How to add dynamically generated headers directory?

Usage
1

Hii all.

I have a C project. This project has depends on a library named bar. bar is built using a custom command. However the issue is, the headers of the bar library is also available only after bar is built. In such a scenario, how would I let my top-level project refer to headers of bar?

$ tree .
.
├── bar
│   ├── baz
│   │   ├── baz.c
│   │   └── baz.h
│   ├── build.sh
│   └── CMakeLists.txt
├── CMakeLists.txt
└── foo.c
  • My project - foo (CMakeLists.txt, foo.c)
  • Library generated via custom command - bar (everything inside bar/).

The thing is, bar’s CMakeLists.txt calls build.sh. build.sh does some magic and generates static library libbar.a and directory include/ inside bar/build directory.

But since, the include directory is generated on-the-fly, I’m not able to set the include directories in bar/CMakeLists.txt.

From the top-level folder, if I do cmake -S . -B build, I get:

-- The C compiler identification is GNU 13.2.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Configuring done (0.3s)
CMake Error in CMakeLists.txt:
  Imported target "bar" includes non-existent path

    "/path/to/foo/bar/build/include"

  in its INTERFACE_INCLUDE_DIRECTORIES.  Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.
-- Generating done (0.0s)
CMake Generate step failed.  Build files cannot be regenerated correctly.

A minimal reproducible example - https://upload.disroot.org/r/aEsMT86V#ai/jUmC2bmro3BqRRD4KkNuDddajAt7+c+z1+YT32QQ=

Two solutions I could think of:

  1. Force users to run bar/build.sh manually before configuring the project.
  2. Include empty include directories in bar/build, so when CMake sees it, the paths at least exist.

The disadvantage of 1 is, users lose convenience of just running cmake -S . -B build.
The disadvantage of 2 is, to enable cross-compilation of bar, I need to create empty directories for all the targets.

(CMake newbie here :sweat_smile:)
Thanks!

[In real life, the bar is a very big project in its own and the headers generated by it are multiple and nested…]