Merge branch 'jk/unpack-entry-fallback-to-another'

* jk/unpack-entry-fallback-to-another:
  unpack_entry: do not die when we fail to apply a delta
  t5303: drop "count=1" from corruption dd

sha1_file.c

@@ -2145,8 +2145,17 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
 		data = patch_delta(base, base_size,
 				   delta_data, delta_size,
 				   &size);
+
+		/*
+		 * We could not apply the delta; warn the user, but keep going.
+		 * Our failure will be noticed either in the next iteration of
+		 * the loop, or if this is the final delta, in the caller when
+		 * we return NULL. Those code paths will take care of making
+		 * a more explicit warning and retrying with another copy of
+		 * the object.
+		 */
 		if (!data)
-			die("failed to apply delta");
+			error("failed to apply delta");
 
 		free(delta_data);
 	}

t/t5303-pack-corruption-resilience.sh

@@ -51,7 +51,7 @@ do_corrupt_object() {
     ofs=`git show-index < ${pack}.idx | grep $1 | cut -f1 -d" "` &&
     ofs=$(($ofs + $2)) &&
     chmod +w ${pack}.pack &&
-    dd of=${pack}.pack count=1 bs=1 conv=notrunc seek=$ofs &&
+    dd of=${pack}.pack bs=1 conv=notrunc seek=$ofs &&
     test_must_fail git verify-pack ${pack}.pack
 }
 
@@ -275,6 +275,33 @@ test_expect_success \
      git cat-file blob $blob_2 > /dev/null &&
      git cat-file blob $blob_3 > /dev/null'
 
+test_expect_success \
+    'corruption of delta base reference pointing to wrong object' \
+    'create_new_pack --delta-base-offset &&
+     git prune-packed &&
+     printf "\220\033" | do_corrupt_object $blob_3 2 &&
+     git cat-file blob $blob_1 >/dev/null &&
+     git cat-file blob $blob_2 >/dev/null &&
+     test_must_fail git cat-file blob $blob_3 >/dev/null'
+
+test_expect_success \
+    '... but having a loose copy allows for full recovery' \
+    'mv ${pack}.idx tmp &&
+     git hash-object -t blob -w file_3 &&
+     mv tmp ${pack}.idx &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
+test_expect_success \
+    '... and then a repack "clears" the corruption' \
+    'do_repack --delta-base-offset --no-reuse-delta &&
+     git prune-packed &&
+     git verify-pack ${pack}.pack &&
+     git cat-file blob $blob_1 > /dev/null &&
+     git cat-file blob $blob_2 > /dev/null &&
+     git cat-file blob $blob_3 > /dev/null'
+
 test_expect_success \
     'corrupting header to have too small output buffer fails unpack' \
     'create_new_pack &&