add-patch: render hunks through the pager

Make the print command trigger the pager when invoked using a capital
'P', to make it easier for the user to review long hunks.

Note that if the PAGER ends unexpectedly before we've been able to send
the payload, perhaps because the user is not interested in the whole
thing, we might receive a SIGPIPE, which would abruptly and unexpectedly
terminate the interactive session for the user.

Therefore, we need to ignore a possible SIGPIPE signal.  Add a test for
this, in addition to the test for normal operation.

For the SIGPIPE test, we need to make sure that we completely fill the
operating system's buffer, otherwise we might not trigger the SIGPIPE
signal.  The normal size of this buffer in different OSs varies from a
few KBs to 1MB.  Use a payload large enough to guarantee that we exceed
this limit.

Signed-off-by: Rubén Justo <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: rjusto

add-patch.c

@@ -7,9 +7,11 @@
 #include "environment.h"
 #include "gettext.h"
 #include "object-name.h"
+#include "pager.h"
 #include "read-cache-ll.h"
 #include "repository.h"
 #include "strbuf.h"
+#include "sigchain.h"
 #include "run-command.h"
 #include "strvec.h"
 #include "pathspec.h"
@@ -1391,7 +1393,7 @@ N_("j - leave this hunk undecided, see next undecided hunk\n"
    "/ - search for a hunk matching the given regex\n"
    "s - split the current hunk into smaller hunks\n"
    "e - manually edit the current hunk\n"
-   "p - print the current hunk\n"
+   "p - print the current hunk, 'P' to use the pager\n"
    "? - print help\n");
 
 static int patch_update_file(struct add_p_state *s,
@@ -1402,7 +1404,7 @@ static int patch_update_file(struct add_p_state *s,
 	struct hunk *hunk;
 	char ch;
 	struct child_process cp = CHILD_PROCESS_INIT;
-	int colored = !!s->colored.len, quit = 0;
+	int colored = !!s->colored.len, quit = 0, use_pager = 0;
 	enum prompt_mode_type prompt_mode_type;
 	enum {
 		ALLOW_GOTO_PREVIOUS_HUNK = 1 << 0,
@@ -1452,9 +1454,18 @@ static int patch_update_file(struct add_p_state *s,
 		strbuf_reset(&s->buf);
 		if (file_diff->hunk_nr) {
 			if (rendered_hunk_index != hunk_index) {
+				if (use_pager) {
+					setup_pager();
+					sigchain_push(SIGPIPE, SIG_IGN);
+				}
 				render_hunk(s, hunk, 0, colored, &s->buf);
 				fputs(s->buf.buf, stdout);
 				rendered_hunk_index = hunk_index;
+				if (use_pager) {
+					sigchain_pop(SIGPIPE);
+					wait_for_pager();
+					use_pager = 0;
+				}
 			}
 
 			strbuf_reset(&s->buf);
@@ -1675,8 +1686,9 @@ static int patch_update_file(struct add_p_state *s,
 				hunk->use = USE_HUNK;
 				goto soft_increment;
 			}
-		} else if (s->answer.buf[0] == 'p') {
+		} else if (ch == 'p') {
 			rendered_hunk_index = -1;
+			use_pager = (s->answer.buf[0] == 'P') ? 1 : 0;
 		} else if (s->answer.buf[0] == '?') {
 			const char *p = _(help_patch_remainder), *eol = p;
 

t/t3701-add-interactive.sh

@@ -591,6 +591,38 @@ test_expect_success 'print again the hunk' '
 	test_cmp expect actual.trimmed
 '
 
+test_expect_success TTY 'print again the hunk (PAGER)' '
+	test_when_finished "git reset" &&
+	cat >expect <<-EOF &&
+	<GREEN>+<RESET><GREEN>15<RESET>
+	 20<RESET>
+	<BOLD;BLUE>(1/2) Stage this hunk [y,n,q,a,d,j,J,g,/,e,p,?]? <RESET>PAGER <CYAN>@@ -1,2 +1,3 @@<RESET>
+	PAGER  10<RESET>
+	PAGER <GREEN>+<RESET><GREEN>15<RESET>
+	PAGER  20<RESET>
+	<BOLD;BLUE>(1/2) Stage this hunk [y,n,q,a,d,j,J,g,/,e,p,?]? <RESET>
+	EOF
+	test_write_lines s y g 1 P |
+	(
+		GIT_PAGER="sed s/^/PAGER\ /" &&
+		export GIT_PAGER &&
+		test_terminal git add -p >actual
+	) &&
+	tail -n 7 <actual | test_decode_color >actual.trimmed &&
+	test_cmp expect actual.trimmed
+'
+
+test_expect_success TTY 'P handles SIGPIPE when writing to pager' '
+	test_when_finished "rm -f huge_file; git reset" &&
+	printf "\n%2500000s" Y >huge_file &&
+	git add -N huge_file &&
+	test_write_lines P q | (
+		GIT_PAGER="head -n 1" &&
+		export GIT_PAGER &&
+		test_terminal git add -p
+	)
+'
+
 test_expect_success 'split hunk "add -p (edit)"' '
 	# Split, say Edit and do nothing.  Then:
 	#