diff: retire "compaction" heuristics

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>

1 files changed, 3 insertions, 20 deletions

diff --git a/diff.c b/diff.c
index 8981477..741ce8c 100644
--- a/diff.c
+++ b/diff.c
@@ -28,7 +28,6 @@
 
 static int diff_detect_rename_default;
 static int diff_indent_heuristic; /* experimental */
-static int diff_compaction_heuristic; /* experimental */
 static int diff_rename_limit_default = 400;
 static int diff_suppress_blank_empty;
 static int diff_use_color_default = -1;
@@ -223,16 +222,8 @@ void init_diff_ui_defaults(void)
 
 int git_diff_heuristic_config(const char *var, const char *value, void *cb)
 {
-	if (!strcmp(var, "diff.indentheuristic")) {
+	if (!strcmp(var, "diff.indentheuristic"))
 		diff_indent_heuristic = git_config_bool(var, value);
-		if (diff_indent_heuristic)
-			diff_compaction_heuristic = 0;
-	}
-	if (!strcmp(var, "diff.compactionheuristic")) {
-		diff_compaction_heuristic = git_config_bool(var, value);
-		if (diff_compaction_heuristic)
-			diff_indent_heuristic = 0;
-	}
 	return 0;
 }
 
@@ -3380,8 +3371,6 @@ void diff_setup(struct diff_options *options)
 	options->xdl_opts |= diff_algorithm;
 	if (diff_indent_heuristic)
 		DIFF_XDL_SET(options, INDENT_HEURISTIC);
-	else if (diff_compaction_heuristic)
-		DIFF_XDL_SET(options, COMPACTION_HEURISTIC);
 
 	options->orderfile = diff_order_file_cfg;
 
@@ -3876,16 +3865,10 @@ int diff_opt_parse(struct diff_options *options,
 		DIFF_XDL_SET(options, IGNORE_WHITESPACE_AT_EOL);
 	else if (!strcmp(arg, "--ignore-blank-lines"))
 		DIFF_XDL_SET(options, IGNORE_BLANK_LINES);
-	else if (!strcmp(arg, "--indent-heuristic")) {
+	else if (!strcmp(arg, "--indent-heuristic"))
 		DIFF_XDL_SET(options, INDENT_HEURISTIC);
-		DIFF_XDL_CLR(options, COMPACTION_HEURISTIC);
-	} else if (!strcmp(arg, "--no-indent-heuristic"))
-		DIFF_XDL_CLR(options, INDENT_HEURISTIC);
-	else if (!strcmp(arg, "--compaction-heuristic")) {
-		DIFF_XDL_SET(options, COMPACTION_HEURISTIC);
+	else if (!strcmp(arg, "--no-indent-heuristic"))
 		DIFF_XDL_CLR(options, INDENT_HEURISTIC);
-	} else if (!strcmp(arg, "--no-compaction-heuristic"))
-		DIFF_XDL_CLR(options, COMPACTION_HEURISTIC);
 	else if (!strcmp(arg, "--patience"))
 		options->xdl_opts = DIFF_WITH_ALG(options, PATIENCE_DIFF);
 	else if (!strcmp(arg, "--histogram"))