sha1_file: fix error message for alternate objects

When we fail to open a corrupt loose object, we report an
error and mention the filename via sha1_file_name().
However, that function will always give us a path in the
local repository, whereas the corrupt object may have come
from an alternate. The result is a very misleading error
message.

Teach the open_sha1_file() and stat_sha1_file() helpers to
pass back the path they found, so that we can report it
correctly.

Note that the pointers we return go to static storage (e.g.,
from sha1_file_name()), which is slightly dangerous.
However, these helpers are static local helpers, and the
names are used for immediately generating error messages.
The simplicity is an acceptable tradeoff for the danger.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/sha1_file.c b/sha1_file.c
index 9c86d1924a23e4c81369f34ec8e1058c2dd15c1f..6c8e4b43dd1eadc4d7ec213d6673d6ceebbcf5d5 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1613,39 +1613,54 @@ int git_open(const char *name)
        }
 }
 
-static int stat_sha1_file(const unsigned char *sha1, struct stat *st)
+/*
+ * Find "sha1" as a loose object in the local repository or in an alternate.
+ * Returns 0 on success, negative on failure.
+ *
+ * The "path" out-parameter will give the path of the object we found (if any).
+ * Note that it may point to static storage and is only valid until another
+ * call to sha1_file_name(), etc.
+ */
+static int stat_sha1_file(const unsigned char *sha1, struct stat *st,
+                         const char **path)
 {
        struct alternate_object_database *alt;
 
-       if (!lstat(sha1_file_name(sha1), st))
+       *path = sha1_file_name(sha1);
+       if (!lstat(*path, st))
                return 0;
 
        prepare_alt_odb();
        errno = ENOENT;
        for (alt = alt_odb_list; alt; alt = alt->next) {
-               const char *path = alt_sha1_path(alt, sha1);
-               if (!lstat(path, st))
+               *path = alt_sha1_path(alt, sha1);
+               if (!lstat(*path, st))
                        return 0;
        }
 
        return -1;
 }
 
-static int open_sha1_file(const unsigned char *sha1)
+/*
+ * Like stat_sha1_file(), but actually open the object and return the
+ * descriptor. See the caveats on the "path" parameter above.
+ */
+static int open_sha1_file(const unsigned char *sha1, const char **path)
 {
        int fd;
        struct alternate_object_database *alt;
        int most_interesting_errno;
 
-       fd = git_open(sha1_file_name(sha1));
+       *path = sha1_file_name(sha1);
+       fd = git_open(*path);
        if (fd >= 0)
                return fd;
        most_interesting_errno = errno;
 
        prepare_alt_odb();
        for (alt = alt_odb_list; alt; alt = alt->next) {
-               const char *path = alt_sha1_path(alt, sha1);
-               fd = git_open(path);
+               *path = alt_sha1_path(alt, sha1);
+               fd = git_open(*path);
                if (fd >= 0)
                        return fd;
                if (most_interesting_errno == ENOENT)
@@ -1657,10 +1672,11 @@ static int open_sha1_file(const unsigned char *sha1)
 
 void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
 {
+       const char *path;
        void *map;
        int fd;
 
-       fd = open_sha1_file(sha1);
+       fd = open_sha1_file(sha1, &path);
        map = NULL;
        if (fd >= 0) {
                struct stat st;
@@ -1669,7 +1685,7 @@ void *map_sha1_file(const unsigned char *sha1, unsigned long *size)
                        *size = xsize_t(st.st_size);
                        if (!*size) {
                                /* mmap() is forbidden on empty files */
-                               error("object file %s is empty", sha1_file_name(sha1));
+                               error("object file %s is empty", path);
                                return NULL;
                        }
                        map = xmmap(NULL, *size, PROT_READ, MAP_PRIVATE, fd, 0);
@@ -2789,8 +2805,9 @@ static int sha1_loose_object_info(const unsigned char *sha1,
         * object even exists.
         */
        if (!oi->typep && !oi->typename && !oi->sizep) {
+               const char *path;
                struct stat st;
-               if (stat_sha1_file(sha1, &st) < 0)
+               if (stat_sha1_file(sha1, &st, &path) < 0)
                        return -1;
                if (oi->disk_sizep)
                        *oi->disk_sizep = st.st_size;
@@ -2986,6 +3003,8 @@ void *read_sha1_file_extended(const unsigned char *sha1,
 {
        void *data;
        const struct packed_git *p;
+       const char *path;
+       struct stat st;
        const unsigned char *repl = lookup_replace_object_extended(sha1, flag);
 
        errno = 0;
@@ -3001,12 +3020,9 @@ void *read_sha1_file_extended(const unsigned char *sha1,
                die("replacement %s not found for %s",
                    sha1_to_hex(repl), sha1_to_hex(sha1));
 
-       if (has_loose_object(repl)) {
-               const char *path = sha1_file_name(sha1);
-
+       if (!stat_sha1_file(repl, &st, &path))
                die("loose object %s (stored in %s) is corrupt",
                    sha1_to_hex(repl), path);
-       }
 
        if ((p = has_packed_and_bad(repl)) != NULL)
                die("packed object %s (stored in %s) is corrupt",

diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 3297d4cb2f8a9750bb49d660a150713170c5486f..f95174c9d86c972118a964efcf7b68f735c2605d 100755 (executable)
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -550,4 +550,14 @@ test_expect_success 'fsck --name-objects' '
        )
 '
 
+test_expect_success 'alternate objects are correctly blamed' '
+       test_when_finished "rm -rf alt.git .git/objects/info/alternates" &&
+       git init --bare alt.git &&
+       echo "../../alt.git/objects" >.git/objects/info/alternates &&
+       mkdir alt.git/objects/12 &&
+       >alt.git/objects/12/34567890123456789012345678901234567890 &&
+       test_must_fail git fsck >out 2>&1 &&
+       grep alt.git out
+'
+
 test_done