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CPAN::Meta::Spec(3pm)  Perl Programmers Reference Guide  CPAN::Meta::Spec(3pm)




NAME

       CPAN::Meta::Spec - specification for CPAN distribution metadata


VERSION

       version 2.150005


SYNOPSIS

         my $distmeta = {
           name => 'Module-Build',
           abstract => 'Build and install Perl modules',
           description =>  "Module::Build is a system for "
             . "building, testing, and installing Perl modules. "
             . "It is meant to ... blah blah blah ...",
           version  => '0.36',
           release_status => 'stable',
           author   => [
             'Ken Williams <kwilliams@cpan.org>',
             'Module-Build List <module-build@perl.org>', # additional contact
           ],
           license  => [ 'perl_5' ],
           prereqs => {
             runtime => {
               requires => {
                 'perl'   => '5.006',
                 'ExtUtils::Install' => '0',
                 'File::Basename' => '0',
                 'File::Compare'  => '0',
                 'IO::File'   => '0',
               },
               recommends => {
                 'Archive::Tar' => '1.00',
                 'ExtUtils::Install' => '0.3',
                 'ExtUtils::ParseXS' => '2.02',
               },
             },
             build => {
               requires => {
                 'Test::More' => '0',
               },
             }
           },
           resources => {
             license => ['http://dev.perl.org/licenses/'],
           },
           optional_features => {
             domination => {
               description => 'Take over the world',
               prereqs     => {
                 develop => { requires => { 'Genius::Evil'     => '1.234' } },
                 runtime => { requires => { 'Machine::Weather' => '2.0'   } },
               },
             },
           },
           dynamic_config => 1,
           keywords => [ qw/ toolchain cpan dual-life / ],
           'meta-spec' => {
             version => '2',
             url     => 'https://metacpan.org/pod/CPAN::Meta::Spec',
           },
           generated_by => 'Module::Build version 0.36',
         };


DESCRIPTION

       This document describes version 2 of the CPAN distribution metadata
       specification, also known as the "CPAN Meta Spec".

       Revisions of this specification for typo corrections and prose
       clarifications may be issued as CPAN::Meta::Spec 2.x.  These revisions
       will never change semantics or add or remove specified behavior.

       Distribution metadata describe important properties of Perl
       distributions. Distribution building tools like Module::Build,
       Module::Install, ExtUtils::MakeMaker or Dist::Zilla should create a
       metadata file in accordance with this specification and include it with
       the distribution for use by automated tools that index, examine,
       package or install Perl distributions.


TERMINOLOGY

       distribution
           This is the primary object described by the metadata. In the
           context of this document it usually refers to a collection of
           modules, scripts, and/or documents that are distributed together
           for other developers to use.  Examples of distributions are
           "Class-Container", "libwww-perl", or "DBI".

       module
           This refers to a reusable library of code contained in a single
           file.  Modules usually contain one or more packages and are often
           referred to by the name of a primary package that can be mapped to
           the file name. For example, one might refer to "File::Spec" instead
           of File/Spec.pm

       package
           This refers to a namespace declared with the Perl "package"
           statement.  In Perl, packages often have a version number property
           given by the $VERSION variable in the namespace.

       consumer
           This refers to code that reads a metadata file, deserializes it
           into a data structure in memory, or interprets a data structure of
           metadata elements.

       producer
           This refers to code that constructs a metadata data structure,
           serializes into a bytestream and/or writes it to disk.

       must, should, may, etc.
           These terms are interpreted as described in IETF RFC 2119.


DATA TYPES

       Fields in the "STRUCTURE" section describe data elements, each of which
       has an associated data type as described herein.  There are four
       primitive types: Boolean, String, List and Map.  Other types are
       subtypes of primitives and define compound data structures or define
       constraints on the values of a data element.

   Boolean
       A Boolean is used to provide a true or false value.  It must be
       represented as a defined value.

   String
       A String is data element containing a non-zero length sequence of
       Unicode characters, such as an ordinary Perl scalar that is not a
       reference.

   List
       A List is an ordered collection of zero or more data elements.
       Elements of a List may be of mixed types.

       Producers must represent List elements using a data structure which
       unambiguously indicates that multiple values are possible, such as a
       reference to a Perl array (an "arrayref").

       Consumers expecting a List must consider a String as equivalent to a
       List of length 1.

   Map
       A Map is an unordered collection of zero or more data elements
       ("values"), indexed by associated String elements ("keys").  The Map's
       value elements may be of mixed types.

   License String
       A License String is a subtype of String with a restricted set of
       values.  Valid values are described in detail in the description of the
       "license" field.

   URL
       URL is a subtype of String containing a Uniform Resource Locator or
       Identifier.  [ This type is called URL and not URI for historical
       reasons. ]

   Version
       A Version is a subtype of String containing a value that describes the
       version number of packages or distributions.  Restrictions on format
       are described in detail in the "Version Formats" section.

   Version Range
       The Version Range type is a subtype of String.  It describes a range of
       Versions that may be present or installed to fulfill prerequisites.  It
       is specified in detail in the "Version Ranges" section.


STRUCTURE

       The metadata structure is a data element of type Map.  This section
       describes valid keys within the Map.

       Any keys not described in this specification document (whether top-
       level or within compound data structures described herein) are
       considered custom keys and must begin with an "x" or "X" and be
       followed by an underscore; i.e. they must match the pattern:
       "qr{\Ax_}i".  If a custom key refers to a compound data structure,
       subkeys within it do not need an "x_" or "X_" prefix.

       Consumers of metadata may ignore any or all custom keys.  All other
       keys not described herein are invalid and should be ignored by
       consumers.  Producers must not generate or output invalid keys.

       For each key, an example is provided followed by a description.  The
       description begins with the version of spec in which the key was added
       or in which the definition was modified, whether the key is required or
       optional and the data type of the corresponding data element.  These
       items are in parentheses, brackets and braces, respectively.

       If a data type is a Map or Map subtype, valid subkeys will be described
       as well.

       Some fields are marked Deprecated.  These are shown for historical
       context and must not be produced in or consumed from any metadata
       structure of version 2 or higher.

   REQUIRED FIELDS
       abstract

       Example:

         abstract => 'Build and install Perl modules'

       (Spec 1.2) [required] {String}

       This is a short description of the purpose of the distribution.

       author

       Example:

         author => [ 'Ken Williams <kwilliams@cpan.org>' ]

       (Spec 1.2) [required] {List of one or more Strings}

       This List indicates the person(s) to contact concerning the
       distribution. The preferred form of the contact string is:

         contact-name <email-address>

       This field provides a general contact list independent of other
       structured fields provided within the "resources" field, such as
       "bugtracker".  The addressee(s) can be contacted for any purpose
       including but not limited to (security) problems with the distribution,
       questions about the distribution or bugs in the distribution.

       A distribution's original author is usually the contact listed within
       this field.  Co-maintainers, successor maintainers or mailing lists
       devoted to the distribution may also be listed in addition to or
       instead of the original author.

       dynamic_config

       Example:

         dynamic_config => 1

       (Spec 2) [required] {Boolean}

       A boolean flag indicating whether a Build.PL or Makefile.PL (or
       similar) must be executed to determine prerequisites.

       This field should be set to a true value if the distribution performs
       some dynamic configuration (asking questions, sensing the environment,
       etc.) as part of its configuration.  This field should be set to a
       false value to indicate that prerequisites included in metadata may be
       considered final and valid for static analysis.

       Note: when this field is true, post-configuration prerequisites are not
       guaranteed to bear any relation whatsoever to those stated in the
       metadata, and relying on them doing so is an error. See also
       "Prerequisites for dynamically configured distributions" in the
       implementors' notes.

       This field explicitly does not indicate whether installation may be
       safely performed without using a Makefile or Build file, as there may
       be special files to install or custom installation targets (e.g. for
       dual-life modules that exist on CPAN as well as in the Perl core).
       This field only defines whether or not prerequisites are exactly as
       given in the metadata.

       generated_by

       Example:

         generated_by => 'Module::Build version 0.36'

       (Spec 1.0) [required] {String}

       This field indicates the tool that was used to create this metadata.
       There are no defined semantics for this field, but it is traditional to
       use a string in the form "Generating::Package version 1.23" or the
       author's name, if the file was generated by hand.

       license

       Example:

         license => [ 'perl_5' ]

         license => [ 'apache_2_0', 'mozilla_1_0' ]

       (Spec 2) [required] {List of one or more License Strings}

       One or more licenses that apply to some or all of the files in the
       distribution.  If multiple licenses are listed, the distribution
       documentation should be consulted to clarify the interpretation of
       multiple licenses.

       The following list of license strings are valid:

        string          description
        -------------   -----------------------------------------------
        agpl_3          GNU Affero General Public License, Version 3
        apache_1_1      Apache Software License, Version 1.1
        apache_2_0      Apache License, Version 2.0
        artistic_1      Artistic License, (Version 1)
        artistic_2      Artistic License, Version 2.0
        bsd             BSD License (three-clause)
        freebsd         FreeBSD License (two-clause)
        gfdl_1_2        GNU Free Documentation License, Version 1.2
        gfdl_1_3        GNU Free Documentation License, Version 1.3
        gpl_1           GNU General Public License, Version 1
        gpl_2           GNU General Public License, Version 2
        gpl_3           GNU General Public License, Version 3
        lgpl_2_1        GNU Lesser General Public License, Version 2.1
        lgpl_3_0        GNU Lesser General Public License, Version 3.0
        mit             MIT (aka X11) License
        mozilla_1_0     Mozilla Public License, Version 1.0
        mozilla_1_1     Mozilla Public License, Version 1.1
        openssl         OpenSSL License
        perl_5          The Perl 5 License (Artistic 1 & GPL 1 or later)
        qpl_1_0         Q Public License, Version 1.0
        ssleay          Original SSLeay License
        sun             Sun Internet Standards Source License (SISSL)
        zlib            zlib License

       The following license strings are also valid and indicate other
       licensing not described above:

        string          description
        -------------   -----------------------------------------------
        open_source     Other Open Source Initiative (OSI) approved license
        restricted      Requires special permission from copyright holder
        unrestricted    Not an OSI approved license, but not restricted
        unknown         License not provided in metadata

       All other strings are invalid in the license field.

       meta-spec

       Example:

         'meta-spec' => {
           version => '2',
           url     => 'http://search.cpan.org/perldoc?CPAN::Meta::Spec',
         }

       (Spec 1.2) [required] {Map}

       This field indicates the version of the CPAN Meta Spec that should be
       used to interpret the metadata.  Consumers must check this key as soon
       as possible and abort further metadata processing if the meta-spec
       version is not supported by the consumer.

       The following keys are valid, but only "version" is required.

       version
           This subkey gives the integer Version of the CPAN Meta Spec against
           which the document was generated.

       url This is a URL of the metadata specification document corresponding
           to the given version.  This is strictly for human-consumption and
           should not impact the interpretation of the document.

           For the version 2 spec, either of these are recommended:

           o   "https://metacpan.org/pod/CPAN::Meta::Spec"

           o   "http://search.cpan.org/perldoc?CPAN::Meta::Spec"

       name

       Example:

         name => 'Module-Build'

       (Spec 1.0) [required] {String}

       This field is the name of the distribution.  This is often created by
       taking the "main package" in the distribution and changing "::" to "-",
       but the name may be completely unrelated to the packages within the
       distribution.  For example, LWP::UserAgent is distributed as part of
       the distribution name "libwww-perl".

       release_status

       Example:

         release_status => 'stable'

       (Spec 2) [required] {String}

       This field provides the  release status of this distribution.  If the
       "version" field contains an underscore character, then "release_status"
       must not be "stable."

       The "release_status" field must have one of the following values:

       stable
           This indicates an ordinary, "final" release that should be indexed
           by PAUSE or other indexers.

       testing
           This indicates a "beta" release that is substantially complete, but
           has an elevated risk of bugs and requires additional testing.  The
           distribution should not be installed over a stable release without
           an explicit request or other confirmation from a user.  This
           release status may also be used for "release candidate" versions of
           a distribution.

       unstable
           This indicates an "alpha" release that is under active development,
           but has been released for early feedback or testing and may be
           missing features or may have serious bugs.  The distribution should
           not be installed over a stable release without an explicit request
           or other confirmation from a user.

       Consumers may use this field to determine how to index the distribution
       for CPAN or other repositories in addition to or in replacement of
       heuristics based on version number or file name.

       version

       Example:

         version => '0.36'

       (Spec 1.0) [required] {Version}

       This field gives the version of the distribution to which the metadata
       structure refers.

   OPTIONAL FIELDS
       description

       Example:

           description =>  "Module::Build is a system for "
             . "building, testing, and installing Perl modules. "
             . "It is meant to ... blah blah blah ...",

       (Spec 2) [optional] {String}

       A longer, more complete description of the purpose or intended use of
       the distribution than the one provided by the "abstract" key.

       keywords

       Example:

         keywords => [ qw/ toolchain cpan dual-life / ]

       (Spec 1.1) [optional] {List of zero or more Strings}

       A List of keywords that describe this distribution.  Keywords must not
       include whitespace.

       no_index

       Example:

         no_index => {
           file      => [ 'My/Module.pm' ],
           directory => [ 'My/Private' ],
           package   => [ 'My::Module::Secret' ],
           namespace => [ 'My::Module::Sample' ],
         }

       (Spec 1.2) [optional] {Map}

       This Map describes any files, directories, packages, and namespaces
       that are private to the packaging or implementation of the distribution
       and should be ignored by indexing or search tools. Note that this is a
       list of exclusions, and the spec does not define what to include - see
       "Indexing distributions a la PAUSE" in the implementors notes for more
       information.

       Valid subkeys are as follows:

       file
           A List of relative paths to files.  Paths must be specified with
           unix conventions.

       directory
           A List of relative paths to directories.  Paths must be specified
           with unix conventions.

           [ Note: previous editions of the spec had "dir" instead of
           "directory" ]

       package
           A List of package names.

       namespace
           A List of package namespaces, where anything below the namespace
           must be ignored, but not the namespace itself.

           In the example above for "no_index", "My::Module::Sample::Foo"
           would be ignored, but "My::Module::Sample" would not.

       optional_features

       Example:

         optional_features => {
           sqlite => {
             description => 'Provides SQLite support',
             prereqs => {
               runtime => {
                 requires => {
                   'DBD::SQLite' => '1.25'
                 }
               }
             }
           }
         }

       (Spec 2) [optional] {Map}

       This Map describes optional features with incremental prerequisites.
       Each key of the "optional_features" Map is a String used to identify
       the feature and each value is a Map with additional information about
       the feature.  Valid subkeys include:

       description
           This is a String describing the feature.  Every optional feature
           should provide a description

       prereqs
           This entry is required and has the same structure as that of the
           "prereqs" key.  It provides a list of package requirements that
           must be satisfied for the feature to be supported or enabled.

           There is one crucial restriction:  the prereqs of an optional
           feature must not include "configure" phase prereqs.

       Consumers must not include optional features as prerequisites without
       explicit instruction from users (whether via interactive prompting, a
       function parameter or a configuration value, etc. ).

       If an optional feature is used by a consumer to add additional
       prerequisites, the consumer should merge the optional feature
       prerequisites into those given by the "prereqs" key using the same
       semantics.  See "Merging and Resolving Prerequisites" for details on
       merging prerequisites.

       Suggestion for disuse: Because there is currently no way for a
       distribution to specify a dependency on an optional feature of another
       dependency, the use of "optional_feature" is discouraged.  Instead,
       create a separate, installable distribution that ensures the desired
       feature is available.  For example, if "Foo::Bar" has a "Baz" feature,
       release a separate "Foo-Bar-Baz" distribution that satisfies
       requirements for the feature.

       prereqs

       Example:

         prereqs => {
           runtime => {
             requires => {
               'perl'          => '5.006',
               'File::Spec'    => '0.86',
               'JSON'          => '2.16',
             },
             recommends => {
               'JSON::XS'      => '2.26',
             },
             suggests => {
               'Archive::Tar'  => '0',
             },
           },
           build => {
             requires => {
               'Alien::SDL'    => '1.00',
             },
           },
           test => {
             recommends => {
               'Test::Deep'    => '0.10',
             },
           }
         }

       (Spec 2) [optional] {Map}

       This is a Map that describes all the prerequisites of the distribution.
       The keys are phases of activity, such as "configure", "build", "test"
       or "runtime".  Values are Maps in which the keys name the type of
       prerequisite relationship such as "requires", "recommends", or
       "suggests" and the value provides a set of prerequisite relations.  The
       set of relations must be specified as a Map of package names to version
       ranges.

       The full definition for this field is given in the "Prereq Spec"
       section.

       provides

       Example:

         provides => {
           'Foo::Bar' => {
             file    => 'lib/Foo/Bar.pm',
             version => '0.27_02',
           },
           'Foo::Bar::Blah' => {
             file    => 'lib/Foo/Bar/Blah.pm',
           },
           'Foo::Bar::Baz' => {
             file    => 'lib/Foo/Bar/Baz.pm',
             version => '0.3',
           },
         }

       (Spec 1.2) [optional] {Map}

       This describes all packages provided by this distribution.  This
       information is used by distribution and automation mechanisms like
       PAUSE, CPAN, metacpan.org and search.cpan.org to build indexes saying
       in which distribution various packages can be found.

       The keys of "provides" are package names that can be found within the
       distribution.  If a package name key is provided, it must have a Map
       with the following valid subkeys:

       file
           This field is required.  It must contain a Unix-style relative file
           path from the root of the distribution directory to a file that
           contains or generates the package.  It may be given as "META.yml"
           or "META.json" to claim a package for indexing without needing a
           "*.pm".

       version
           If it exists, this field must contains a Version String for the
           package.  If the package does not have a $VERSION, this field must
           be omitted.

       resources

       Example:

         resources => {
           license     => [ 'http://dev.perl.org/licenses/' ],
           homepage    => 'http://sourceforge.net/projects/module-build',
           bugtracker  => {
             web    => 'http://rt.cpan.org/Public/Dist/Display.html?Name=CPAN-Meta',
             mailto => 'meta-bugs@example.com',
           },
           repository  => {
             url  => 'git://github.com/dagolden/cpan-meta.git',
             web  => 'http://github.com/dagolden/cpan-meta',
             type => 'git',
           },
           x_twitter   => 'http://twitter.com/cpan_linked/',
         }

       (Spec 2) [optional] {Map}

       This field describes resources related to this distribution.

       Valid subkeys include:

       homepage
           The official home of this project on the web.

       license
           A List of URL's that relate to this distribution's license.  As
           with the top-level "license" field, distribution documentation
           should be consulted to clarify the interpretation of multiple
           licenses provided here.

       bugtracker
           This entry describes the bug tracking system for this distribution.
           It is a Map with the following valid keys:

             web    - a URL pointing to a web front-end for the bug tracker
             mailto - an email address to which bugs can be sent

       repository
           This entry describes the source control repository for this
           distribution.  It is a Map with the following valid keys:

             url  - a URL pointing to the repository itself
             web  - a URL pointing to a web front-end for the repository
             type - a lowercase string indicating the VCS used

           Because a url like "http://myrepo.example.com/" is ambiguous as to
           type, producers should provide a "type" whenever a "url" key is
           given.  The "type" field should be the name of the most common
           program used to work with the repository, e.g. "git", "svn", "cvs",
           "darcs", "bzr" or "hg".

   DEPRECATED FIELDS
       build_requires

       (Deprecated in Spec 2) [optional] {String}

       Replaced by "prereqs"

       configure_requires

       (Deprecated in Spec 2) [optional] {String}

       Replaced by "prereqs"

       conflicts

       (Deprecated in Spec 2) [optional] {String}

       Replaced by "prereqs"

       distribution_type

       (Deprecated in Spec 2) [optional] {String}

       This field indicated 'module' or 'script' but was considered
       meaningless, since many distributions are hybrids of several kinds of
       things.

       license_uri

       (Deprecated in Spec 1.2) [optional] {URL}

       Replaced by "license" in "resources"

       private

       (Deprecated in Spec 1.2) [optional] {Map}

       This field has been renamed to "no_index".

       recommends

       (Deprecated in Spec 2) [optional] {String}

       Replaced by "prereqs"

       requires

       (Deprecated in Spec 2) [optional] {String}

       Replaced by "prereqs"


VERSION NUMBERS

   Version Formats
       This section defines the Version type, used by several fields in the
       CPAN Meta Spec.

       Version numbers must be treated as strings, not numbers.  For example,
       1.200 must not be serialized as 1.2.  Version comparison should be
       delegated to the Perl version module, version 0.80 or newer.

       Unless otherwise specified, version numbers must appear in one of two
       formats:

       Decimal versions
           Decimal versions are regular "decimal numbers", with some
           limitations.  They must be non-negative and must begin and end with
           a digit.  A single underscore may be included, but must be between
           two digits.  They must not use exponential notation ("1.23e-2").

              version => '1.234'       # OK
              version => '1.23_04'     # OK

              version => '1.23_04_05'  # Illegal
              version => '1.'          # Illegal
              version => '.1'          # Illegal

       Dotted-integer versions
           Dotted-integer (also known as dotted-decimal) versions consist of
           positive integers separated by full stop characters (i.e. "dots",
           "periods" or "decimal points").  This are equivalent in format to
           Perl "v-strings", with some additional restrictions on form.  They
           must be given in "normal" form, which has a leading "v" character
           and at least three integer components.  To retain a one-to-one
           mapping with decimal versions, all components after the first
           should be restricted to the range 0 to 999.  The final component
           may be separated by an underscore character instead of a period.

              version => 'v1.2.3'      # OK
              version => 'v1.2_3'      # OK
              version => 'v1.2.3.4'    # OK
              version => 'v1.2.3_4'    # OK
              version => 'v2009.10.31' # OK

              version => 'v1.2'          # Illegal
              version => '1.2.3'         # Illegal
              version => 'v1.2_3_4'      # Illegal
              version => 'v1.2009.10.31' # Not recommended

   Version Ranges
       Some fields (prereq, optional_features) indicate the particular
       version(s) of some other module that may be required as a prerequisite.
       This section details the Version Range type used to provide this
       information.

       The simplest format for a Version Range is just the version number
       itself, e.g. 2.4.  This means that at least version 2.4 must be
       present.  To indicate that any version of a prerequisite is okay, even
       if the prerequisite doesn't define a version at all, use the version 0.

       Alternatively, a version range may use the operators < (less than), <=
       (less than or equal), > (greater than), >= (greater than or equal), ==
       (equal), and != (not equal).  For example, the specification "< 2.0"
       means that any version of the prerequisite less than 2.0 is suitable.

       For more complicated situations, version specifications may be AND-ed
       together using commas.  The specification ">= 1.2, != 1.5, < 2.0"
       indicates a version that must be at least 1.2, less than 2.0, and not
       equal to 1.5.


PREREQUISITES

   Prereq Spec
       The "prereqs" key in the top-level metadata and within
       "optional_features" define the relationship between a distribution and
       other packages.  The prereq spec structure is a hierarchical data
       structure which divides prerequisites into Phases of activity in the
       installation process and Relationships that indicate how prerequisites
       should be resolved.

       For example, to specify that "Data::Dumper" is "required" during the
       "test" phase, this entry would appear in the distribution metadata:

         prereqs => {
           test => {
             requires => {
               'Data::Dumper' => '2.00'
             }
           }
         }

       Phases

       Requirements for regular use must be listed in the "runtime" phase.
       Other requirements should be listed in the earliest stage in which they
       are required and consumers must accumulate and satisfy requirements
       across phases before executing the activity. For example, "build"
       requirements must also be available during the "test" phase.

         before action       requirements that must be met
         ----------------    --------------------------------
         perl Build.PL       configure
         perl Makefile.PL

         make                configure, runtime, build
         Build

         make test           configure, runtime, build, test
         Build test

       Consumers that install the distribution must ensure that runtime
       requirements are also installed and may install dependencies from other
       phases.

         after action        requirements that must be met
         ----------------    --------------------------------
         make install        runtime
         Build install

       configure
           The configure phase occurs before any dynamic configuration has
           been attempted.  Libraries required by the configure phase must be
           available for use before the distribution building tool has been
           executed.

       build
           The build phase is when the distribution's source code is compiled
           (if necessary) and otherwise made ready for installation.

       test
           The test phase is when the distribution's automated test suite is
           run.  Any library that is needed only for testing and not for
           subsequent use should be listed here.

       runtime
           The runtime phase refers not only to when the distribution's
           contents are installed, but also to its continued use.  Any library
           that is a prerequisite for regular use of this distribution should
           be indicated here.

       develop
           The develop phase's prereqs are libraries needed to work on the
           distribution's source code as its author does.  These tools might
           be needed to build a release tarball, to run author-only tests, or
           to perform other tasks related to developing new versions of the
           distribution.

       Relationships

       requires
           These dependencies must be installed for proper completion of the
           phase.

       recommends
           Recommended dependencies are strongly encouraged and should be
           satisfied except in resource constrained environments.

       suggests
           These dependencies are optional, but are suggested for enhanced
           operation of the described distribution.

       conflicts
           These libraries cannot be installed when the phase is in operation.
           This is a very rare situation, and the "conflicts" relationship
           should be used with great caution, or not at all.

   Merging and Resolving Prerequisites
       Whenever metadata consumers merge prerequisites, either from different
       phases or from "optional_features", they should merged in a way which
       preserves the intended semantics of the prerequisite structure.
       Generally, this means concatenating the version specifications using
       commas, as described in the "Version Ranges" section.

       Another subtle error that can occur in resolving prerequisites comes
       from the way that modules in prerequisites are indexed to distribution
       files on CPAN.  When a module is deleted from a distribution,
       prerequisites calling for that module could indicate an older
       distribution should be installed, potentially overwriting files from a
       newer distribution.

       For example, as of Oct 31, 2009, the CPAN index file contained these
       module-distribution mappings:

         Class::MOP                   0.94  D/DR/DROLSKY/Class-MOP-0.94.tar.gz
         Class::MOP::Class            0.94  D/DR/DROLSKY/Class-MOP-0.94.tar.gz
         Class::MOP::Class::Immutable 0.04  S/ST/STEVAN/Class-MOP-0.36.tar.gz

       Consider the case where "Class::MOP" 0.94 is installed.  If a
       distribution specified "Class::MOP::Class::Immutable" as a
       prerequisite, it could result in Class-MOP-0.36.tar.gz being installed,
       overwriting any files from Class-MOP-0.94.tar.gz.

       Consumers of metadata should test whether prerequisites would result in
       installed module files being "downgraded" to an older version and may
       warn users or ignore the prerequisite that would cause such a result.


SERIALIZATION

       Distribution metadata should be serialized (as a hashref) as JSON-
       encoded data and packaged with distributions as the file META.json.

       In the past, the distribution metadata structure had been packed with
       distributions as META.yml, a file in the YAML Tiny format (for which,
       see YAML::Tiny).  Tools that consume distribution metadata from disk
       should be capable of loading META.yml, but should prefer META.json if
       both are found.


NOTES FOR IMPLEMENTORS

   Extracting Version Numbers from Perl Modules
       To get the version number from a Perl module, consumers should use the
       "MM->parse_version($file)" method provided by ExtUtils::MakeMaker or
       Module::Metadata.  For example, for the module given by $mod, the
       version may be retrieved in one of the following ways:

         # via ExtUtils::MakeMaker
         my $file = MM->_installed_file_for_module($mod);
         my $version = MM->parse_version($file)

       The private "_installed_file_for_module" method may be replaced with
       other methods for locating a module in @INC.

         # via Module::Metadata
         my $info = Module::Metadata->new_from_module($mod);
         my $version = $info->version;

       If only a filename is available, the following approach may be used:

         # via Module::Build
         my $info = Module::Metadata->new_from_file($file);
         my $version = $info->version;

   Comparing Version Numbers
       The version module provides the most reliable way to compare version
       numbers in all the various ways they might be provided or might exist
       within modules.  Given two strings containing version numbers, $v1 and
       $v2, they should be converted to "version" objects before using
       ordinary comparison operators.  For example:

         use version;
         if ( version->new($v1) <=> version->new($v2) ) {
           print "Versions are not equal\n";
         }

       If the only comparison needed is whether an installed module is of a
       sufficiently high version, a direct test may be done using the string
       form of "eval" and the "use" function.  For example, for module $mod
       and version prerequisite $prereq:

         if ( eval "use $mod $prereq (); 1" ) {
           print "Module $mod version is OK.\n";
         }

       If the values of $mod and $prereq have not been scrubbed, however, this
       presents security implications.

   Prerequisites for dynamically configured distributions
       When "dynamic_config" is true, it is an error to presume that the
       prerequisites given in distribution metadata will have any relationship
       whatsoever to the actual prerequisites of the distribution.

       In practice, however, one can generally expect such prerequisites to be
       one of two things:

       o   The minimum prerequisites for the distribution, to which dynamic
           configuration will only add items

       o   Whatever the distribution configured with on the releaser's machine
           at release time

       The second case often turns out to have identical results to the first
       case, albeit only by accident.

       As such, consumers may use this data for informational analysis, but
       presenting it to the user as canonical or relying on it as such is
       invariably the height of folly.

   Indexing distributions a la PAUSE
       While no_index tells you what must be ignored when indexing, this spec
       holds no opinion on how you should get your initial candidate list of
       things to possibly index. For "normal" distributions you might consider
       simply indexing the contents of lib/, but there are many fascinating
       oddities on CPAN and many dists from the days when it was normal to put
       the main .pm file in the root of the distribution archive - so PAUSE
       currently indexes all .pm and .PL files that are not either (a)
       specifically excluded by no_index (b) in "inc", "xt", or "t"
       directories, or common 'mistake' directories such as "perl5".

       Or: If you're trying to be PAUSE-like, make sure you skip "inc", "xt"
       and "t" as well as anything marked as no_index.

       Also remember: If the META file contains a provides field, you
       shouldn't be indexing anything in the first place - just use that.


SEE ALSO

       o   CPAN, <http://www.cpan.org/>

       o   JSON, <http://json.org/>

       o   YAML, <http://www.yaml.org/>

       o   CPAN

       o   CPANPLUS

       o   ExtUtils::MakeMaker

       o   Module::Build

       o   Module::Install


HISTORY

       Ken Williams wrote the original CPAN Meta Spec (also known as the
       "META.yml spec") in 2003 and maintained it through several revisions
       with input from various members of the community.  In 2005, Randy Sims
       redrafted it from HTML to POD for the version 1.2 release.  Ken
       continued to maintain the spec through version 1.4.

       In late 2009, David Golden organized the version 2 proposal review
       process.  David and Ricardo Signes drafted the final version 2 spec in
       April 2010 based on the version 1.4 spec and patches contributed during
       the proposal process.


AUTHORS

       o   David Golden <dagolden@cpan.org>

       o   Ricardo Signes <rjbs@cpan.org>


COPYRIGHT AND LICENSE

       This software is copyright (c) 2010 by David Golden and Ricardo Signes.

       This is free software; you can redistribute it and/or modify it under
       the same terms as the Perl 5 programming language system itself.



perl v5.24.0                      2016-03-01             CPAN::Meta::Spec(3pm)

perl 5.24 - Generated Sat Nov 5 08:42:20 CDT 2016
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