refactor(rust): try to better compose cross toolchains

rust/flake.nix

@@ -35,50 +35,62 @@
               overlays = [ (final: prev: { ${packageName} = self.packages.${system}.${packageName}; }) ];
             };
 
-            fenix-pkgs = fenix.packages.${system};
+            fenixPkgsFor = pkgs: fenix.packages.${pkgs.system};
-            fenix-channel = fenix-pkgs.toolchainOf {
+            fenixChannelFor =
-              channel = "nightly";
+              pkgs:
-              date =
+              (fenixPkgsFor pkgs).toolchainOf {
-                builtins.replaceStrings [ "nightly-" ] [ "" ]
+                channel = "nightly";
-                  (builtins.fromTOML (builtins.readFile ./rust-toolchain.toml)).toolchain.channel;
+                date =
-              sha256 = "sha256-SzEeSoO54GiBQ2kfANPhWrt0EDRxqEvhIbTt2uJt/TQ=";
+                  builtins.replaceStrings [ "nightly-" ] [ "" ]
-            };
+                    (builtins.fromTOML (builtins.readFile ./rust-toolchain.toml)).toolchain.channel;
+                sha256 = "sha256-SzEeSoO54GiBQ2kfANPhWrt0EDRxqEvhIbTt2uJt/TQ=";
+              };
 
-            makeCrossPackage =
+            toolchainFor =
-              packageName: pkgsCross:
+              pkgs:
               let
-                pkgs = builtins.throw "defining cross pkg, accessing pkgs is a bug";
+                fenix-pkgs = fenixPkgsFor pkgs;
+              in
+              with fenix-pkgs;
+              combine [
+                minimal.cargo
+                minimal.rustc
+                targets.${pkgs.rust.lib.toRustTarget pkgs.stdenv.targetPlatform}.latest.rust-std
+              ];
+
+            rustPlatformFor =
+              pkgs:
+              let
+                toolchain = toolchainFor pkgs;
+              in
+              pkgs.makeRustPlatform {
+                cargo = toolchain;
+                rustc = toolchain;
+              };
+
+            crossPackageFor =
+              pkgs:
+              let
+                rustPlatform = rustPlatformFor pkgs;
               in
               {
-                "${packageName}-cross-${pkgsCross.stdenv.hostPlatform.config}${
+                "${packageName}-cross-${pkgs.stdenv.hostPlatform.config}${
-                  if pkgsCross.stdenv.hostPlatform.isStatic then "-static" else ""
+                  if pkgs.stdenv.hostPlatform.isStatic then "-static" else ""
-                }" =
+                }" = pkgs.callPackage (./. + "/nix/packages/${packageName}.nix") {
-                  let
+                  inherit cargoMeta rustPlatform;
-                    toolchain =
+                  flake-self = self;
-                      with fenix-pkgs;
+                };
-                      combine [
-                        minimal.cargo
-                        minimal.rustc
-                        targets.${pkgsCross.rust.lib.toRustTarget pkgsCross.stdenv.targetPlatform}.latest.rust-std
-                      ];
-                  in
-                  pkgsCross.callPackage (./. + "/nix/packages/${packageName}.nix") {
-                    inherit cargoMeta;
-                    flake-self = self;
-                    rustPlatform = pkgsCross.makeRustPlatform {
-                      cargo = toolchain;
-                      rustc = toolchain;
-                    };
-                  };
               };
           in
           function {
             inherit
               system
               pkgs
-              fenix-pkgs
+              fenixPkgsFor
-              fenix-channel
+              fenixChannelFor
-              makeCrossPackage
+              toolchainFor
+              rustPlatformFor
+              crossPackageFor
               ;
           }
         );
@@ -89,11 +101,14 @@
       packages = forSystems (
         {
           pkgs,
-          fenix-channel,
+          fenixChannelFor,
           system,
-          makeCrossPackage,
+          crossPackageFor,
           ...
         }:
+        let
+          fenix-channel = fenixChannelFor pkgs;
+        in
         {
           ${packageName} = pkgs.callPackage (./. + "/nix/packages/${packageName}.nix") {
             inherit cargoMeta;
@@ -105,21 +120,17 @@
           };
           default = self.packages.${system}.${packageName};
         }
-        // makeCrossPackage packageName pkgs.pkgsCross.musl64.pkgsStatic
+        // crossPackageFor pkgs.pkgsCross.musl64.pkgsStatic
-        // makeCrossPackage packageName pkgs.pkgsCross.musl32.pkgsStatic
+        // crossPackageFor pkgs.pkgsCross.musl32.pkgsStatic
-        // makeCrossPackage packageName pkgs.pkgsCross.aarch64-multiplatform-musl.pkgsStatic
+        // crossPackageFor pkgs.pkgsCross.aarch64-multiplatform-musl.pkgsStatic
-        // makeCrossPackage packageName pkgs.pkgsCross.armv7l-hf-multiplatform.pkgsStatic
+        // crossPackageFor pkgs.pkgsCross.armv7l-hf-multiplatform.pkgsStatic
-        // makeCrossPackage packageName pkgs.pkgsCross.mingwW64.pkgsStatic
+        // crossPackageFor pkgs.pkgsCross.mingwW64.pkgsStatic
       );
 
       devShells = forSystems (
-        {
+        { pkgs, fenixChannelFor, ... }:
-          pkgs,
-          fenix-pkgs,
-          fenix-channel,
-          ...
-        }:
         let
+          fenix-channel = fenixChannelFor pkgs;
           fenixRustToolchain = fenix-channel.withComponents [
             "cargo"
             "clippy-preview"