Objects received by git-receive-pack(1) are quarantined in a temporary
"incoming" directory and migrated into the object database prior to the
reference updates. The quarantine is currently managed through
`tmp_objdir` directly. In a pluggable ODB future, how exactly an object
gets written to a transaction may vary for a given ODB source. Refactor
git-receive-pack(1) to use the ODB transaction interfaces to manage the
object staging area in a more agnostic manner accordingly.
Note that the temporary directory created for git-receive-pack(1) is
eagerly created and uses a different prefix name. This behavior is
special cased in the "files" backend by having `odb_transaction_begin()`
callers that require this behavior provide an `ODB_TRANSACTION_RECEIVE`
flag.
Signed-off-by: Justin Tobler <jltobler@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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