar Todd Zullinger14-28/+28
The mailing address for the FSF has changed over the years. Rather than updating the address across all files, refer readers to gnu.org, as the GNU GPL documentation now suggests for license notices. The mailing address is retained in the full license files (COPYING and LGPL-2.1). The old address is still present in t/diff-lib/COPYING. This is intentional, as the file is used in tests and the contents are not expected to change. Signed-off-by: Todd Zullinger <tmz@pobox.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-11-08diff: --ignore-cr-at-eolLibravatar Junio C Hamano2-3/+39
A new option --ignore-cr-at-eol tells the diff machinery to treat a carriage-return at the end of a (complete) line as if it does not exist. Just like other "--ignore-*" options to ignore various kinds of whitespace differences, this will help reviewing the real changes you made without getting distracted by spurious CRLF<->LF conversion made by your editor program. Helped-by: Johannes Schindelin <Johannes.Schindelin@gmx.de> [jch: squashed in command line completion by Dscho] Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-27xdiff: reassign xpparm_t.flags bitsLibravatar Junio C Hamano1-10/+14
We have packed the bits too tightly in such a way that it is not easy to add a new type of whitespace ignoring option, a new type of LCS algorithm, or a new type of post-cleanup heuristics. Reorder bits a bit to give room for these three classes of options to grow. Also make use of XDF_WHITESPACE_FLAGS macro where we check any of these bits are on, instead of using DIFF_XDL_TST() macro on individual possibilities. That way, the "is any of the bits on?" code does not have to change when we add more ways to ignore whitespaces. While at it, add a comment in front of the bit definitions to clarify in which structure these defined bits may appear. Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-10-10cleanup: fix possible overflow errors in binary searchLibravatar Derrick Stolee1-1/+1
A common mistake when writing binary search is to allow possible integer overflow by using the simple average: mid = (min + max) / 2; Instead, use the overflow-safe version: mid = min + (max - min) / 2; This translation is safe since the operation occurs inside a loop conditioned on "min < max". The included changes were found using the following git grep: git grep '/ *2;' '*.c' Making this cleanup will prevent future review friction when a new binary search is contructed based on existing code. Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Reviewed-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-01-15xdiff -W: relax end-of-file function detectionLibravatar Vegard Nossum1-8/+6
When adding a new function to the end of a file, it's enough to know that 1) the addition is at the end of the file; and 2) there is a function _somewhere_ in there. If we had simply been changing the end of an existing function, then we would also be deleting something from the old version. This fixes the case where we add e.g. // Begin of dummy static int dummy(void) { } to the end of the file. Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com> Acked-by: René Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2017-01-10Merge branch 'jc/retire-compaction-heuristics'Libravatar Junio C Hamano2-35/+1
"git diff" and its family had two experimental heuristics to shift the contents of a hunk to make the patch easier to read. One of them turns out to be better than the other, so leave only the "--indent-heuristic" option and remove the other one. * jc/retire-compaction-heuristics: diff: retire "compaction" heuristics
2016-12-23diff: retire "compaction" heuristicsLibravatar Junio C Hamano2-35/+1
When a patch inserts a block of lines, whose last lines are the same as the existing lines that appear before the inserted block, "git diff" can choose any place between these existing lines as the boundary between the pre-context and the added lines (adjusting the end of the inserted block as appropriate) to come up with variants of the same patch, and some variants are easier to read than others. We have been trying to improve the choice of this boundary, and Git 2.11 shipped with an experimental "compaction-heuristic". Since then another attempt to improve the logic further resulted in a new "indent-heuristic" logic. It is agreed that the latter gives better result overall, and the former outlived its usefulness. Retire "compaction", and keep "indent" as an experimental feature. The latter hopefully will be turned on by default in a future release, but that should be done as a separate step. Suggested-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-12-06xdiff: drop XDL_FAST_HASHLibravatar Jeff King1-106/+0
The xdiff code hashes every line of both sides of a diff, and then compares those hashes to find duplicates. The overall performance depends both on how fast we can compute the hashes, but also on how many hash collisions we see. The idea of XDL_FAST_HASH is to speed up the hash computation. But the generated hashes have worse collision behavior. This means that in some cases it speeds diffs up (running "git log -p" on git.git improves by ~8% with it), but in others it can slow things down. One pathological case saw over a 100x slowdown[1]. There may be a better hash function that covers both properties, but in the meantime we are better off with the original hash. It's slightly slower in the common case, but it has fewer surprising pathological cases. [1] http://public-inbox.org/git/20141222041944.GA441@peff.net/ Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-10-03Merge branch 'mh/diff-indent-heuristic'Libravatar Junio C Hamano1-7/+7
Clean-up for a recently graduated topic. * mh/diff-indent-heuristic: xdiff: rename "struct group" to "struct xdlgroup"
2016-09-29Merge branch 'rs/xdiff-merge-overlapping-hunks-for-W-context' into maintLibravatar Junio C Hamano1-1/+1
"git diff -W" output needs to extend the context backward to include the header line of the current function and also forward to include the body of the entire current function up to the header line of the next one. This process may have to merge to adjacent hunks, but the code forgot to do so in some cases. * rs/xdiff-merge-overlapping-hunks-for-W-context: xdiff: fix merging of hunks with -W context and -u context
2016-09-27xdiff: rename "struct group" to "struct xdlgroup"Libravatar Jeff King1-7/+7
Commit e8adf23 (xdl_change_compact(): introduce the concept of a change group, 2016-08-22) added a "struct group" type to xdiff/xdiffi.c. But the POSIX system header "grp.h" already defines "struct group" (it is part of the getgrnam interface). This happens to work because the new type is local to xdiffi.c, and the xdiff code includes a relatively small set of system headers. But it will break compilation if xdiff ever switches to using git-compat-util.h. It can also probably cause confusion with tools that look at the whole code base, like coccinelle or ctags. Let's resolve by giving the xdiff variant a scoped name, which is closer to other xdiff types anyway (e.g., xdlfile_t, though note that xdiff is fond if typedefs when Git usually is not). Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-09-26Merge branch 'mh/diff-indent-heuristic'Libravatar Junio C Hamano2-98/+538
Output from "git diff" can be made easier to read by selecting which lines are common and which lines are added/deleted intelligently when the lines before and after the changed section are the same. A command line option is added to help with the experiment to find a good heuristics. * mh/diff-indent-heuristic: blame: honor the diff heuristic options and config parse-options: add parse_opt_unknown_cb() diff: improve positioning of add/delete blocks in diffs xdl_change_compact(): introduce the concept of a change group recs_match(): take two xrecord_t pointers as arguments is_blank_line(): take a single xrecord_t as argument xdl_change_compact(): only use heuristic if group can't be matched xdl_change_compact(): fix compaction heuristic to adjust ixo
2016-09-21Merge branch 'rs/xdiff-merge-overlapping-hunks-for-W-context'Libravatar Junio C Hamano1-1/+1
"git diff -W" output needs to extend the context backward to include the header line of the current function and also forward to include the body of the entire current function up to the header line of the next one. This process may have to merge to adjacent hunks, but the code forgot to do so in some cases. * rs/xdiff-merge-overlapping-hunks-for-W-context: xdiff: fix merging of hunks with -W context and -u context
2016-09-19diff: improve positioning of add/delete blocks in diffsLibravatar Michael Haggerty2-0/+326
Some groups of added/deleted lines in diffs can be slid up or down, because lines at the edges of the group are not unique. Picking good shifts for such groups is not a matter of correctness but definitely has a big effect on aesthetics. For example, consider the following two diffs. The first is what standard Git emits: --- a/9c572b21dd090a1e5c5bb397053bf8043ffe7fb4:git-send-email.perl +++ b/6dcfa306f2b67b733a7eb2d7ded1bc9987809edb:git-send-email.perl @@ -231,6 +231,9 @@ if (!defined $initial_reply_to && $prompting) { } if (!$smtp_server) { + $smtp_server = $repo->config('sendemail.smtpserver'); +} +if (!$smtp_server) { foreach (qw( /usr/sbin/sendmail /usr/lib/sendmail )) { if (-x $_) { $smtp_server = $_; The following diff is equivalent, but is obviously preferable from an aesthetic point of view: --- a/9c572b21dd090a1e5c5bb397053bf8043ffe7fb4:git-send-email.perl +++ b/6dcfa306f2b67b733a7eb2d7ded1bc9987809edb:git-send-email.perl @@ -230,6 +230,9 @@ if (!defined $initial_reply_to && $prompting) { $initial_reply_to =~ s/(^\s+|\s+$)//g; } +if (!$smtp_server) { + $smtp_server = $repo->config('sendemail.smtpserver'); +} if (!$smtp_server) { foreach (qw( /usr/sbin/sendmail /usr/lib/sendmail )) { if (-x $_) { This patch teaches Git to pick better positions for such "diff sliders" using heuristics that take the positions of nearby blank lines and the indentation of nearby lines into account. The existing Git code basically always shifts such "sliders" as far down in the file as possible. The only exception is when the slider can be aligned with a group of changed lines in the other file, in which case Git favors depicting the change as one add+delete block rather than one add and a slightly offset delete block. This naive algorithm often yields ugly diffs. Commit d634d61ed6 improved the situation somewhat by preferring to position add/delete groups to make their last line a blank line, when that is possible. This heuristic does more good than harm, but (1) it can only help if there are blank lines in the right places, and (2) always picks the last blank line, even if there are others that might be better. The end result is that it makes perhaps 1/3 as many errors as the default Git algorithm, but that still leaves a lot of ugly diffs. This commit implements a new and much better heuristic for picking optimal "slider" positions using the following approach: First observe that each hypothetical positioning of a diff slider introduces two splits: one between the context lines preceding the group and the first added/deleted line, and the other between the last added/deleted line and the first line of context following it. It tries to find the positioning that creates the least bad splits. Splits are evaluated based only on the presence and locations of nearby blank lines, and the indentation of lines near the split. Basically, it prefers to introduce splits adjacent to blank lines, between lines that are indented less, and between lines with the same level of indentation. In more detail: 1. It measures the following characteristics of a proposed splitting position in a `struct split_measurement`: * the number of blank lines above the proposed split * whether the line directly after the split is blank * the number of blank lines following that line * the indentation of the nearest non-blank line above the split * the indentation of the line directly below the split * the indentation of the nearest non-blank line after that line 2. It combines the measured attributes using a bunch of empirically-optimized weighting factors to derive a `struct split_score` that measures the "badness" of splitting the text at that position. 3. It combines the `split_score` for the top and the bottom of the slider at each of its possible positions, and selects the position that has the best `split_score`. I determined the initial set of weighting factors by collecting a corpus of Git histories from 29 open-source software projects in various programming languages. I generated many diffs from this corpus, and determined the best positioning "by eye" for about 6600 diff sliders. I used about half of the repositories in the corpus (corresponding to about 2/3 of the sliders) as a training set, and optimized the weights against this corpus using a crude automated search of the parameter space to get the best agreement with the manually-determined values. Then I tested the resulting heuristic against the full corpus. The results are summarized in the following table, in column `indent-1`: | repository | count | Git 2.9.0 | compaction | compaction-fixed | indent-1 | indent-2 | | --------------------- | ----- | -------------- | -------------- | ---------------- | -------------- | -------------- | | afnetworking | 109 | 89 (81.7%) | 37 (33.9%) | 37 (33.9%) | 2 (1.8%) | 2 (1.8%) | | alamofire | 30 | 18 (60.0%) | 14 (46.7%) | 15 (50.0%) | 0 (0.0%) | 0 (0.0%) | | angular | 184 | 127 (69.0%) | 39 (21.2%) | 23 (12.5%) | 5 (2.7%) | 5 (2.7%) | | animate | 313 | 2 (0.6%) | 2 (0.6%) | 2 (0.6%) | 2 (0.6%) | 2 (0.6%) | | ant | 380 | 356 (93.7%) | 152 (40.0%) | 148 (38.9%) | 15 (3.9%) | 15 (3.9%) | * | bugzilla | 306 | 263 (85.9%) | 109 (35.6%) | 99 (32.4%) | 14 (4.6%) | 15 (4.9%) | * | corefx | 126 | 91 (72.2%) | 22 (17.5%) | 21 (16.7%) | 6 (4.8%) | 6 (4.8%) | | couchdb | 78 | 44 (56.4%) | 26 (33.3%) | 28 (35.9%) | 6 (7.7%) | 6 (7.7%) | * | cpython | 937 | 158 (16.9%) | 50 (5.3%) | 49 (5.2%) | 5 (0.5%) | 5 (0.5%) | * | discourse | 160 | 95 (59.4%) | 42 (26.2%) | 36 (22.5%) | 18 (11.2%) | 13 (8.1%) | | docker | 307 | 194 (63.2%) | 198 (64.5%) | 253 (82.4%) | 8 (2.6%) | 8 (2.6%) | * | electron | 163 | 132 (81.0%) | 38 (23.3%) | 39 (23.9%) | 6 (3.7%) | 6 (3.7%) | | git | 536 | 470 (87.7%) | 73 (13.6%) | 78 (14.6%) | 16 (3.0%) | 16 (3.0%) | * | gitflow | 127 | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | | ionic | 133 | 89 (66.9%) | 29 (21.8%) | 38 (28.6%) | 1 (0.8%) | 1 (0.8%) | | ipython | 482 | 362 (75.1%) | 167 (34.6%) | 169 (35.1%) | 11 (2.3%) | 11 (2.3%) | * | junit | 161 | 147 (91.3%) | 67 (41.6%) | 66 (41.0%) | 1 (0.6%) | 1 (0.6%) | * | lighttable | 15 | 5 (33.3%) | 0 (0.0%) | 2 (13.3%) | 0 (0.0%) | 0 (0.0%) | | magit | 88 | 75 (85.2%) | 11 (12.5%) | 9 (10.2%) | 1 (1.1%) | 0 (0.0%) | | neural-style | 28 | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | 0 (0.0%) | | nodejs | 781 | 649 (83.1%) | 118 (15.1%) | 111 (14.2%) | 4 (0.5%) | 5 (0.6%) | * | phpmyadmin | 491 | 481 (98.0%) | 75 (15.3%) | 48 (9.8%) | 2 (0.4%) | 2 (0.4%) | * | react-native | 168 | 130 (77.4%) | 79 (47.0%) | 81 (48.2%) | 0 (0.0%) | 0 (0.0%) | | rust | 171 | 128 (74.9%) | 30 (17.5%) | 27 (15.8%) | 16 (9.4%) | 14 (8.2%) | | spark | 186 | 149 (80.1%) | 52 (28.0%) | 52 (28.0%) | 2 (1.1%) | 2 (1.1%) | | tensorflow | 115 | 66 (57.4%) | 48 (41.7%) | 48 (41.7%) | 5 (4.3%) | 5 (4.3%) | | test-more | 19 | 15 (78.9%) | 2 (10.5%) | 2 (10.5%) | 1 (5.3%) | 1 (5.3%) | * | test-unit | 51 | 34 (66.7%) | 14 (27.5%) | 8 (15.7%) | 2 (3.9%) | 2 (3.9%) | * | xmonad | 23 | 22 (95.7%) | 2 (8.7%) | 2 (8.7%) | 1 (4.3%) | 1 (4.3%) | * | --------------------- | ----- | -------------- | -------------- | ---------------- | -------------- | -------------- | | totals | 6668 | 4391 (65.9%) | 1496 (22.4%) | 1491 (22.4%) | 150 (2.2%) | 144 (2.2%) | | totals (training set) | 4552 | 3195 (70.2%) | 1053 (23.1%) | 1061 (23.3%) | 86 (1.9%) | 88 (1.9%) | | totals (test set) | 2116 | 1196 (56.5%) | 443 (20.9%) | 430 (20.3%) | 64 (3.0%) | 56 (2.6%) | In this table, the numbers are the count and percentage of human-rated sliders that the corresponding algorithm got *wrong*. The columns are * "repository" - the name of the repository used. I used the diffs between successive non-merge commits on the HEAD branch of the corresponding repository. * "count" - the number of sliders that were human-rated. I chose most, but not all, sliders to rate from those among which the various algorithms gave different answers. * "Git 2.9.0" - the default algorithm used by `git diff` in Git 2.9.0. * "compaction" - the heuristic used by `git diff --compaction-heuristic` in Git 2.9.0. * "compaction-fixed" - the heuristic used by `git diff --compaction-heuristic` after the fixes from earlier in this patch series. Note that the results are not dramatically different than those for "compaction". Both produce non-ideal diffs only about 1/3 as often as the default `git diff`. * "indent-1" - the new `--indent-heuristic` algorithm, using the first set of weighting factors, determined as described above. * "indent-2" - the new `--indent-heuristic` algorithm, using the final set of weighting factors, determined as described below. * `*` - indicates that repo was part of training set used to determine the first set of weighting factors. The fact that the heuristic performed nearly as well on the test set as on the training set in column "indent-1" is a good indication that the heuristic was not over-trained. Given that fact, I ran a second round of optimization, using the entire corpus as the training set. The resulting set of weights gave the results in column "indent-2". These are the weights included in this patch. The final result gives consistently and significantly better results across the whole corpus than either `git diff` or `git diff --compaction-heuristic`. It makes only about 1/30 as many errors as the former and about 1/10 as many errors as the latter. (And a good fraction of the remaining errors are for diffs that involve weirdly-formatted code, sometimes apparently machine-generated.) The tools that were used to do this optimization and analysis, along with the human-generated data values, are recorded in a separate project [1]. This patch adds a new command-line option `--indent-heuristic`, and a new configuration setting `diff.indentHeuristic`, that activate this heuristic. This interface is only meant for testing purposes, and should be finalized before including this change in any release. [1] https://github.com/mhagger/diff-slider-tools Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-09-14xdiff: fix merging of hunks with -W context and -u contextLibravatar René Scharfe1-1/+1
If the function context for a hunk (with -W) reaches the beginning of the next hunk then we need to merge these two -- otherwise we'd show some lines twice, which looks strange and even confuses git apply. We already do this checking and merging in xdl_emit_diff(), but forget to consider regular context (with -u or -U). Fix that by merging hunks already if function context of the first one touches or overlaps regular context of the second one. Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-09-07xdiff: remove unneeded declarationsLibravatar Stefan Beller1-9/+0
Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-23xdl_change_compact(): introduce the concept of a change groupLibravatar Michael Haggerty1-90/+203
The idea of xdl_change_compact() is fairly simple: * Proceed through groups of changed lines in the file to be compacted, keeping track of the corresponding location in the "other" file. * If possible, slide the group up and down to try to give the most aesthetically pleasing diff. Whenever it is slid, the current location in the other file needs to be adjusted. But these simple concepts are obfuscated by a lot of index handling that is written in terse, subtle, and varied patterns. I found it very hard to convince myself that the function was correct. So introduce a "struct group" that represents a group of changed lines in a file. Add some functions that perform elementary operations on groups: * Initialize a group to the first group in a file * Move to the next or previous group in a file * Slide a group up or down Even though the resulting code is longer, I think it is easier to understand and review. Its performance is not changed appreciably (though it would be if `group_next()` and `group_previous()` were not inlined). ...and in fact, the rewriting helped me discover another bug in the --compaction-heuristic code: The update of blank_lines was never done for the highest possible position of the group. This means that it could fail to slide the group to its highest possible position, even if that position had a blank line as its last line. So for example, it yielded the following diff: $ git diff --no-index --compaction-heuristic a.txt b.txt diff --git a/a.txt b/b.txt index e53969f..0d60c5fe 100644 --- a/a.txt +++ b/b.txt @@ -1,3 +1,7 @@ 1 A + +B + +A 2 when in fact the following diff is better (according to the rules of --compaction-heuristic): $ git diff --no-index --compaction-heuristic a.txt b.txt diff --git a/a.txt b/b.txt index e53969f..0d60c5fe 100644 --- a/a.txt +++ b/b.txt @@ -1,3 +1,7 @@ 1 +A + +B + A 2 The new code gives the bottom answer. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-23recs_match(): take two xrecord_t pointers as argumentsLibravatar Michael Haggerty1-7/+7
There is no reason for it to take an array and two indexes as argument, as it only accesses two elements of the array. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-23is_blank_line(): take a single xrecord_t as argumentLibravatar Michael Haggerty1-4/+4
There is no reason for it to take an array and index as argument, as it only accesses a single element of the array. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-23xdl_change_compact(): only use heuristic if group can't be matchedLibravatar Michael Haggerty1-19/+19
If the changed group of lines can be matched to a group in the other file, then that positioning should take precedence over the compaction heuristic. The old code tried the heuristic unconditionally, which cost redundant effort and also was broken if the matching code had already shifted the group higher than the blank line. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-23xdl_change_compact(): fix compaction heuristic to adjust ixoLibravatar Michael Haggerty1-0/+1
The code branch used for the compaction heuristic forgot to keep ixo in sync while the group was shifted. This is certainly wrong, as it causes the two counters to get out of sync. I *think* that this bug could also have caused the function to read past the end of the rchgo array, though I haven't done the work to prove it for sure. Here is my reasoning: If ixo is not decremented correctly during one iteration of the outer while loop, then it will loose sync with the ix counter. In particular, ixo will be too large. Suppose that the next iterations of the outer while loop (i.e., processing the next block of add/delete lines) don't have any sliders. Then the ixo counter would be incremented by the number of non-changed lines in xdf, which is the same as the number of non-changed lines in xdfo that *should have* followed the group that experienced the malfunction. But since ixo was too large at the end of that iteration, it will be incremented past the end of the xdfo->rchg array, and will try to read that memory illegally. Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-08-08Merge branch 'js/ignore-space-at-eol' into maintLibravatar Junio C Hamano2-3/+5
An age old bug that caused "git diff --ignore-space-at-eol" misbehave has been fixed. * js/ignore-space-at-eol: diff: fix a double off-by-one with --ignore-space-at-eol diff: demonstrate a bug with --patience and --ignore-space-at-eol
2016-07-11diff: fix a double off-by-one with --ignore-space-at-eolLibravatar Johannes Schindelin2-3/+5
When comparing two lines, ignoring any whitespace at the end, we first try to match as many bytes as possible and break out of the loop only upon mismatch, to let the remainder be handled by the code shared with the other whitespace-ignoring code paths. When comparing the bytes, however, we incremented the counters always, even if the bytes did not match. And because we fall through to the space-at-eol handling at that point, it is as if that mismatch never happened. Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-06-27Merge branch 'rs/xdiff-hunk-with-func-line' into maintLibravatar Junio C Hamano1-8/+57
"git show -W" (extend hunks to cover the entire function, delimited by lines that match the "funcname" pattern) used to show the entire file when a change added an entire function at the end of the file, which has been fixed. * rs/xdiff-hunk-with-func-line: xdiff: fix merging of appended hunk with -W grep: -W: don't extend context to trailing empty lines t7810: add test for grep -W and trailing empty context lines xdiff: don't trim common tail with -W xdiff: -W: don't include common trailing empty lines in context xdiff: ignore empty lines before added functions with -W xdiff: handle appended chunks better with -W xdiff: factor out match_func_rec() t4051: rewrite, add more tests
2016-06-20Merge branch 'rs/xdiff-hunk-with-func-line'Libravatar Junio C Hamano1-8/+57
"git show -W" (extend hunks to cover the entire function, delimited by lines that match the "funcname" pattern) used to show the entire file when a change added an entire function at the end of the file, which has been fixed. * rs/xdiff-hunk-with-func-line: xdiff: fix merging of appended hunk with -W grep: -W: don't extend context to trailing empty lines t7810: add test for grep -W and trailing empty context lines xdiff: don't trim common tail with -W xdiff: -W: don't include common trailing empty lines in context xdiff: ignore empty lines before added functions with -W xdiff: handle appended chunks better with -W xdiff: factor out match_func_rec() t4051: rewrite, add more tests
2016-06-09xdiff: fix merging of appended hunk with -WLibravatar René Scharfe1-1/+2
When -W is given we search the lines between the end of the current context and the next change for a function line. If there is none then we merge those two hunks as they must be part of the same function. If the next change is an appended chunk we abort the search early in get_func_line(), however, because its line number is out of range. Fix that by searching from the end of the pre-image in that case instead. Reported-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-05-31xdiff: -W: don't include common trailing empty lines in contextLibravatar René Scharfe1-0/+2
Empty lines between functions are shown by diff -W, as it considers them to be part of the function preceding them. They are not interesting in most languages. The previous patch stopped showing them in the special case of a function added at the end of a file. Stop extending context to those empty lines by skipping back over them from the start of the next function. Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-05-31xdiff: ignore empty lines before added functions with -WLibravatar René Scharfe1-2/+20
If a new function and a preceding empty line is appended, diff -W shows the previous function in full in order to provide context for that empty line. In most languages empty lines between sections are not interesting in and off themselves and showing a whole extra function for them is not what we want. Skip empty lines when checking of the appended chunk starts with a function line, thereby avoiding to extend the context just for them. Helped-by: Ramsay Jones <ramsay@ramsayjones.plus.com> Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-05-31xdiff: handle appended chunks better with -WLibravatar René Scharfe1-3/+24
If lines are added at the end of a file, diff -W shows the whole file. That's because get_func_line() only considers the pre-image and gives up if it sees a record index beyond its end. Consider the post-image as well to see if the added lines already make up a full function. If it doesn't then search for the previous function line by starting from the bottom of the pre-image, thereby avoiding to confuse get_func_line(). Reuse the existing label called "again", as it's exactly where we need to jump to when we're done handling the pre-context, but rename it to "post_context_calculation" in order to document its new purpose better. Reported-by: Junio C Hamano <gitster@pobox.com> Initial-patch-by: Junio C Hamano <gitster@pobox.com> Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-05-31xdiff: factor out match_func_rec()Libravatar René Scharfe1-4/+11
Add match_func_rec(), a helper that wraps accessing a record and calling the appropriate function for checking if it contains a function line. Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-05-06Merge branch 'jk/diff-compact-heuristic'Libravatar Junio C Hamano2-4/+38
Patch output from "git diff" and friends has been tweaked to be more readable by using a blank line as a strong hint that the contents before and after it belong to a logically separate unit. * jk/diff-compact-heuristic: diff: undocument the compaction heuristic knobs for experimentation xdiff: implement empty line chunk heuristic xdiff: add recs_match helper function
2016-04-19xdiff: implement empty line chunk heuristicLibravatar Stefan Beller2-0/+28
In order to produce the smallest possible diff and combine several diff hunks together, we implement a heuristic from GNU Diff which moves diff hunks forward as far as possible when we find common context above and below a diff hunk. This sometimes produces less readable diffs when writing C, Shell, or other programming languages, ie: ... /* + * + * + */ + +/* ... instead of the more readable equivalent of ... +/* + * + * + */ + /* ... Implement the following heuristic to (optionally) produce the desired output. If there are diff chunks which can be shifted around, shift each hunk such that the last common empty line is below the chunk with the rest of the context above. This heuristic appears to resolve the above example and several other common issues without producing significantly weird results. However, as with any heuristic it is not really known whether this will always be more optimal. Thus, it can be disabled via diff.compactionHeuristic. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-04-18xdiff: add recs_match helper functionLibravatar Jacob Keller1-4/+10
It is a common pattern in xdl_change_compact to check that hashes and strings match. The resulting code to perform this change causes very long lines and makes it hard to follow the intention. Introduce a helper function recs_match which performs both checks to increase code readability. Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
2016-04-03Merge branch 'rj/xdiff-prepare-plug-leak-on-error-codepath'Libravatar Junio C Hamano1-1/+2
A small memory leak in an error codepath has been plugged in xdiff code. * rj/xdiff-prepare-plug-leak-on-error-codepath: xdiff/xprepare: fix a memory leak xdiff/xprepare: use the XDF_DIFF_ALG() macro to access flag bits