Add mpgen.mk makefile rules

Simplify writing external mpgen build rules.

Author: ryanofsky

CMakeLists.txt

@@ -51,6 +51,7 @@ install(TARGETS mpgen EXPORT Multiprocess RUNTIME DESTINATION bin)
 configure_file(include/mp/config.h.in "${CMAKE_CURRENT_BINARY_DIR}/include/mp/config.h")
 configure_file(pkgconfig/libmultiprocess.pc.in "${CMAKE_CURRENT_BINARY_DIR}/pkgconfig/libmultiprocess.pc" @ONLY)
 install(FILES "${CMAKE_CURRENT_BINARY_DIR}/pkgconfig/libmultiprocess.pc" DESTINATION "lib/pkgconfig")
+install(FILES "include/mpgen.mk" DESTINATION "include")
 
 install(EXPORT Multiprocess DESTINATION lib/cmake/Multiprocess)
 

include/mp/config.h.in

@@ -5,6 +5,7 @@
 #ifndef MP_CONFIG_H
 #define MP_CONFIG_H
 
+#cmakedefine CMAKE_INSTALL_PREFIX "@CMAKE_INSTALL_PREFIX@"
 #cmakedefine capnp_PREFIX "@capnp_PREFIX@"
 
 #endif // MP_CONFIG_H

include/mpgen.mk

@@ -0,0 +1,4 @@
+%.capnp:
+	@:
+%.capnp.c++ %.capnp.h %.capnp.proxy-client.c++ %.capnp.proxy-types.h %.capnp.proxy-server.c++ %.capnp.proxy-types.c++ %.capnp.proxy.h: %.capnp
+	$(AM_V_GEN) $(MPGEN_PREFIX)/bin/mpgen '$(srcdir)' '$(srcdir)' $<

src/mp/gen.cpp

@@ -528,6 +528,11 @@ int main(int argc, char** argv)
         exit(1);
     }
     std::vector<kj::StringPtr> import_paths;
+    auto fs = kj::newDiskFilesystem();
+    auto cwd = fs->getCurrentPath();
+    for (const char* path : {CMAKE_INSTALL_PREFIX "/include", capnp_PREFIX "/include"}) {
+        KJ_IF_MAYBE(dir, fs->getRoot().tryOpenSubdir(cwd.evalNative(path))) { import_paths.emplace_back(path); }
+    }
     for (size_t i = 4; i < argc; ++i) {
         import_paths.push_back(argv[i]);
     }