Log Message:
Update to 1.4.12. From the changelog:

API:

* Xapian::PostingSource: When a PostingSource without a clone() method is used
  with a Database containing multiple shards, the documented behaviour has
  always been that Xapian::InvalidOperationError is thrown.  However, since at
  least 1.4.0, this exception hasn't been thrown, but instead a single
  PostingSource object would get used for all the shards, typically leading to
  incorrect results.  The actual behaviour now matches what was documented.

* Xapian::Database: Add size() method which reports the number of shards.

* Xapian::Database::check(): You can now pass a stub database which will check
  all the databases listed in it (or throw Xapian::UnimplementError for
  backends which don't support checking).

* Xapian::Document: When updating a document use a emplace_hint() to make the
  bulk insertion O(n) instead of O(n·log(n)), and use std::move() to avoid
  copying OmDocumentTerm objects.

* Xapian::Query: Add missing get_unique_terms_end() method.

* Xapian::iterator_valid(): Implement for Utf8Iterator

testsuite:

* Fix keepalive1 failures on some platforms.  On some platforms a timeout
  gives NetworkTimeoutError and on others NetworkError - since 1.4.10 changed
  to checking the exact exception type, keepalive1 has been failing on the
  former set of platforms.  We now just check for NetworkError or a subclass
  here (since NetworkTimeoutError is a subclass of NetworkError).

* Run cursordelbug1 testcase with multi databases too.

matcher:

* Ownership of PostingSource objects during the match now makes use of the
  optional reference-counting mechanism rather than a separate flag.

remote backend:

* Fix remote protocol design bug.  Previously some messages didn't send a reply
  but could result in an exception being sent over the link.  That exception
  would then get read as a response to the next message instead of its actual
  response so we'd be out of step.  Fixes #783, reported by Germán M. Bravo.
  This fix necessitated a minor version bump in the remote protocol (to 39.1).
  If you are upgrading a live system which uses the remote backend, upgrade the
  servers before the clients.

* Fix socket leaks on errors during opening a database.  Fixes
  https://github.com/xapian/xapian/pull/237 and #781, reported by Germán M.
  Bravo.

* Don't close remote DB socket on receiving EOF as the levels above won't
  know it's been closed and may try to perform operations on it, which would be
  problematic if that fd gets reused in the meantime.  Leaving it open means
  any further operations will also get EOF.  Reported by Germán M. Bravo.

* We add a wrapper around the libc socket() function which deals with the
  corner case where SOCK_CLOEXEC is defined but socket() fails if it is
  specified (which can happen with a newer libc and older kernel).
  Unfortunately, this wrapper wasn't checking the returned value from socket()
  correctly, so when SOCK_CLOEXEC was specified and non-zero it would create
  the socket() with SOCK_CLOEXEC, then leak that one and create it again
  without SOCK_CLOEXEC.  We now check the return value properly.

* Fix potential infinite loop in ValueCountMatchSpy::merge_results() if passed
  serialised results with extra data appended (which shouldn't happen in normal
  use).

build system:

* Current versions of valgrind result in false positives on current versions of
  macOS, so on this platform configure now only enables use of valgrind if it's
  specified explicitly.  Fixes #713, reported by Germán M. Bravo.

* Refactor macros to probe for compiler flags so they automatically cache
  their results and consistently report success/failure.

* Rename our custom TYPE_SOCKLEN_T macro to XAPIAN_TYPE_SOCKLEN_T.  The
  AX_TYPE_SOCKLEN_T macro defines an alias of TYPE_SOCKLEN_T for itself which
  means it can get used instead in some situations, but it isn't compatible
  with our macro.  We can't just switch to AX_TYPE_SOCKLEN_T as it doesn't
  handle cases we need, so just rename our macro to avoid potential problems.

documentation:

* Improve API documentation for Xapian::Query class.  Add missing doc
  comments and improve some of the existing ones.  Problems highlighted by
  Дилян Палаузов in #790.

* Add Unicode consortium names and codes for categories from Chapter 4, Version
  11 of the Unicode standard.  Patch from David Bremner.

* Improve configure --help output - drop "[default=no]" for --enable-*
  options which default off.  Fixes #791, reported by and patch from Дилян
  Палаузов.

* Fix API documentation typo - Query::op (the type) not op_ (a parameter name).

* Note which version Document::remove_postings() was added in.

* In the remote protocol documentation, MSG_REPLACEDOCUMENTTERM was documented
  as not having a reply, but actually REPLY_ADDDOCUMENT is sent.

* Update list of <xapian/iterator.h> users.

tools:

* copydatabase: A change in 1.4.6 which added support for \ as directory
  separator on platforms where that's the norm broke the code in copydatabase
  which removes a trailing slash from input databases.  Bug reported and
  culprit commit identified by Eric Wong.

portability:

* Resolve crash on Windows when using clang-cl and MSVC.  Reported by Christian
  Mollekopf in https://github.com/xapian/xapian/pull/256.

* Add missing '#include <cstring>'.  Patch from Tanmay Sachan.

* Fix str() helper function when converting the most negative value
  of a signed integer type.

* Avoid calling close() on fd we know must actually be a WIN32 SOCKET.

* Include <ios> not <iomanip> for std::boolalpha.

* Rework setenv() compatibility handling.  Now that Solaris 9 is dead we can
  assume setenv() is provided by Unix-like platforms (POSIX requires it).  For
  other platforms, provide a compatibility implementation of setenv() which
  so the compatibility code is encapsulated in one place rather than replicated
  at every use.

* Fix maintainer-mode builds on Solaris where /bin/tr is not POSIX compliant.
  We now use the simple workaround suggested by the autoconf manual.

* Improve support for Sun C++ (see #631):

  + Suppress unhelpful warning for lambda with multiple return statements.

  + Enable reporting the tags corresponding to warnings, which we need
    to know in order to suppress any new unhelpful warnings.

  + Adjust our workaround for bug with this compiler's <cmath> header to avoid
    a compiler warning.

  + Use -xldscope=symbolic for Sun C++.  This flag is roughly equivalent to
    -Bsymbolic-functions which we've probed for with GNU ld since Xapian 1.0.0.

And from the changelog for the language bindings:

Documentation:

* Update bindings HACKING document.  Reported as out of date by Niwesh Gupta.

CSharp:

* Work around mono terminfo parsing bug - older cli-sn fails with e.g.
  TERM=xterm-256color due to: https://github.com/mono/mono/issues/6752
  Encountered on Kubuntu 18.10 and debugged by Tejasvi Tomar.  Seems to be
  fixed in the mono version in Debian buster.

Perl:

* Suppress warnings from older Perl headers due to use of constructs which look
  like C++11 user-defined literals.  They're fixed in newer versions so they're
  just noise in our build.  We were working around these in the CI build, so
  drop that workaround as we want to make the build warning-clean for users
  too.  Reported by daniel93 on #xapian.

Python3:

* Fix build for changes in Sphinx 2.0 (which drops support for sphinx.main()).
  Fixes #778, reported by karolyi.  Also reported by Gaurav Arora.

* We now throw UnicodeEncodeError for bad Unicode string input.  Previously
  cases such as a lone surrogate would be handled by quietly skipping the bad
  codepoints when converting to UTF-8 to pass to Xapian.

* We no longer use the deprecated old-style Py_UNICODE API, which currently
  gives deprecation warnings and is slated to be removed in Python 4.0.

Ruby:

* Add support for block iteration.  All the iterator methods in the Ruby API
  now accept an optional block.  If no block is given an array is returned so
  existing code will still work.  Partly based on a patch in
  https://github.com/xapian/xapian/pull/232 from Cong Ding.

* Add missing wrappers for all the C++ methods returning iterators which
  weren't wrapped for Ruby.  Fixes #777, reported by do.

* Suppress warnings from Ruby 2.3 headers due to use of register and
  constructs which look like C++11 user-defined literals.  They're fixed in
  newer versions so they're just noise in our build.  We were working around
  these in the CI build, so drop that workaround as we want to make the build
  warning-clean for users too.  Reported by daniel93 on #xapian.

* smoketest.rb: Don't leave temporary databases behind in /tmp.