add -p: fix checking of user input

When a file has been deleted the C version of add -p allows the user
to edit a hunk even though 'e' is not in the list of allowed
responses. (I think 'e' is disallowed because if the file is edited it
is no longer a deletion and we're not set up to rewrite the diff
header).

The invalid response was allowed because the test that determines
whether to display 'e' was not duplicated correctly in the code that
processes the user's choice. Fix this by using flags that are set when
constructing the prompt and checked when processing the user's choice
rather than repeating the check itself.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

add-patch.c

diff --git a/add-patch.c b/add-patch.c
index a15fa40..907c05b 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -1352,6 +1352,15 @@ static int patch_update_file(struct add_p_state *s,
 	struct child_process cp = CHILD_PROCESS_INIT;
 	int colored = !!s->colored.len, quit = 0;
 	enum prompt_mode_type prompt_mode_type;
+	enum {
+		ALLOW_GOTO_PREVIOUS_HUNK = 1 << 0,
+		ALLOW_GOTO_PREVIOUS_UNDECIDED_HUNK = 1 << 1,
+		ALLOW_GOTO_NEXT_HUNK = 1 << 2,
+		ALLOW_GOTO_NEXT_UNDECIDED_HUNK = 1 << 3,
+		ALLOW_SEARCH_AND_GOTO = 1 << 4,
+		ALLOW_SPLIT = 1 << 5,
+		ALLOW_EDIT = 1 << 6
+	} permitted = 0;
 
 	if (!file_diff->hunk_nr)
 		return 0;
@@ -1388,22 +1397,35 @@ static int patch_update_file(struct add_p_state *s,
 		fputs(s->buf.buf, stdout);
 
 		strbuf_reset(&s->buf);
-		if (undecided_previous >= 0)
+		if (undecided_previous >= 0) {
+			permitted |= ALLOW_GOTO_PREVIOUS_UNDECIDED_HUNK;
 			strbuf_addstr(&s->buf, ",k");
-		if (hunk_index)
+		}
+		if (hunk_index) {
+			permitted |= ALLOW_GOTO_PREVIOUS_HUNK;
 			strbuf_addstr(&s->buf, ",K");
-		if (undecided_next >= 0)
+		}
+		if (undecided_next >= 0) {
+			permitted |= ALLOW_GOTO_NEXT_UNDECIDED_HUNK;
 			strbuf_addstr(&s->buf, ",j");
-		if (hunk_index + 1 < file_diff->hunk_nr)
+		}
+		if (hunk_index + 1 < file_diff->hunk_nr) {
+			permitted |= ALLOW_GOTO_NEXT_HUNK;
 			strbuf_addstr(&s->buf, ",J");
-		if (file_diff->hunk_nr > 1)
+		}
+		if (file_diff->hunk_nr > 1) {
+			permitted |= ALLOW_SEARCH_AND_GOTO;
 			strbuf_addstr(&s->buf, ",g,/");
-		if (hunk->splittable_into > 1)
+		}
+		if (hunk->splittable_into > 1) {
+			permitted |= ALLOW_SPLIT;
 			strbuf_addstr(&s->buf, ",s");
+		}
 		if (hunk_index + 1 > file_diff->mode_change &&
-		    !file_diff->deleted)
+		    !file_diff->deleted) {
+			permitted |= ALLOW_EDIT;
 			strbuf_addstr(&s->buf, ",e");
-
+		}
 		if (file_diff->deleted)
 			prompt_mode_type = PROMPT_DELETION;
 		else if (file_diff->added)
@@ -1452,22 +1474,22 @@ static int patch_update_file(struct add_p_state *s,
 				break;
 			}
 		} else if (s->answer.buf[0] == 'K') {
-			if (hunk_index)
+			if (permitted & ALLOW_GOTO_PREVIOUS_HUNK)
 				hunk_index--;
 			else
 				err(s, _("No previous hunk"));
 		} else if (s->answer.buf[0] == 'J') {
-			if (hunk_index + 1 < file_diff->hunk_nr)
+			if (permitted & ALLOW_GOTO_NEXT_HUNK)
 				hunk_index++;
 			else
 				err(s, _("No next hunk"));
 		} else if (s->answer.buf[0] == 'k') {
-			if (undecided_previous >= 0)
+			if (permitted & ALLOW_GOTO_PREVIOUS_UNDECIDED_HUNK)
 				hunk_index = undecided_previous;
 			else
 				err(s, _("No previous hunk"));
 		} else if (s->answer.buf[0] == 'j') {
-			if (undecided_next >= 0)
+			if (permitted & ALLOW_GOTO_NEXT_UNDECIDED_HUNK)
 				hunk_index = undecided_next;
 			else
 				err(s, _("No next hunk"));
@@ -1475,7 +1497,7 @@ static int patch_update_file(struct add_p_state *s,
 			char *pend;
 			unsigned long response;
 
-			if (file_diff->hunk_nr < 2) {
+			if (!(permitted & ALLOW_SEARCH_AND_GOTO)) {
 				err(s, _("No other hunks to goto"));
 				continue;
 			}
@@ -1512,7 +1534,7 @@ static int patch_update_file(struct add_p_state *s,
 			regex_t regex;
 			int ret;
 
-			if (file_diff->hunk_nr < 2) {
+			if (!(permitted & ALLOW_SEARCH_AND_GOTO)) {
 				err(s, _("No other hunks to search"));
 				continue;
 			}
@@ -1557,7 +1579,7 @@ static int patch_update_file(struct add_p_state *s,
 			hunk_index = i;
 		} else if (s->answer.buf[0] == 's') {
 			size_t splittable_into = hunk->splittable_into;
-			if (splittable_into < 2)
+			if (!(permitted & ALLOW_SPLIT))
 				err(s, _("Sorry, cannot split this hunk"));
 			else if (!split_hunk(s, file_diff,
 					     hunk - file_diff->hunk))
@@ -1565,7 +1587,7 @@ static int patch_update_file(struct add_p_state *s,
 						 _("Split into %d hunks."),
 						 (int)splittable_into);
 		} else if (s->answer.buf[0] == 'e') {
-			if (hunk_index + 1 == file_diff->mode_change)
+			if (!(permitted & ALLOW_EDIT))
 				err(s, _("Sorry, cannot edit this hunk"));
 			else if (edit_hunk_loop(s, file_diff, hunk) >= 0) {
 				hunk->use = USE_HUNK;