Merge branch 'jk/add-i-diff-filter'

The "interactive.diffFilter" used by "git add -i" must retain
one-to-one correspondence between its input and output, but it was
not enforced and caused end-user confusion.  We now at least make
sure the filtered result has the same number of lines as its input
to detect a broken filter.

* jk/add-i-diff-filter:
  add--interactive: detect bogus diffFilter output
  t3701: add a test for interactive.diffFilter

Author: gitster

git-add--interactive.perl

@@ -705,6 +705,14 @@ sub parse_diff {
 	}
 	my (@hunk) = { TEXT => [], DISPLAY => [], TYPE => 'header' };
 
+	if (@colored && @colored != @diff) {
+		print STDERR
+		  "fatal: mismatched output from interactive.diffFilter\n",
+		  "hint: Your filter must maintain a one-to-one correspondence\n",
+		  "hint: between its input and output lines.\n";
+		exit 1;
+	}
+
 	for (my $i = 0; $i < @diff; $i++) {
 		if ($diff[$i] =~ /^@@ /) {
 			push @hunk, { TEXT => [], DISPLAY => [],

t/t3701-add-interactive.sh

@@ -397,6 +397,26 @@ test_expect_success TTY 'diffs can be colorized' '
 	grep "$(printf "\\033")" output
 '
 
+test_expect_success TTY 'diffFilter filters diff' '
+	git reset --hard &&
+
+	echo content >test &&
+	test_config interactive.diffFilter "sed s/^/foo:/" &&
+	printf y | test_terminal git add -p >output 2>&1 &&
+
+	# avoid depending on the exact coloring or content of the prompts,
+	# and just make sure we saw our diff prefixed
+	grep foo:.*content output
+'
+
+test_expect_success TTY 'detect bogus diffFilter output' '
+	git reset --hard &&
+
+	echo content >test &&
+	test_config interactive.diffFilter "echo too-short" &&
+	printf y | test_must_fail test_terminal git add -p
+'
+
 test_expect_success 'patch-mode via -i prompts for files' '
 	git reset --hard &&