Module Builder

SCons.Builder

Builder object subsystem.

A Builder object is a callable that encapsulates information about how
to execute actions to create a target Node (file) from source Nodes
(files), and how to create those dependencies for tracking.

The main entry point here is the Builder() factory method.  This provides
a procedural interface that creates the right underlying Builder object
based on the keyword arguments supplied and the types of the arguments.

The goal is for this external interface to be simple enough that the
vast majority of users can create new Builders as necessary to support
building new types of files in their configurations, without having to
dive any deeper into this subsystem.

The base class here is BuilderBase.  This is a concrete base class which
does, in fact, represent the Builder objects that we (or users) create.

There is also a proxy that looks like a Builder:

    CompositeBuilder

        This proxies for a Builder with an action that is actually a
        dictionary that knows how to map file suffixes to a specific
        action.  This is so that we can invoke different actions
        (compilers, compile options) for different flavors of source
        files.

Builders and their proxies have the following public interface methods
used by other modules:

    __call__()
        THE public interface.  Calling a Builder object (with the
        use of internal helper methods) sets up the target and source
        dependencies, appropriate mapping to a specific action, and the
        environment manipulation necessary for overridden construction
        variable.  This also takes care of warning about possible mistakes
        in keyword arguments.

    add_emitter()
        Adds an emitter for a specific file suffix, used by some Tool
        modules to specify that (for example) a yacc invocation on a .y
        can create a .h *and* a .c file.

    add_action()
        Adds an action for a specific file suffix, heavily used by
        Tool modules to add their specific action(s) for turning
        a source file into an object file to the global static
        and shared object file Builders.

There are the following methods for internal use within this module:

    _execute()
        The internal method that handles the heavily lifting when a
        Builder is called.  This is used so that the __call__() methods
        can set up warning about possible mistakes in keyword-argument
        overrides, and *then* execute all of the steps necessary so that
        the warnings only occur once.

    get_name()
        Returns the Builder's name within a specific Environment,
        primarily used to try to return helpful information in error
        messages.

    adjust_suffix()
    get_prefix()
    get_suffix()
    get_src_suffix()
    set_src_suffix()
        Miscellaneous stuff for handling the prefix and suffix
        manipulation we use in turning source file names into target
        file names.

Validate that the lists of target and source nodes are
legal for this builder and environment.  Raise errors or
issue warnings as appropriate.

"Returns True iff the specified obj is one of our Builder classes.

The test is complicated a bit by the fact that CompositeBuilder
is a proxy, not a subclass of BuilderBase.