replace: add --graft option

The usage string for this option is:

git replace [-f] --graft <commit> [<parent>...]

First we create a new commit that is the same as <commit>
except that its parents are [<parents>...]

Then we create a replace ref that replace <commit> with
the commit we just created.

With this new option, it should be straightforward to
convert grafts to replace refs.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
replace: add test for --graft

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Documentation: replace: add --graft option

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
contrib: add convert-grafts-to-replace-refs.sh

This patch adds into contrib/ an example script to convert
grafts from an existing grafts file into replace refs using
the new --graft option of "git replace".

While at it let's mention this new script in the
"git replace" documentation for the --graft option.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
DONTMERGE: wise to wait for peff's commit->buffer length series
alloc: include any-object allocations in alloc_report

When 2c1cbec (Use proper object allocators for unknown
object nodes too, 2007-04-16), added a special "any_object"
allocator, it never taught alloc_report to report on it. To
do so we need to add an extra type argument to the REPORT
macro, as that commit did for DEFINE_ALLOCATOR.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
commit: push commit_index update into alloc_commit_node

Whenever we create a commit object via lookup_commit, we
give it a unique index to be used with the commit-slab API.
The theory is that any "struct commit" we create would
follow this code path, so any such struct would get an
index. However, callers could use alloc_commit_node()
directly (and get multiple commits with index 0).

Let's push the indexing into alloc_commit_node so that it's
hard for callers to get it wrong.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
do not create "struct commit" with xcalloc

In both blame and merge-recursive, we sometimes create a
"fake" commit struct for convenience (e.g., to represent the
HEAD state as if we would commit it). By allocating
ourselves rather than using alloc_commit_node, we do not
properly set the "index" field of the commit. This can
produce subtle bugs if we then use commit-slab on the
resulting commit, as we will share the "0" index with
another commit.

We can fix this by using alloc_commit_node() to allocate.
Note that we cannot free the result, as it is part of our
commit allocator. However, both cases were already leaking
the allocated commit anyway, so there's nothing to fix up.

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

The return value from logmsg_reencode may be either a newly
allocated buffer or a pointer to the existing commit->buffer.
We would not want the caller to accidentally free() or
modify the latter, so let's mark it as const.  We can cast
away the constness in logmsg_free, but only once we have
determined that it is a free-able buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
sequencer: use logmsg_reencode in get_message

This simplifies the code, as logmsg_reencode handles the
reencoding for us in a single call. It also means we learn
logmsg_reencode's trick of pulling the buffer from disk when
commit->buffer is NULL (we currently just silently return!).
It is doubtful this matters in practice, though, as
sequencer operations would not generally turn off
save_commit_buffer.

Note that we may be fixing a bug here. The existing code
does:

  if (same_encoding(to, from))
	  reencode_string(buf, to, from);

That probably should have been "!same_encoding".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
provide a helper to free commit buffer

This converts two lines into one at each caller. But more
importantly, it abstracts the concept of freeing the buffer,
which will make it easier to change later.

Note that we also need to provide a "detach" mechanism for
the weird case in fsck which passes the buffer back to be
freed.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
provide a helper to set the commit buffer

Right now this is just a one-liner, but abstracting it will
make it easier to change later.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
provide helpers to access the commit buffer

Many sites look at commit->buffer to get more detailed
information than what is in the parsed commit struct.
However, we sometimes drop commit->buffer to save memory,
in which case the caller would need to read the object
afresh. Some callers do this (leading to duplicated code),
and others do not (which opens the possibility of a segfault
if somebody else frees the buffer).

Let's provide a pair of helpers, "get" and "unuse", that let
callers easily get the buffer. They will use the cached
buffer when possible, and otherwise load from disk using
read_sha1_file.

Note that we also need to add a "get_cached" variant which
returns NULL when we do not have a cached buffer. At first
glance this seems to defeat the purpose of "get", which is
to always provide a return value. However, some log code
paths actually use the NULL-ness of commit->buffer as a
boolean flag to decide whether to try to printing the
commit. At least for now, we want to continue supporting
that use.

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

Some call sites check commit->buffer to see whether we have
a cached buffer, and if so, do some work with it. In the
long run we may want to switch these code paths to make
their decision on a different boolean flag (because checking
the cache may get a little more expensive in the future).
But for now, we can easily support them by converting the
calls to use get_cached_commit_buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
use get_commit_buffer to avoid duplicate code

For both of these sites, we already do the "fallback to
read_sha1_file" trick. But we can shorten the code by just
using get_commit_buffer.

Note that the error cases are slightly different when
read_sha1_file fails. get_commit_buffer will die() if the
object cannot be loaded, or is a non-commit.

For get_sha1_oneline, this will almost certainly never
happen, as we will have just called parse_object (and if it
does, it's probably worth complaining about).

For record_author_date, the new behavior is probably better;
we notify the user of the error instead of silently ignoring
it. And because it's used only for sorting by author-date,
somebody examining a corrupt can fallback to the regular
traversal order.

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

Like the callsites in the previous commit, logmsg_reencode
already falls back to read_sha1_file when necessary.
However, I split its conversion out into its own commit
because it's a bit more complex.

We return either:

  1. The original commit->buffer

  2. A newly allocated buffer from read_sha1_file

  3. A reencoded buffer (based on either 1 or 2 above).

while trying to do as few extra reads/allocations as
possible. Callers currently free the result with
logmsg_free, but we can simplify this by pointing them
straight to unuse_commit_buffer. This is a slight layering
violation, in that we may be passing a buffer from (3).
However, since the end result is to free() anything except
(1), a behavior which is unlikely to change, and because
this makes the interface much simpler, it's a reasonable
bending of the rules.

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

Each of these sites assumes that commit->buffer is valid.
Since they would segfault if this was not the case, they are
likely to be correct in practice. However, we can
future-proof them by using get_commit_buffer.

And as a side effect, we abstract away the final bare uses
of commit->buffer.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
commit-slab: provide a static initializer

Callers currently must use init_foo_slab() at runtime before
accessing a slab. For global slabs, it's much nicer if we
can initialize them in BSS, so that each user does not have
to add code to check-and-initialize.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
commit: convert commit->buffer to a slab

This will make it easier to manage the buffer cache
independently of the "struct commit" objects. It also
shrinks "struct commit" by one pointer, which may be
helpful.

Unfortunately it does not reduce the max memory size of
something like "rev-list", because rev-list uses
get_cached_commit_buffer() to decide not to show each
commit's output (and due to the design of slab_at, accessing
the slab requires us to extend it, allocating exactly the
same number of buffer pointers we dropped from the commit
structs).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
commit: record buffer length in cache

Most callsites which use the commit buffer try to use the
cached version attached to the commit, rather than
re-reading from disk. Unfortunately, that interface provides
only a pointer to the NUL-terminated buffer, with no
indication of the original length.

For the most part, this doesn't matter. People do not put
NULs in their commit messages, and the log code is happy to
treat it all as a NUL-terminated string. However, some code
paths do care. For example, when checking signatures, we
want to be very careful that we verify all the bytes to
avoid malicious trickery.

This patch just adds an optional "size" out-pointer to
get_commit_buffer and friends. The existing callers all pass
NULL (there did not seem to be any obvious sites where we
could avoid an immediate strlen() call, though perhaps with
some further refactoring we could).

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