libbuild2-autoconf

GNU Autoconf emulation build system module for build2.

Specifically, this module provides an in-based rule for processing config.h.in files. Besides the Autoconf special line flavor (#undef), it also supports the CMake (#cmakedefine) and Meson (#mesondefine) variants.

Similar to Autoconf, this module provides built-in support for a number of common HAVE_* configuration options. However, the values of these options are not discovered by dynamic probing, such as trying to compile a test program to check if the feature is present. Instead, they are set to static expected values based on the platform/compiler macro checks (see note at the beginning of Project Configuration for rationale).

See libbuild2/autoconf/checks/ for the list of available build-in checks.

Using in your projects

This module is part of the standard pre-installed build2 modules and no extra integration steps are required other than the using directive in your buildfile. For example, for Autoconf config.h.in:

using autoconf

h{config}: in{config}

Or for CMake config.h.cmake:

using autoconf

h{config}: in{config.h.cmake}

The default falvor is autoconf but if the input file has the .cmake or .meson extension, then the cmake or meson flavors are selected automatically. If, however, the standard config.h.in file is re-used for CMake/Meson, then the flavor must be specified explicitly with the autoconf.flavor variable, for example:

using autoconf

h{config}: in{config}
{
  autoconf.flavor = meson
}

Besides the built-in configuration options, custom substitutions can be specified as buildfile variables in the same way as with the in module. For example:

h{config}: in{config}
{
  PACKAGE_NAME = $project
  PACKAGE_VERSION = $version
}

This mechanism can also be used to override the build-in checks, for example:

h{config}: in{config}
{
  HAVE_STRLCPY = true
}

Adding new checks

To add a check for a new configuration option <NAME> simply create the <NAME>.h header file with the corresponding check and place it into libbuild2/autoconf/checks/ (use existing checks for inspiration).

The first line in this header file must be in the form:

// <NAME>

Subsequent lines should be C-style comments or preprocessor directives that #define or #undef <NAME> depending on whether the feature is available (though there can be idiosyncrasies; see const.h, for example). Note that there should be no double-quotes or backslashes except for line continuations. For example:

// HAVE_FOO
#ifndef _WIN32
#  define HAVE_FOO 1
#else
#  undef HAVE_FOO /* No foo on Windows. */
#endif