106 lines
3.0 KiB
Markdown
106 lines
3.0 KiB
Markdown
# libbuild2-autoconf
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GNU Autoconf emulation build system module for `build2`.
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Specifically, this module provides an [`in`][module-in]-based rule for
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processing `config.h.in` files. Besides the Autoconf special line flavor
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(`#undef`), it also supports the CMake (`#cmakedefine`) and Meson
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(`#mesondefine`) variants.
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Similar to Autoconf, this module provides built-in support for a number of
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common `HAVE_*` configuration options. However, the values of these options
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are not discovered by dynamic probing, such as trying to compile a test
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program to check if the feature is present. Instead, they are set to static
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expected values based on the platform/compiler macro checks (see note at the
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beginning of [Project Configuration][proj-config] for rationale).
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See [`libbuild2/autoconf/checks/`][checks] for the list of available build-in
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checks.
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## Using in your projects
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This module is part of the standard pre-installed `build2` modules and no
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extra integration steps are required other than the `using` directive in
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your `buildfile`. For example, for Autoconf `config.h.in`:
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```
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using autoconf
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h{config}: in{config}
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```
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Or for CMake `config.h.cmake`:
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```
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using autoconf
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h{config}: in{config.h.cmake}
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```
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The default falvor is `autoconf` but if the input file has the `.cmake` or
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`.meson` extension, then the `cmake` or `meson` flavors are selected
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automatically. If, however, the standard `config.h.in` file is re-used for
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CMake/Meson, then the flavor must be specified explicitly with the
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`autoconf.flavor` variable, for example:
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```
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using autoconf
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h{config}: in{config}
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{
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autoconf.flavor = meson
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}
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```
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Besides the built-in configuration options, custom substitutions can be
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specified as `buildfile` variables in the same way as with the
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[`in`][module-in] module. For example:
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```
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h{config}: in{config}
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{
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PACKAGE_NAME = $project
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PACKAGE_VERSION = $version
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}
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```
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This mechanism can also be used to override the build-in checks, for example:
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```
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h{config}: in{config}
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{
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HAVE_STRLCPY = true
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}
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```
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## Adding new checks
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To add a check for a new configuration option `<NAME>` simply create the
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`<NAME>.h` header file with the corresponding check and place it into
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[`libbuild2/autoconf/checks/`][checks] (use existing checks for inspiration).
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The first line in this header file must be in the form:
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```
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// <NAME>
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```
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Subsequent lines should be C-style comments or preprocessor directives that
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`#define` or `#undef` `<NAME>` depending on whether the feature is available
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(though there can be idiosyncrasies; see `const.h`, for example). Note that
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there should be no double-quotes or backslashes except for line
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continuations. For example:
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```
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// HAVE_FOO
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#ifndef _WIN32
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# define HAVE_FOO 1
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#else
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# undef HAVE_FOO /* No foo on Windows. */
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#endif
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```
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[module-in]: https://build2.org/build2/doc/build2-build-system-manual.xhtml#module-in
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[proj-config]: https://build2.org/build2/doc/build2-build-system-manual.xhtml#proj-config
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[checks]: https://github.com/build2/libbuild2-autoconf/tree/master/libbuild2-autoconf/libbuild2/autoconf/checks/
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