From 89c8559367aae771006cc0956b6f5e54cc8c614c Mon Sep 17 00:00:00 2001
From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Fri, 6 Dec 2019 13:08:24 +0000
Subject: git add -p: use non-zero exit code when the diff generation failed

The first thing `git add -p` does is to generate a diff. If this diff
cannot be generated, `git add -p` should not continue as if nothing
happened, but instead fail.

What we *actually* do here is much broader: we now verify for *every*
`run_cmd_pipe()` call that the spawned process actually succeeded.

Note that we have to change two callers in this patch, as we need to
store the spawned process' output in a local variable, which means that
the callers can no longer decide whether to interpret the `return <$fh>`
in array or in scalar context.

This bug was noticed while writing a test case for the diff.algorithm
feature, and we let that test case double as a regression test for this
fixed bug, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-add--interactive.perl b/git-add--interactive.perl
index 52659bb..10fd30a 100755
--- a/git-add--interactive.perl
+++ b/git-add--interactive.perl
@@ -177,7 +177,9 @@ sub run_cmd_pipe {
 	} else {
 		my $fh = undef;
 		open($fh, '-|', @_) or die;
-		return <$fh>;
+		my @out = <$fh>;
+		close $fh || die "Cannot close @_ ($!)";
+		return @out;
 	}
 }
 
@@ -224,7 +226,7 @@ my $status_head = sprintf($status_fmt, __('staged'), __('unstaged'), __('path'))
 	sub get_empty_tree {
 		return $empty_tree if defined $empty_tree;
 
-		$empty_tree = run_cmd_pipe(qw(git hash-object -t tree /dev/null));
+		($empty_tree) = run_cmd_pipe(qw(git hash-object -t tree /dev/null));
 		chomp $empty_tree;
 		return $empty_tree;
 	}
@@ -1127,7 +1129,7 @@ aborted and the hunk is left unchanged.
 EOF2
 	close $fh;
 
-	chomp(my $editor = run_cmd_pipe(qw(git var GIT_EDITOR)));
+	chomp(my ($editor) = run_cmd_pipe(qw(git var GIT_EDITOR)));
 	system('sh', '-c', $editor.' "$@"', $editor, $hunkfile);
 
 	if ($? != 0) {
diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
index f436341..5db6432 100755
--- a/t/t3701-add-interactive.sh
+++ b/t/t3701-add-interactive.sh
@@ -530,7 +530,7 @@ test_expect_success 'diff.algorithm is passed to `git diff-files`' '
 	>file &&
 	git add file &&
 	echo changed >file &&
-	git -c diff.algorithm=bogus add -p 2>err &&
+	test_must_fail git -c diff.algorithm=bogus add -p 2>err &&
 	test_i18ngrep "error: option diff-algorithm accepts " err
 '
 
-- 
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