[PATCH v4 1/2] t4013: improve diff-post-processor logic

[Đoàn Trần Công Danh <congdanhqx@xxxxxxxxx>]

From: "brian m. carlson" <sandals@xxxxxxxxxxxxxxxxxxxx>

>From 72f936b1 (t4013: make test hash independent, 2020-02-07),
we started to adjust metadata of git-diff's output in order to
ignore uninteresting metadata which is dependent of underlying hash
algorithm.

However, we forgot to special case all-zero object names, which is
special for not-exist objects, in consequence, we could't catch
possible future bugs where object names is all-zeros including but
not limiting to:
* show intend-to-add entry
* deleted entry
* diff between index and working tree with new file

In addition, in the incoming change, we would like to test for
diff with 10 characters index, which is also not covered by current
diff-processor logic.

Let's fix the bug for all-zero object names and extend object names'
abbrev to 16 while we're at it.

Based-on-patch-by: Junio C Hamano <gitster@xxxxxxxxx>
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
Signed-off-by: brian m. carlson <sandals@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Đoàn Trần Công Danh <congdanhqx@xxxxxxxxx>
---
 t/t4013-diff-various.sh | 60 ++++++++++++++++++++++++++---------------
 1 file changed, 39 insertions(+), 21 deletions(-)

diff --git a/t/t4013-diff-various.sh b/t/t4013-diff-various.sh
index 5f97dd6d65..f6bdfc13fd 100755
--- a/t/t4013-diff-various.sh
+++ b/t/t4013-diff-various.sh
@@ -130,27 +130,45 @@ test_expect_success setup '
 EOF
 
 process_diffs () {
-	_x04="[0-9a-f][0-9a-f][0-9a-f][0-9a-f]" &&
-	_x07="$_x05[0-9a-f][0-9a-f]" &&
-	sed -e "s/$OID_REGEX/$ZERO_OID/g" \
-	    -e "s/From $_x40 /From $ZERO_OID /" \
-	    -e "s/from $_x40)/from $ZERO_OID)/" \
-	    -e "s/commit $_x40\$/commit $ZERO_OID/" \
-	    -e "s/commit $_x40 (/commit $ZERO_OID (/" \
-	    -e "s/$_x40 $_x40 $_x40/$ZERO_OID $ZERO_OID $ZERO_OID/" \
-	    -e "s/$_x40 $_x40 /$ZERO_OID $ZERO_OID /" \
-	    -e "s/^$_x40 $_x40$/$ZERO_OID $ZERO_OID/" \
-	    -e "s/^$_x40 /$ZERO_OID /" \
-	    -e "s/^$_x40$/$ZERO_OID/" \
-	    -e "s/$_x07\.\.$_x07/fffffff..fffffff/g" \
-	    -e "s/$_x07,$_x07\.\.$_x07/fffffff,fffffff..fffffff/g" \
-	    -e "s/$_x07 $_x07 $_x07/fffffff fffffff fffffff/g" \
-	    -e "s/$_x07 $_x07 /fffffff fffffff /g" \
-	    -e "s/Merge: $_x07 $_x07/Merge: fffffff fffffff/g" \
-	    -e "s/$_x07\.\.\./fffffff.../g" \
-	    -e "s/ $_x04\.\.\./ ffff.../g" \
-	    -e "s/ $_x04/ ffff/g" \
-	    "$1"
+	perl -e '
+		my $oid_length = length($ARGV[0]);
+		my $x40 = "[0-9a-f]{40}";
+		my $xab = "[0-9a-f]{4,16}";
+		my $orx = "[0-9a-f]" x $oid_length;
+
+		sub munge_oid {
+			my ($oid) = @_;
+			my $x;
+
+			return "" unless length $oid;
+
+			if ($oid =~ /^(100644|100755|120000)$/) {
+				return $oid;
+			}
+
+			if ($oid =~ /^0*$/) {
+				$x = "0";
+			} else {
+				$x = "f";
+			}
+
+			if (length($oid) == 40) {
+				return $x x $oid_length;
+			} else {
+				return $x x length($oid);
+			}
+		}
+
+		while (<STDIN>) {
+			s/($orx)/munge_oid($1)/ge;
+			s/From ($x40)( |\))/"From " . munge_oid($1) . $2/ge;
+			s/commit ($x40)($| \(from )($x40?)/"commit " .  munge_oid($1) . $2 . munge_oid($3)/ge;
+			s/\b($x40)( |\.\.|$)/munge_oid($1) . $2/ge;
+			s/^($x40)($| )/munge_oid($1) . $2/e;
+			s/($xab)(\.\.|,| |\.\.\.|$)/munge_oid($1) . $2/ge;
+			print;
+		}
+	' "$ZERO_OID" <"$1"
 }
 
 V=$(git version | sed -e 's/^git version //' -e 's/\./\\./g')
-- 
2.28.0.143.g760df7782d.dirty