[PATCH] diff: resurrect XDF_NEED_MINIMAL with --minimal

Earlier, 582aa00 (git diff too slow for a file, 2010-05-02)
unconditionally dropped XDF_NEED_MINIMAL option from the internal xdiff
invocation to help performance on pathological cases, while hinting that a
follow-up patch could reintroduce it with "--minimal" option from the
command line.

Make it so.

Signed-off-by: Junio C Hamano <redacted>
---
 * This together with René's c5aa906 (Revert removal of multi-match
   discard heuristic in 27af01, 2011-09-25) on top of v1.7.7 seems to give
   identical diff output as v1.7.1 (e.g. "git diff-tree -p v2.6.39 v3.0"
   in the kernel repository, with "--minimal").

 diff.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/diff.c b/diff.c
index 93ef9a2..34a88db 100644
--- a/diff.c
+++ b/diff.c

@@ -3511,6 +3511,10 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 	}
 	else if (!strcmp(arg, "--abbrev"))
 		options->abbrev = DEFAULT_ABBREV;
+	else if (!strcmp(arg, "--minimal"))
+		DIFF_XDL_SET(options, NEED_MINIMAL);
+	else if (!strcmp(arg, "--no-minimal"))
+		DIFF_XDL_CLR(options, NEED_MINIMAL);
 	else if (!prefixcmp(arg, "--abbrev=")) {
 		options->abbrev = strtoul(arg + 9, NULL, 10);
 		if (options->abbrev < MINIMUM_ABBREV)

-- 
1.7.7

Junio C Hamano wrote:

 * This together with René's c5aa906 (Revert removal of multi-match
   discard heuristic in 27af01, 2011-09-25) on top of v1.7.7 seems to give
   identical diff output as v1.7.1 (e.g. "git diff-tree -p v2.6.39 v3.0"
   in the kernel repository, with "--minimal").

Very neat.

I think this would fit well near --patience (the "xdiff options"
section), instead of hidden between the unsticked and sticked forms of
--abbrev. ;-)

Like this:

diff --git i/Documentation/diff-options.txt w/Documentation/diff-options.txt
index b620b3af..4d87256e 100644
--- i/Documentation/diff-options.txt
+++ w/Documentation/diff-options.txt

@@ -48,6 +48,10 @@ endif::git-format-patch[]
 --patience::
 	Generate a diff using the "patience diff" algorithm.
 
+--minimal::
+	Spend extra time to make sure the smallest possible
+	diff is produced.
+
 --stat[=<width>[,<name-width>[,<count>]]]::
 	Generate a diffstat.  You can override the default
 	output width for 80-column terminal by `--stat=<width>`.

diff --git i/diff.c w/diff.c
index fcc00780..2282f86f 100644
--- i/diff.c
+++ w/diff.c

@@ -3393,6 +3393,10 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 		DIFF_XDL_SET(options, IGNORE_WHITESPACE_AT_EOL);
 	else if (!strcmp(arg, "--patience"))
 		DIFF_XDL_SET(options, PATIENCE_DIFF);
+	else if (!strcmp(arg, "--minimal"))
+		DIFF_XDL_SET(options, NEED_MINIMAL);
+	else if (!strcmp(arg, "--no-minimal"))
+		DIFF_XDL_CLR(options, NEED_MINIMAL);
 	else if (!strcmp(arg, "--histogram"))
 		DIFF_XDL_SET(options, HISTOGRAM_DIFF);
 

On Mon, Oct 3, 2011 at 8:38 PM, Jonathan Nieder [off-list ref] wrote:

Thanks for the Cc, Johnathan.

Junio C Hamano wrote:

quoted

 * This together with René's c5aa906 (Revert removal of multi-match
   discard heuristic in 27af01, 2011-09-25) on top of v1.7.7 seems to give
   identical diff output as v1.7.1 (e.g. "git diff-tree -p v2.6.39 v3.0"
   in the kernel repository, with "--minimal").

Very neat.

Interesting. Clearly there is more than just the multi-match discard
heuristic in (xdl_clean_mmatch() and xdl_cleanup_records()).

That's an improvement, but it would be even better if it was placed
above the --<strategy> options, instead of being placed between them.

-- 
Cheers,
Ray Chuan