Merge #238: cmake, ci: updates for recent nixpkgs

db7acb3 ci: Fix shell.nix compatibility with CMake 4.0 (Ryan Ofsky)
91a7759 cmake: Fix IWYU in nix by adding CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES (Ryan Ofsky)

Pull request description:

  This PR fixes two problems that happen with recent nixpkgs. The first commit works around compilation errors that happen when IWYU is enabled with (`-DMP_ENABLE_IWYU=ON`) that were caused by NixOS/nixpkgs#445095. The second commit fixes problems building old versions of Cap'n Proto with CMake 4.0 in shell.nix.

  Neither problem has showed up so far running in github actions, only running locally with unstable nixpkgs. More details about the problems and fixes are in the commit messages.

ACKs for top commit:
  sedited:
    ACK db7acb3
  hebasto:
    re-ACK db7acb3.

Tree-SHA512: b56e2c3cdb31de181c5b5ae1ffdb9f978c0c6268bb717e7c1eedf00a8320cf61beda43437e2e2ba37cc9ce335b387902851d3820de434882fc7d6b4a80c5c0e3

Author: ryanofsky

CMakeLists.txt

@@ -90,13 +90,6 @@ if(MP_ENABLE_CLANG_TIDY)
     message(FATAL_ERROR "MP_ENABLE_CLANG_TIDY is ON but clang-tidy is not found.")
   endif()
   set(CMAKE_CXX_CLANG_TIDY "${CLANG_TIDY_EXECUTABLE}")
-
-  # Workaround for nix from https://gitlab.kitware.com/cmake/cmake/-/issues/20912#note_793338
-  # Nix injects header paths via $NIX_CFLAGS_COMPILE; CMake tags these as
-  # CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES and omits them from the compile
-  # database, so clang-tidy, which ignores $NIX_CFLAGS_COMPILE, can't find capnp
-  # headers. Setting them as standard passes them to clang-tidy.
-  set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
 endif()
 
 option(MP_ENABLE_IWYU "Run include-what-you-use with the compiler." OFF)
@@ -111,6 +104,15 @@ if(MP_ENABLE_IWYU)
   endif()
 endif()
 
+if(MP_ENABLE_CLANG_TIDY OR MP_ENABLE_IWYU)
+  # Workaround for nix from https://gitlab.kitware.com/cmake/cmake/-/issues/20912#note_793338
+  # Nix injects header paths via $NIX_CFLAGS_COMPILE; CMake tags these as
+  # CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES and omits them from the compile
+  # database, so clang-tidy, which ignores $NIX_CFLAGS_COMPILE, can't find capnp
+  # headers. Setting them as standard passes them to clang-tidy.
+  set(CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES ${CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES})
+endif()
+
 include("cmake/compat_config.cmake")
 include("cmake/pthread_checks.cmake")
 include(GNUInstallDirs)

shell.nix

@@ -39,6 +39,7 @@ let
       hash  = lib.attrByPath [capnprotoVersion] "" capnprotoHashes;
     };
     patches = lib.optionals (lib.versionAtLeast capnprotoVersion "0.9.0" && lib.versionOlder capnprotoVersion "0.10.4") [ ./ci/patches/spaceship.patch ];
+    cmakeFlags = (old.cmakeFlags or []) ++ (lib.optionals (lib.versionAtLeast "1.1.0" capnprotoVersion) ["-DCMAKE_POLICY_VERSION_MINIMUM=3.5"]);
   } // (lib.optionalAttrs (lib.versionOlder capnprotoVersion "0.10") {
     env = { }; # Drop -std=c++20 flag forced by nixpkgs
   }));