cache_name_compare(): do not truncate while comparing paths

We failed to use ce_namelen() equivalent and instead only compared
up to the CE_NAMEMASK bytes by mistake.  Adding an overlong path
that shares the same common prefix as an existing entry in the index
did not add a new entry, but instead replaced the existing one, as
the result.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

read-cache.c

@@ -405,10 +405,15 @@ int df_name_compare(const char *name1, int len1, int mode1,
 
 int cache_name_compare(const char *name1, int flags1, const char *name2, int flags2)
 {
-	int len1 = flags1 & CE_NAMEMASK;
-	int len2 = flags2 & CE_NAMEMASK;
-	int len = len1 < len2 ? len1 : len2;
-	int cmp;
+	int len1, len2, len, cmp;
+
+	len1 = flags1 & CE_NAMEMASK;
+	if (CE_NAMEMASK <= len1)
+		len1 = strlen(name1 + CE_NAMEMASK) + CE_NAMEMASK;
+	len2 = flags2 & CE_NAMEMASK;
+	if (CE_NAMEMASK <= len2)
+		len2 = strlen(name2 + CE_NAMEMASK) + CE_NAMEMASK;
+	len = len1 < len2 ? len1 : len2;
 
 	cmp = memcmp(name1, name2, len);
 	if (cmp)

t/t3006-ls-files-long.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+test_description='overly long paths'
+. ./test-lib.sh
+
+test_expect_success setup '
+	p=filefilefilefilefilefilefilefile &&
+	p=$p$p$p$p$p$p$p$p$p$p$p$p$p$p$p$p &&
+	p=$p$p$p$p$p$p$p$p$p$p$p$p$p$p$p$p &&
+
+	path_a=${p}_a &&
+	path_z=${p}_z &&
+
+	blob_a=$(echo frotz | git hash-object -w --stdin) &&
+	blob_z=$(echo nitfol | git hash-object -w --stdin) &&
+
+	pat="100644 %s 0\t%s\n"
+'
+
+test_expect_success 'overly-long path by itself is not a problem' '
+	printf "$pat" "$blob_a" "$path_a" |
+	git update-index --add --index-info &&
+	echo "$path_a" >expect &&
+	git ls-files >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'overly-long path does not replace another by mistake' '
+	printf "$pat" "$blob_a" "$path_a" "$blob_z" "$path_z" |
+	git update-index --add --index-info &&
+	(
+		echo "$path_a"
+		echo "$path_z"
+	) >expect &&
+	git ls-files >actual &&
+	test_cmp expect actual
+'
+
+test_done