built-in add -p: prepare for patch modes other than "stage"

The Perl script backing `git add -p` is used not only for that command,
but also for `git stash -p`, `git reset -p` and `git checkout -p`.

In preparation for teaching the C version of `git add -p` to support
also the latter commands, let's abstract away what is "stage" specific
into a dedicated data structure describing the differences between the
patch modes.

Finally, please note that the Perl version tries to make sure that the
diffs are only generated for the modified files. This is not actually
necessary, as the calls to Git's diff machinery already perform that
work, and perform it well. This makes it unnecessary to port the
`FILTER` field of the `%patch_modes` struct, as well as the
`get_diff_reference()` function.

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

4 files changed, 85 insertions, 30 deletions

diff --git a/add-interactive.c b/add-interactive.c
index 6a5048c83e..a5bb14f2f4 100644
--- a/add-interactive.c
+++ b/add-interactive.c
@@ -924,7 +924,7 @@ static int run_patch(struct add_i_state *s, const struct pathspec *ps,
 		parse_pathspec(&ps_selected,
 			       PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
 			       PATHSPEC_LITERAL_PATH, "", args.argv);
-		res = run_add_p(s->r, &ps_selected);
+		res = run_add_p(s->r, ADD_P_ADD, NULL, &ps_selected);
 		argv_array_clear(&args);
 		clear_pathspec(&ps_selected);
 	}
diff --git a/add-interactive.h b/add-interactive.h
index 062dc3646c..e29a769aba 100644
--- a/add-interactive.h
+++ b/add-interactive.h
@@ -22,6 +22,12 @@ void init_add_i_state(struct add_i_state *s, struct repository *r);
 struct repository;
 struct pathspec;
 int run_add_i(struct repository *r, const struct pathspec *ps);
-int run_add_p(struct repository *r, const struct pathspec *ps);
+
+enum add_p_mode {
+	ADD_P_ADD,
+};
+
+int run_add_p(struct repository *r, enum add_p_mode mode,
+	      const char *revision, const struct pathspec *ps);
 
 #endif
diff --git a/add-patch.c b/add-patch.c
index 2c46fe5b33..71356fbd9a 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -8,13 +8,41 @@
 #include "diff.h"
 
 enum prompt_mode_type {
-	PROMPT_MODE_CHANGE = 0, PROMPT_DELETION, PROMPT_HUNK
+	PROMPT_MODE_CHANGE = 0, PROMPT_DELETION, PROMPT_HUNK,
+	PROMPT_MODE_MAX, /* must be last */
 };
 
-static const char *prompt_mode[] = {
-	N_("Stage mode change [y,n,a,q,d%s,?]? "),
-	N_("Stage deletion [y,n,a,q,d%s,?]? "),
-	N_("Stage this hunk [y,n,a,q,d%s,?]? ")
+struct patch_mode {
+	/*
+	 * The magic constant 4 is chosen such that all patch modes
+	 * provide enough space for three command-line arguments followed by a
+	 * trailing `NULL`.
+	 */
+	const char *diff_cmd[4], *apply_args[4], *apply_check_args[4];
+	unsigned is_reverse:1, apply_for_checkout:1;
+	const char *prompt_mode[PROMPT_MODE_MAX];
+	const char *edit_hunk_hint, *help_patch_text;
+};
+
+static struct patch_mode patch_mode_add = {
+	.diff_cmd = { "diff-files", NULL },
+	.apply_args = { "--cached", NULL },
+	.apply_check_args = { "--cached", NULL },
+	.prompt_mode = {
+		N_("Stage mode change [y,n,q,a,d%s,?]? "),
+		N_("Stage deletion [y,n,q,a,d%s,?]? "),
+		N_("Stage this hunk [y,n,q,a,d%s,?]? ")
+	},
+	.edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
+			     "will immediately be marked for staging."),
+	.help_patch_text =
+		N_("y - stage this hunk\n"
+		   "n - do not stage this hunk\n"
+		   "q - quit; do not stage this hunk or any of the remaining "
+			"ones\n"
+		   "a - stage this hunk and all later hunks in the file\n"
+		   "d - do not stage this hunk or any of the later hunks in "
+			"the file\n")
 };
 
 struct hunk_header {
@@ -47,6 +75,10 @@ struct add_p_state {
 		unsigned deleted:1, mode_change:1,binary:1;
 	} *file_diff;
 	size_t file_diff_nr;
+
+	/* patch mode */
+	struct patch_mode *mode;
+	const char *revision;
 };
 
 static void err(struct add_p_state *s, const char *fmt, ...)
@@ -162,9 +194,18 @@ static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
 	struct hunk *hunk = NULL;
 	int res;
 
+	argv_array_pushv(&args, s->mode->diff_cmd);
+	if (s->revision) {
+		struct object_id oid;
+		argv_array_push(&args,
+				/* could be on an unborn branch */
+				!strcmp("HEAD", s->revision) &&
+				get_oid("HEAD", &oid) ?
+				empty_tree_oid_hex() : s->revision);
+	}
+	color_arg_index = args.argc;
 	/* Use `--no-color` explicitly, just in case `diff.color = always`. */
-	argv_array_pushl(&args, "diff-files", "-p", "--no-color", "--", NULL);
-	color_arg_index = args.argc - 2;
+	argv_array_pushl(&args, "--no-color", "-p", "--", NULL);
 	for (i = 0; i < ps->nr; i++)
 		argv_array_push(&args, ps->items[i].original);
 
@@ -382,7 +423,10 @@ static void render_hunk(struct add_p_state *s, struct hunk *hunk,
 				- header->colored_extra_start;
 		}
 
-		new_offset += delta;
+		if (s->mode->is_reverse)
+			old_offset -= delta;
+		else
+			new_offset += delta;
 
 		strbuf_addf(out, "@@ -%lu,%lu +%lu,%lu @@",
 			    old_offset, header->old_count,
@@ -805,11 +849,10 @@ static int edit_hunk_manually(struct add_p_state *s, struct hunk *hunk)
 				"(context).\n"
 				"To remove '%c' lines, delete them.\n"
 				"Lines starting with %c will be removed.\n"),
-			      '-', '+', comment_line_char);
-	strbuf_commented_addf(&s->buf,
-			      _("If the patch applies cleanly, the edited hunk "
-				"will immediately be\n"
-				"marked for staging.\n"));
+			      s->mode->is_reverse ? '+' : '-',
+			      s->mode->is_reverse ? '-' : '+',
+			      comment_line_char);
+	strbuf_commented_addf(&s->buf, "%s", _(s->mode->edit_hunk_hint));
 	/*
 	 * TRANSLATORS: 'it' refers to the patch mentioned in the previous
 	 * messages.
@@ -890,7 +933,8 @@ static int run_apply_check(struct add_p_state *s,
 	reassemble_patch(s, file_diff, 1, &s->buf);
 
 	setup_child_process(s, &cp,
-			    "apply", "--cached", "--check", NULL);
+			    "apply", "--check", NULL);
+	argv_array_pushv(&cp.args, s->mode->apply_check_args);
 	if (pipe_command(&cp, s->buf.buf, s->buf.len, NULL, 0, NULL, 0))
 		return error(_("'git apply --cached' failed"));
 
@@ -1005,13 +1049,6 @@ static size_t display_hunks(struct add_p_state *s,
 	return end_index;
 }
 
-static const char help_patch_text[] =
-N_("y - stage this hunk\n"
-   "n - do not stage this hunk\n"
-   "q - quit; do not stage this hunk or any of the remaining ones\n"
-   "a - stage this and all the remaining hunks\n"
-   "d - do not stage this hunk nor any of the remaining hunks\n");
-
 static const char help_patch_remainder[] =
 N_("j - leave this hunk undecided, see next undecided hunk\n"
    "J - leave this hunk undecided, see next hunk\n"
@@ -1097,7 +1134,8 @@ static int patch_update_file(struct add_p_state *s,
 			      (uintmax_t)hunk_index + 1,
 			      (uintmax_t)file_diff->hunk_nr);
 		color_fprintf(stdout, s->s.prompt_color,
-			      _(prompt_mode[prompt_mode_type]), s->buf.buf);
+			      _(s->mode->prompt_mode[prompt_mode_type]),
+			      s->buf.buf);
 		fflush(stdout);
 		if (strbuf_getline(&s->answer, stdin) == EOF)
 			break;
@@ -1254,7 +1292,7 @@ soft_increment:
 			const char *p = _(help_patch_remainder), *eol = p;
 
 			color_fprintf(stdout, s->s.help_color, "%s",
-				      _(help_patch_text));
+				      _(s->mode->help_patch_text));
 
 			/*
 			 * Show only those lines of the remainder that are
@@ -1288,10 +1326,11 @@ soft_increment:
 		reassemble_patch(s, file_diff, 0, &s->buf);
 
 		discard_index(s->s.r->index);
-		setup_child_process(s, &cp, "apply", "--cached", NULL);
+		setup_child_process(s, &cp, "apply", NULL);
+		argv_array_pushv(&cp.args, s->mode->apply_args);
 		if (pipe_command(&cp, s->buf.buf, s->buf.len,
 				 NULL, 0, NULL, 0))
-			error(_("'git apply --cached' failed"));
+			error(_("'git apply' failed"));
 		if (!repo_read_index(s->s.r))
 			repo_refresh_and_write_index(s->s.r, REFRESH_QUIET, 0,
 						     1, NULL, NULL, NULL);
@@ -1301,7 +1340,8 @@ soft_increment:
 	return quit;
 }
 
-int run_add_p(struct repository *r, const struct pathspec *ps)
+int run_add_p(struct repository *r, enum add_p_mode mode,
+	      const char *revision, const struct pathspec *ps)
 {
 	struct add_p_state s = {
 		{ r }, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
@@ -1310,6 +1350,9 @@ int run_add_p(struct repository *r, const struct pathspec *ps)
 
 	init_add_i_state(&s.s, r);
 
+	s.mode = &patch_mode_add;
+	s.revision = revision;
+
 	if (discard_index(r->index) < 0 || repo_read_index(r) < 0 ||
 	    repo_refresh_and_write_index(r, REFRESH_QUIET, 0, 1,
 					 NULL, NULL, NULL) < 0 ||
diff --git a/builtin/add.c b/builtin/add.c
index 1deb59a642..006016267e 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -194,12 +194,18 @@ int run_add_interactive(const char *revision, const char *patch_mode,
 				    &use_builtin_add_i);
 
 	if (use_builtin_add_i == 1) {
+		enum add_p_mode mode;
+
 		if (!patch_mode)
 			return !!run_add_i(the_repository, pathspec);
-		if (strcmp(patch_mode, "--patch"))
+
+		if (!strcmp(patch_mode, "--patch"))
+			mode = ADD_P_ADD;
+		else
 			die("'%s' not yet supported in the built-in add -p",
 			    patch_mode);
-		return !!run_add_p(the_repository, pathspec);
+
+		return !!run_add_p(the_repository, mode, revision, pathspec);
 	}
 
 	argv_array_push(&argv, "add--interactive");