[PATCH v3] add-patch: response to unknown command

["Rubén Justo" <rjusto@gmail.com>]

When the user gives an unknown command to the "add -p" prompt, the list
of accepted commands with their explanation is given.  This is the same
output they get when they say '?'.

However, the unknown command may be due to a user input error rather
than the user not knowing the valid command.

To reduce the likelihood of user confusion and error repetition, instead
of displaying the list of accepted commands, display a short error
message with the unknown command received, as feedback to the user.

Include a reminder about the current command '?' in the new message, to
guide the user if they want help.

Signed-off-by: Rubén Justo <rjusto@gmail.com>
---

Thanks.

Range-diff against v2:
1:  c94c838fad ! 1:  ddd8d380a7 add-patch: response to invalid command
    @@ Metadata
     Author: Rubén Justo <rjusto@gmail.com>
     
      ## Commit message ##
    -    add-patch: response to invalid command
    +    add-patch: response to unknown command
     
    -    When the user enters an invalid command, we respond with a list of
    -    accepted commands; the response we give to the command '?'.
    +    When the user gives an unknown command to the "add -p" prompt, the list
    +    of accepted commands with their explanation is given.  This is the same
    +    output they get when they say '?'.
     
    -    However, the invalid command may be due to either a user input error or
    -    a malfunctioning interface component, rather than the user not knowing
    -    the valid command.
    +    However, the unknown command may be due to a user input error rather
    +    than the user not knowing the valid command.
     
    -    Our response is unlikely to provide help in such situations.
    -
    -    To reduce the likelihood of user confusion and error repetition, if an
    -    unrecognized command is received, stop displaying the help text and
    -    display a short error message with the invalid command received, as
    -    feedback to the user.
    +    To reduce the likelihood of user confusion and error repetition, instead
    +    of displaying the list of accepted commands, display a short error
    +    message with the unknown command received, as feedback to the user.
     
         Include a reminder about the current command '?' in the new message, to
         guide the user if they want help.
    @@ t/t3701-add-interactive.sh: export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
      diff_cmp () {
      	for x
      	do
    -@@ t/t3701-add-interactive.sh: test_expect_success 'setup (initial)' '
    - 	echo more >>file &&
    - 	echo lines >>file
    +@@ t/t3701-add-interactive.sh: test_expect_success 'warn about add.interactive.useBuiltin' '
    + 	done
      '
    -+
    + 
     +test_expect_success 'unknown command' '
    -+	test_when_finished "git reset command && rm command" &&
    ++	test_when_finished "git reset --hard; rm -f command" &&
     +	echo W >command &&
     +	git add -N command &&
     +	cat >expect <<-EOF &&
    @@ t/t3701-add-interactive.sh: test_expect_success 'setup (initial)' '
     +	test_cmp expect actual
     +'
     +
    - test_expect_success 'status works (initial)' '
    - 	git add -i </dev/null >output &&
    - 	grep "+1/-0 *+2/-0 file" output
    + test_expect_success 'setup (initial)' '
    + 	echo content >file &&
    + 	git add file &&
     @@ t/t3701-add-interactive.sh: test_expect_success 'setup file' '
      '
      

 add-patch.c                |  5 ++++-
 t/t3701-add-interactive.sh | 22 +++++++++++++++++++++-
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/add-patch.c b/add-patch.c
index a06dd18985..7be142d448 100644
--- a/add-patch.c
+++ b/add-patch.c
@@ -1667,7 +1667,7 @@ static int patch_update_file(struct add_p_state *s,
 			}
 		} else if (s->answer.buf[0] == 'p') {
 			rendered_hunk_index = -1;
-		} else {
+		} else if (s->answer.buf[0] == '?') {
 			const char *p = _(help_patch_remainder), *eol = p;
 
 			color_fprintf(stdout, s->s.help_color, "%s",
@@ -1691,6 +1691,9 @@ static int patch_update_file(struct add_p_state *s,
 				color_fprintf_ln(stdout, s->s.help_color,
 						 "%.*s", (int)(eol - p), p);
 			}
+		} else {
+			err(s, _("Unknown command '%s' (use '?' for help)"),
+			    s->answer.buf);
 		}
 	}
 
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index bc55255b0a..d974bddcf2 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -7,6 +7,8 @@ export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-terminal.sh
 
+SP=" "
+
 diff_cmp () {
 	for x
 	do
@@ -55,6 +57,25 @@ test_expect_success 'warn about add.interactive.useBuiltin' '
 	done
 '
 
+test_expect_success 'unknown command' '
+	test_when_finished "git reset --hard; rm -f command" &&
+	echo W >command &&
+	git add -N command &&
+	cat >expect <<-EOF &&
+	diff --git a/command b/command
+	new file mode 100644
+	index 0000000..a42d8ff
+	--- /dev/null
+	+++ b/command
+	@@ -0,0 +1 @@
+	+W
+	(1/1) Stage addition [y,n,q,a,d,e,p,?]? Unknown command ${SQ}W${SQ} (use ${SQ}?${SQ} for help)
+	(1/1) Stage addition [y,n,q,a,d,e,p,?]?$SP
+	EOF
+	git add -p -- command <command >actual 2>&1 &&
+	test_cmp expect actual
+'
+
 test_expect_success 'setup (initial)' '
 	echo content >file &&
 	git add file &&
@@ -231,7 +252,6 @@ test_expect_success 'setup file' '
 '
 
 test_expect_success 'setup patch' '
-	SP=" " &&
 	NULL="" &&
 	cat >patch <<-EOF
 	@@ -1,4 +1,4 @@
-- 
2.45.0.rc0.1.gddd8d380a7