builtin-am: implement -i/--interactive

Since d1c5f2a (Add git-am, applymbox replacement., 2005-10-07),
git-am.sh supported the --interactive mode. After parsing the patch mail
and extracting the patch, commit message and authorship info, an
interactive session will begin that allows the user to choose between:

* applying the patch

* applying the patch and all subsequent patches (by disabling
  interactive mode in subsequent patches)

* skipping the patch

* editing the commit message

Since f89ad67 (Add [v]iew patch in git-am interactive., 2005-10-25),
git-am.sh --interactive also supported viewing the patch to be applied.

When --resolved-ing in --interactive mode, we need to take care to
update the patch with the contents of the index, such that the correct
patch will be displayed when the patch is viewed in interactive mode.

Re-implement the above in builtin/am.c

Signed-off-by: Paul Tan <pyokagan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/am.c

@@ -25,6 +25,7 @@
 #include "log-tree.h"
 #include "notes-utils.h"
 #include "rerere.h"
+#include "prompt.h"
 
 /**
  * Returns 1 if the file is empty or does not exist, 0 otherwise.
@@ -119,6 +120,7 @@ struct am_state {
 	int prec;
 
 	/* various operating modes and command line options */
+	int interactive;
 	int threeway;
 	int quiet;
 	int signoff;
@@ -1171,7 +1173,7 @@ static void NORETURN die_user_resolve(const struct am_state *state)
 	if (state->resolvemsg) {
 		printf_ln("%s", state->resolvemsg);
 	} else {
-		const char *cmdline = "git am";
+		const char *cmdline = state->interactive ? "git am -i" : "git am";
 
 		printf_ln(_("When you have resolved this problem, run \"%s --continue\"."), cmdline);
 		printf_ln(_("If you prefer to skip this patch, run \"%s --skip\" instead."), cmdline);
@@ -1403,6 +1405,36 @@ static void write_commit_patch(const struct am_state *state, struct commit *comm
 	log_tree_commit(&rev_info, commit);
 }
 
+/**
+ * Writes the diff of the index against HEAD as a patch to the state
+ * directory's "patch" file.
+ */
+static void write_index_patch(const struct am_state *state)
+{
+	struct tree *tree;
+	unsigned char head[GIT_SHA1_RAWSZ];
+	struct rev_info rev_info;
+	FILE *fp;
+
+	if (!get_sha1_tree("HEAD", head))
+		tree = lookup_tree(head);
+	else
+		tree = lookup_tree(EMPTY_TREE_SHA1_BIN);
+
+	fp = xfopen(am_path(state, "patch"), "w");
+	init_revisions(&rev_info, NULL);
+	rev_info.diff = 1;
+	rev_info.disable_stdin = 1;
+	rev_info.no_commit_id = 1;
+	rev_info.diffopt.output_format = DIFF_FORMAT_PATCH;
+	rev_info.diffopt.use_color = 0;
+	rev_info.diffopt.file = fp;
+	rev_info.diffopt.close_file = 1;
+	add_pending_object(&rev_info, &tree->object, "");
+	diff_setup_done(&rev_info.diffopt);
+	run_diff_index(&rev_info, 1);
+}
+
 /**
  * Like parse_mail(), but parses the mail by looking up its commit ID
  * directly. This is used in --rebasing mode to bypass git-mailinfo's munging
@@ -1654,6 +1686,65 @@ static void validate_resume_state(const struct am_state *state)
 			am_path(state, "author-script"));
 }
 
+/**
+ * Interactively prompt the user on whether the current patch should be
+ * applied.
+ *
+ * Returns 0 if the user chooses to apply the patch, 1 if the user chooses to
+ * skip it.
+ */
+static int do_interactive(struct am_state *state)
+{
+	assert(state->msg);
+
+	if (!isatty(0))
+		die(_("cannot be interactive without stdin connected to a terminal."));
+
+	for (;;) {
+		const char *reply;
+
+		puts(_("Commit Body is:"));
+		puts("--------------------------");
+		printf("%s", state->msg);
+		puts("--------------------------");
+
+		/*
+		 * TRANSLATORS: Make sure to include [y], [n], [e], [v] and [a]
+		 * in your translation. The program will only accept English
+		 * input at this point.
+		 */
+		reply = git_prompt(_("Apply? [y]es/[n]o/[e]dit/[v]iew patch/[a]ccept all: "), PROMPT_ECHO);
+
+		if (!reply) {
+			continue;
+		} else if (*reply == 'y' || *reply == 'Y') {
+			return 0;
+		} else if (*reply == 'a' || *reply == 'A') {
+			state->interactive = 0;
+			return 0;
+		} else if (*reply == 'n' || *reply == 'N') {
+			return 1;
+		} else if (*reply == 'e' || *reply == 'E') {
+			struct strbuf msg = STRBUF_INIT;
+
+			if (!launch_editor(am_path(state, "final-commit"), &msg, NULL)) {
+				free(state->msg);
+				state->msg = strbuf_detach(&msg, &state->msg_len);
+			}
+			strbuf_release(&msg);
+		} else if (*reply == 'v' || *reply == 'V') {
+			const char *pager = git_pager(1);
+			struct child_process cp = CHILD_PROCESS_INIT;
+
+			if (!pager)
+				pager = "cat";
+			argv_array_push(&cp.args, pager);
+			argv_array_push(&cp.args, am_path(state, "patch"));
+			run_command(&cp);
+		}
+	}
+}
+
 /**
  * Applies all queued mail.
  *
@@ -1702,6 +1793,9 @@ static void am_run(struct am_state *state, int resume)
 			write_commit_msg(state);
 		}
 
+		if (state->interactive && do_interactive(state))
+			goto next;
+
 		if (run_applypatch_msg_hook(state))
 			exit(1);
 
@@ -1787,10 +1881,17 @@ static void am_resolve(struct am_state *state)
 		die_user_resolve(state);
 	}
 
+	if (state->interactive) {
+		write_index_patch(state);
+		if (do_interactive(state))
+			goto next;
+	}
+
 	rerere(0);
 
 	do_commit(state);
 
+next:
 	am_next(state);
 	am_run(state, 0);
 }
@@ -2036,6 +2137,8 @@ int cmd_am(int argc, const char **argv, const char *prefix)
 	};
 
 	struct option options[] = {
+		OPT_BOOL('i', "interactive", &state.interactive,
+			N_("run interactively")),
 		OPT_BOOL('3', "3way", &state.threeway,
 			N_("allow fall back on 3way merging if needed")),
 		OPT__QUIET(&state.quiet, N_("be quiet")),