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program configure()

Bootstrap and configure the package.

birch configure


Usually one just calls build, which calls configure implicitly.

The configuration of the package is influenced by command-line options, environment variables, and a build configuration file.

Command-line options

Basic options

  • --enable-debug / --disable-debug (default enabled): Enable/disable debug mode build. In debug mode, assertion checking is enabled for e.g. array bounds, and most compiler optimizations are disabled. This is recommended when developing code.
  • --enable-test / --disable-test (default disabled): Enable/disable test mode build. Test mode is similar to debug mode, but additionally tracks code coverage.
  • --enable-release / --disable-release (default disabled): Enable/disable release mode build. In release mode, all assertion checking is disabled and all compiler optimizations are enabled. This is recommended for running tested code when performance is critical. It offers substantial performance gains, usually several times faster than debug or test mode.
  • --enable-warnings / --disable-warnings (default enabled): Enable/disable compiler warnings.
  • --enable-notes / --disable-notes (default disabled): Enable/disable compiler notes.
  • --enable-translate / --disable-translate (default enabled): Enable/disable translation of C++ compiler messages.
  • --enable-verbose / --disable-verbose (default disabled): Enable/disable verbose reporting.
  • --prefix (default imputed): Installation prefix. Defaults to the same prefix used when installing the birch driver program.

Advanced options

  • --enable-openmp / --disable-openmp (default enabled): Enable/disable OpenMP. OpenMP is used for multi-threading. When running single-threaded, disabling OpenMP can have significant performance advantages, as it also disables the atomic operations used for thread synchronization.
  • --enable-static / --disable-static (default disabled): Enable/disable building of a static library.
  • --enable-shared / --disable-shared (default enabled): Enable/disable building of a shared library.


Building a static library is not well tested, and at any rate should only be tried for library packages, not end-user packages, which must be built into a shared library in order to be dynamically loaded by birch.

  • --arch (default empty, valid values native, wasm, js): Target architecture for the build. If empty, then default settings are used. If native, additional optimizations for the current architecture can be applied (e.g. SIMD instructions), if wasm (WebAssembly) or js (JavaScript), the Emscipten compiler can be used to compiler for the web.


Compiling to WebAssembly or JavaScript with Emscripten may currently be broken.

  • --unit (default dir, valid values unity, dir, file): Set the compile unit when transpiling Birch to C++. This can significantly influence build times. If unity, a single C++ source file is generated for all Birch source files. If dir, a single C++ source file is generated for each directory of Birch source files. If file, a C++ source file is generated for each Birch source file. Typically, unity builds can provide the fastest build times from scratch but cannot be parallelized; file builds can provide the fastest build times incrementally and can be parallelized, but for large projects can be very slow due to the overhead for each compile unit; dir offers a good balance, and can be parallelized.
  • --jobs (default imputed): Number of parallel jobs when building. Defaults to twice the number of hardware threads.

Environment variables

The following environment variables influence the build:

  • $BIRCH_MODE (valid values debug, test, release): Overrides the default build mode (which is otherwise debug).
  • $BIRCH_PREFIX: Overrides the default installation prefix (which is otherwise the prefix used when installing the birch driver program).
  • $BIRCH_SHARE_PATH: Additional paths to search for shared files (those that typically install to share directories).
  • $BIRCH_INCLUDE_PATH: Additional paths to search for header files (those that typically install to include directories).
  • $BIRCH_LIBRARY_PATH: Additional path to search for libraries (those that typically install to lib or lib64 directories).

Birch will search for shared files in the following directories, in order, where $PREFIX is the prefix used when installing the birch driver program:

  1. paths given in $BIRCH_SHARE_PATH, then
  2. $PREFIX/share.

For header files:

  1. paths given in $BIRCH_INCLUDE_PATH,
  2. $PREFIX/include,
  3. /usr/local/include, then
  4. /usr/include.

For libraries:

  1. .libs in the current directory,
  2. paths given in $BIRCH_LIBRARY_PATH,
  3. $PREFIX/lib64, then
  4. $PREFIX/lib.

Build configuration file

The build configuration file is a file named birch.yml in the root directory of the package. Alternative names that are supported include birch.yaml and birch.json.

The file is a YAML or JSON file with the following keys:

  • name : The name of the package.

  • version : The version of the package.

  • description : A short description of the package.

  • manifest : An object containing the following keys, listing the files to be included in the package.

    • source : A list of patterns identifying the Birch source files to be compiled. Each pattern is either the name of a file with a file extension of .birch, or a glob pattern that expands to a list of such files. The glob patterns supported are as for C glob function (see man 3 glob).

    • data : A list of data files to be installed. These are typically config and input files provided by the package.

    • other : A list of other files to be distributed but not installed. These are typically meta files, such as, LICENSE, and the build configuration file itself.

  • require : An object containing the following keys, describing the dependencies of the package. These dependencies are checked by configure.

    • package : A list of other Birch packages.

    • header : A list of external C/C++ header files.

    • library : A list of external libraries.

    • program : A list of external programs.