From 9bddac0d57d86cf10bb2d1d738e9f13894e86960 Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Fri, 8 Mar 2019 15:58:27 +0100
Subject: [PATCH] built-in add -i: re-implement the `diff` command

It is not only laziness that we simply spawn `git diff -p --cached`
here: this command needs to use the pager, and the pager needs to exit
when the diff is done. Currently we do not have any way to make that
happen if we run the diff in-process. So let's just spawn.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 add-interactive.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/add-interactive.c b/add-interactive.c
index e95dd4af35..ab7b39ee41 100644
--- a/add-interactive.c
+++ b/add-interactive.c
@@ -918,6 +918,47 @@ static int run_patch(struct add_i_state *s, const struct pathspec *ps,
 	return res;
 }
 
+static int run_diff(struct add_i_state *s, const struct pathspec *ps,
+		    struct prefix_item_list *files,
+		    struct list_and_choose_options *opts)
+{
+	int res = 0;
+	ssize_t count, i;
+
+	struct object_id oid;
+	int is_initial = !resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &oid,
+					     NULL);
+	if (get_modified_files(s->r, INDEX_ONLY, files, ps, NULL, NULL) < 0)
+		return -1;
+
+	if (!files->items.nr) {
+		putchar('\n');
+		return 0;
+	}
+
+	opts->prompt = N_("Review diff");
+	opts->flags = IMMEDIATE;
+	count = list_and_choose(s, files, opts);
+	opts->flags = 0;
+	if (count >= 0) {
+		struct argv_array args = ARGV_ARRAY_INIT;
+
+		argv_array_pushl(&args, "git", "diff", "-p", "--cached",
+				 oid_to_hex(!is_initial ? &oid :
+					    s->r->hash_algo->empty_tree),
+				 "--", NULL);
+		for (i = 0; i < files->items.nr; i++)
+			if (files->selected[i])
+				argv_array_push(&args,
+						files->items.items[i].string);
+		res = run_command_v_opt(args.argv, 0);
+		argv_array_clear(&args);
+	}
+
+	putchar('\n');
+	return res;
+}
+
 static int run_help(struct add_i_state *s, const struct pathspec *unused_ps,
 		    struct prefix_item_list *unused_files,
 		    struct list_and_choose_options *opts)
@@ -1016,6 +1057,7 @@ int run_add_i(struct repository *r, const struct pathspec *ps)
 		{ "revert", run_revert },
 		{ "add untracked", run_add_untracked },
 		{ "patch", run_patch },
+		{ "diff", run_diff },
 		{ "help", run_help },
 	};
 	struct prefix_item_list commands = PREFIX_ITEM_LIST_INIT;