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264 lines
11 KiB
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264 lines
11 KiB
Plaintext
The enclosed two messages describe a bug in GNU diff 2.6 and 2.7 which
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may cause CVS to perform an erroneous merge. You may wish to use GNU
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diff 2.5 or apply the patch supplied by Loren James Rittle below. It
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would be nice to add this to the CVS testsuite, but I haven't done so
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because probably a lot of people who would like to run the testsuite
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are using the buggy diff.
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From: friedman@splode.com (Noah Friedman)
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To: bug-gnu-utils@prep.ai.mit.edu
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Cc: info-cvs@prep.ai.mit.edu
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Subject: diffutils 2.7 -- diff3 merge bug
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Date: Tue, 29 Oct 96 17:02:54 CST
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I believe a change first introduced in GNU diff 2.6 causes diff3 sometimes
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to produce incorrect merges.
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Since this is a not a bug in CVS itself but can cause commits to CVS
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repositories to be incorrect, am warning info-cvs@prep.ai.mit.edu as
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well as reporting the bug to bug-gnu-utils@prep.ai.mit.edu.
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I am including a simple test case as well as some sample outputs from
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different versions of `diff' and `diff3' in the enclosed shar archive.
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In addition, the file DESCRIPTION in that archive describes the problem
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more fully.
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If anyone has any advice for how to fix or to work around this bug, I would
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appreciate it. Using diff 2.5 seems like the most immediately obvious
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solution, but I don't know if it will introduce other problems.
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I do not understand the algorithms used by GNU diff well enough to suggest
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any patches.
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Unshar and enjoy. ;-)
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begin 666 merge-testcase.shar.gz
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-&.@X_P&I*Y$W($H``"'+
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`
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end
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Date: Wed, 30 Oct 96 14:54:13 CST
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From: Loren James Rittle <rittle@comm.mot.com>
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To: friedman@splode.com
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Cc: bug-gnu-utils@prep.ai.mit.edu, info-cvs@prep.ai.mit.edu
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Subject: Re: diffutils 2.7 -- diff3 merge bug
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Noah,
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I have seen the problem you discuss in your e-mail, however I fail to
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see how this situation is as critical as might be implied since it can
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never arise without at least some user involvement (an update that
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caused a merge is never automatically followed by a commit --- the
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user has a chance to inspect the merged file). However, I will agree
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that I don't always look very closely at non-conflicted merges before
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checking them back in.
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You didn't give the exact CVS commands used to create a lossage,
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but I added the following to your Makefile, to help me see the problem
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in a CVS usage context:
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t-older: testcase-older
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cp testcase-older t-older
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t-yours: testcase-yours
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cp testcase-yours t-yours
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t-mine: testcase-mine
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cp testcase-mine t-mine
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# Assume cvs-1.9
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cvs-test: t-older t-yours t-mine
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rm -rf /tmp/cvs-test-root x x2
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cvs -d /tmp/cvs-test-root init
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mkdir x
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cp t-older x/testcase
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cd x; cvs -d /tmp/cvs-test-root import -m '' x X X1
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rm -rf x
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cvs -d /tmp/cvs-test-root co x
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cvs -d /tmp/cvs-test-root co -d x2 x
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cp t-yours x/testcase
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cp t-mine x2/testcase
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cd x; cvs ci -m ''
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-cd x2; cvs ci -m ''
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cd x2; cvs update
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cat x2/testcase # at this point, user may commit blindly
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It looks like whomever added shift_boundaries() in analyze.c, which
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seems to be the source of the diff3 induced mischief, already provided
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a means to disable the boundary shifting optimization (at least with
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a recompile).
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Here is the patch I applied to diff to disable this (currently)
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overaggressive optimization:
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[ rittle@supra ]; diff -c analyze.c-old analyze.c
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*** analyze.c-old Wed Oct 30 14:10:27 1996
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--- analyze.c Wed Oct 30 13:48:57 1996
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***************
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*** 616,622 ****
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but usually it is cleaner to consider the following identical line
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to be the "change". */
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! int inhibit;
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static void
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shift_boundaries (filevec)
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--- 616,622 ----
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but usually it is cleaner to consider the following identical line
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to be the "change". */
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! int inhibit = 1;
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static void
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shift_boundaries (filevec)
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Now, diff-2.7 with the above patch produces:
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[ rittle@supra ]; make diff-mine-yours 'DIFF=/usr/src/diffutils-2.7/diff'
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/usr/src/diffutils-2.7/diff -a --horizon-lines=11 -- testcase-mine testcase-yours; true
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16,18c16,18
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< // _titleColor = Color.black;
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< // _disabledTitleColor = Color.gray;
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< // _titleFont = Font.defaultFont ();
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---
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> _titleColor = Color.black;
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> _disabledTitleColor = Color.gray;
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> _titleFont = Font.defaultFont ();
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20,30d19
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<
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< /* Convenience constructor for instantiating a Button with
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< * bounds x, y, width, and height. Equivalent to
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< * foo = new Button ();
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< * foo.init (x, y, width, height);
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< */
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< public Button (int x, int y, int width, int height)
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< {
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< this ();
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< init (x, y, width, height);
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< }
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Whereas, stock diff-2.7 produces:
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[ rittle@supra ]; make diff-mine-yours
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diff -a --horizon-lines=11 -- testcase-mine testcase-yours; true
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16,29c16,18
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< // _titleColor = Color.black;
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< // _disabledTitleColor = Color.gray;
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< // _titleFont = Font.defaultFont ();
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< }
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<
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< /* Convenience constructor for instantiating a Button with
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< * bounds x, y, width, and height. Equivalent to
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< * foo = new Button ();
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< * foo.init (x, y, width, height);
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< */
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< public Button (int x, int y, int width, int height)
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< {
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< this ();
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< init (x, y, width, height);
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---
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> _titleColor = Color.black;
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> _disabledTitleColor = Color.gray;
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> _titleFont = Font.defaultFont ();
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A better solution might be to disable the boundary shifting code
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unless explicitly turned on via command line argument. That way
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programs, like diff3, expecting unoptimized diff regions will work
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correctly, yet users can get smaller diffs, if desired. The problem
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is that diff3 doesn't properly track changes once they have been
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optimized.
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BTW, I never did like the look of the `optimized diff regions', so I
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consider this a good change for other reasons... :-)
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Enjoy!
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Regards,
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Loren
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--
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Loren J. Rittle (rittle@comm.mot.com) PGP KeyIDs: 1024/B98B3249 2048/ADCE34A5
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Systems Technology Research (IL02/2240) FP1024:6810D8AB3029874DD7065BC52067EAFD
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Motorola, Inc. FP2048:FDC0292446937F2A240BC07D42763672
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(847) 576-7794 Call for verification of fingerprints.
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