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Re: [PATCH v2 1/2] xdiff: implement a zealous diff3, or "zdiff3"

From
PWPhillip Wood <phillip.wood123@gmail.com>
Date
Sep 15, 2021, 10:25 UTC
Message-ID
<b6818661-ac6e-fbde-2cab-429c5550a0da@gmail.com>
In-Reply-To
<06e04c88dea3e15a90f0a11795b7a8eea3533bc8.1631379829.git.gitgitgadget@gmail.com>
Hi Elijah
On 11/09/2021 18:03, Elijah Newren via GitGitGadget wrote:
Show 20 quoted lines
> From: Elijah Newren <newren@gmail.com>
> [...] 
> diff --git a/t/t6427-diff3-conflict-markers.sh b/t/t6427-diff3-conflict-markers.sh
> index 25c4b720e72..de9c6190b9c 100755
> --- a/t/t6427-diff3-conflict-markers.sh
> +++ b/t/t6427-diff3-conflict-markers.sh
> @@ -211,4 +211,60 @@ test_expect_success 'rebase --apply describes fake ancestor base' '
>   	)
>   '
>   
> +test_setup_zdiff3 () {
> +	test_create_repo zdiff3 &&
> +	(
> +		cd zdiff3 &&
> +
> +		test_write_lines 1 2 3 4 5 6 7 8 9 >basic &&
> +		test_write_lines 1 2 3 AA 4 5 BB 6 7 8 >middle-common &&
> +		test_write_lines 1 2 3 4 5 6 7 8 9 >interesting &&
> +
> +		git add basic middle-common &&
interesting does not get committed
> +		git commit -m base &&
adding "base=$(git rev-parse --short HEAD^1)" here ...
Show 30 quoted lines
> +
> +		git branch left &&
> +		git branch right &&
> +
> +		git checkout left &&
> +		test_write_lines 1 2 3 4 A B C D E 7 8 9 >basic &&
> +		test_write_lines 1 2 3 CC 4 5 DD 6 7 8 >middle-common &&
> +		test_write_lines 1 2 3 4 A B C D E F G H I J 7 8 9 >interesting &&
> +		git add -u &&
> +		git commit -m letters &&
> +
> +		git checkout right &&
> +		test_write_lines 1 2 3 4 A X C Y E 7 8 9 >basic &&
> +		test_write_lines 1 2 3 EE 4 5 FF 6 7 8 >middle-common &&
> +		test_write_lines 1 2 3 4 A B C 5 6 G H I J 7 8 9 >interesting &&
> +		git add -u &&
> +		git commit -m permuted
> +	)
> +}
> +
> +test_expect_failure 'check zdiff3 markers' '
> +	test_setup_zdiff3 &&
> +	(
> +		cd zdiff3 &&
> +
> +		git checkout left^0 &&
> +
> +		test_must_fail git -c merge.conflictstyle=zdiff3 merge -s recursive right^0 &&
> +
> +		test_write_lines 1 2 3 4 A "<<<<<<< HEAD" B C D "||||||| $(git rev-parse --short HEAD^1)" 5 6 ======= X C Y ">>>>>>> right^0" E 7 8 9 >expect &&
... and then using $base rather than $(git rev-parse ...) would shorten 
these lines. It might be clearer if they were split up something like 
this as well
	
	test_write_lines \
		1 2 3 4 A \
		"<<<<<<< HEAD" B C D \
		"||||||| $base" 5 6 ======= \
		X C Y ">>>>>>> right^0"\
		 E 7 8 9 >expect &&
Show 11 quoted lines
> +		test_cmp expect basic &&
> +
> +		test_write_lines 1 2 3 "<<<<<<< HEAD" CC "||||||| $(git rev-parse --short HEAD^1)" AA ======= EE ">>>>>>> right^0" 4 5 "<<<<<<< HEAD" DD "||||||| $(git rev-parse --short HEAD^1)" BB ======= FF ">>>>>>> right^0" 6 7 8 >expect &&
> +		test_cmp expect middle-common &&
> +
> +		# Not passing this one yet.  For some reason, after extracting
> +		# the common lines "A B C" and "G H I J", the remaining part
> +		# is comparing "5 6" in the base to "5 6" on the left and
> +		# "D E F" on the right.  And zdiff3 currently picks the side
> +		# that matches the base as the merge result.  Weird.
> +		test_write_lines 1 2 3 4 A B C D E F G H I J 7 8 9 >expect &&

I might be about to make a fool of myself but I don't think this is right for expect. 5 and 6 are deleted on the left so the two sides should conflict. Manually comparing the result of merging with diff3 and zdiff3 the zdiff3 result looked correct to me.

I do wonder (though a brief try failed to trigger it) if there are cases where the diff algorithm does something "clever" which means it does not treat a common prefix or suffix as unchanged (see d2f82950a9 ("Re(-re)*fix trim_common_tail()", 2007-12-20) for a related issue). We could just trim the common prefix and suffix from the two sides ourselves using xdl_recmatch().

Best Wishes
Phillip
Show 156 quoted lines
> +		test_cmp expect interesting
> +	)
> +'
> +
>   test_done
> diff --git a/xdiff-interface.c b/xdiff-interface.c
> index 609615db2cd..9977813a9d3 100644
> --- a/xdiff-interface.c
> +++ b/xdiff-interface.c
> @@ -308,6 +308,8 @@ int git_xmerge_config(const char *var, const char *value, void *cb)
>   			die("'%s' is not a boolean", var);
>   		if (!strcmp(value, "diff3"))
>   			git_xmerge_style = XDL_MERGE_DIFF3;
> +		else if (!strcmp(value, "zdiff3"))
> +			git_xmerge_style = XDL_MERGE_ZEALOUS_DIFF3;
>   		else if (!strcmp(value, "merge"))
>   			git_xmerge_style = 0;
>   		/*
> diff --git a/xdiff/xdiff.h b/xdiff/xdiff.h
> index 7a046051468..8629ae287c7 100644
> --- a/xdiff/xdiff.h
> +++ b/xdiff/xdiff.h
> @@ -65,6 +65,7 @@ extern "C" {
>   
>   /* merge output styles */
>   #define XDL_MERGE_DIFF3 1
> +#define XDL_MERGE_ZEALOUS_DIFF3 2
>   
>   typedef struct s_mmfile {
>   	char *ptr;
> diff --git a/xdiff/xmerge.c b/xdiff/xmerge.c
> index 1659edb4539..df0c6041778 100644
> --- a/xdiff/xmerge.c
> +++ b/xdiff/xmerge.c
> @@ -230,7 +230,7 @@ static int fill_conflict_hunk(xdfenv_t *xe1, const char *name1,
>   	size += xdl_recs_copy(xe1, m->i1, m->chg1, needs_cr, 1,
>   			      dest ? dest + size : NULL);
>   
> -	if (style == XDL_MERGE_DIFF3) {
> +	if (style == XDL_MERGE_DIFF3 || style == XDL_MERGE_ZEALOUS_DIFF3) {
>   		/* Shared preimage */
>   		if (!dest) {
>   			size += marker_size + 1 + needs_cr + marker3_size;
> @@ -327,7 +327,7 @@ static int xdl_fill_merge_buffer(xdfenv_t *xe1, const char *name1,
>    * lines. Try hard to show only these few lines as conflicting.
>    */
>   static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
> -		xpparam_t const *xpp)
> +				xpparam_t const *xpp, int style)
>   {
>   	for (; m; m = m->next) {
>   		mmfile_t t1, t2;
> @@ -368,6 +368,42 @@ static int xdl_refine_conflicts(xdfenv_t *xe1, xdfenv_t *xe2, xdmerge_t *m,
>   			continue;
>   		}
>   		x = xscr;
> +		if (style == XDL_MERGE_ZEALOUS_DIFF3) {
> +			int advance1 = xscr->i1, advance2 = xscr->i2;
> +
> +			/*
> +			 * Advance m->i1 and m->i2 so that conflict for sides
> +			 * 1 and 2 start after common region.  Decrement
> +			 * m->chg[12] since there are now fewer conflict lines
> +			 * for those sides.
> +			 */
> +			m->i1 += advance1;
> +			m->i2 += advance2;
> +			m->chg1 -= advance1;
> +			m->chg2 -= advance2;
> +
> +			/*
> +			 * Splitting conflicts due to internal common regions
> +			 * on the two sides would be inappropriate since we
> +			 * are also showing the merge base and have no
> +			 * reasonable way to split the merge base text.
> +			 */
> +			while (xscr->next)
> +				xscr = xscr->next;
> +
> +			/*
> +			 * Lower the number of conflict lines to not include
> +			 * the final common lines, if any.  Do this by setting
> +			 * number of conflict lines to
> +			 *   (line offset for start of conflict in xscr) +
> +			 *   (number of lines in the conflict in xscr)
> +			 */
> +			m->chg1 = (xscr->i1 - advance1) + (xscr->chg1);
> +			m->chg2 = (xscr->i2 - advance2) + (xscr->chg2);
> +			xdl_free_env(&xe);
> +			xdl_free_script(x);
> +			continue;
> +		}
>   		m->i1 = xscr->i1 + i1;
>   		m->chg1 = xscr->chg1;
>   		m->i2 = xscr->i2 + i2;
> @@ -419,6 +455,7 @@ static int lines_contain_alnum(xdfenv_t *xe, int i, int chg)
>   static void xdl_merge_two_conflicts(xdmerge_t *m)
>   {
>   	xdmerge_t *next_m = m->next;
> +	m->chg0 = next_m->i0 + next_m->chg0 - m->i0;
>   	m->chg1 = next_m->i1 + next_m->chg1 - m->i1;
>   	m->chg2 = next_m->i2 + next_m->chg2 - m->i2;
>   	m->next = next_m->next;
> @@ -430,12 +467,12 @@ static void xdl_merge_two_conflicts(xdmerge_t *m)
>    * it appears simpler -- because it takes up less (or as many) lines --
>    * if the lines are moved into the conflicts.
>    */
> -static int xdl_simplify_non_conflicts(xdfenv_t *xe1, xdmerge_t *m,
> +static int xdl_simplify_non_conflicts(xdfenv_t *xe1, xdmerge_t *m, int style,
>   				      int simplify_if_no_alnum)
>   {
>   	int result = 0;
>   
> -	if (!m)
> +	if (!m || style == XDL_MERGE_ZEALOUS_DIFF3)
>   		return result;
>   	for (;;) {
>   		xdmerge_t *next_m = m->next;
> @@ -482,6 +519,25 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
>   	int style = xmp->style;
>   	int favor = xmp->favor;
>   
> +	/*
> +	 * XDL_MERGE_DIFF3 does not attempt to refine conflicts by looking
> +	 * at common areas of sides 1 & 2, because the base (side 0) does
> +	 * not match and is being shown.  Similarly, simplification of
> +	 * non-conflicts is also skipped due to the skipping of conflict
> +	 * refinement.
> +	 *
> +	 * XDL_MERGE_ZEALOUS_DIFF3, on the other hand, will attempt to
> +	 * refine conflicts looking for common areas of sides 1 & 2.
> +	 * However, since the base is being shown and does not match,
> +	 * it will only look for common areas at the beginning or end
> +	 * of the conflict block.  Since XDL_MERGE_ZEALOUS_DIFF3's
> +	 * conflict refinement is much more limited in this fashion, the
> +	 * conflict simplification will be skipped.
> +	 *
> +	 * See xdl_refine_conflicts() and xdl_simplify_non_conflicts()
> +	 * for more details, particularly looking for
> +	 * XDL_MERGE_ZEALOUS_DIFF3.
> +	 */
>   	if (style == XDL_MERGE_DIFF3) {
>   		/*
>   		 * "diff3 -m" output does not make sense for anything
> @@ -604,8 +660,8 @@ static int xdl_do_merge(xdfenv_t *xe1, xdchange_t *xscr1,
>   		changes = c;
>   	/* refine conflicts */
>   	if (XDL_MERGE_ZEALOUS <= level &&
> -	    (xdl_refine_conflicts(xe1, xe2, changes, xpp) < 0 ||
> -	     xdl_simplify_non_conflicts(xe1, changes,
> +	    (xdl_refine_conflicts(xe1, xe2, changes, xpp, style) < 0 ||
> +	     xdl_simplify_non_conflicts(xe1, changes, style,
>   					XDL_MERGE_ZEALOUS < level) < 0)) {
>   		xdl_cleanup_merge(changes);
>   		return -1;
>
Previous: Elijah Newren via GitGitGadgetNext: Phillip Wood
Message 22 of 39 in “RFC: implement new zdiff3 conflict style”
  1. 0/2 RFC: implement new zdiff3 conflict styleElijah Newren via GitGitGadget, Jun 15, 2021
  2. 1/2 xdiff: implement a zealous diff3, or "zdiff3"Elijah Newren via GitGitGadget, Jun 15, 2021
  3. Junio C HamanoJun 15, 2021
  4. Felipe ContrerasJun 15, 2021
  5. Elijah NewrenJun 15, 2021
  6. Sergey OrganovJun 15, 2021
  7. 2/2 update documentation for new zdiff3 conflictStyleElijah Newren via GitGitGadget, Jun 15, 2021
  8. Junio C HamanoJun 15, 2021
  9. Jeff KingJun 15, 2021
  10. Elijah NewrenJun 15, 2021
  11. Phillip WoodJun 16, 2021
  12. Jeff KingJun 16, 2021
  13. Phillip WoodJun 23, 2021
  14. Jeff KingJun 23, 2021
  15. Elijah NewrenJun 17, 2021
  16. Johannes SixtJun 15, 2021
  17. Elijah NewrenJun 15, 2021
  18. Johannes SixtJun 16, 2021
  19. Elijah NewrenJun 16, 2021
  20. 0/2 RFC: implement new zdiff3 conflict styleElijah Newren via GitGitGadget, Sep 11, 2021
  21. 1/2 xdiff: implement a zealous diff3, or "zdiff3"Elijah Newren via GitGitGadget, Sep 11, 2021
  22. Phillip WoodSep 15, 2021
  23. Phillip WoodSep 15, 2021
  24. Elijah NewrenSep 18, 2021
  25. Phillip WoodSep 24, 2021
  26. Elijah NewrenSep 18, 2021
  27. Phillip WoodSep 24, 2021
  28. 2/2 update documentation for new zdiff3 conflictStyleElijah Newren via GitGitGadget, Sep 11, 2021
  29. 0/2 RFC: implement new zdiff3 conflict styleElijah Newren via GitGitGadget, Sep 18, 2021
  30. 1/2 xdiff: implement a zealous diff3, or "zdiff3"Elijah Newren via GitGitGadget, Sep 18, 2021
  31. 2/2 update documentation for new zdiff3 conflictStyleElijah Newren via GitGitGadget, Sep 18, 2021
  32. 0/2 Implement new zdiff3 conflict styleElijah Newren via GitGitGadget, Nov 16, 2021
  33. 1/2 xdiff: implement a zealous diff3, or "zdiff3"Phillip Wood via GitGitGadget, Nov 16, 2021
  34. 2/2 update documentation for new zdiff3 conflictStyleElijah Newren via GitGitGadget, Nov 16, 2021
  35. 0/2 Implement new zdiff3 conflict styleElijah Newren via GitGitGadget, Dec 1, 2021
  36. 1/2 xdiff: implement a zealous diff3, or "zdiff3"Phillip Wood via GitGitGadget, Dec 1, 2021
  37. 2/2 update documentation for new zdiff3 conflictStyleElijah Newren via GitGitGadget, Dec 1, 2021
  38. Bagas SanjayaDec 2, 2021
  39. Eric SunshineDec 2, 2021

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