[PATCH 09/32] index: make narrow index incompatible with older git

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Index in narrow repos is not a full index and should not be used
to create commits without modification (to be explained later on).

Also save narrow prefix inside index and check against
$GIT_DIR/narrow, just in case.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 cache.h                |    1 +
 read-cache.c           |   35 +++++++++++++++++++++++++++++++----
 t/t6060-narrow-tree.sh |   28 ++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 4 deletions(-)
 create mode 100755 t/t6060-narrow-tree.sh

diff --git a/cache.h b/cache.h
index ff401ec..6bc80b3 100644
--- a/cache.h
+++ b/cache.h
@@ -293,6 +293,7 @@ struct index_state {
 	struct string_list *resolve_undo;
 	struct cache_tree *cache_tree;
 	struct cache_time timestamp;
+	char *narrow_prefix;
 	void *alloc;
 	unsigned name_hash_initialized : 1,
 		 initialized : 1;
diff --git a/read-cache.c b/read-cache.c
index 881dd93..20b619c 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -25,8 +25,9 @@ static struct cache_entry *refresh_cache_entry(struct cache_entry *ce, int reall
  */
 
 #define CACHE_EXT(s) ( (s[0]<<24)|(s[1]<<16)|(s[2]<<8)|(s[3]) )
-#define CACHE_EXT_TREE 0x54524545	/* "TREE" */
+#define CACHE_EXT_TREE 0x54524545	  /* "TREE" */
 #define CACHE_EXT_RESOLVE_UNDO 0x52455543 /* "REUC" */
+#define CACHE_EXT_NARROW 0x4e415257	  /* "NARW" */
 
 struct index_state the_index;
 
@@ -1168,7 +1169,9 @@ static int verify_hdr(struct cache_header *hdr, unsigned long size)
 
 	if (hdr->hdr_signature != htonl(CACHE_SIGNATURE))
 		return error("bad signature");
-	if (hdr->hdr_version != htonl(2) && hdr->hdr_version != htonl(3))
+	if (hdr->hdr_version != htonl(2) &&
+	    hdr->hdr_version != htonl(3) &&
+	    hdr->hdr_version != htonl(4))
 		return error("bad index version");
 	git_SHA1_Init(&c);
 	git_SHA1_Update(&c, hdr, size - 20);
@@ -1188,6 +1191,9 @@ static int read_index_extension(struct index_state *istate,
 	case CACHE_EXT_RESOLVE_UNDO:
 		istate->resolve_undo = resolve_undo_read(data, sz);
 		break;
+	case CACHE_EXT_NARROW:
+		istate->narrow_prefix = xstrdup(data);
+		break;
 	default:
 		if (*ext < 'A' || 'Z' < *ext)
 			return error("index uses %.4s extension, which we do not understand",
@@ -1352,6 +1358,16 @@ int read_index_from(struct index_state *istate, const char *path)
 		src_offset += extsize;
 	}
 	munmap(mmap, mmap_size);
+
+	if ((!get_narrow_prefix() && !istate->narrow_prefix) ||
+	    (get_narrow_prefix() && istate->narrow_prefix &&
+	     !strcmp(get_narrow_prefix(), istate->narrow_prefix)))
+		;		/* good */
+	else
+		die("Incompatible index and narrow mode (%s/%s)",
+		    get_narrow_prefix(),
+		    istate->narrow_prefix);
+
 	return istate->cache_nr;
 
 unmap:
@@ -1549,7 +1565,7 @@ int write_index(struct index_state *istate, int newfd)
 {
 	git_SHA_CTX c;
 	struct cache_header hdr;
-	int i, err, removed, extended;
+	int i, err, removed, extended, ver;
 	struct cache_entry **cache = istate->cache;
 	int entries = istate->cache_nr;
 	struct stat st;
@@ -1568,7 +1584,11 @@ int write_index(struct index_state *istate, int newfd)
 
 	hdr.hdr_signature = htonl(CACHE_SIGNATURE);
 	/* for extended format, increase version so older git won't try to read it */
-	hdr.hdr_version = htonl(extended ? 3 : 2);
+	ver = extended ? 3 : 2;
+	if (get_narrow_prefix() && ver < 4)
+		ver = 4;	/* narrow-unaware git should to touch this index */
+
+	hdr.hdr_version = htonl(ver);
 	hdr.hdr_entries = htonl(entries - removed);
 
 	git_SHA1_Init(&c);
@@ -1607,6 +1627,13 @@ int write_index(struct index_state *istate, int newfd)
 		if (err)
 			return -1;
 	}
+	if (get_narrow_prefix()) {
+		int len = strlen(get_narrow_prefix())+1;
+		err = write_index_ext_header(&c, newfd, CACHE_EXT_NARROW, len) < 0 ||
+			ce_write(&c, newfd, get_narrow_prefix(), len) < 0;
+		if (err)
+			return -1;
+	}
 
 	if (ce_flush(&c, newfd) || fstat(newfd, &st))
 		return -1;
diff --git a/t/t6060-narrow-tree.sh b/t/t6060-narrow-tree.sh
new file mode 100755
index 0000000..0e561c8
--- /dev/null
+++ b/t/t6060-narrow-tree.sh
@@ -0,0 +1,28 @@
+#!/bin/sh
+
+test_description='narrow-tree tests'
+
+. ./test-lib.sh
+
+test_expect_success setup '
+	: >test
+'
+
+test_expect_success 'index ver 4 in narrow mode' '
+	echo foo >.git/narrow &&
+	git update-index --add test &&
+	echo 4 >expected &&
+	test-index-version < .git/index >result &&
+	test_cmp expected result
+'
+
+test_expect_success 'index ver < 4 when narrow mode is gone' '
+	rm .git/narrow &&
+	rm .git/index &&
+	git update-index --add test &&
+	echo 2 >expected &&
+	test-index-version < .git/index >result &&
+	test_cmp expected result
+'
+
+test_done
-- 
1.7.1.rc1.69.g24c2f7