Using FetchContent with nanobind?

[astrogewgaw]

My project, shazam, is a C++ library with Python bindings. I am using CPM.cmake, which is a thin wrapper around CMake's FetchContent module. I cannot seem to add the fmt library as a dependency no matter what I do. If I remove the nanobind part from my CMakeLists.txt file, everything works. Should FetchContent work transparently with nanobind, or do I need to take additional steps?

My CMakeLists.txt file can be found here: https://github.com/astrogewgaw/shazam/blob/main/CMakeLists.txt. If I try to install my project with either:

pip install .

or:

pip install --no-build-isolation -Ceditable.rebuild=true -ve .

I get the following error:

  FAILED: [code=1] CMakeFiles/core.dir/src/frb.cc.o
  /usr/sbin/g++  -pthread -B /home/upanda/micromamba/envs/shazam/compiler_compat -Dcore_EXPORTS -I/home/upanda/micromamba/envs/shazam/include/python3.10 -I/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/include -O3 -DNDEBUG -fPIC -fvisibility=hidden -fno-stack-protector -Os -ffunction-sections -fdata-sections -MD -MT CMakeFiles/core.dir/src/frb.cc.o -MF CMakeFiles/core.dir/src/frb.cc.o.d -o CMakeFiles/core.dir/src/frb.cc.o -c /home/upanda/codes/c/shazam/src/frb.cc
  /home/upanda/codes/c/shazam/src/frb.cc:3:10: fatal error: fmt/chrono.h: No such file or directory
      3 | #include <fmt/chrono.h>
        |          ^~~~~~~~~~~~~~
  compilation terminated.

The complete error is here:

Details

Installing...
Using pip 25.2 from /home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/pip (python 3.10)
Obtaining file:///home/upanda/codes/c/shazam
  Running command Checking if build backend supports build_editable
  Checking if build backend supports build_editable ... done
  Running command Preparing editable metadata (pyproject.toml)
  *** scikit-build-core 0.11.5 using CMake 4.2.1 (metadata_editable)
  Preparing editable metadata (pyproject.toml) ... done
Requirement already satisfied: numpy in /home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages (from shazam==0.1.dev43+gda8d758.d20251213) (2.2.6)
Requirement already satisfied: typing_extensions in /home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages (from shazam==0.1.dev43+gda8d758.d20251213) (4.14.1)
Building wheels for collected packages: shazam
  Running command Building editable for shazam (pyproject.toml)
  *** scikit-build-core 0.11.5 using CMake 4.2.1 (editable)
  *** Configuring CMake...
  loading initial cache file build/cp310-cp310-linux_x86_64/CMakeInit.txt
  -- The CXX compiler identification is GNU 15.2.1
  -- Detecting CXX compiler ABI info
  -- Detecting CXX compiler ABI info - done
  -- Check for working CXX compiler: /usr/sbin/g++ - skipped
  -- Detecting CXX compile features
  -- Detecting CXX compile features - done
  -- CPM: Adding package [email protected] (v1.8.0)
  -- CPM: Adding package [email protected] (12.1.0)
  -- {fmt} version: 12.1.0
  -- Build type: Release
  -- Found Python: /home/upanda/micromamba/envs/shazam/bin/python3.10 (found suitable version "3.10.0", minimum required is "3.10") found components: Interpreter Development.Module
  -- Configuring done (4.0s)
  -- Generating done (0.0s)
  -- Build files have been written to: /home/upanda/codes/c/shazam/build/cp310-cp310-linux_x86_64
  *** Building project with Ninja...
  [1/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_ft.cpp.o
  [2/24] Building CXX object CMakeFiles/core.dir/src/hdr.cc.o
  [3/24] Building CXX object CMakeFiles/core.dir/src/frb.cc.o
  FAILED: [code=1] CMakeFiles/core.dir/src/frb.cc.o
  /usr/sbin/g++  -pthread -B /home/upanda/micromamba/envs/shazam/compiler_compat -Dcore_EXPORTS -I/home/upanda/micromamba/envs/shazam/include/python3.10 -I/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/include -O3 -DNDEBUG -fPIC -fvisibility=hidden -fno-stack-protector -Os -ffunction-sections -fdata-sections -MD -MT CMakeFiles/core.dir/src/frb.cc.o -MF CMakeFiles/core.dir/src/frb.cc.o.d -o CMakeFiles/core.dir/src/frb.cc.o -c /home/upanda/codes/c/shazam/src/frb.cc
  /home/upanda/codes/c/shazam/src/frb.cc:3:10: fatal error: fmt/chrono.h: No such file or directory
      3 | #include <fmt/chrono.h>
        |          ^~~~~~~~~~~~~~
  compilation terminated.
  [4/24] Building CXX object CMakeFiles/shazam.dir/src/hdr.cc.o
  [5/24] Building CXX object CMakeFiles/core.dir/src/tel.cc.o
  [6/24] Building CXX object _deps/fmt-build/CMakeFiles/fmt.dir/src/os.cc.o
  [7/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_static_property.cpp.o
  [8/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/implicit.cpp.o
  [9/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/trampoline.cpp.o
  [10/24] Building CXX object CMakeFiles/shazam.dir/src/tel.cc.o
  [11/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_ndarray.cpp.o
  [12/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_internals.cpp.o
  [13/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/error.cpp.o
  [14/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_func.cpp.o
  [15/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/common.cpp.o
  [16/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_enum.cpp.o
  [17/24] Building CXX object CMakeFiles/shazam.dir/src/frb.cc.o
  [18/24] Building CXX object CMakeFiles/nanobind-static.dir/home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/nanobind/src/nb_type.cpp.o
  [19/24] Building CXX object CMakeFiles/core.dir/python/shazam/bind.cc.o
  [20/24] Building CXX object _deps/fmt-build/CMakeFiles/fmt.dir/src/format.cc.o
  ninja: build stopped: subcommand failed.

  *** CMake build failed
  error: subprocess-exited-with-error

  × Building editable for shazam (pyproject.toml) did not run successfully.
  │ exit code: 1
  ╰─> See above for output.

  note: This error originates from a subprocess, and is likely not a problem with pip.
  full command: /home/upanda/micromamba/envs/shazam/bin/python3.10 /home/upanda/micromamba/envs/shazam/lib/python3.10/site-packages/pip/_vendor/pyproject_hooks/_in_process/_in_process.py build_editable /tmp/tmp8i4oe73k
  cwd: /home/upanda/codes/c/shazam
  Building editable for shazam (pyproject.toml) ... error
  ERROR: Failed building editable for shazam
Failed to build shazam
error: failed-wheel-build-for-install

× Failed to build installable wheels for some pyproject.toml based projects
╰─> shazam
error: Recipe `install` failed on line 38 with exit code 1

I installed nanobind via pip, like so:

pip install scikit-build-core[pyproject] nanobind setuptools_scm

Let me know if there is any more info I can provide which might help debug this. I am horribly stuck, and could really use some advice.