Documentation: move some AsciiDoc parameters into variables

Asciidoctor takes slightly different arguments from AsciiDoc in some
cases.  It has a different name for the HTML backend and the "docbook"
backend produces DocBook 5, not DocBook 4.5.  Also, Asciidoctor does not
accept the -f option.  Move these values into variables so that they can
be overridden by users wishing to use Asciidoctor instead of Asciidoc.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Documentation: implement linkgit macro for Asciidoctor

AsciiDoc uses a configuration file to implement macros like linkgit,
while Asciidoctor uses Ruby extensions.  Implement a Ruby extension that
implements the linkgit macro for Asciidoctor in the same way that
asciidoc.conf does for AsciiDoc.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
foreach_alt_odb: propagate return value from callback

We check the return value of the callback and stop iterating
if it is non-zero. However, we do not make the non-zero
return value available to the caller, so they have no way of
knowing whether the operation succeeded or not (technically
they can keep their own error flag in the callback data, but
that is unlike our other for_each functions).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
isxdigit: cast input to unsigned char

Otherwise, callers must do so or risk triggering warnings
-Wchar-subscript (and rightfully so; a signed char might
cause us to use a bogus negative index into the
hexval_table).

While we are dropping the now-unnecessary casts from the
caller in urlmatch.c, we can get rid of similar casts in
actually parsing the hex by using the hexval() helper, which
implicitly casts to unsigned (but note that we cannot
implement isxdigit in terms of hexval(), as it also casts
its return value to unsigned).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
object_array: factor out slopbuf-freeing logic

This is not a lot of code, but it's a logical construct that
should not need to be repeated (and we are about to add a
third repetition).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
object_array: add a "clear" function

There's currently no easy way to free the memory associated
with an object_array (and in most cases, we simply leak the
memory in a rev_info's pending array). Let's provide a
helper to make this easier to handle.

We can make use of it in list-objects.c, which does the same
thing by hand (but fails to free the "name" field of each
entry, potentially leaking memory).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
clean up name allocation in prepare_revision_walk

When we enter prepare_revision_walk, we have zero or more
entries in our "pending" array. We disconnect that array
from the rev_info, and then process each entry:

  1. If the entry is a commit and the --source option is in
     effect, we keep a pointer to the object name.

  2. Otherwise, we re-add the item to the pending list with
     a blank name.

We then throw away the old array by freeing the array
itself, but do not touch the "name" field of each entry. For
any items of type (2), we leak the memory associated with
the name. This commit fixes that by calling object_array_clear,
which handles the cleanup for us.

That breaks (1), though, because it depends on the memory
pointed to by the name to last forever. We can solve that by
making a copy of the name. This is slightly less efficient,
but it shouldn't matter in practice, as we do it only for
the tip commits of the traversal.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
reachable: use traverse_commit_list instead of custom walk

To find the set of reachable objects, we add a bunch of
possible sources to our rev_info, call prepare_revision_walk,
and then launch into a custom walker that handles each
object top. This is a subset of what traverse_commit_list
does, so we can just reuse that code (it can also handle
more complex cases like UNINTERESTING commits and pathspecs,
but we don't use those features).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
reachable: reuse revision.c "add all reflogs" code

We want to add all reflog entries as tips for finding
reachable objects. The revision machinery can already do
this (to support "rev-list --reflog"); we can reuse that
code.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
prune: factor out loose-object directory traversal

Prune has to walk $GIT_DIR/objects/?? in order to find the
set of loose objects to prune. Other parts of the code
(e.g., count-objects) want to do the same. Let's factor it
out into a reusable for_each-style function.

Note that this is not quite a straight code movement. The
original code had strange behavior when it found a file of
the form "[0-9a-f]{2}/.{38}" that did _not_ contain all hex
digits. It executed a "break" from the loop, meaning that we
stopped pruning in that directory (but still pruned other
directories!). This was probably a bug; we do not want to
process the file as an object, but we should keep going
otherwise (and that is how the new code handles it).

We are also a little more careful with loose object
directories which fail to open. The original code silently
ignored any failures, but the new code will complain about
any problems besides ENOENT.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
reachable: mark index blobs as SEEN

When we mark all reachable objects for pruning, that
includes blobs mentioned by the index. However, we do not
mark these with the SEEN flag, as we do for objects that we
find by traversing (we also do not add them to the pending
list, but that is because there is nothing further to
traverse with them).

This doesn't cause any problems with prune, because it
checks only that the object exists in the global object
hash, and not its flags. However, let's mark these objects
to be consistent and avoid any later surprises.

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

This saves us from manually traversing the directory
structure ourselves.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
count-objects: do not use xsize_t when counting object size

The point of xsize_t is to safely cast an off_t into a size_t
(because we are about to mmap). But in count-objects, we are
summing the sizes in an off_t. Using xsize_t means that
count-objects could fail on a 32-bit system with a 4G
object (not likely, as other parts of git would fail, but
we should at least be correct here).

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

This drops our line count considerably, and should make
things more readable by keeping the counting logic separate
from the traversal.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
sha1_file: add for_each iterators for loose and packed objects

We typically iterate over the reachable objects in a
repository by starting at the tips and walking the graph.
There's no easy way to iterate over all of the objects,
including unreachable ones. Let's provide a way of doing so.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
prune: keep objects reachable from recent objects

Our current strategy with prune is that an object falls into
one of three categories:

  1. Reachable (from ref tips, reflogs, index, etc).

  2. Not reachable, but recent (based on the --expire time).

  3. Not reachable and not recent.

We keep objects from (1) and (2), but prune objects in (3).
The point of (2) is that these objects may be part of an
in-progress operation that has not yet updated any refs.

However, it is not always the case that objects for an
in-progress operation will have a recent mtime. For example,
the object database may have an old copy of a blob (from an
abandoned operation, a branch that was deleted, etc). If we
create a new tree that points to it, a simultaneous prune
will leave our tree, but delete the blob. Referencing that
tree with a commit will then work (we check that the tree is
in the object database, but not that all of its referred
objects are), as will mentioning the commit in a ref. But
the resulting repo is corrupt; we are missing the blob
reachable from a ref.

One way to solve this is to be more thorough when
referencing a sha1: make sure that not only do we have that
sha1, but that we have objects it refers to, and so forth
recursively. The problem is that this is very expensive.
Creating a parent link would require traversing the entire
object graph!

Instead, this patch pushes the extra work onto prune, which
runs less frequently (and has to look at the whole object
graph anyway). It creates a new category of objects: objects
which are not recent, but which are reachable from a recent
object. We do not prune these objects, just like the
reachable and recent ones.

This lets us avoid the recursive check above, because if we
have an object, even if it is unreachable, we should have
its referent. We can make a simple inductive argument that
with this patch, this property holds (that there are no
objects with missing referents in the repository):

  0. When we have no objects, we have nothing to refer or be
     referred to, so the property holds.

  1. If we add objects to the repository, their direct
     referents must generally exist (e.g., if you create a
     tree, the blobs it references must exist; if you create
     a commit to point at the tree, the tree must exist).
     This is already the case before this patch. And it is
     not 100% foolproof (you can make bogus objects using
     `git hash-object`, for example), but it should be the
     case for normal usage.

     Therefore for any sequence of object additions, the
     property will continue to hold.

  2. If we remove objects from the repository, then we will
     not remove a child object (like a blob) if an object
     that refers to it is being kept. That is the part
     implemented by this patch.

     Note, however, that our reachability check and the
     actual pruning are not atomic. So it _is_ still
     possible to violate the property (e.g., an object
     becomes referenced just as we are deleting it). This
     patch is shooting for eliminating problems where the
     mtimes of dependent objects differ by hours or days,
     and one is dropped without the other. It does nothing
     to help with short races.

Naively, the simplest way to implement this would be to add
all recent objects as tips to the reachability traversal.
However, this does not perform well. In a recently-packed
repository, all reachable objects will also be recent, and
therefore we have to look at each object twice. This patch
instead performs the reachability traversal, then follows up
with a second traversal for recent objects, skipping any
that have already been marked.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
pack-objects: refactor unpack-unreachable expiration check

When we are loosening unreachable packed objects, we do not
bother to process objects that would simply be pruned
immediately anyway. The "would be pruned" check is a simple
comparison, but is about to get more complicated. Let's pull
it out into a separate function.

Note that this is slightly less efficient than the original,
which avoided even opening old packs, since no object in
them could pass the current check, which cares only about
the pack mtime.  But the new rules will depend on the exact
object, so we need to perform the check even for old packs.

Note also that we fix a minor buglet when the pack mtime is
exactly the same as the expiration time. The prune code
considers that worth pruning, whereas our check here
considered it worth keeping. This wasn't a big deal. Besides
being unlikely to happen, the result was simply that the
object was loosened and then pruned, missing the
optimization. Still, we can easily fix it while we are here.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
pack-objects: match prune logic for discarding objects

A recent commit taught git-prune to keep non-recent objects
that are reachable from recent ones. However, pack-objects,
when loosening unreachable objects, tries to optimize out
the write in the case that the object will be immediately
pruned. It now gets this wrong, since its rule does not
reflect the new prune code (and this can be seen by running
t6501 with a strategically placed repack).

Let's teach pack-objects similar logic.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
write_sha1_file: freshen existing objects

When we try to write a loose object file, we first check
whether that object already exists. If so, we skip the
write as an optimization. However, this can interfere with
prune's strategy of using mtimes to mark files in progress.

For example, if a branch contains a particular tree object
and is deleted, that tree object may become unreachable, and
have an old mtime. If a new operation then tries to write
the same tree, this ends up as a noop; we notice we
already have the object and do nothing. A prune running
simultaneously with this operation will see the object as
old, and may delete it.

We can solve this by "freshening" objects that we avoid
writing by updating their mtime. The algorithm for doing so
is essentially the same as that of has_sha1_file. Therefore
we provide a new (static) interface "check_and_freshen",
which finds and optionally freshens the object. It's trivial
to implement freshening and simple checking by tweaking a
single parameter.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
make add_object_array_with_context interface more sane

When you resolve a sha1, you can optionally keep any context
found during the resolution, including the path and mode of
a tree entry (e.g., when looking up "HEAD:subdir/file.c").

The add_object_array_with_context function lets you then
attach that context to an entry in a list. Unfortunately,
the interface for doing so is horrible. The object_context
structure is large and most object_array users do not use
it. Therefore we keep a pointer to the structure to avoid
burdening other users too much. But that means when we do
use it that we must allocate the struct ourselves. And the
struct contains a fixed PATH_MAX-sized buffer, which makes
this wholly unsuitable for any large arrays.

We can observe that there is only a single user of the
"with_context" variant: builtin/grep.c. And in that use
case, the only element we care about is the path. We can
therefore store only the path as a pointer (the context's
mode field was redundant with the object_array_entry itself,
and nobody actually cared about the surrounding tree). This
still requires a strdup of the pathname, but at least we are
only consuming the minimum amount of memory for each string.

We can also handle the copying ourselves in
add_object_array_*, and free it as appropriate in
object_array_release_entry.

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