THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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1.
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Background
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A.
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Shared
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Context
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in
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Systems
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of
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Interchangeable
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Components
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Most
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large,
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component-oriented
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systems
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provide
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a
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shared
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context
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for
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their
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components,
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so
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alternative
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component
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implementations
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are
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not
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dependent
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on
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a
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single,
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restrictive
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(or,
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even
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worse,
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all-anticipating)
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API
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to
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pass
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information
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across
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multiple
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subsystems.
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Such
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parameter-passing
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leads
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to
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bloated
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or
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inadequate
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APIs,
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since
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the
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API
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designer
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can
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choose
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either
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to
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try
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to
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accommodate
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every
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possible
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implementation
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for
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a
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component,
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or
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he
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can
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restrict
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the
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API
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to
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the
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minimum
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necessary
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to
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do
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the
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job
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with
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the
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original
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implementation.
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Resources
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like
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database
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connection
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pools
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are
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a
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good
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example
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of
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items
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that
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live
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in
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this
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shared
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context.
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Components
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that
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require
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such
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resources
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simply
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look
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them
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up,
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or
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are
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wired
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to
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use
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them
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by
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a
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composing
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container,
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instead
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of
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forcing
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all
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APIs
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in
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between
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the
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connection
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pool
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initializer
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and
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consumer
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to
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pass
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the
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pool
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instance
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around.
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B.
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Relevance
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to
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Maven
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Maven
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is
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a
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large,
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component-oriented
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application
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built
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on
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top
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of
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a
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container
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(Plexus)
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which
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is
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capable
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of
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this
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sort
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of
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composition.
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However,
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Maven's
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component
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implementations
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are
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currently
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restricted
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to
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the
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APIs
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used
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to
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pass
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information
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around
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the
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system.
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They
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don't
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have
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ready
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access
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to
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a
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shared
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context
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for
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reading
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build-time
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information.
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Also,
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they
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cannot
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coordinate
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build
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activities
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with
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one
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another.
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This
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lack
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of
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shared
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context
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leads
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to
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an
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unnecessarily
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restrictive
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set
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of
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component
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implementations
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and
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inefficient
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build
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processes.
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Maven
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component
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implementations
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-
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including,
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but
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not
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restricted
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to,
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plugins
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-
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must
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have
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the
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ability
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to
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retrieve
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as
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much
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information
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as
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possible
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about
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the
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current
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build
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environment.
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2.
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Problem
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A.
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No
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Support
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for
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Querying
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Dynamic,
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Build-Time
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State
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Currently,
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Maven
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provides
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a
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mechanism
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for
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injecting
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static
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information
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about
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the
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current
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build
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into
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plugins.
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It
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also
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supports
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wiring
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plugins
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and
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other
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components
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with
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component
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requirements,
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which
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allow
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them
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to
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retrieve
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further
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information
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about
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the
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current
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build,
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though
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this
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information
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currently
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is
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not
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cached
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for
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successive
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querying
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in
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a
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threadsafe
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way.
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It
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does
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not
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provide
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a
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mechanism
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for
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retrieving
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dynamic
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build-time
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state
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or
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progress
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for
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custom
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components
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and
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plugins
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to
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use.
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B.
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Embeddable
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Property-Passing
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The
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simple
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act
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of
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passing
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System
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properties
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in
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an
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embeddable
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way
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(where
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"System"
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properties
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need
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to
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vary
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across
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multiple
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threads
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in
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a
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single
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Maven
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instance)
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introduces
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major
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API
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changes,
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since
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these
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properties,
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which
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are
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initialized
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at
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the
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beginning
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of
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the
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build,
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must
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be
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passed
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throughout
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the
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system
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until
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they
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reach
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the
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appropriate
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components.
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In
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some
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cases,
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these
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properties
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must
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propagate
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through
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five
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or
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six
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layers
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of
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Maven
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APIs
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before
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they
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can
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be
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used.
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Yet
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in
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many
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ways,
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the
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System
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properties
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represent
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a
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shared
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context
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(though
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too
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widely
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shared,
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in
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the
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embedded
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scenario)
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by
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which
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component-specific
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configurations
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can
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be
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communicated
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from
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the
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application
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entry
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point
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to
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the
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appropriate
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component.
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C.
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Plugins
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in
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Silos
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Additionally,
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there
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is
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no
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way
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for
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plugins
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to
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mark
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progress
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in
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a
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build,
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or
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signal
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that
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they
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have
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detected
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a
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state
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where
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the
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build
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has
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not
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failed
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but
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also
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should
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not
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proceed.
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Multiple
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mojos
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within
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a
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single
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plugin
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can
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pass
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information
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by
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way
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of
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a
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context
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map,
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but
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this
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context
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map
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restricts
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the
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consuming
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mojos
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to
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usage
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scenarios
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that
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also
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involve
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their
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counterpart
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mojos,
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since
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they
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cannot
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function
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properly
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without
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their
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counterparts
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in
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place,
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regardless
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of
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whether
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the
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functions
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of
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these
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counterparts
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could
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be
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fulfilled
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in
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other
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ways.
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3.
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Proposed
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Solution
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A.
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The
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Build
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Context
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As
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a
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solution
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to
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the
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problem
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of
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a
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build-time
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shared
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context,
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a
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new
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project
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called
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maven-build-context
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should
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be
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created.
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This
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project
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would
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provide
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a
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formal
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mechanism
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for
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storing
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and
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retrieving
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structured
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data
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from
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the
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Plexus
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container's
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Context
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map.
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By
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using
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a
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set
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of
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tools
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to
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access
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the
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shared
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context,
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it
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can
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be
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scoped
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appropriately
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(per-project,
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per-thread,
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etc.)
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in
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such
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a
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way
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as
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to
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avoid
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the
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problems
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encountered
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when
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using
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System
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properties
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in
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an
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embedded
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environment.
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By
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using
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structured
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data,
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it's
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possible
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to
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avoid
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datatype-conversion
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problems
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(coercing
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a
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String
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to
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an
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int,
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for
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example).
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B.
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Plugin
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Cooperation
By using a shared datatype with a controlled vocabulary, it's
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possible
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for
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plugins
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to
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cooperatively
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determine
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whether
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to
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execute,
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based
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on
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the
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actions
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of
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other
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plugins
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that
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were
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registered
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in
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the
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shared
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context.
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Plugins
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that
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go
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further
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in
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detecting
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build
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configurations
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beyond
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that
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explicitly
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laid
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out
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in
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the
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POM
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could
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inject
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this
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detected
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configuration
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for
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use
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by
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other
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plugins.
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Such
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advanced
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state
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might
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include
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the
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source
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or
...
method
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used
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to
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resolve
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each
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project
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dependency,
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so
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that
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dependencies
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from
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certain
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sources
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can
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be
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handled
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differently
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when
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the
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project
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is
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deployed
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(imagine
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building
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certain
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dependencies
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from
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source,
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then
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deploying
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those
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built
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dependencies
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alongside
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the
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main
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project
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artifact
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automatically).
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C.
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Baking
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it
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into
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the
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Container
Ideally,
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these
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shared-context
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objects
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should
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be
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wired
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in
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as
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part
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of
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the
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composition
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process
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for
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dependent
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components,
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and
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injected
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into
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mojos
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along
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with
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things
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like
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$
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{localRepository}
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or
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$
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{project}.
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The
...
act
...
of
...
querying
...
the
...
application
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for
...
this
...
build-time
...
information
...
makes
...
it
...
much
...
more
...
difficult
...
to
...
chart
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dependencies
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between
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components
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that
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produce
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and
...
consume
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such
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information.
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Therefore,
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it's
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important
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to
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specify
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this
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information
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as
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declaratively
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as
...
possible,
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in
...
order
...
to
...
catch
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potential
...
problems
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ahead
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of
...
time,
...
before
...
the
...
build
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is
...
in
...
progress.
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Rudimentary
...
specification
...
of
...
a
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<dependency/>
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element
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in
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each
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component's
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POM
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that
...
points
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to
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the
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shared
...
datatype
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is
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a
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good
...
start,
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but
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still
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doesn't
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enable
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a
...
more
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advanced
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validation
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that
...
producer
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and
...
consumer
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of
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this
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shared
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datatype
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are
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present
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and
...
aligned
...
properly.
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4.
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Potential
...
Drawbacks
A.
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Inter-Plugin
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Dependencies
...
Obviously,
...
the
...
biggest
...
concern
...
here
...
is
...
the
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ability
...
to
...
form
...
inter-plugin
...
dependencies
...
by
...
specifying
...
a
...
shared
...
datatype
...
in
...
one
...
plugin,
...
and
...
developing
...
another
...
plugin
...
that
...
depends
...
on
...
that
...
datatype.
...
However,
...
such
...
a
...
dependency
...
doesn't
...
preclude
...
a
...
new
...
plugin
...
from
...
specifying
...
a
...
binary
...
(not
...
lifecycle)
...
dependency
...
on
...
the
...
original
...
plugin
...
(the
...
one
...
with
...
shared
...
the
...
datatype),
...
then
...
acting
...
as
...
an
...
alternative
...
producer.
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An
...
even
...
better
...
approach
...
would
...
be
...
to
...
specify
...
the
...
shared
...
datatype
...
in
...
its
...
own
...
project,
...
then
...
provide
...
dependencies
...
on
...
this
...
new
...
project
...
for
...
each
...
of
...
the
...
three
...
plugins.
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By
...
doing
...
this,
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a
...
developer
...
effectively
...
creates
...
an
...
open
...
protocol
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for
...
an
...
infinite
...
array
...
of
...
plugins
...
to
...
communicate
...
with
...
one
...
another
...
through
...
the
...
shared
...
context
...
of
...
the
...
build.
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5.
...
Relevant
...
Conversations
...
A.
...
Transcripts
...
...
...
...
...
...
...
...
...
B.
...
Paraphrased
...
Comments
...
from
...
Maven
...
Developers'
...
List
| Panel | ||||||
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It would be useful to allow reading Maven project instances from sources other than XML files, so we could create them from Manifest.mf/plugin.xml files for Eclipse plugins. Alternately, it would be useful to allow modification of the sorted project list in the reactor (possibly by way of a build-context data element) to allow a plugin to perform a second pass at project-building, and inject those built from Manifests, etc. {panel} {panel|title= |
| Panel | ||||
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| }
It would be nice if Maven could detect whether any action was taken in a previous lifecycle phase, and avoid later actions if they don't need to be performed. Big example here is the jar plugin skipping repackaging if the compile/resources phases didn't execute. {panel} |