.. _default-latest-version-specifiers:

Default and latest version specifiers
=====================================

Configuration
-------------

- Rely on ``advanced_version_spec`` option

    - No need for an extra configuration option
    - When option is on it automatically enables use of these two new version specifiers
    - When ``advanced_version_spec`` is off, ``mod@latest`` is considered as a modulefile name to find
    - in case ``implicit_default`` is disabled

        - means a ``default`` symbol or a ``latest`` symbol should be found defined to respectively make use of the ``@default`` or ``@latest`` specifiers
        - a not found error is otherwise raised, as specified version does not exist


Specification
-------------

- When a ``default`` or a ``latest`` symbol is defined

    - ``@default`` or respectively ``@latest`` will resolve to the symbol target

- When no ``default`` or ``latest`` symbol is defined

    - ``@default`` and ``@latest`` point to the highest existing version (also called the implicit default)
    - note that if a ``default`` symbol is defined but not a ``latest`` symbol, ``@default`` points to the defined default and ``@latest`` points to the highest version that exists

- ``default`` or ``latest`` version specifiers can be employed:

    - in single version specification: ``@default`` or ``@latest``
    - in version list: ``@vers1,default`` or ``@latest,default,vers2``

- ``default`` or ``latest`` version specifiers cannot be employed in version range

    - otherwise an error is raised

- ``default`` or ``latest`` version specifiers can also be specified with the traditionnal ``mod/version`` syntax

    - for instance ``mod/default`` or ``mod/latest``

- When a ``default`` or ``latest`` modulefile exists

    - ``@default`` or respectively ``@latest`` will resolve to the existing modulefile
    - no automatic symbol will be recorded in this case as ``default`` or ``latest`` are regular versions

- To be included in module search result, the version specifiers should fully match search query or search query should not target a specific module version

    - the automatically defined symbolic versions are included in results for queries like ``mod@latest`` or ``mod``
    - but not for queries like ``mod@la``, ``mod@def``, ``mod@lat*``, ``mod@def??lt``

- Automatically defined ``default`` and ``latest`` version specifiers are not displayed to avoid overloading output:

    - on ``module list`` output
    - on ``module avail`` output
    - those two sub-commands only display symbolic versions manually defined

- Alternative module names deduced from the automatically defined version specifiers need to be tracked

    - in loaded environment for each targeted module loaded
    - to keep track loaded module is default or latest version
    - thus keeping ability to answer queries like ``is-loaded mod@latest`` from further modulefile evaluation or module command-line
    - this information is kept in the ``MODULES_LMALTNAME`` environment variable, along other alternative names
    - Auto symbols in this variable are recorded with a ``as|`` prefix to distinguish them from other alternative names

        - for instance ``mod/1.2&mod/regular_symbol&as|mod/latest``
        - it helps to filter auto symbols from regular symbols that need to be displayed
