rustPlatform.bindgenHook: init

doc/languages-frameworks/rust.section.md

···
   be disabled by setting `dontUseCargoParallelTests`.
 * `cargoInstallHook`: install binaries and static/shared libraries
   that were built using `cargoBuildHook`.
+* `bindgenHook`: for crates which use `bindgen` as a build dependency, lets
+  `bindgen` find `libclang` and `libclang` find the libraries in `buildInputs`.
 
 ### Examples {#examples}
 

pkgs/build-support/rust/hooks/default.nix

···
 { buildPackages
 , callPackage
 , cargo
+, clang
 , diffutils
 , lib
 , makeSetupHook
···
           rustBuildPlatform rustTargetPlatform rustTargetPlatformSpec;
       };
     } ./maturin-build-hook.sh) {};
+
+    bindgenHook = callPackage ({}: makeSetupHook {
+      name = "rust-bindgen-hook";
+      substitutions = {
+        libclang = clang.cc.lib;
+        inherit clang;
+      };
+    }
+    ./rust-bindgen-hook.sh) {};
 }

pkgs/build-support/rust/hooks/rust-bindgen-hook.sh

···
+# populates LIBCLANG_PATH and BINDGEN_EXTRA_CLANG_ARGS for rust projects that
+# depend on the bindgen crate
+
+# if you modify this, you probably also need to modify the wrapper for the cli
+# of bindgen in pkgs/development/tools/rust/bindgen/wrapper.sh
+
+populateBindgenEnv () {
+    export LIBCLANG_PATH=@libclang@/lib
+    BINDGEN_EXTRA_CLANG_ARGS="$(< @clang@/nix-support/cc-cflags) $(< @clang@/nix-support/libc-cflags) $(< @clang@/nix-support/libcxx-cxxflags) $NIX_CFLAGS_COMPILE"
+    export BINDGEN_EXTRA_CLANG_ARGS
+}
+
+postHook="${postHook:-}"$'\n'"populateBindgenEnv"$'\n'

pkgs/development/compilers/rust/make-rust-platform.nix

···
   # Hooks
   inherit (callPackage ../../../build-support/rust/hooks {
     inherit stdenv cargo rustc;
-  }) cargoBuildHook cargoCheckHook cargoInstallHook cargoSetupHook maturinBuildHook;
+  }) cargoBuildHook cargoCheckHook cargoInstallHook cargoSetupHook maturinBuildHook bindgenHook;
 }

pkgs/development/tools/rust/bindgen/default.nix

···
           touch $out
         '';
       };
-    } ''
+    }
+    # if you modify the logic to find the right clang flags, also modify rustPlatform.bindgenHook
+    ''
     mkdir -p $out/bin
     export cincludes="$(< ${clang}/nix-support/cc-cflags) $(< ${clang}/nix-support/libc-cflags)"
     export cxxincludes="$(< ${clang}/nix-support/libcxx-cxxflags)"