Introduce `range-diff` to compare iterations of a topic branch

This command does not do a whole lot so far, apart from showing a usage
that is oddly similar to that of `git tbdiff`. And for a good reason:
the next commits will turn `range-branch` into a full-blown replacement
for `tbdiff`.

At this point, we ignore tbdiff's color options, as they will all be
implemented later using diff_options.

Since f318d73915 (generate-cmds.sh: export all commands to
command-list.h, 2018-05-10), every new command *requires* a man page to
build right away, so let's also add a blank man page, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

.gitignore

@@ -113,6 +113,7 @@
 /git-pull
 /git-push
 /git-quiltimport
+/git-range-diff
 /git-read-tree
 /git-rebase
 /git-rebase--am

Documentation/git-range-diff.txt

@@ -0,0 +1,10 @@
+git-range-diff(1)
+=================
+
+NAME
+----
+git-range-diff - Compare two commit ranges (e.g. two versions of a branch)
+
+GIT
+---
+Part of the linkgit:git[1] suite

Makefile

@@ -1063,6 +1063,7 @@ BUILTIN_OBJS += builtin/prune-packed.o
 BUILTIN_OBJS += builtin/prune.o
 BUILTIN_OBJS += builtin/pull.o
 BUILTIN_OBJS += builtin/push.o
+BUILTIN_OBJS += builtin/range-diff.o
 BUILTIN_OBJS += builtin/read-tree.o
 BUILTIN_OBJS += builtin/rebase--helper.o
 BUILTIN_OBJS += builtin/receive-pack.o

builtin.h

@@ -201,6 +201,7 @@ extern int cmd_prune(int argc, const char **argv, const char *prefix);
 extern int cmd_prune_packed(int argc, const char **argv, const char *prefix);
 extern int cmd_pull(int argc, const char **argv, const char *prefix);
 extern int cmd_push(int argc, const char **argv, const char *prefix);
+extern int cmd_range_diff(int argc, const char **argv, const char *prefix);
 extern int cmd_read_tree(int argc, const char **argv, const char *prefix);
 extern int cmd_rebase__helper(int argc, const char **argv, const char *prefix);
 extern int cmd_receive_pack(int argc, const char **argv, const char *prefix);

builtin/range-diff.c

@@ -0,0 +1,25 @@
+#include "cache.h"
+#include "builtin.h"
+#include "parse-options.h"
+
+static const char * const builtin_range_diff_usage[] = {
+N_("git range-diff [<options>] <old-base>..<old-tip> <new-base>..<new-tip>"),
+N_("git range-diff [<options>] <old-tip>...<new-tip>"),
+N_("git range-diff [<options>] <base> <old-tip> <new-tip>"),
+NULL
+};
+
+int cmd_range_diff(int argc, const char **argv, const char *prefix)
+{
+	int creation_factor = 60;
+	struct option options[] = {
+		OPT_INTEGER(0, "creation-factor", &creation_factor,
+			    N_("Percentage by which creation is weighted")),
+		OPT_END()
+	};
+
+	argc = parse_options(argc, argv, NULL, options,
+			     builtin_range_diff_usage, 0);
+
+	return 0;
+}

command-list.txt

@@ -139,6 +139,7 @@ git-prune-packed                        plumbingmanipulators
 git-pull                                mainporcelain           remote
 git-push                                mainporcelain           remote
 git-quiltimport                         foreignscminterface
+git-range-diff                          mainporcelain
 git-read-tree                           plumbingmanipulators
 git-rebase                              mainporcelain           history
 git-receive-pack                        synchelpers

git.c

@@ -520,6 +520,7 @@ static struct cmd_struct commands[] = {
 	{ "prune-packed", cmd_prune_packed, RUN_SETUP },
 	{ "pull", cmd_pull, RUN_SETUP | NEED_WORK_TREE },
 	{ "push", cmd_push, RUN_SETUP },
+	{ "range-diff", cmd_range_diff, RUN_SETUP | USE_PAGER },
 	{ "read-tree", cmd_read_tree, RUN_SETUP | SUPPORT_SUPER_PREFIX},
 	{ "rebase--helper", cmd_rebase__helper, RUN_SETUP | NEED_WORK_TREE },
 	{ "receive-pack", cmd_receive_pack },