path: root/libbuild2/b.cli

// file      : libbuild2/b.cli
// license   : MIT; see accompanying LICENSE file

include <set>;

include <libbuild2/common.cli>;

"\section=1"
"\name=b"
"\summary=build system driver"

namespace build2
{
  {
    "<options>
     <variables>
     <buildspec> <meta-operation> <operation> <target> <parameters>",

    "\h|SYNOPSIS|

     \c{\b{b --help}\n
        \b{b --version}\n
        \b{b} [<options>] [<variables>] [<buildspec>]}

     \c{<buildspec> = <meta-operation>\b{(}<operation>\b{(}<target>...[\b{,}<parameters>]\b{)}...\b{)}...}

     \h|DESCRIPTION|

     The \cb{build2} build system driver executes a set of meta-operations on
     operations on targets according to the build specification, or
     \i{buildspec} for short.  This process can be controlled by specifying
     driver <options> and build system <variables>.

     Note that <options>, <variables>, and <buildspec> fragments can be
     specified in any order. To avoid treating an argument that starts with
     \cb{'-'} as an option, add the \cb{'--'} separator. To avoid treating an
     argument that contains \cb{'='} as a variable, add the second \cb{'--'}
     separator."
  }

  // For usage it's nice to see the list of options on the first page. So
  // let's not put this "extended" description into usage.
  //
  {
    "<meta-operation> <operation> <target> <parameters> <src-base>",
    "",

    "All components in the buildspec can be omitted. If <meta-operation> is
     omitted, then it defaults to \cb{perform}. If <operation> is omitted,
     then it defaults to the default operation for this meta-operation. For
     \cb{perform} it is \cb{update}. Finally, if <target> is omitted, then it
     defaults to the current working directory. A meta-operation on operation
     is called an \i{action}. Some operations and meta-operations may take
     additional <parameters>. For example:

     \
     $ b                       # perform(update(./))
     $ b foo/                  # perform(update(foo/))
     $ b foo/ bar/             # perform(update(foo/ bar/))
     $ b update                # perform(update(./))
     $ b 'clean(../)'          # perform(clean(../))
     $ b perform               # perform(update(./))
     $ b configure             # configure(?(./))
     $ b 'configure(../)'      # configure(?(../))
     $ b clean update          # perform(clean(./) update(./))
     $ b configure update      # configure(?(./)) perform(update(./))
     $ b 'create(conf/, cxx)'  # create(?(conf/), cxx)
     \

     Notice the question mark used to show the (imaginary) default operation
     for the \cb{configure} meta-operation. For \cb{configure} the default
     operation is \"all operations\". That is, it will configure all the
     operations for the specified target.

     You can also \"generate\" multiple operations for the same set of targets.
     Compare:

     \
     $ b 'clean(foo/ bar/)' 'update(foo/ bar/)'
     $ b '{clean update}(foo/ bar/)'
     \

     Some more useful buildspec examples:

     \
     $ b '{clean update}(...)'        # rebuild
     $ b '{clean update clean}(...)'  # make sure builds
     $ b '{clean test clean}(...)'    # make sure passes tests
     $ b '{clean disfigure}(...)'     # similar to distclean
     \

     In POSIX shells parenthesis are special characters and must be quoted
     when used in a buildspec. Besides being an inconvenience in itself,
     quoting also inhibits path auto-completion. To help with this situation a
     shortcut syntax is available for executing a single operation or
     meta-operation, for example:

     \
     $ b clean: foo/ bar/                # clean(foo/ bar/)
     $ b configure: src/@out/            # configure(src/@out/)
     $ b create: conf/, cxx              # create(conf/, cxx)
     $ b configure: config.cxx=g++ src/  # configure(src/) config.cxx=g++
     \

     To activate the shortcut syntax the first buildspec argument must start
     with an operation or meta-operation name and end with a colon (\cb{:}).
     To transform the shortcut syntax to the normal buildspec syntax the colon
     is replaced with the opening parenthesis ('\cb{(}'), the rest of the
     buildspec arguments are treated as is, and the final closing parenthesis
     ('\cb{)}') is added.

     For each <target> the driver expects to find \cb{buildfile} either in the
     target's directory or, if the directory is part of the \cb{out} tree
     (\cb{out_base}), in the corresponding \cb{src} directory (\cb{src_base}).

     For example, assuming \cb{foo/} is the source directory of a project:

     \
     $ b foo/              # out_base=src_base=foo/
     $ b foo-out/          # out_base=foo-out/ src_base=foo/
     $ b foo-out/exe{foo}  # out_base=foo-out/ src_base=foo/
     \

     An exception to this requirement is a directory target in which case,
     provided the directory has subdirectories, an \i{implied} \cb{buildfile}
     with the following content is assumed:

     \
     # Implied directory buildfile: build all subdirectories.
     #
     ./: */
     \

     In the above example, we assumed that the build system driver was able to
     determine the association between \cb{out_base} and \cb{src_base}. In
     case \cb{src_base} and \cb{out_base} are not the same directory, this is
     achieved in one of two ways: the \cb{config} module (which implements the
     \cb{configure}, \cb{disfigure}, and \cb{create} meta-operations) saves
     this association as part of the configuration process. If, however, the
     association hasn't been saved, then we have to specify \cb{src_base}
     explicitly using the following extended <target> syntax:

     \c{<src-base>/@<target>}

     Continuing with the previous example:

     \
     $ b foo/@foo-out/exe{foo}  # out_base=foo-out/ src_base=foo/
     \

     Normally, you would need to specify \cb{src_base} explicitly only once,
     during configuration. For example, a typical usage would be:

     \
     $ b configure: foo/@foo-out/  # src_base is saved
     $ b foo-out/                  # no need to specify src_base
     $ b clean: foo-out/exe{foo}   # no need to specify src_base
     \

     Besides in and out of source builds, \cb{build2} also supports
     configuring a project's source directory as \i{forwarded} to an out of
     source build. With such a forwarded configuration in place, if we run the
     build system driver from the source directory, it will automatically
     build in the output directory and \i{backlink} (using symlinks or another
     suitable mechanism) certain \"interesting\" targets (executables,
     documentation, etc) to the source directory for easy access. Continuing
     with the previous example:

     \
     $ b configure: foo/@foo-out/,forward  # foo/ forwarded to foo-out/
     $ cd foo/
     $ b                                   # build in foo-out/
     $ ./foo                               # symlink to foo-out/foo
     \

     The ability to specify \cb{build2} variables as part of the command line
     is normally used to pass configuration values, for example:

     \
     $ b config.cxx=clang++ config.cxx.coptions=-O3
     \

     Similar to buildspec, POSIX shells often inhibit path auto-completion on
     the right hand side of a variable assignment. To help with this situation
     the assignment can be broken down into three separate command line
     arguments, for example:

     \
     $ b config.import.libhello = ../libhello/
     \

     The build system has the following built-in and pre-defined
     meta-operations:

     \dl|

     \li|\cb{perform}

         Perform an operation.|

     \li|\cb{configure}

         Configure all operations supported by a project and save the result
         in the project's \cb{build/config.build} file. Implemented by the
         \cb{config} module. For example:

         \
         $ b configure                      \
             config.cxx=clang++             \
             config.cxx.coptions=-O3        \
             config.install.root=/usr/local \
             config.install.root.sudo=sudo
         \

         Use the \cb{forward} parameter to instead configure a source
         directory as forwarded to an out of source build. For example:

         \
         $ b configure: src/@out/,forward
         \

         |

     \li|\cb{disfigure}

         Disfigure all operations supported by a project and remove the
         project's \cb{build/config.build} file. Implemented by the
         \cb{config} module.

         Use the \cb{forward} parameter to instead disfigure forwarding of a
         source directory to an out of source build. For example:

         \
         $ b disfigure: src/,forward
         \

         |

     \li|\cb{create}

         Create and configure a \i{configuration} project. Implemented by the
         \cb{config} module.

         Normally a \cb{build2} project is created manually by writing the
         \cb{bootstrap.build} and \cb{config.build} files, adding source
         files, and so on. However, a special kind of project, which we call
         \i{configuration}, is often useful. Such a project doesn't have any
         source files of its own. Instead, it serves as an amalgamation for
         building other projects as part of it. Doing it this way has two
         major benefits: sub-projects automatically resolve their imports
         to other projects in the amalgamation and sub-projects inherits their
         configuration from the amalgamation (which means if we want to change
         something, we only need to do it in one place).

         As an example, let's assume we have two C++ projects: the
         \cb{libhello} library in \cb{libhello/} and the \cb{hello} executable
         that imports it in \cb{hello/}. And we want to build \cb{hello} with
         \cb{clang++}.

         One way to do it would be to configure and build each project in its
         own directory, for example:

         \
         $ b configure: libhello/@libhello-clang/ config.cxx=clang++
         $ b configure: hello/@hello-clang/ config.cxx=clang++ \
             config.import.libhello=libhello-clang/
         \

         The two drawbacks, as mentioned above, are the need to explicitly
         resolve the import and having to make changes in multiple places
         should, for example, we want to switch from \cb{clang++} to \cb{g++}.

         We can, however, achieve the same end result but without any of the
         drawbacks using the configuration project:

         \
         $ b create: clang/,cxx config.cxx=clang++  # Creates clang/.
         $ b configure: libhello/@clang/libhello/
         $ b configure: hello/@clang/hello/
         \

         The targets passed to the \cb{create} meta-operation must be
         directories which should either not exist or be empty. For each
         such directory \cb{create} first initializes a project as described
         below and then configures it by executing the \cb{configure}
         meta-operation.

         The first optional parameter to \cb{create} is the list of modules to
         load in \cb{root.build}. By default, \cb{create} appends \cb{.config}
         to the names of these modules so that only their configurations are
         loaded. You can override this behavior by specifying the period
         (\cb{.})  after the module name. You can also instruct \cb{create} to
         use the optional module load by prefixing the module name with the
         question mark (\cb{?}).

         The second optional parameter is the list of modules to load in
         \cb{bootstrap.build}. If not specified, then the \cb{test},
         \cb{dist}, and \cb{install} modules are loaded by default. The
         \cb{config} module is always loaded first.

         Besides creating project's \cb{bootstrap.build} and \cb{root.build},
         \cb{create} also writes the root \cb{buildfile} with the following
         contents:

         \
         ./: {*/ -build/}
         \

         If used, this \cb{buildfile} will build all the sub-projects
         currently present in the configuration.|

     \li|\cb{dist}

         Prepare a distribution containing all files necessary to perform all
         operations in a project. Implemented by the \cb{dist} module.|

     \li|\cb{info}

         Print basic information (name, version, source and output
         directories, etc) about one or more projects to \cb{stdout},
         separating multiple projects with a blank line. Each project is
         identified by its root directory target. For example (some output
         is omitted):

         \
         $ b info: libfoo/ libbar/
         project: libfoo
         version: 1.0.0
         src_root: /tmp/libfoo
         out_root: /tmp/libfoo
         subprojects: @tests

         project: libbar
         version: 2.0.0
         src_root: /tmp/libbar
         out_root: /tmp/libbar-out
         subprojects: @tests
         \

         To omit discovering and printing subprojects information, use the
         \cb{no_subprojects} parameter, for example:

         \
         $ b info: libfoo/,no_subprojects
         \

         To instead print this information in the JSON format, use the
         \cb{json} parameter, for example:

         \
         $ b info: libfoo/,json
         \

         In this case the output is a JSON array of objects which are the
         serialized representation of the following C++ \cb{struct}
         \cb{project_info}:

         \
         struct subproject
         {
           string           path;
           optional<string> name;
         };

         struct project_info
         {
           optional<string>   project;
           optional<string>   version;
           optional<string>   summary;
           optional<string>   url;
           string             src_root;
           string             out_root;
           optional<string>   amalgamation;
           vector<subproject> subprojects;
           vector<string>     operations;
           vector<string>     meta_operations;
           vector<string>     modules;
         };
         \

         For example:

         \
         [
           {
             \"project\": \"libfoo\",
             \"version\": \"1.0.0\",
             \"summary\": \"libfoo C++ library\",
             \"src_root\": \"/tmp/libfoo\",
             \"out_root\": \"/tmp/gcc-debug/libfoo\",
             \"amalgamation\": \"..\",
             \"subprojects\": [
               {
                 \"path\": \"tests\"
               }
             ],
             \"operations\": [
               \"update\",
               \"clean\",
               \"test\",
               \"update-for-test\",
               \"install\",
               \"uninstall\",
               \"update-for-install\"
             ],
             \"meta-operations\": [
               \"perform\",
               \"configure\",
               \"disfigure\",
               \"dist\",
               \"info\"
             ],
             \"modules\": [
               \"version\",
               \"config\",
               \"test\",
               \"install\",
               \"dist\"
             ]
           }
         ]
         \

         See the JSON OUTPUT section below for details on the overall
         properties of this format and the semantics of the \cb{struct}
         serialization.

         ||

     The build system has the following built-in and pre-defined operations:

     \dl|

     \li|\cb{update}

         Update a target.|

     \li|\cb{clean}

         Clean a target.|

     \li|\cb{test}

         Test a target. Performs \cb{update} as a pre-operation. Implemented by
         the \cb{test} module.|

     \li|\cb{update-for-test}

         Update a target for testing. This operation is equivalent to the
         \cb{update} pre-operation as executed by the \cb{test} operation and
         can be used to only update what is necessary for testing. Implemented
         by the \cb{test} module.|

     \li|\cb{install}

         Install a target. Performs \cb{update} as a pre-operation. Implemented
         by the \cb{install} module.|


     \li|\cb{uninstall}

         Uninstall a target. Performs \cb{update} as a pre-operation.
         Implemented by the \cb{install} module.|

     \li|\cb{update-for-install}

         Update a target for installation. This operation is equivalent to the
         \cb{update} pre-operation as executed by the \cb{install} operation
         and can be used to only update what is necessary for
         installation. Implemented by the \cb{install} module.||

     Note that buildspec and command line variable values are treated as
     \cb{buildfile} fragments and so can use quoting and escaping as well as
     contain variable expansions and evaluation contexts. However, to be more
     usable on various platforms, escaping in these two situations is limited
     to the \i{effective sequences} of \cb{\\'}, \cb{\\\"}, \cb{\\\\},
     \cb{\\$}, and \cb{\\(} with all other sequences interpreted as is.
     Together with double-quoting this is sufficient to represent any value.
     For example:

     \
     $ b config.install.root=c:\projects\install
     $ b \"config.install.root='c:\Program Files\test\'\"
     $ b 'config.cxx.poptions=-DFOO_STR=\"foo\"'
     \
     "
  }

  class b_options
  {
    "\h#options|OPTIONS|"

    uint64_t --build2-metadata; // Leave undocumented/hidden.

    bool -v
    {
      "Print actual commands being executed. This options is equivalent to
       \cb{--verbose 2}."
    }

    bool -V
    {
      "Print all underlying commands being executed. This options is
       equivalent to \cb{--verbose 3}."
    }

    bool --quiet|-q
    {
      "Run quietly, only printing error messages in most contexts. In certain
       contexts (for example, while updating build system modules) this
       verbosity level may be ignored. Use \cb{--silent} to run quietly in all
       contexts. This option is equivalent to \cb{--verbose 0}."
    }

    bool --silent
    {
      "Run quietly, only printing error messages in all contexts."
    }

    uint16_t --verbose = 1
    {
      "<level>",
      "Set the diagnostics verbosity to <level> between 0 and 6. Level 0
       disables any non-error messages (but see the difference between
       \cb{--quiet} and \cb{--silent}) while level 6 produces lots of
       information, with level 1 being the default. The following additional
       types of diagnostics are produced at each level:

       \ol|

       \li|High-level information messages.|

       \li|Essential underlying commands being executed.|

       \li|All underlying commands being executed.|

       \li|Information that could be helpful to the user.|

       \li|Information that could be helpful to the developer.|

       \li|Even more detailed information.||"
    }

    bool --stat
    {
      "Display build statistics."
    }

    bool --progress
    {
      "Display build progress. If printing to a terminal the progress is
       displayed by default for low verbosity levels. Use \cb{--no-progress}
       to suppress."
    }

    bool --no-progress
    {
      "Don't display build progress."
    }

    bool --diag-color
    {
      "Use color in diagnostics. If printing to a terminal the color is used
       by default provided the terminal is not dumb. Use \cb{--no-diag-color}
       to suppress.

       This option affects the diagnostics printed by the build system itself.
       Some rules may also choose to propagate its value to tools (such as
       compilers) that they invoke."
    }

    bool --no-diag-color
    {
      "Don't use color in diagnostics."
    }

    size_t --jobs|-j
    {
      "<num>",
      "Number of active jobs to perform in parallel. This includes both the
       number of active threads inside the build system as well as the number
       of external commands (compilers, linkers, etc) started but not yet
       finished. If this option is not specified or specified with the \cb{0}
       value, then the number of available hardware threads is used."
    }

    size_t --max-jobs|-J
    {
      "<num>",
      "Maximum number of jobs (threads) to create. The default is 8x the
       number of active jobs (\cb{--jobs|j}) on 32-bit architectures and 32x
       on 64-bit. See the build system scheduler implementation for details."
    }

    size_t --queue-depth|-Q = 4
    {
      "<num>",
      "The queue depth as a multiplier over the number of active jobs.
       Normally we want a deeper queue if the jobs take long (for example,
       compilation) and shorter if they are quick (for example, simple tests).
       The default is 4. See the build system scheduler implementation for
       details."
    }

    string --file-cache
    {
      "<impl>",
      "File cache implementation to use for intermediate build results. Valid
       values are \cb{noop} (no caching or compression) and \cb{sync-lz4} (no
       caching with synchronous LZ4 on-disk compression). If this option is
       not specified, then a suitable default implementation is used
       (currently \cb{sync-lz4})."
    }

    size_t --max-stack
    {
      "<num>",
      "The maximum stack size in KBytes to allow for newly created threads.
       For \i{pthreads}-based systems the driver queries the stack size of
       the main thread and uses the same size for creating additional threads.
       This allows adjusting the stack size using familiar mechanisms, such
       as \cb{ulimit}. Sometimes, however, the stack size of the main thread
       is excessively large. As a result, the driver checks if it is greater
       than a predefined limit (64MB on 64-bit systems and 32MB on 32-bit
       ones) and caps it to a more sensible value (8MB) if that's the case.
       This option allows you to override this check with the special zero
       value indicating that the main thread stack size should be used as is."
    }

    bool --serial-stop|-s
    {
      "Run serially and stop at the first error. This mode is useful to
       investigate build failures that are caused by build system errors
       rather than compilation errors. Note that if you don't want to keep
       going but still want parallel execution, add \cb{--jobs|-j} (for
       example \cb{-j\ 0} for default concurrency). Note also that during
       serial execution there is no diagnostics buffering and child
       process' \cb{stderr} is a terminal (unless redirected; see
       \cb{--no-diag-buffer} for details)."
    }

    bool --dry-run|-n
    {
      "Print commands without actually executing them. Note that commands
       that are required to create an accurate build state will still be
       executed and the extracted auxiliary dependency information saved. In
       other words, this is not the \i{\"don't touch the filesystem\"} mode
       but rather \i{\"do minimum amount of work to show what needs to be
       done\"}. Note also that only the \cb{perform} meta-operation supports
       this mode."
    }

    bool --no-diag-buffer
    {
      "Do not buffer diagnostics from child processes. By default, unless
       running serially, such diagnostics is buffered and printed all at
       once after each child exits in order to prevent interleaving.
       However, this can have side-effects since the child process'
       \cb{stderr} is no longer a terminal. Most notably, the use of
       color in diagnostics may be disabled by some programs. On the
       other hand, depending on the platform and programs invoked, the
       interleaving diagnostics may not break lines and thus could be
       tolerable."
    }

    bool --match-only
    {
      "Match the rules but do not execute the operation. This mode is primarily
       useful for profiling."
    }

    bool --no-external-modules
    {
      "Don't load external modules during project bootstrap. Note that this
       option can only be used with meta-operations that do not load the
       project's \cb{buildfiles}, such as \cb{info}."
    }

    structured_result_format --structured-result
    {
      "<fmt>",

      "Write the result of execution in a structured form. In this mode,
       instead of printing to \cb{stderr} diagnostics messages about the
       outcome of executing actions on targets, the driver writes to
       \cb{stdout} a machine-readable result description in the specified
       format. Valid values for this option are \cb{lines} and \cb{json}.
       Note that currently only the \cb{perform} meta-operation supports
       the structured result output.

       If the output format is \cb{lines}, then the result is written one line
       per the buildspec action/target pair. Each line has the following form:

       \c{\i{state} \i{meta-operation} \i{operation} \i{target}}

       Where \ci{state} can be one of \cb{unchanged}, \cb{changed}, or
       \cb{failed}. If the action is a pre or post operation, then the
       outer operation is specified in parenthesis. For example:

       \
       unchanged perform update(test) /tmp/dir{hello/}
       changed perform test /tmp/hello/exe{test}
       \

       If the output format is \cb{json}, then the output is a JSON array of
       objects which are the serialized representation of the following C++
       \cb{struct} \cb{target_action_result}:

       \
       struct target_action_result
       {
         string           target;
         string           quoted_target;
         string           target_type;
         optional<string> target_path;
         string           meta_operation;
         string           operation;
         optional<string> outer_operation;
         string           state;
       };
       \

       For example:

       \
       [
         {
           \"target\": \"/tmp/dir{hello/}\",
           \"quoted_target\": \"/tmp/dir{hello/}\",
           \"target_type\": \"dir\",
           \"target_path\": \"/tmp/hello\",
           \"meta_operation\": \"perform\",
           \"operation\": \"update\",
           \"outer_operation\": \"test\",
           \"state\": \"unchanged\"
         },
         {
           \"target\": \"/tmp/dir{hello/}\",
           \"quoted_target\": \"/tmp/dir{hello/}\",
           \"target_type\": \"dir\",
           \"target_path\": \"/tmp/hello\",
           \"meta_operation\": \"perform\",
           \"operation\": \"test\",
           \"state\": \"changed\"
         }
       ]
       \

       See the JSON OUTPUT section below for details on the overall
       properties of this format and the semantics of the \cb{struct}
       serialization.

       The \cb{target} member is a \"display\" target name, the same as in the
       \cb{lines} format. The \cb{quoted_target} member is a target name that,
       if required, is quoted so that it can be passed back to the driver on
       the command line. The \cb{target_type} member is the type of target.
       The \cb{target_path} member is an absolute path to the target if the
       target type is path-based or \cb{dir}.
       "
    }

    bool --mtime-check
    {
      "Perform file modification time sanity checks. These checks can be
       helpful in diagnosing spurious rebuilds and are enabled by default
       on Windows (which is known not to guarantee monotonically increasing
       mtimes) and for the staged version of the build system on other
       platforms. Use \cb{--no-mtime-check} to disable."
    }

    bool --no-mtime-check
    {
      "Don't perform file modification time sanity checks. See
       \cb{--mtime-check} for details."
    }

    std::set<string> --dump
    {
      "<phase>",
      "Dump the build system state after the specified phase. Valid <phase>
       values are \cb{load} (after loading \cb{buildfiles}) and \cb{match}
       (after matching rules to targets). Repeat this option to dump the
       state after multiple phases."
    }

    std::vector<name> --trace-match
    {
      "<target>",
      "Trace rule matching for the specified target. This is primarily useful
       during troubleshooting. Repeat this option to trace multiple targets."
    }

    std::vector<name> --trace-execute
    {
      "<target>",
      "Trace rule execution for the specified target. This is primarily useful
       during troubleshooting. Repeat this option to trace multiple targets."
    }

    bool --no-column
    {
      "Don't print column numbers in diagnostics."
    }

    bool --no-line
    {
      "Don't print line and column numbers in diagnostics."
    }

    path --buildfile
    {
      "<path>",
      "The alternative file to read build information from. The default is
       \cb{buildfile} or \cb{build2file}, depending on the project's build
       file/directory naming scheme. If <path> is '\cb{-}', then read from
       \cb{stdin}. Note that this option only affects the files read as part
       of the buildspec processing. Specifically, it has no effect on the
       \cb{source} and \cb{include} directives. As a result, this option is
       primarily intended for testing rather than changing the build file
       names in real projects."
    }

    path --config-guess
    {
      "<path>",
      "The path to the \cb{config.guess(1)} script that should be used to
       guess the host machine triplet. If this option is not specified, then
       \cb{b} will fall back on to using the target it was built for as host."
    }

    path --config-sub
    {
      "<path>",
      "The path to the \cb{config.sub(1)} script that should be used to
       canonicalize machine triplets. If this option is not specified, then
       \cb{b} will use its built-in canonicalization support which should
       be sufficient for commonly-used platforms."
    }

    string --pager // String to allow empty value.
    {
      "<path>",
      "The pager program to be used to show long text. Commonly used pager
       programs are \cb{less} and \cb{more}. You can also specify additional
       options that should be passed to the pager program with
       \cb{--pager-option}. If an empty string is specified as the pager
       program, then no pager will be used. If the pager program is not
       explicitly specified, then \cb{b} will try to use \cb{less}. If it
       is not available, then no pager will be used."
    }

    strings --pager-option
    {
      "<opt>",
      "Additional option to be passed to the pager program. See \cb{--pager}
       for more information on the pager program. Repeat this option to
       specify multiple pager options."
    }

    // The following option is "fake" in that it is actually handled by
    // argv_file_scanner. We have it here for documentation.
    //
    string --options-file
    {
      "<file>",
      "Read additional options from <file>. Each option should appear on a
       separate line optionally followed by space or equal sign (\cb{=}) and
       an option value. Empty lines and lines starting with \cb{#} are
       ignored. Option values can be enclosed in double (\cb{\"}) or single
       (\cb{'}) quotes to preserve leading and trailing whitespaces as well as
       to specify empty values. If the value itself contains trailing or
       leading quotes, enclose it with an extra pair of quotes, for example
       \cb{'\"x\"'}. Non-leading and non-trailing quotes are interpreted as
       being part of the option value.

       The semantics of providing options in a file is equivalent to providing
       the same set of options in the same order on the command line at the
       point where the \cb{--options-file} option is specified except that
       the shell escaping and quoting is not required. Repeat this option
       to specify more than one options file."
    }

    dir_path --default-options
    {
      "<dir>",
      "The directory to load additional default options files from."
    }

    bool --no-default-options
    {
      "Don't load default options files."
    }

    bool --help {"Print usage information and exit."}
    bool --version {"Print version and exit."}
  };

  "
  \h|DEFAULT OPTIONS FILES|

  Instead of having a separate config file format for tool configuration, the
  \cb{build2} toolchain uses \i{default options files} which contain the same
  options as what can be specified on the command line. The default options
  files are like options files that one can specify with \cb{--options-file}
  except that they are loaded by default.

  The default options files for the build system driver are called
  \cb{b.options} and are searched for in the \cb{.build2/} subdirectory of the
  home directory and in the system directory (for example, \cb{/etc/build2/})
  if configured. Note that besides options these files can also contain global
  variable overrides.

  Once the search is complete, the files are loaded in the reverse order, that
  is, beginning from the system directory (if any), followed by the home
  directory, and finishing off with the options specified on the command line.
  In other words, the files are loaded from the more generic to the more
  specific with the command line options having the ability to override any
  values specified in the default options files.

  If a default options file contains \cb{--no-default-options}, then the
  search is stopped at the directory containing this file and no outer files
  are loaded. If this option is specified on the command line, then none of
  the default options files are searched for or loaded.

  An additional directory containing default options files can be specified
  with \cb{--default-options}. Its configuration files are loaded after the
  home directory.

  The order in which default options files are loaded is traced at the
  verbosity level 3 (\cb{-V} option) or higher.

  \h|JSON OUTPUT|

  Commands that support the JSON output specify their formats as a
  serialized representation of a C++ \cb{struct} or an array thereof. For
  example:

  \
  struct package
  {
    string name;
  };

  struct configuration
  {
    uint64_t         id;
    string           path;
    optional<string> name;
    bool             default;
    vector<package>  packages;
  };
  \

  An example of the serialized JSON representation of \cb{struct}
  \cb{configuration}:

  \
  {
    \"id\": 1,
    \"path\": \"/tmp/hello-gcc\",
    \"name\": \"gcc\",
    \"default\": true,
    \"packages\": [
      {
        \"name\": \"hello\"
      }
    ]
  }
  \

  This sections provides details on the overall properties of such formats
  and the semantics of the \cb{struct} serialization.

  The order of members in a JSON object is fixed as specified in the
  corresponding \cb{struct}. While new members may be added in the
  future (and should be ignored by older consumers), the semantics of the
  existing members (including whether the top-level entry is an object or
  array) may not change.

  An object member is required unless its type is \cb{optional<>},
  \cb{bool}, or \cb{vector<>} (array). For \cb{bool} members absent means
  \cb{false}. For \cb{vector<>} members absent means empty. An empty
  top-level array is always present.

  For example, the following JSON text is a possible serialization of
  the above \cb{struct} \cb{configuration}:

  \
  {
    \"id\": 1,
    \"path\": \"/tmp/hello-gcc\"
  }
  \

  \h|EXIT STATUS|

  Non-zero exit status is returned in case of an error.
  "

  // NOTE: remember to update --build2-metadata output if adding any relevant
  //       new environment variables.
  //
  "
  \h|ENVIRONMENT|

  The \cb{HOME} environment variable is used to determine the user's home
  directory. If it is not set, then \cb{getpwuid(3)} is used instead. This
  value is used to shorten paths printed in diagnostics by replacing the home
  directory with \cb{~/}. It is also made available to \cb{buildfile}'s as the
  \cb{build.home} variable.

  The \cb{BUILD2_VAR_OVR} environment variable is used to propagate global
  variable overrides to nested build system driver invocations. Its value is a
  list of global variable assignments separated with newlines.

  The \cb{BUILD2_DEF_OPT} environment variable is used to suppress loading of
  default options files in nested build system driver invocations. Its values
  are \cb{false} or \cb{0} to suppress and \cb{true} or \cb{1} to load.
  "
}