printfdebugging - build-system

Build System Migration - Meson + Autotools + CMake = PkgConfig!

2026-07-01T00:00:00+00:00

The Problem</h1>

What happens when you use one build system and try to use libraries with another build system?

CMake can't include Meson projects</li>
Meson can't include Autotools projects</li>
Autotools + Make doesn't generate a `compile_commands.json</code> file</li>`
Custom scripts in build system specific scripting languages get ugly quite quickly</li> </ul> </li> </ul> Potential Ways to Fix it</h1> The Better One of the Bunch - Meson</strong>!</p> It can integrate</em> CMake projects</li> It can build</em> Autotools projects as one would do manually with some custom scripting (haven't tried it myself).</li> </ul> </li> How build systems talk to each other</p> There's no standard way to do it at build time</li> Each build system supports pkgconfig</a>, so the installed artifacts can be consumed through that interface.</li> It is build system agnostic, so as long as a .pc</code> file is generated, we can consume that project.</li> CollaboraOffice</a> uses this approach to consume external libraries (with some Make metaprogramming)</li> </ul> </li> </ul> The Migration Process</h1> Data & Code Separation</h2> Architectural overview The configure & build commands are pretty standard for any build system</li> The only thing which changes is the configure options. We separated them from the build commands.</li> For each exteral project foo</em>, there are 4 config files, config/external/foo/flags.{common,linux,apple,windows}</code></li> These contain the configure flags for the specific build system.</li> We then have a scripts/make/exports.mk</code></a> script which looks like this...</li> </ul> </li> </ul> 1</span>#</span> scripts/make/exports.mk</span></span> 2</span>EXTERNALS</span> =</span> $(</span>shell</span> realpath ./external</span>)</span></span> 3</span>EXTERNALS_CONFIG</span> =</span> $(</span>shell</span> realpath ./config/external</span>)</span></span> 4</span>INSTALL_DIRECTORY</span> =</span> $(</span>shell</span> realpath ./install</span>)</span></span> 5</span>BUILD_DIRECTORY</span> =</span> $(</span>shell</span> realpath ./build</span>)</span></span> 6</span>CLANGD_CONFIG</span> =</span> $(</span>shell</span> realpath ./.clangd</span>)</span></span> 7</span>PLATFORM</span> =</span> $(</span>shell</span> uname -s</span>)</span></span> 8</span>MESON_BUILD_TYPE</span> =</span> debug</span></span> 9</span>CMAKE_BUILD_TYPE</span> =</span> Debug</span></span> 10</span>SHELL</span> :=</span> /bin/bash</span></span> 11</span></span> 12</span>ifeq</span> (</span>$(</span>PLATFORM</span>)</span>,</span>Linux)</span></span> 13</span> PLATFORM_CONFIG_EXTENSION = linu</span>x</span></span> 14</span>else ifeq</span> (</span>$(</span>PLATFORM</span>)</span>,</span>Darwin)</span></span> 15</span> PLATFORM_CONFIG_EXTENSION = appl</span>e</span></span> 16</span>else ifeq</span> (</span>$(</span>PLATFORM</span>)</span>,</span>MINGW64)</span></span> 17</span> PLATFORM_CONFIG_EXTENSION = window</span>s</span></span> 18</span>else</span></span> 19</span> PLATFORM_CONFIG_EXTENSION = unknow</span>n</span></span> 20</span>endif</span></span></code></pre> About exports.mk</p> Here we define some paths and some variables which would be used in the build scripts</li> Platform detection sets the flags file extension which we need to include other than flags.common</code></li> </ul> </li> Make metaprogramming</p> The metaprograms define build wrappers in scripts/make/build_wrappers.mk</code></a> and eval call them from Makefile</code></a></li> There's one for Meson, Autotools and CMake</li> For a project foo</code>, we generate foo</code>, foo.configure</code>, foo.build</code>, foo.clangd</code>, foo.install</code> and foo.clean</code></li> We get the common and platform specific configure flags from the flag files in config/external/foo</code></li> Target foo</code> depends on all those foo</code> prefixed targets</li> </ul> </li> </ul> 1</span>#</span> scripts/make/build_wrappers.mk</span></span> 2</span>define</span> build_wrapper_cmake</span></span> 3</span>$(</span>1</span>)</span>_CONFIGURE_FLAGS=</span>$$</span>(shell cat </span>$$</span>(EXTERNALS_CONFIG)/</span>$(</span>1</span>)</span>/{flags.common,flags.</span>$$</span>(PLATFORM_CONFIG_EXTENSION)} | xargs)</span></span> 4</span></span> 5</span>$(</span>1</span>)</span>: </span>$(</span>1</span>)</span>.configure </span>$(</span>1</span>)</span>.build </span>$(</span>1</span>)</span>.install </span>$(</span>1</span>)</span>.clangd</span></span> 6</span></span> 7</span>$(</span>1</span>)</span>.configure:</span></span> 8</span> cmake \</span></span> 9</span> -DCMAKE_BUILD_TYPE=</span>$$</span>(CMAKE_BUILD_TYPE) \</span></span> 10</span> -DCMAKE_INSTALL_PREFIX=</span>$$</span>(INSTALL_DIRECTORY) \</span></span> 11</span> -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \</span></span> 12</span> $$</span>(</span>$(</span>1</span>)</span>_CONFIGURE_FLAGS) \</span></span> 13</span> -B "</span>$$</span>(BUILD_DIRECTORY)/</span>$(</span>1</span>)</span>" \</span></span> 14</span> -S "</span>$$</span>(EXTERNALS)/</span>$(</span>1</span>)</span>"</span></span> 15</span></span> 16</span>$(</span>1</span>)</span>.build:</span></span> 17</span> cmake --build "</span>$$</span>(BUILD_DIRECTORY)/</span>$(</span>1</span>)</span>"</span></span> 18</span></span> 19</span>$(</span>1</span>)</span>.clangd:</span></span> 20</span> $$</span>(call clangd_config_string,</span>$(</span>1</span>)</span>,</span>$$</span>(BUILD_DIRECTORY)/</span>$(</span>1</span>)</span>)</span></span> 21</span></span> 22</span>$(</span>1</span>)</span>.install:</span></span> 23</span> cmake --install "</span>$$</span>(BUILD_DIRECTORY)/</span>$(</span>1</span>)</span>" --prefix "</span>$$</span>(INSTALL_DIRECTORY)"</span></span> 24</span></span> 25</span>$(</span>1</span>)</span>.clean:</span></span> 26</span> rm -rf "</span>$$</span>(BUILD_DIRECTORY)/</span>$(</span>1</span>)</span>"</span></span> 27</span>endef</span></span> 28</span>...</span></span></code></pre> 1</span>#</span> Makefile</span></span> 2</span>$(</span>eval</span> $(</span>call</span> build_wrapper_meson</span>,</span>fontconfig</span>)</span>)</span></span> 3</span>$(</span>eval</span> $(</span>call</span> build_wrapper_cmake</span>,</span>cglm</span>)</span>)</span></span> 4</span>$(</span>eval</span> $(</span>call</span> build_wrapper_cmake</span>,</span>freetype</span>)</span>)</span></span> 5</span>$(</span>eval</span> $(</span>call</span> build_wrapper_meson</span>,</span>harfbuzz</span>)</span>)</span></span> 6</span>$(</span>eval</span> $(</span>call</span> build_wrapper_cmake</span>,</span>glfw</span>)</span>)</span></span> 7</span>$(</span>eval</span> $(</span>call</span> build_wrapper_cmake</span>,</span>glad</span>)</span>)</span></span> 8</span>$(</span>eval</span> $(</span>call</span> build_wrapper_autotools</span>,</span>ffmpeg</span>)</span>)</span></span></code></pre>A Note on Clangd integration</h2> Clangd & CompDB</p> By default, it looks for compile_commands.json</code> file in the project root and the build/</code> directory</li> External projects generate the compdb in their respective build directories</li> Compdb file generated with Meson + Ninja has relative paths, so it's good only if read from the build directory</li> So we can't merge multiple compdb files into one, that would unnecessarily complicate things</li> </ul> </li> One way is to use an external tool</em> like bear</code> to wrap all the build commands & append their compdb files</p> This is actually not that impractical since we have to do that for Autotools projects anyways</li> Also bear is available on all major desktop platforms.</li> I did this successfully</a> some time ago in bash. I had to create a config file</a> for bear.</li> If this works for you, it's not a bad solution. But since I had to redo it, I was looking for something better</li> </ul> </li> Clangd configuration</p> We can set CompileFlags.CompilationDatabase</code> in .clangd</code> to tell clang where to look for the compdb file</li> But this is only for a single compdb file, we have many of them in different build directories</li> We can use pattern matching and conditionally change the CompilationDatabase</code> path This was suggested by Arsen</a> on the mesonbuild matrix channel</a>, thanks!</li> Configuration - CompilationDatabase</a></li> Configuration - If</a></li> LSP setup - Managarm Handbook</a></li> </ul> </li> This solution is elegant and we can integrate this with some metaprogramming</li> </ul> </li> </ul> 1</span>#</span> scripts/make/build_wrappers.mk</span></span> 2</span>define</span> clangd_config_string</span></span> 3</span> @touch </span>$(</span>CLANGD_CONFIG</span>)</span></span> 4</span> @if ! grep -q </span>$(</span>1</span>)</span> $(</span>CLANGD_CONFIG</span>)</span>; then \</span></span> 5</span> { echo "---"; \</span></span> 6</span> echo "If:"; \</span></span> 7</span> echo " PathMatch: .</span>$(</span>1</span>)</span>.*"; \</span></span> 8</span> echo "CompileFlags:"; \</span></span> 9</span> echo " CompilationDatabase: </span>$(</span>2</span>)</span>"; \</span></span> 10</span> } | tee -a </span>$(</span>CLANGD_CONFIG</span>)</span>; \</span></span> 11</span>endef</span></span> 12</span></span> 13</span>#</span> Makefile</span></span> 14</span>clangd</span>:</span></span> 15</span> $(</span>call</span> clangd_config_string</span>,</span>engine</span>,</span>$(</span>BUILD_DIRECTORY</span>)</span>)</span></span> 16</span> $(</span>call</span> clangd_config_string</span>,</span>projects</span>,</span>$(</span>BUILD_DIRECTORY</span>)</span>)</span></span></code></pre> Clangd config generation We grep from .clangd</code> to avoid duplication</li> For each external library foo</em> we generate foo.clangd</code> where we call this metaprogram</li> This works!</li> </ul> </li> </ul> Advantages</h1> Officially supported build systems are always better Harfbuzz had some issues</a> linking static libraries built with CMake. With Meson, it links just fine.</li> I don't like to use LLMs, and manually writing/maintaining build scripts is just not practical</li> Bash/Make is easy to debug</li> </ul> </li> </ul> Github PRs build system migration by printfdebugging · Pull Request #5 · printfdebugging/graphics</a></li> compilation database fixes by printfdebugging · Pull Request #6 · printfdebugging/graphics</a></li> </ul> </li> </ul>