Previously, there was no protection against a caller invoking an
operation on an old database version that would effectively corrupt
the database by treating it like a newer version.
According to notmuch.h, any caller that opens the database in
read/write mode is supposed to check if the database needs upgrading
and perform an upgrade if it does. This would protect against this,
but nobody (even the CLI) actually does this.
However, with features, it's easy to protect against incompatible
operations on a fine-grained basis. This lightweight change allows
callers to safely operate on old database versions, while preventing
specific operations that would corrupt the database with an
informative error message.
Previously, some parts of upgrade didn't report progress and for
others it was possible for the progress meter to restart at 0 part way
through the upgrade because each stage was reported separately.
Fix this by computing the total amount of work that needs to be done
up-front and updating completed work monotonically.
Rather than potentially making multiple passes over the same type of
data in the database, reorganize upgrade around each type of data that
may be upgraded. This eliminates code duplication, will make
multi-version upgrades faster, and will let us improve progress
reporting.
Previously, we had database version information hard-coded in the
upgrade code. Slightly re-organize the upgrade process around the set
of new database features to be enabled by the upgrade.
Previously, the upgrade was organized as two passes -- an upgrade
pass, and a separate cleanup pass -- so the database was always in a
valid state. This change substantially simplifies this code by
performing the upgrade in a transaction and combining both passes in
to one. This 1) eliminates a lot of duplicate code between the
passes, 2) speeds up the upgrade process, 3) makes progress reporting
more accurate, 4) eliminates the potential for stale data if the
upgrade is interrupted during the cleanup pass, and 5) makes it easier
to reason about the safety of the upgrade code.
Previously, our database schema was versioned by a single number.
Each database schema change had to occur "atomically" in Notmuch's
development history: before some commit, Notmuch used version N, after
that commit, it used version N+1. Hence, each new schema version
could introduce only one change, the task of developing a schema
change fell on a single person, and it all had to happen and be
perfect in a single commit series. This made introducing a new schema
version hard. We've seen only two schema changes in the history of
Notmuch.
This commit introduces database schema version 3; hopefully the last
schema version we'll need for a while. With this version, we switch
from a single version number to "features": a set of named,
independent aspects of the database schema.
Features should make backwards compatibility easier. For many things,
it should be easy to support databases both with and without a
feature, which will allow us to make upgrades optional and will enable
"unstable" features that can be developed and tested over time.
Features also make forwards compatibility easier. The features
recorded in a database include "compatibility flags," which can
indicate to an older version of Notmuch when it must support a given
feature to open the database for read or for write. This lets us
replace the old vague "I don't recognize this version, so something
might go wrong, but I promise to try my best" warnings upon opening a
database with an unknown version with precise errors. If a database
is safe to open for read/write despite unknown features, an older
version will know that and issue no message at all. If the database
is not safe to open for read/write because of unknown features, an
older version will know that, too, and can tell the user exactly which
required features it lacks support for.
According to RFC2822 References and In-Reply-To headers are supposed
to contain one or more Message-IDs, however older RFC822 allowed
almost any content. When both References and In-Reply-To headers ends
with something else that a Message-ID (see e.g. [1]), the thread
structure presented by notmuch is incorrect. The reason is that
notmuch treats this case as if the email contained no "replyto"
information (see _notmuch_database_link_message_to_parents).
This patch changes the parse_references() function to return the last
valid Message-ID encountered rather than NULL resulting from the last
hunk of text not being the Message-ID.
[1] https://lkml.org/lkml/headers/2014/5/19/864
As noted in devel/STYLE, every private library function should start
with _notmuch. This patch corrects function naming that did not adhere
to this style in lib/notmuch-private.h. In particular, the old function
names that now begin with _notmuch are
notmuch_sha1_of_file
notmuch_sha1_of_string
notmuch_message_file_close
notmuch_message_file_get_header
notmuch_message_file_open
notmuch_message_get_author
notmuch_message_set_author
Signed-off-by: Charles Celerier <cceleri@cs.stanford.edu>
notmuch_database_close may fail in Xapian ->flush() or ->close(), so
report the status. Similarly for notmuch_database_destroy which calls
close.
This is required for notmuch insert to report error status if message
indexing failed.
The notmuch library includes a full blown message header parser. Yet
the same message headers are parsed by gmime during indexing. Switch
to gmime parsing completely.
These are the main changes:
* Gmime stops header parsing at the first invalid header, and presumes
the message body starts from there. The current parser is quite
liberal in accepting broken headers. The change means we will be
much pickier about accepting invalid messages.
* The current parser converts tabs used in header folding to
spaces. Gmime preserve the tabs. Due to a broken python library used
in mailman, there are plenty of mailing lists that produce headers
with tabs in header folding, and we'll see plenty of tabs. (This
change has been mitigated in preparatory patches.)
* For pure header parsing, the current parser is likely faster than
gmime, which parses the whole message rather than just the
headers. Since we parse the message and its headers using gmime for
indexing anyway, this avoids and extra header parsing round when
adding new messages. In case of duplicate messages, we'll end up
parsing the full message although just headers would be
sufficient. All in all this should still speed up 'notmuch new'.
* Calls to notmuch_message_get_header() may be slightly slower than
previously for headers that are not indexed in the database, due to
parsing of the whole message. Within the notmuch code base, notmuch
reply is the only such user.
In xapian terms, convert folder: prefix from probabilistic to boolean
prefix, matching the paths, relative from the maildir root, of the
message files, ignoring the maildir new and cur leaf directories.
folder:foo matches all message files in foo, foo/new, and foo/cur.
folder:foo/new does *not* match message files in foo/new.
folder:"" matches all message files in the top level maildir and its
new and cur subdirectories.
This change constitutes a database change: bump the database version
and add database upgrade support for folder: terms. The upgrade also
adds path: terms.
Finally, fix the folder search test for literal folder: search, as
some of the folder: matching capabilities are lost in the
probabilistic to boolean prefix change.
The path: prefix is a literal boolean prefix matching the paths,
relative from the maildir root, of the message files.
path:foo matches all message files in foo (but not in foo/new or
foo/cur).
path:foo/new matches all message files in foo/new.
path:"" matches all message files in the top level maildir.
path:foo/** matches all message files in foo and recursively in all
subdirectories of foo.
path:** matches all message files recursively, i.e. all messages.
In case previous notmuch compact has been interrupted there is old
work-in-progress database compact directory partially filled. Remove
it just before starting to fill the directory with new files.
It is less error prone and window of failure opportunity is smaller
if the old (backup) database is always renamed (instead of sometimes
rmtree'd) before new (compacted) database is put into its place.
Finally rmtree() old database in case old database backup is not kept.
catch Xapian::Error in compact code in lib/database.cc to be consistent
with other code in addition to not making software crash on uncaught
other Xapian error.
The extra path component added by the lib is a magic value that the
caller just has to know. This is demonstrated by the current code,
which indeed has "xapian.old" both sides of the interface. Use the
backup path provided by the lib caller verbatim, without adding
anything to it.
This function uses Xapian's Compactor machinery to compact the notmuch
database. The compacted database is built in a temporary directory and
later moved into place while the original uncompacted database is
preserved.
Signed-off-by: Ben Gamari <bgamari.foss@gmail.com>
As explained by Jeffrey Stedfast, the author of GMime, quoted in [1]:
> Passing the GMIME_ENABLE_RFC2047_WORKAROUNDS flag to g_mime_init()
> *should* solve the decoding problem mentioned in the thread. This
> flag should be safe to pass into g_mime_init() without any bad side
> effects and my unit tests do test that code-path.
The thread being referred to is [2].
[1] id:87bo56viyo.fsf@nikula.org
[2] id:08cb1dcd-c5db-4e33-8b09-7730cb3d59a2@gmail.com
Presently, the code which finds the parent of a message as it is being
added to the database assumes that the first Message-ID-like substring
of the In-Reply-To header is the parent Message ID. Some mail clients,
however, put stuff other than the Message-ID of the parent in the
In-Reply-To header, such as the email address of the sender of the
parent. This can fool notmuch.
The updated algorithm prefers the last Message ID in the References
header. The References header lists messages oldest-first, so the last
Message ID is the parent (RFC2822, p. 24). The References header is
also less likely to be in a non-standard
syntax (http://cr.yp.to/immhf/thread.html,
http://www.jwz.org/doc/threading.html). In case the References header
is not to be found, fall back to the old behavior.
V2 of this patch, incorporating feedback from Jani and (indirectly)
Austin.
Previously, we would treat multi-message mboxes as one giant email,
which, besides the obvious incorrect indexing, often led to
out-of-memory errors for archival mboxes. Now we explicitly reject
multi-message mboxes. For historical reasons, we retain support for
single-message mboxes, but official deprecate this behavior.
Add a custom value range processor to enable date and time searches of
the form date:since..until, where "since" and "until" are expressions
understood by the previously added date/time parser, to restrict the
results to messages within a particular time range (based on the Date:
header).
If "since" or "until" describes date/time at an accuracy of days or
less, the values are rounded according to the accuracy, towards past
for "since" and towards future for "until". For example,
date:november..yesterday would match from the beginning of November
until the end of yesterday. Expressions such as date:today..today
means since the beginning of today until the end of today.
Open-ended ranges are supported (since Xapian 1.2.1), i.e. you can
specify date:..until or date:since.. to not limit the start or end
date, respectively.
CAVEATS:
Xapian does not support spaces in range expressions. You can replace
the spaces with '_', or (in most cases) '-', or (in some cases) leave
the spaces out altogether.
Entering date:expr without ".." (for example date:yesterday) will not
work as you might expect. You can achieve the expected result by
duplicating the expr both sides of ".." (for example
date:yesterday..yesterday).
Open-ended ranges won't work with pre-1.2.1 Xapian, but they don't
produce an error either.
Signed-off-by: Jani Nikula <jani@nikula.org>
Previously, _notmuch_database_filename_to_direntry would abort with an
internal error when called on a read-only database. Now that creating
the directory document is optional,
notmuch_database_find_message_by_filename can disable directory
document creation (as it should) and, as a result, not abort on
read-only databases.
Using the new support from _notmuch_directory_create, this makes
notmuch_database_get_directory a read-only operation that simply
returns the directory object if it exists or NULL otherwise. This
also means that notmuch_database_get_directory can work on read-only
databases.
This change breaks the directory mtime workaround in notmuch-new.c by
fixing the exact issue it was working around. This permits mtime
update races to prevent scans of changed directories, which
non-deterministically breaks a few tests. The next patch fixes this.
Now _notmuch_database_filename_to_direntry takes a flags argument and
can indicate if the necessary directory documents do not exist.
Again, callers have been updated, but retain their original behavior.
Now _notmuch_database_find_directory_id takes a flags argument, which
it passes through to _notmuch_directory_create and can indicate if the
directory does not exist. Again, callers have been updated, but
retain their original behavior.
Previously this function would create directory documents if they
didn't exist. As a result, it could only be used on writable
databases. This adds an argument to make creation optional and to
make this function work on read-only databases. We use a flag
argument to avoid a bare boolean and to permit future expansion.
Both callers have been updated, but currently retain the old behavior.
We'll take advantage of the new argument in the following patches.
Previously, notmuch_database_get_directory had no way to indicate how
it had failed. This changes its prototype to return a status code and
set an out-argument to the retrieved directory, like similar functions
in the library API. This does *not* change its currently broken
behavior of creating directory objects when they don't exist, but it
does document it and paves the way for fixing this. Also, it can now
check for a read-only database and return
NOTMUCH_STATUS_READ_ONLY_DATABASE instead of crashing.
In the interest of atomicity, this also updates calls from the CLI so
that notmuch still compiles.
This is the notmuch_database_create equivalent of the previous change.
In this case, there were places where errors were not being propagated
correctly in notmuch_database_create or in calls to it. These have
been fixed, using the new status value.
It has been a long-standing issue that notmuch_database_open doesn't
return any indication of why it failed. This patch changes its
prototype to return a notmuch_status_t and set an out-argument to the
database itself, like other functions that return both a status and an
object.
In the interest of atomicity, this also updates every use in the CLI
so that notmuch still compiles. Since this patch does not update the
bindings, the Python bindings test fails.
Formerly notmuch_database_close closed the xapian database and
destroyed the talloc structure associated with the notmuch database
object. Split notmuch_database_close into notmuch_database_close and
notmuch_database_destroy.
This makes it possible for long running programs to close the xapian
database and thus release the lock associated with it without
destroying the data structures obtained from it.
This also makes the api more consistent since every other data
structure has a destructor function.
The comments in notmuch.h are a courtesy of Austin Clements.
Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>
Formerly it was possible for *message_ret to be left
uninitialized. The documentation however clearly states that "[o]n any
failure or when the message is not found, this function initializes
'*message' to NULL".
Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>
Formerly the xapian database object was deleted and closed in its
destructor once the object was garbage collected. Explicitly call
close() so that the database and the associated lock is released
immediately.
The comment is a courtesy of Austin Clements.
Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>
Previously opening a notmuch database in read write mode that has been
locked resulted in the notmuch_database_open function executing
notmuch_database_close as a cleanup function. notmuch_database_close
failed to check whether the xapian database has in fact been created.
Add a check whether the xapian database object has actually been
created before trying to call its flush method.
Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>
Previously, we manually "free"d various pointers in
notmuch_database_open. Use a local talloc context instead to simplify
cleanup and eliminate various NULL pointer initializations and
conditionals.
In the error-handling paths of notmuch_database_open, we call
notmuch_database_close, which "delete"s several objects referenced by
the notmuch_database_t object. However, some of these pointers may be
uninitialized, resulting in undefined behavior. Hence, allocate the
notmuch_database_t with talloc_zero to make sure these pointers are
NULL so that "delete"ing them is harmless.
As reported in
id:"CAEbOPGyuHnz4BPtDutnTPUHcP3eYcRCRkXhYoJR43RUMw671+g@mail.gmail.com"
sometimes gmime tries to access a NULL pointer, e.g. g_mime_iconv_open()
tries to access iconv_cache that is NULL if g_mime_init() is not called.
This causes notmuch to segfault when calling gmime functions.
Calling g_mime_init() initializes iconv_cache and others variables needed
by gmime, making sure they are initialized when notmuch calls gmime
functions.
Test marked fix by db.
Commit 567bcbc2 introduced two new values for each message (content of the
"From" and "Subject" headers), but the comments about the database schema had
not been updated accordingly.
This is a rebase and cleanup of Istvan Marko's patch from
id:m3pqnj2j7a.fsf@zsu.kismala.com
Search retrieves these headers for every message in the search
results. Previously, this required opening and parsing every message
file. Storing them directly in the database significantly reduces IO
and computation, speeding up search by between 50% and 10X.
Taking full advantage of this requires a database rebuild, but it will
fall back to the old behavior for messages that do not have headers
stored in the database.
Apparently the method was renamed in Xapian 1.1.0 but the old method
name will stay around for a while. It seems better to stick with the
old name to make notmuch compile with older versions of Xapian, at
least for now.
We keep the lib/xutil.c version. As a consequence, also factor out
_internal_error and associated macros. It might be overkill to make a
new file error_util.c for this, but _internal_error does not really
belong in database.cc.
Previously, the functions notmuch_database_find_message() and
notmuch_database_find_message_by_filename() functions did not properly
report error condition to the library user.
For more information, read the thread on the notmuch mailing list
starting with my mail "id:871uv2unfd.fsf@gmail.com"
Make these functions accept a pointer to 'notmuch_message_t' as argument
and return notmuch_status_t which may be used to check for any error
condition.
restore: Modify for the new notmuch_database_find_message()
new: Modify for the new notmuch_database_find_message_by_filename()
Adding a message may involve changes to multiple database documents,
and thus needs to be done in a transaction. This makes add_message
(and, I think, the whole library) atomicity-safe: library callers only
needs to use atomic sections if they needs atomicity across multiple
library calls.
notmuch_database_find_message_by_filename is mostly stolen from
notmuch_database_remove_message, so this patch also vastly simplfies
the latter using the former.
This API is also useful in its own right and will be used in a later
patch for eager maildir flag synchronization.
Previously, notmuch_database_remove_message would remove the message
file name, sync the change to the message document, re-find the
message document, and then delete it if there were no more file names.
An interruption after sync'ing would result in a file-name-less,
permanently un-removable zombie message that would produce errors and
odd results in searches. We could wrap this in an atomic section, but
it's much simpler to eliminate the round-about approach and just
delete the message document instead of sync'ing it if we removed the
last filename.
notmuch_database_t now keeps a nesting count and we only start a
transaction or commit for the outermost atomic section.
Introduces a new error, NOTMUCH_STATUS_UNBALANCED_ATOMIC.
Various typo fixes in comments within the source code.
Signed-off-by: Pieter Praet <pieter@praet.org>
Edited-by: Carl Worth <cworth@cworth.org> Restricted to just
source-code comments, (and fixed fix of "descriptios" to "descriptors"
rather than "descriptions").
Replace _notmuch_convert_tags with this and simplify
_create_filenames_for_terms_with_prefix. This will also come in handy
shortly to get the message file name list.
This replaces the guts of the filename list and tag list, making those
interfaces simple iterators over the generic string list. The
directory, message filename, and tags-related code now build generic
string lists and then wraps them in specific iterators. The real wins
come in later patches, when we use these for even more generic
functionality.
As a nice side-effect, this also eliminates the annoying dependency on
GList in the tag list.
A new "folder:" prefix in the query string can now be used to match
the directories in which mail files are stored.
The addition of this feature causes the recently added
search-by-folder tests to now pass.
Using the local talloc context ensures that the memory we are using
here will be freed shortly, (rather than hanging on for a long time
with the notmuch database object).
This rather ugly hack was recently obviated by the removal of the
notmuch_database_set_maildir_sync function. Now, clients must make
explicit calls to do any syncrhonization between maildir flags and
tags. So the library no longer needs to worry about doing inconsistent
synchronization while a message is only partially added.
Instead of having an API for setting a library-wide flag for
synchronization (notmuch_database_set_maildir_sync) we instead
implement maildir synchronization with two new library functions:
notmuch_message_maildir_flags_to_tags
and notmuch_message_tags_to_maildir_flags
These functions are nicely documented here, (though the implementation
does not quite match the documentation yet---as plainly evidenced by
the current results of the test suite).
This adds group [maildir] and key 'synchronize_flags' to the
configuration file. Its value enables (true) or diables (false) the
synchronization between notmuch tags and maildir flags. By default,
the synchronization is disabled.
This patch allows bi-directional synchronization between maildir
flags and certain tags. The flag-to-tag mapping is defined by flag2tag
array.
The synchronization works this way:
1) Whenever notmuch new is executed, the following happens:
o New messages are tagged with configured new_tags.
o For new or renamed messages with maildir info present in the file
name, the tags defined in flag2tag are either added or removed
depending on the flags from the file name.
2) Whenever notmuch tag (or notmuch restore) is executed, a new set of
flags based on the tags is constructed for every message and a new
file name is prepared based on the old file name but with the new
flags. If the flags differs and the old message was in 'new'
directory then this is replaced with 'cur' in the new file name. If
the new and old file names differ, the file is renamed and notmuch
database is updated accordingly.
The rename happens before the database is updated. In case of crash
between rename and database update, the next run of notmuch new
brings the database in sync with the mail store again.
These various functions and data are all used only locally, so should
be marked static. Ensuring we get these right will avoid us accidentally
leaking unintended symbols through the library interface.
Thanks to the new git-based test suite, it's easy to run the whole
test suite in valgrind, (simply "make test OPTIONS="--valgrind"), and
doing so showed this obvious use-after-free bug, (triggered by the
thread-order tests).
Scott Henson reported an internal error that occurred when he tried to
add a message that referenced another message with a message ID well
over 300 characters in length. The bug here was running into a Xapian
limit for the length of metadata key names, (which is even more
restrictive than the Xapian limit for the length of terms).
We fix this by noticing long message ID values and instead using a
message ID of the form "notmuch-sha1-<sha1_sum_of_message_id>". That
is, we use SHA1 to generate a compressed, (but still unique), version
of the message ID.
We add support to the test suite to exercise this fix. The tests add a
message referencing the long message ID, then add the message with the
long message ID, then finally add another message referencing the long
ID. Each of these tests exercise different code paths where the
special handling is implemented.
A final test ensures that all three messages are stitched together
into a single thread---guaranteeing that the three code paths all act
consistently.
Previously we were using Xapian's add_document to allocate document ID
values for notmuch_message_t objects. This had the drawback of adding
a partially constructed mail document to the database. If notmuch was
subsequently interrupted before fully populating this document, then
later runs would be quite confused when seeing the partial documents.
There are reports from the wild of people hitting internal errors of
the form "Message ... has no thread ID" for example, (which is
currently an unrecoverable error).
We fix this by manually allocating document IDs without adding
documents. With this change, we never call Xapian's add_document
method, but only replace_document with either the current document ID
of a message or a new one that we have allocated.
Our current approach is for top-level entry poitns in the library
to have try/catch blocks that catch any Xapian exception and print
a message. Add a few missing blocks and fix up the documentation.
Previously, we were only adding the reference terms for cases where
the referenced message did not yet exist in the database. For thread
presentation, it's useful to have the connection information provided
by the references, even when the messages are present. So add this
term unconditionally.
This function was recently modified, (to include a metadata lookup for
a message's thread ID before looking for parent/child thread IDs), but
the documentation wasn't updated. Fix that.
There are two primary cases in this function, (the message exists in
the database or it does not). Previously the code for these two cases
was split and intermingled with goto-spaghetti connections.
This allows us to thread messages even when we receive them out of
order, or never receive the root.
The thread ids for messages that aren't present but are referred to are
stored as metadata in the database and then retrieved if we ever get
that message.
When determining the thread id for a message we also check for this
metadata so that we can thread descendants of a message together before
we receive it.
Edited by Carl Worth <cworth@cworth.org>: Split this portion of the
commit from the earlier-applied portion adding test cases.
We rename 'has_more' to 'valid' so that it can function whether
iterating in a forward or reverse direction. We also rename
'advance' to 'move_to_next' to setup parallel naming with
the proposed functions 'move_to_first', 'move_to_last', and
'move_to_previous'.
Thanks to Michal Sojka <sojkam1@fel.cvut.cz> for pointing out the
correct fix, which I verified in the freely-available WG14/N1124 draft
(from the C99 working group) which is available here:
http://www.open-std.org/JTC1/SC22/wg14/www/docs/n1124.pdf
The sequential identifiers have the advantage of being guaranteed to
be unique (until we overflow a 64-bit unsigned integer), and also take
up half as much space in the "notmuch search" output (16 columns
rather than 32).
This change also has the side effect of fixing a bug where notmuch
could block on /dev/random at startup (waiting for some entropy to
appear). This bug was hit hard by the test suite, (which could easily
exhaust the available entropy on common systems---resulting in large
delays of the test suite).
Previously we were printing a number of messages upgraded so far. The
original motivation for this was to accurately reflect the fact that
there are two passes, (so each message is processed twice and it's not
accurate to represent with a single count). But as it turns out, the
second pass takes zero time (relatively speaking) so we're still not
accounting for it.
If nothing else, the percentage-based reporting makes for a cleaner
API for the progress_notify function.
The first phase copies data from the old format to the new format
without deleting anything. This allows an old notmuch to still use the
database if the upgrade process gets interrupted. The second phase
performs the deletion (after updating the database version number). If
the second phase is interrupted, there will be some unused data in the
database, but it shouldn't cause any actual harm.
The recent support for renames in the database is our first time
(since notmuch has had more than a single user) that we have a
database format change. To support smooth upgrades we now encode a
database format version number in the Xapian metadata.
Going forward notmuch will emit a warning if used to read from a
database with a newer version than it natively supports, and will
refuse to write to a database with a newer version.
The library also provides functions to query the database format
version:
notmuch_database_get_version
to ask if notmuch wants a newer version than that:
notmuch_database_needs_upgrade
and a function to actually perform that upgrade:
notmuch_database_upgrade
Previously we had NOTMUCH_DATABASE_MODE_READ_ONLY but
NOTMUCH_STATUS_READONLY_DATABASE which was ugly and confusing. Rename
the latter to NOTMUCH_STATUS_READ_ONLY_DATABASE for consistency.
Previously, many checks were deep in the library just before a cast
operation. These have now been replaced with internal errors and new
checks have instead been added at the beginning of all top-levelentry
points requiring a read-write database.
The new checks now also use a single function for checking and
printing the error message. This will give us a convenient location to
extend the check, (such as based on database version as well).
The original wording made it sound like this function was just doing
some string manipulation. But this function actually creates new
directory documents as a side effect. So make that explicit in its
documentation.
Similar to the return value of notmuch_database_add_message, we now
enhance the return value of notmuch_database_remove_message to
indicate whether the message document was entirely removed (SUCCESS)
or whether only this filename was removed and the document exists
under other filenamed (DUPLICATE_MESSAGE_ID).
This new directory ojbect provides all the infrastructure needed to
detect when files or directories are deleted or renamed. There's still
code needed on top of this (within "notmuch new") to actually do that
detection.
This will allow applications to support the removal of messages, (such
as when a file is deleted from the mail store). No removal support is
provided yet in commands such as "notmuch new".
The existing find_doc_ids function is convenient when the caller
doesn't want to be bothered constructing a term. But when the caller
*does* have the term already, that interface is just wasteful. So we
export a lower-level interface that maps a pre-constructed term to a
document-ID iterators.
