cmake files shipped with the "fmt" library are broken

[delroth]

Describe the bug
The .cmake files shipped in the dev output of the fmt library refer to invalid include paths. This prevents building software with the library if they trying finding it using cmake (instead of pkg-config).

To Reproduce
Steps to reproduce the behavior:

1. Add fmt to buildInputs of the dolphinEmuMaster package (currently it's falling back on its vendored copy).
2. nix-build the package.

Expected behavior
dolphinEmuMaster builds.

Additional context
In /nix/store/63l9fc9j8d565aass76jkx3wzxgalzfm-fmt-6.2.0-dev/lib/cmake/fmt/fmt-targets.cmake:

set(_IMPORT_PREFIX "/nix/store/8ngsi39v983v7xnjx5pqwimkfz73mh7m-fmt-6.2.0")

# Create imported target fmt::fmt
add_library(fmt::fmt SHARED IMPORTED)

set_target_properties(fmt::fmt PROPERTIES
  INTERFACE_COMPILE_DEFINITIONS "FMT_LOCALE;FMT_SHARED"
  INTERFACE_COMPILE_FEATURES "cxx_variadic_templates"
  INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
  INTERFACE_LINK_LIBRARIES "-Wl,--as-needed"
)

The include directory is invalid, looking up /include in the default output.

Notify maintainers

cc @jeroendehaas

Metadata

• system: "x86_64-linux"
• host os: Linux 5.5.13-hardened, NixOS, 20.09.git.53bbb34d874 (Nightingale)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.3.4
• channels(delroth): ""
• nixpkgs: /etc/nixpkgs

[delroth]

(Seems like a variant of fmtlib/fmt#1657 -- cc @jtojnar as well)

[jtojnar]

The file seems to be generated here: https://github.com/fmtlib/fmt/blob/963ee0831049b2e07d2b37e975a4b974a437749f/CMakeLists.txt#L280-L283

Maybe it is a CMake bug? I do not understand CMake enough to be able to tell for sure.