Incompatible with FetchContent

[gregjohnson2017]

Using libpng with FetchContent does not work because header files are missing. I am using Windows 10 and I don't have libpng installed elsewhere. I ran cmake . --preset=default -B build and then cmake --build build --verbose.
Minimal reproducible example:

main.c

#include <png.h>

int main() { return 0; }

CMakePresets.json

{
    "version": 6,
    "configurePresets": [
        {
            "name": "default",
            "displayName": "Default Config",
            "description": "Default build using Unix Makefiles generator",
            "generator": "Unix Makefiles"
        }
    ],
    "buildPresets": [
        {
            "name": "default",
            "configurePreset": "default"
        }
    ]
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.25)
project(png-usage)

include(FetchContent)

FetchContent_Declare(
  libpng
  GIT_REPOSITORY "https://github.com/glennrp/libpng.git"
  GIT_TAG "e519af8")
set(PNG_TESTS OFF)
FetchContent_MakeAvailable(libpng)

add_executable(usage main.c)

target_link_libraries(usage png_static)

Snippet from error output:

[ 35%] Building C object CMakeFiles/usage.dir/main.c.obj
C:/Users/Greg/scoop/apps/msys2/current/mingw64/bin/cc.exe    -MD -MT CMakeFiles/usage.dir/main.c.obj -MF CMakeFiles/usage.dir/main.c.obj.d -o CMakeFiles/usage.dir/main.c.obj -c C:/Users/Greg/code/cmake-problem-example/main.c
C:/Users/Greg/code/cmake-problem-example/main.c:1:10: fatal error: png.h: No such file or directory
    1 | #include <png.h>
      |          ^~~~~~~
compilation terminated.

error_output.txt

The include file is not being included automatically through the target. I think that it is related to this line and this line because it is private by default.

[ctruta]

Thank you for the report. I want to release libpng-1.6.40 right now, but I will take a closer look at this issue after that.

[jbowler]

Using libpng with FetchContent does not work because header files are missing. I am using Windows 10 and I don't have libpng installed elsewhere.

Does FetchContent work correctly in cross-build environments?