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.. highlight:: none


.. index::
   pair: library version mechanism; design

.. _design-version-library:


Library version mechanism
=========================

.. mps:prefix:: design.mps.version-library


Introduction
------------

:mps:tag:`intro` This describes the design of a mechanism to be used to
determine the version (that is, product, version, and release) of an
MPS library.


Readership
----------

:mps:tag:`readership` Any MPS developer.


Source
------

:mps:tag:`source` Various requirements demand such a mechanism. See
request.epcore.160021_: There is no way to tell which version and
release of the MM one is using.

.. _request.epcore.160021: https://info.ravenbrook.com/project/mps/import/2001-11-05/mmprevol/request/epcore/160021

Overview
--------

:mps:tag:`overview` This is the design for determining which version of the
library one has linked against. There are two aspects to the design,
allowing humans to determine the version of an MPS library, and
allowing programs to determine the version of an MPS library. Only the
former is currently designed (a method for humans to determine which
version of an MPS library is being used).

:mps:tag:`overview.impl` The overall design is to have a distinctive string
compiled into the library binary. Various programs and tools will be
able to extract the string and display it. The string will identify
the version of the MPS begin used.


Architecture
------------

:mps:tag:`arch.structure` The design consists of two components:

#. :mps:tag:`arch.string` A string embedded into any delivered library
   binaries (which will encode the necessary information).

#. :mps:tag:`arch.proc` Procedures by which the string is modified
   appropriately whenever releases are made.

#. :mps:tag:`arch.tool` A tool and its documentation (it is expected that
   standard tools can be used). The tool will be used to extract the
   version string from a delivered library or an executable linked
   with the library.

The string will contain information to identify the following items:

#. :mps:tag:`arch.string.platform` the platform being used.

#. :mps:tag:`arch.string.product` the name of the product.

#. :mps:tag:`arch.string.variety` the variety of the product.

#. :mps:tag:`arch.string.version` the version and release of the product.


Implementation
--------------

:mps:tag:`impl.file` The version string itself is a declared C object
``MPSVersionString`` in the file ``version.c`` (impl.c.version). It
consists of a concatenation of various strings which are defined in
other modules.

:mps:tag:`impl.variety` The string containing the name of the variety is the
expansion of the macro :c:macro:`MPS_VARIETY_STRING` defined by ``config.h``
(impl.h.config).

:mps:tag:`impl.product` The string containing the name of the product is the
expansion of the macro :c:macro:`MPS_PROD_STRING` defined by ``config.h``
(impl.h.config). Note that there is now only one product, so this is
always ``"mps"`` (see design.mps.config.req.prod_).

.. _design.mps.config.req.prod: config.html#design.mps.config.req.prod

:mps:tag:`impl.platform` The string containing the name of the platform is
the expansion of the macro :c:macro:`MPS_PF_STRING` defined by ``mpstd.h``
(impl.h.mpstd).

:mps:tag:`impl.date` The string contains the date and time of compilation by
using the ``__DATE__`` and ``__TIME__`` macros defined by ISO C
ยง6.8.8.

:mps:tag:`impl.version` The string contains the version and release of the
product. This is by the expansion of the macro :c:macro:`MPS_RELEASE` which
is defined in this module (``version.c``).

:mps:tag:`impl.proc` The :c:macro:`MPS_RELEASE` macro (see impl.c.version.release)
is edited after making a release so that it contains the name of the
next release to be made from the sources on that branch. For example, after
making version 1.117, the source on the master branch is updated to say::

    #define MPS_RELEASE "release/1.118.0"

and after making release 1.117.0, the source on the version/1.117 branch is updated to say::

    #define MPS_RELEASE "release/1.117.1"

See the version creation and release build procedures respectively.

:mps:tag:`impl.tool` The version string starts with the characters
``"@(#)"``. This is recognized by the standard Unix utility |what|_. For example::

    $ what mps.a
    mps.a
            Ravenbrook MPS, product.mps, release/1.117.0, platform.xci6ll, variety.asserted.logging.nonstats, compiled on Oct 18 2016 13:57:08

.. |what| replace:: ``what(1)``
.. _what: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/what.html