built-in add -i: implement the update command

After `status` and `help`, it is now turn to port the `update` command
to C, the second command that is shown in the main loop menu of `git add
-i`.

This `git add -i` command is the first one which lets the user choose a
subset of a list of files, and as such, this patch lays the groundwork
for the other commands of that category:

- It teaches the `print_file_item()` function to show a unique prefix
  if we found any (the code to find it had been added already in the
  previous patch where we colored the unique prefixes of the main loop
  commands, but that patch uses the `print_command_item()` function to
  display the menu items).

- This patch also adds the help text that is shown when the user input
  to select items from the shown list could not be parsed.

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

add-interactive.c

@@ -6,6 +6,7 @@
 #include "revision.h"
 #include "refs.h"
 #include "prefix-map.h"
+#include "lockfile.h"
 
 struct add_i_state {
 	struct repository *r;
@@ -459,8 +460,8 @@ static int is_valid_prefix(const char *prefix, size_t prefix_len)
 }
 
 struct print_file_item_data {
-	const char *modified_fmt;
-	struct strbuf buf, index, worktree;
+	const char *modified_fmt, *color, *reset;
+	struct strbuf buf, name, index, worktree;
 };
 
 static void print_file_item(int i, int selected, struct prefix_item *item,
@@ -468,21 +469,34 @@ static void print_file_item(int i, int selected, struct prefix_item *item,
 {
 	struct file_item *c = (struct file_item *)item;
 	struct print_file_item_data *d = print_file_item_data;
+	const char *highlighted = NULL;
 
 	strbuf_reset(&d->index);
 	strbuf_reset(&d->worktree);
 	strbuf_reset(&d->buf);
 
+	/* Format the item with the prefix highlighted. */
+	if (item->prefix_length > 0 &&
+	    is_valid_prefix(item->name, item->prefix_length)) {
+		strbuf_reset(&d->name);
+		strbuf_addf(&d->name, "%s%.*s%s%s", d->color,
+			    (int)item->prefix_length, item->name, d->reset,
+			    item->name + item->prefix_length);
+		highlighted = d->name.buf;
+	}
+
 	populate_wi_changes(&d->worktree, &c->worktree, _("nothing"));
 	populate_wi_changes(&d->index, &c->index, _("unchanged"));
 	strbuf_addf(&d->buf, d->modified_fmt,
-		    d->index.buf, d->worktree.buf, item->name);
+		    d->index.buf, d->worktree.buf,
+		    highlighted ? highlighted : item->name);
 
 	printf("%c%2d: %s", selected ? '*' : ' ', i + 1, d->buf.buf);
 }
 
 static int run_status(struct add_i_state *s, const struct pathspec *ps,
-		      struct file_list *files, struct list_options *opts)
+		      struct file_list *files,
+		      struct list_and_choose_options *opts)
 {
 	reset_file_list(files);
 
@@ -491,14 +505,72 @@ static int run_status(struct add_i_state *s, const struct pathspec *ps,
 
 	if (files->nr)
 		list((struct prefix_item **)files->file, NULL, files->nr,
-		     s, opts);
+		     s, &opts->list_opts);
 	putchar('\n');
 
 	return 0;
 }
 
+static int run_update(struct add_i_state *s, const struct pathspec *ps,
+		      struct file_list *files,
+		      struct list_and_choose_options *opts)
+{
+	int res = 0, fd, *selected = NULL;
+	size_t count, i;
+	struct lock_file index_lock;
+
+	reset_file_list(files);
+
+	if (get_modified_files(s->r, WORKTREE_ONLY, files, ps) < 0)
+		return -1;
+
+	if (!files->nr) {
+		putchar('\n');
+		return 0;
+	}
+
+	opts->prompt = N_("Update");
+	CALLOC_ARRAY(selected, files->nr);
+
+	count = list_and_choose((struct prefix_item **)files->file,
+				selected, files->nr, s, opts);
+	if (count <= 0) {
+		putchar('\n');
+		free(selected);
+		return 0;
+	}
+
+	fd = repo_hold_locked_index(s->r, &index_lock, LOCK_REPORT_ON_ERROR);
+	if (fd < 0) {
+		putchar('\n');
+		free(selected);
+		return -1;
+	}
+
+	for (i = 0; i < files->nr; i++) {
+		const char *name = files->file[i]->item.name;
+		if (selected[i] &&
+		    add_file_to_index(s->r->index, name, 0) < 0) {
+			res = error(_("could not stage '%s'"), name);
+			break;
+		}
+	}
+
+	if (!res && write_locked_index(s->r->index, &index_lock, COMMIT_LOCK) < 0)
+		res = error(_("could not write index"));
+
+	if (!res)
+		printf(Q_("updated %d path\n",
+			  "updated %d paths\n", count), (int)count);
+
+	putchar('\n');
+	free(selected);
+	return res;
+}
+
 static int run_help(struct add_i_state *s, const struct pathspec *ps,
-		    struct file_list *files, struct list_options *opts)
+		    struct file_list *files,
+		    struct list_and_choose_options *opts)
 {
 	const char *help_color = s->help_color;
 
@@ -518,6 +590,27 @@ static int run_help(struct add_i_state *s, const struct pathspec *ps,
 	return 0;
 }
 
+static void choose_prompt_help(struct add_i_state *s)
+{
+	const char *help_color = s->help_color;
+	color_fprintf_ln(stdout, help_color, "%s",
+			 _("Prompt help:"));
+	color_fprintf_ln(stdout, help_color, "1          - %s",
+			 _("select a single item"));
+	color_fprintf_ln(stdout, help_color, "3-5        - %s",
+			 _("select a range of items"));
+	color_fprintf_ln(stdout, help_color, "2-3,6-9    - %s",
+			 _("select multiple ranges"));
+	color_fprintf_ln(stdout, help_color, "foo        - %s",
+			 _("select item based on unique prefix"));
+	color_fprintf_ln(stdout, help_color, "-...       - %s",
+			 _("unselect specified items"));
+	color_fprintf_ln(stdout, help_color, "*          - %s",
+			 _("choose all items"));
+	color_fprintf_ln(stdout, help_color, "           - %s",
+			 _("(empty) finish selecting"));
+}
+
 struct print_command_item_data {
 	const char *color, *reset;
 };
@@ -539,7 +632,8 @@ static void print_command_item(int i, int selected, struct prefix_item *item,
 struct command_item {
 	struct prefix_item item;
 	int (*command)(struct add_i_state *s, const struct pathspec *ps,
-		       struct file_list *files, struct list_options *opts);
+		       struct file_list *files,
+		       struct list_and_choose_options *opts);
 };
 
 static void command_prompt_help(struct add_i_state *s)
@@ -564,17 +658,20 @@ int run_add_i(struct repository *r, const struct pathspec *ps)
 	};
 	struct command_item
 		status = { { "status" }, run_status },
+		update = { { "update" }, run_update },
 		help = { { "help" }, run_help };
 	struct command_item *commands[] = {
-		&status,
+		&status, &update,
 		&help
 	};
 
 	struct print_file_item_data print_file_item_data = {
-		"%12s %12s %s", STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
+		"%12s %12s %s", NULL, NULL,
+		STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
 	};
-	struct list_options opts = {
-		0, NULL, print_file_item, &print_file_item_data
+	struct list_and_choose_options opts = {
+		{ 0, NULL, print_file_item, &print_file_item_data },
+		NULL, 0, choose_prompt_help
 	};
 	struct strbuf header = STRBUF_INIT;
 	struct file_list files = { NULL };
@@ -595,11 +692,13 @@ int run_add_i(struct repository *r, const struct pathspec *ps)
 		data.color = "[";
 		data.reset = "]";
 	}
+	print_file_item_data.color = data.color;
+	print_file_item_data.reset = data.reset;
 
 	strbuf_addstr(&header, "      ");
 	strbuf_addf(&header, print_file_item_data.modified_fmt,
 		    _("staged"), _("unstaged"), _("path"));
-	opts.header = header.buf;
+	opts.list_opts.header = header.buf;
 
 	repo_refresh_and_write_index(r, REFRESH_QUIET, 1);
 	if (run_status(&s, ps, &files, &opts) < 0)
@@ -619,6 +718,7 @@ int run_add_i(struct repository *r, const struct pathspec *ps)
 
 	release_file_list(&files);
 	strbuf_release(&print_file_item_data.buf);
+	strbuf_release(&print_file_item_data.name);
 	strbuf_release(&print_file_item_data.index);
 	strbuf_release(&print_file_item_data.worktree);
 	strbuf_release(&header);