From ae0c55abf8217bb06422f9eafcd7a30b2c8f9e8b Mon Sep 17 00:00:00 2001
From: Eric Sunshine <sunshine@sunshineco.com>
Date: Thu, 1 Sep 2022 00:29:51 +0000
Subject: [PATCH] chainlint.pl: allow `|| echo` to signal failure upstream of a
 pipe

The use of `|| return` (or `|| exit`) to signal failure within a loop
isn't effective when the loop is upstream of a pipe since the pipe
swallows all upstream exit codes and returns only the exit code of the
final command in the pipeline.

To work around this limitation, tests may adopt an alternative strategy
of signaling failure by emitting text which would never be emitted in
the non-failing case. For instance:

    while condition
    do
        command1 &&
        command2 ||
        echo "impossible text"
    done |
    sort >actual &&

Such usage indicates deliberate thought about failure cases by the test
author, thus flagging them as missing `|| return` (or `|| exit`) is not
helpful. Therefore, take this case into consideration when checking for
explicit loop termination.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/chainlint.pl                        |  3 +++
 t/chainlint/loop-upstream-pipe.expect | 10 ++++++++++
 t/chainlint/loop-upstream-pipe.test   | 11 +++++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 t/chainlint/loop-upstream-pipe.expect
 create mode 100644 t/chainlint/loop-upstream-pipe.test

diff --git a/t/chainlint.pl b/t/chainlint.pl
index 674b3ddf69..386999ce65 100755
--- a/t/chainlint.pl
+++ b/t/chainlint.pl
@@ -487,6 +487,9 @@ sub parse_loop_body {
 	my @tokens = $self->SUPER::parse_loop_body(@_);
 	# did loop signal failure via "|| return" or "|| exit"?
 	return @tokens if !@tokens || grep(/^(?:return|exit|\$\?)$/, @tokens);
+	# did loop upstream of a pipe signal failure via "|| echo 'impossible
+	# text'" as the final command in the loop body?
+	return @tokens if ends_with(\@tokens, [qr/^\|\|$/, "\n", qr/^echo$/, qr/^.+$/]);
 	# flag missing "return/exit" handling explicit failure in loop body
 	my $n = find_non_nl(\@tokens);
 	splice(@tokens, $n + 1, 0, '?!LOOP?!');
diff --git a/t/chainlint/loop-upstream-pipe.expect b/t/chainlint/loop-upstream-pipe.expect
new file mode 100644
index 0000000000..0b82ecc4b9
--- /dev/null
+++ b/t/chainlint/loop-upstream-pipe.expect
@@ -0,0 +1,10 @@
+(
+	git rev-list --objects --no-object-names base..loose |
+	while read oid
+	do
+		path="$objdir/$(test_oid_to_path "$oid")" &&
+		printf "%s %d\n" "$oid" "$(test-tool chmtime --get "$path")" ||
+		echo "object list generation failed for $oid"
+	done |
+	sort -k1
+) >expect &&
diff --git a/t/chainlint/loop-upstream-pipe.test b/t/chainlint/loop-upstream-pipe.test
new file mode 100644
index 0000000000..efb77da897
--- /dev/null
+++ b/t/chainlint/loop-upstream-pipe.test
@@ -0,0 +1,11 @@
+(
+	git rev-list --objects --no-object-names base..loose |
+	while read oid
+	do
+# LINT: "|| echo" signals failure in loop upstream of a pipe
+		path="$objdir/$(test_oid_to_path "$oid")" &&
+		printf "%s %d\n" "$oid" "$(test-tool chmtime --get "$path")" ||
+		echo "object list generation failed for $oid"
+	done |
+	sort -k1
+) >expect &&