多项目结构下Meson custom_target生成源文件输出目录咨询

Let’s walk through how Meson manages output directories for files generated by custom_target, specifically tailored to your multi-project setup (main project + project_A/project_B subprojects):

Default Output Directory Behavior #

By default, Meson automatically places all files generated by custom_target in a private, build-dir-specific subdirectory tied to the subproject where the target is defined. For your project_A setup:

• If your root build directory is build/, the generated files (soapC.cpp, soapH.h, etc.) will live under a path like build/subprojects/project_A/[unique-target-identifier]/
• You don’t need to manually reference this exact path—Meson tracks the generated files as part of the custom_target object, so you can use the object directly in your build rules.

Customizing the Output Directory #

If you want to control where generated files are placed (e.g., grouping them in a dedicated generated/ folder), use the output_dir parameter in your custom_target definition. For example:

gen_empty_soap_src = custom_target(
  'empty_soap_src',
  input : 'empty.gsoap',
  output : ['soapC.cpp', 'soapH.h', 'soapStub.h', 'soap.nsmap'],
  depend_files : soap_gen_depend_files,
  command : [soap_compiler, '-n', '-I', '.', '@INPUT@'],
  output_dir : meson.current_build_dir() / 'generated'
)

• meson.current_build_dir() points to the build directory corresponding to project_A’s source directory, so this will place the files in build/subprojects/project_A/generated/
• Always use Meson’s built-in path functions (like current_build_dir(), current_source_dir()) instead of hardcoded paths to maintain out-of-source build compatibility.

Referencing Generated Files Correctly #

Within the Same Subproject (project_A) #

You can directly pass the custom_target object to your library/executable sources—Meson handles resolving the correct file paths automatically:

# Example: Add generated files to a project_A library
lib_project_a = library(
  'project_a',
  sources : ['core.cpp'] + gen_empty_soap_src,
  # other build parameters...
)

Across Subprojects (project_B using project_A’s generated files) #

If project_B needs access to these generated files, you’ll need to expose them via a Meson dependency in project_A:

1. In project_A’s meson.build, declare a dependency that includes the generated files:

   project_a_generated_dep = declare_dependency(
     sources : gen_empty_soap_src,
     include_directories : meson.current_build_dir() / 'generated' # Expose headers if needed
   )
   meson.override_dependency('project_a_generated', project_a_generated_dep)
   

2. In project_B’s meson.build, fetch the dependency and use it:

   project_a_gen_dep = dependency('project_a_generated')
   lib_project_b = library(
     'project_b',
     sources : ['util.cpp'],
     dependencies : project_a_gen_dep,
     # other build parameters...
   )
   

Key Notes #

• Never hardcode paths to generated files—rely on Meson’s custom_target objects or dependency declarations to avoid breakage when build configurations change.
• The depend_files parameter you’re using works as intended: it tells Meson to re-run the custom_target whenever any of the soap_gen_depend_files are modified, ensuring your generated files stay up-to-date.

内容的提问来源于stack exchange，提问作者Kostiantyn Ponomarenko