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>
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>
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>
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>
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>
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>
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>
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>
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>
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>
The goal of the patch is to introduce the GNU diff
-B/--ignore-blank-lines as closely as possible. The short option is not
available because it's already used for "break-rewrites".
When this option is used, git-diff will not create hunks that simply
add or remove empty lines, but will still show empty lines
addition/suppression if they are close enough to "valuable" changes.
There are two differences between this option and GNU diff -B option:
- GNU diff doesn't have "--inter-hunk-context", so this must be handled
- The following sequence looks like a bug (context is displayed twice):
$ seq 5 >file1
$ cat <<EOF >file2
change
1
2
3
4
5
change
EOF
$ diff -u -B file1 file2
--- file1 2013-06-08 22:13:04.471517834 +0200
+++ file2 2013-06-08 22:13:23.275517855 +0200
@@ -1,5 +1,7 @@
+change
1
2
+
3
4
5
@@ -3,3 +5,4 @@
3
4
5
+change
So here is a more thorough description of the option:
- real changes are interesting
- blank lines that are close enough (less than context size) to
interesting changes are considered interesting (recursive definition)
- "context" lines are used around each hunk of interesting changes
- If two hunks are separated by less than "inter-hunk-context", they
will be merged into one.
The implementation does the "interesting changes selection" in a single
pass.
Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Most of these were found using Lucas De Marchi's codespell tool.
Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Acked-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Add a way to register a callback function that is gets passed the
start line and line count of each hunk of a diff. Only standard
types are used.
Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Because the default Myers, patience and histogram algorithms cannot be in
effect at the same time, XDL_PATIENCE_DIFF and XDL_HISTOGRAM_DIFF are not
independent bits. Instead of wasting one bit per algorithm, define a few
macros to access the few bits they occupy and update the code that access
them.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Port JGit's HistogramDiff algorithm over to C. Rough numbers (TODO) show
that it is faster than its --patience cousin, as well as the default
Meyers algorithm.
The implementation has been reworked to use structs and pointers,
instead of bitmasks, thus doing away with JGit's 2^28 line limit.
We also use xdiff's default hash table implementation (xdl_hash_bits()
with XDL_HASHLONG()) for convenience.
Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
http-push.c::finish_request():
request is initialized by the for loop
index-pack.c::free_base_data():
b is initialized by the for loop
merge-recursive.c::process_renames():
move compare to narrower scope, and remove unused assignments to it
remove unused variable renames2
xdiff/xdiffi.c::xdl_recs_cmp():
remove unused variable ec
xdiff/xemit.c::xdl_emit_diff():
xche is always overwritten
Signed-off-by: Benjamin Kramer <benny.kra@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The patience diff algorithm produces slightly more intuitive output
than the classic Myers algorithm, as it does not try to minimize the
number of +/- lines first, but tries to preserve the lines that are
unique.
To this end, it first determines lines that are unique in both files,
then the maximal sequence which preserves the order (relative to both
files) is extracted.
Starting from this initial set of common lines, the rest of the lines
is handled recursively, with Myers' algorithm as a fallback when
the patience algorithm fails (due to no common unique lines).
This patch includes memory leak fixes by Pierre Habouzit.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
For some users (e.g. git blame), getting textual patch output is just
extra work, as they can get all the information they need from the low-
level diff structures. Allow for an alternate low-level emit function
to be defined to allow bypassing the textual patch generation; set
xemitconf_t's emit_func member to enable this.
The (void (*)()) type is pretty ugly, but the alternative would be to
include most of the private xdiff headers in xdiff.h to get the types
required for the "proper" function prototype. Also, a (void *) won't
work, as ANSI C doesn't allow a function pointer to be cast to an
object pointer.
Signed-off-by: Brian Downing <bdowning@lavos.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Solaris Workshop Compiler found a few unreachable statements.
Signed-off-by: Guido Ostkamp <git@ostkamp.fastmail.fm>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This uses "git-apply --whitespace=strip" to fix whitespace errors that have
crept in to our source files over time. There are a few files that need
to have trailing whitespaces (most notably, test vectors). The results
still passes the test, and build result in Documentation/ area is unchanged.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This new function implements the functionality of RCS merge, but
in-memory. It returns < 0 on error, otherwise the number of conflicts.
Finding the conflicting lines can be a very expensive task. You can
control the eagerness of this algorithm:
- a level value of 0 means that all overlapping changes are treated
as conflicts,
- a value of 1 means that if the overlapping changes are identical,
it is not treated as a conflict.
- If you set level to 2, overlapping changes will be analyzed, so that
almost identical changes will not result in huge conflicts. Rather,
only the conflicting lines will be shown inside conflict markers.
With each increasing level, the algorithm gets slower, but more accurate.
Note that the code for level 2 depends on the simple definition of
mmfile_t specific to git, and therefore it will be harder to port that
to LibXDiff.
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>
The only visible change is that git-blame doesn't understand
"--compability" anymore, but it does accept "--compatibility" instead,
which is already documented.
Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
This adds -b (--ignore-space-change) and -w (--ignore-all-space) flags to
diff. The main part of the patch is teaching libxdiff about it.
[jc: renamed xdl_line_match() to xdl_recmatch() since the former is used
for different purposes in xpatchi.c which is in the parts of the upstream
source we do not use.]
Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>
Compiling this module gave the following warnings (some double dutch!):
xdiff/xdiffi.c: In functie 'xdl_recs_cmp':
xdiff/xdiffi.c:298: let op: 'spl.i1' may be used uninitialized in this function
xdiff/xdiffi.c:298: let op: 'spl.i2' may be used uninitialized in this function
xdiff/xdiffi.c:219: let op: 'fbest1' may be used uninitialized in this function
xdiff/xdiffi.c:219: let op: 'bbest1' may be used uninitialized in this function
A superficial tracking of their usage, without deeper knowledge about the
algorithm, indeed confirms that there are code paths on which these
variables will be used uninitialized. In practice these code paths might never
be reached, but then these fixes will not change the algorithm. If these
code paths are ever reached we now at least have a predictable outcome. And
should the very small performance impact of these initializations be
noticeable, then they should at least be replaced by comments why certain
code paths will never be reached.
Some extra initializations in this patch now fix the warnings.
This uses a simplified libxdiff setup to generate unified diffs _without_
doing fork/execve of GNU "diff".
This has several huge advantages, for example:
Before:
[torvalds@g5 linux]$ time git diff v2.6.16.. > /dev/null
real 0m24.818s
user 0m13.332s
sys 0m8.664s
After:
[torvalds@g5 linux]$ time git diff v2.6.16.. > /dev/null
real 0m4.563s
user 0m2.944s
sys 0m1.580s
and the fact that this should be a lot more portable (ie we can ignore all
the issues with doing fork/execve under Windows).
Perhaps even more importantly, this allows us to do diffs without actually
ever writing out the git file contents to a temporary file (and without
any of the shell quoting issues on filenames etc etc).
NOTE! THIS PATCH DOES NOT DO THAT OPTIMIZATION YET! I was lazy, and the
current "diff-core" code actually will always write the temp-files,
because it used to be something that you simply had to do. So this current
one actually writes a temp-file like before, and then reads it into memory
again just to do the diff. Stupid.
But if this basic infrastructure is accepted, we can start switching over
diff-core to not write temp-files, which should speed things up even
further, especially when doing big tree-to-tree diffs.
Now, in the interest of full disclosure, I should also point out a few
downsides:
- the libxdiff algorithm is different, and I bet GNU diff has gotten a
lot more testing. And the thing is, generating a diff is not an exact
science - you can get two different diffs (and you will), and they can
both be perfectly valid. So it's not possible to "validate" the
libxdiff output by just comparing it against GNU diff.
- GNU diff does some nice eye-candy, like trying to figure out what the
last function was, and adding that information to the "@@ .." line.
libxdiff doesn't do that.
- The libxdiff thing has some known deficiencies. In particular, it gets
the "\No newline at end of file" case wrong. So this is currently for
the experimental branch only. I hope Davide will help fix it.
That said, I think the huge performance advantage, and the fact that it
integrates better is definitely worth it. But it should go into a
development branch at least due to the missing newline issue.
Technical note: this is based on libxdiff-0.17, but I did some surgery to
get rid of the extraneous fat - stuff that git doesn't need, and seriously
cutting down on mmfile_t, which had much more capabilities than the diff
algorithm either needed or used. In this version, "mmfile_t" is just a
trivial <pointer,length> tuple.
That said, I tried to keep the differences to simple removals, so that you
can do a diff between this and the libxdiff origin, and you'll basically
see just things getting deleted. Even the mmfile_t simplifications are
left in a state where the diffs should be readable.
Apologies to Davide, whom I'd love to get feedback on this all from (I
wrote my own "fill_mmfile()" for the new simpler mmfile_t format: the old
complex format had a helper function for that, but I did my surgery with
the goal in mind that eventually we _should_ just do
mmfile_t mf;
buf = read_sha1_file(sha1, type, &size);
mf->ptr = buf;
mf->size = size;
.. use "mf" directly ..
which was really a nightmare with the old "helpful" mmfile_t, and really
is that easy with the new cut-down interfaces).
[ Btw, as any hawk-eye can see from the diff, this was actually generated
with itself, so it is "self-hosting". That's about all the testing it
has gotten, along with the above kernel diff, which eye-balls correctly,
but shows the newline issue when you double-check it with "git-apply" ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
