range-diff: make --dual-color the default mode

After using this command extensively for the last two months, this
developer came to the conclusion that even if the dual color mode still
leaves a lot of room for confusion what was actually changed, the
non-dual color mode is substantially worse in that regard.

Therefore, we really want to make the dual color mode the default.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Documentation/git-range-diff.txt

@@ -31,11 +31,14 @@ all of their ancestors have been shown.
 
 OPTIONS
 -------
---dual-color::
-	When the commit diffs differ, recreate the original diffs'
-	coloring, and add outer -/+ diff markers with the *background*
-	being red/green to make it easier to see e.g. when there was a
-	change in what exact lines were added.
+--no-dual-color::
+	When the commit diffs differ, `git range-diff` recreates the
+	original diffs' coloring, and add outer -/+ diff markers with
+	the *background* being red/green to make it easier to see e.g.
+	when there was a change in what exact lines were added. This is
+	known to `range-diff` as "dual coloring". Use `--no-dual-color`
+	to revert to color all lines according to the outer diff markers
+	(and completely ignore the inner diff when it comes to color).
 
 --creation-factor=<percent>::
 	Set the creation/deletion cost fudge factor to `<percent>`.

builtin/range-diff.c

@@ -20,11 +20,11 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 {
 	int creation_factor = 60;
 	struct diff_options diffopt = { NULL };
-	int dual_color = 0;
+	int simple_color = -1;
 	struct option options[] = {
 		OPT_INTEGER(0, "creation-factor", &creation_factor,
 			    N_("Percentage by which creation is weighted")),
-		OPT_BOOL(0, "dual-color", &dual_color,
+		OPT_BOOL(0, "no-dual-color", &simple_color,
 			    N_("color both diff and diff-between-diffs")),
 		OPT_END()
 	};
@@ -53,8 +53,10 @@ int cmd_range_diff(int argc, const char **argv, const char *prefix)
 	argc = j;
 	diff_setup_done(&diffopt);
 
-	if (dual_color) {
-		diffopt.use_color = 1;
+	if (simple_color < 1) {
+		if (!simple_color)
+			/* force color when --dual-color was used */
+			diffopt.use_color = 1;
 		diffopt.flags.dual_color_diffed_diffs = 1;
 	}
 

contrib/completion/git-completion.bash

@@ -1981,7 +1981,7 @@ _git_range_diff ()
   case "$cur" in
   --*)
           __gitcomp "
-	  	--creation-factor= --dual-color
+	  	--creation-factor= --no-dual-color
                   $__git_diff_common_options
                   "
           return