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+// Copyright 2012 Jesse van den Kieboom. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package flags provides an extensive command line option parser.
+The flags package is similar in functionality to the go built-in flag package
+but provides more options and uses reflection to provide a convenient and
+succinct way of specifying command line options.
+
+
+Supported features
+
+The following features are supported in go-flags:
+
+    Options with short names (-v)
+    Options with long names (--verbose)
+    Options with and without arguments (bool v.s. other type)
+    Options with optional arguments and default values
+    Option default values from ENVIRONMENT_VARIABLES, including slice and map values
+    Multiple option groups each containing a set of options
+    Generate and print well-formatted help message
+    Passing remaining command line arguments after -- (optional)
+    Ignoring unknown command line options (optional)
+    Supports -I/usr/include -I=/usr/include -I /usr/include option argument specification
+    Supports multiple short options -aux
+    Supports all primitive go types (string, int{8..64}, uint{8..64}, float)
+    Supports same option multiple times (can store in slice or last option counts)
+    Supports maps
+    Supports function callbacks
+    Supports namespaces for (nested) option groups
+
+Additional features specific to Windows:
+    Options with short names (/v)
+    Options with long names (/verbose)
+    Windows-style options with arguments use a colon as the delimiter
+    Modify generated help message with Windows-style / options
+    Windows style options can be disabled at build time using the "forceposix"
+    build tag
+
+
+Basic usage
+
+The flags package uses structs, reflection and struct field tags
+to allow users to specify command line options. This results in very simple
+and concise specification of your application options. For example:
+
+    type Options struct {
+        Verbose []bool `short:"v" long:"verbose" description:"Show verbose debug information"`
+    }
+
+This specifies one option with a short name -v and a long name --verbose.
+When either -v or --verbose is found on the command line, a 'true' value
+will be appended to the Verbose field. e.g. when specifying -vvv, the
+resulting value of Verbose will be {[true, true, true]}.
+
+Slice options work exactly the same as primitive type options, except that
+whenever the option is encountered, a value is appended to the slice.
+
+Map options from string to primitive type are also supported. On the command
+line, you specify the value for such an option as key:value. For example
+
+    type Options struct {
+        AuthorInfo string[string] `short:"a"`
+    }
+
+Then, the AuthorInfo map can be filled with something like
+-a name:Jesse -a "surname:van den Kieboom".
+
+Finally, for full control over the conversion between command line argument
+values and options, user defined types can choose to implement the Marshaler
+and Unmarshaler interfaces.
+
+
+Available field tags
+
+The following is a list of tags for struct fields supported by go-flags:
+
+    short:            the short name of the option (single character)
+    long:             the long name of the option
+    required:         if non empty, makes the option required to appear on the command
+                      line. If a required option is not present, the parser will
+                      return ErrRequired (optional)
+    description:      the description of the option (optional)
+    long-description: the long description of the option. Currently only
+                      displayed in generated man pages (optional)
+    no-flag:          if non-empty, this field is ignored as an option (optional)
+
+    optional:       if non-empty, makes the argument of the option optional. When an
+                    argument is optional it can only be specified using
+                    --option=argument (optional)
+    optional-value: the value of an optional option when the option occurs
+                    without an argument. This tag can be specified multiple
+                    times in the case of maps or slices (optional)
+    default:        the default value of an option. This tag can be specified
+                    multiple times in the case of slices or maps (optional)
+    default-mask:   when specified, this value will be displayed in the help
+                    instead of the actual default value. This is useful
+                    mostly for hiding otherwise sensitive information from
+                    showing up in the help. If default-mask takes the special
+                    value "-", then no default value will be shown at all
+                    (optional)
+    env:            the default value of the option is overridden from the
+                    specified environment variable, if one has been defined.
+                    (optional)
+    env-delim:      the 'env' default value from environment is split into
+                    multiple values with the given delimiter string, use with
+                    slices and maps (optional)
+    value-name:     the name of the argument value (to be shown in the help)
+                    (optional)
+    choice:         limits the values for an option to a set of values.
+                    This tag can be specified multiple times (optional)
+    hidden:         if non-empty, the option is not visible in the help or man page.
+
+    base: a base (radix) used to convert strings to integer values, the
+          default base is 10 (i.e. decimal) (optional)
+
+    ini-name:       the explicit ini option name (optional)
+    no-ini:         if non-empty this field is ignored as an ini option
+                    (optional)
+
+    group:                when specified on a struct field, makes the struct
+                          field a separate group with the given name (optional)
+    namespace:            when specified on a group struct field, the namespace
+                          gets prepended to every option's long name and
+                          subgroup's namespace of this group, separated by
+                          the parser's namespace delimiter (optional)
+    command:              when specified on a struct field, makes the struct
+                          field a (sub)command with the given name (optional)
+    subcommands-optional: when specified on a command struct field, makes
+                          any subcommands of that command optional (optional)
+    alias:                when specified on a command struct field, adds the
+                          specified name as an alias for the command. Can be
+                          be specified multiple times to add more than one
+                          alias (optional)
+    positional-args:      when specified on a field with a struct type,
+                          uses the fields of that struct to parse remaining
+                          positional command line arguments into (in order
+                          of the fields). If a field has a slice type,
+                          then all remaining arguments will be added to it.
+                          Positional arguments are optional by default,
+                          unless the "required" tag is specified together
+                          with the "positional-args" tag. The "required" tag
+                          can also be set on the individual rest argument
+                          fields, to require only the first N positional
+                          arguments. If the "required" tag is set on the
+                          rest arguments slice, then its value determines
+                          the minimum amount of rest arguments that needs to
+                          be provided (e.g. `required:"2"`) (optional)
+    positional-arg-name:  used on a field in a positional argument struct; name
+                          of the positional argument placeholder to be shown in
+                          the help (optional)
+
+Either the `short:` tag or the `long:` must be specified to make the field eligible as an
+option.
+
+
+Option groups
+
+Option groups are a simple way to semantically separate your options. All
+options in a particular group are shown together in the help under the name
+of the group. Namespaces can be used to specify option long names more
+precisely and emphasize the options affiliation to their group.
+
+There are currently three ways to specify option groups.
+
+    1. Use NewNamedParser specifying the various option groups.
+    2. Use AddGroup to add a group to an existing parser.
+    3. Add a struct field to the top-level options annotated with the
+       group:"group-name" tag.
+
+
+
+Commands
+
+The flags package also has basic support for commands. Commands are often
+used in monolithic applications that support various commands or actions.
+Take git for example, all of the add, commit, checkout, etc. are called
+commands. Using commands you can easily separate multiple functions of your
+application.
+
+There are currently two ways to specify a command.
+
+    1. Use AddCommand on an existing parser.
+    2. Add a struct field to your options struct annotated with the
+       command:"command-name" tag.
+
+The most common, idiomatic way to implement commands is to define a global
+parser instance and implement each command in a separate file. These
+command files should define a go init function which calls AddCommand on
+the global parser.
+
+When parsing ends and there is an active command and that command implements
+the Commander interface, then its Execute method will be run with the
+remaining command line arguments.
+
+Command structs can have options which become valid to parse after the
+command has been specified on the command line, in addition to the options
+of all the parent commands. I.e. considering a -v flag on the parser and an
+add command, the following are equivalent:
+
+    ./app -v add
+    ./app add -v
+
+However, if the -v flag is defined on the add command, then the first of
+the two examples above would fail since the -v flag is not defined before
+the add command.
+
+
+Completion
+
+go-flags has builtin support to provide bash completion of flags, commands
+and argument values. To use completion, the binary which uses go-flags
+can be invoked in a special environment to list completion of the current
+command line argument. It should be noted that this `executes` your application,
+and it is up to the user to make sure there are no negative side effects (for
+example from init functions).
+
+Setting the environment variable `GO_FLAGS_COMPLETION=1` enables completion
+by replacing the argument parsing routine with the completion routine which
+outputs completions for the passed arguments. The basic invocation to
+complete a set of arguments is therefore:
+
+    GO_FLAGS_COMPLETION=1 ./completion-example arg1 arg2 arg3
+
+where `completion-example` is the binary, `arg1` and `arg2` are
+the current arguments, and `arg3` (the last argument) is the argument
+to be completed. If the GO_FLAGS_COMPLETION is set to "verbose", then
+descriptions of possible completion items will also be shown, if there
+are more than 1 completion items.
+
+To use this with bash completion, a simple file can be written which
+calls the binary which supports go-flags completion:
+
+    _completion_example() {
+        # All arguments except the first one
+        args=("${COMP_WORDS[@]:1:$COMP_CWORD}")
+
+        # Only split on newlines
+        local IFS=$'\n'
+
+        # Call completion (note that the first element of COMP_WORDS is
+        # the executable itself)
+        COMPREPLY=($(GO_FLAGS_COMPLETION=1 ${COMP_WORDS[0]} "${args[@]}"))
+        return 0
+    }
+
+    complete -F _completion_example completion-example
+
+Completion requires the parser option PassDoubleDash and is therefore enforced if the environment variable GO_FLAGS_COMPLETION is set.
+
+Customized completion for argument values is supported by implementing
+the flags.Completer interface for the argument value type. An example
+of a type which does so is the flags.Filename type, an alias of string
+allowing simple filename completion. A slice or array argument value
+whose element type implements flags.Completer will also be completed.
+*/
+package flags