build-support/rust: Organize

- `toRustTarget` and friends pulled out from rust tools into rust
   library. Since they don't depend on any packages they can be more
   widely useable.

 - `build-rust-package` gets its own directory

 - `fetch-cargo-tarball` gets its own directory

(cherry picked from commit 18ed048c7b27e288a6c9ba894790a7e67ed5080d)

pkgs/build-support/rust/fetch-cargo-tarball/default.nix

@@ -9,8 +9,8 @@ let cargo-vendor-normalise = stdenv.mkDerivation {
   postFixup = "wrapPythonPrograms";
   doInstallCheck = true;
   installCheckPhase = ''
-    # check that ./fetchcargo-default-config.toml is a fix point
-    reference=${./fetchcargo-default-config.toml}
+    # check that ../fetchcargo-default-config.toml is a fix point
+    reference=${../fetchcargo-default-config.toml}
     < $reference $out/bin/cargo-vendor-normalise > test;
     cmp test $reference
   '';

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

@@ -0,0 +1,37 @@
+{ lib }:
+
+rec {
+  # https://doc.rust-lang.org/reference/conditional-compilation.html#target_arch
+  toTargetArch = platform:
+    if platform.isAarch32 then "arm"
+    else platform.parsed.cpu.name;
+
+  # https://doc.rust-lang.org/reference/conditional-compilation.html#target_os
+  toTargetOs = platform:
+    if platform.isDarwin then "macos"
+    else platform.parsed.kernel.name;
+
+  # Returns the name of the rust target, even if it is custom. Adjustments are
+  # because rust has slightly different naming conventions than we do.
+  toRustTarget = platform: let
+    inherit (platform.parsed) cpu vendor kernel abi;
+    cpu_ = platform.rustc.platform.arch or {
+      "armv7a" = "armv7";
+      "armv7l" = "armv7";
+      "armv6l" = "arm";
+      "armv5tel" = "armv5te";
+      "riscv64" = "riscv64gc";
+    }.${cpu.name} or cpu.name;
+    vendor_ = platform.rustc.platform.vendor or {
+      "w64" = "pc";
+    }.${vendor.name} or vendor.name;
+  in platform.rustc.config
+    or "${cpu_}-${vendor_}-${kernel.name}${lib.optionalString (abi.name != "unknown") "-${abi.name}"}";
+
+  # Returns the name of the rust target if it is standard, or the json file
+  # containing the custom target spec.
+  toRustTargetSpec = platform:
+    if (platform.rustc or {}) ? platform
+    then builtins.toFile (toRustTarget platform + ".json") (builtins.toJSON platform.rustc.platform)
+    else toRustTarget platform;
+}

pkgs/development/compilers/rust/default.nix

@@ -17,38 +17,17 @@
 , CoreFoundation, Security
 , pkgsBuildTarget, pkgsBuildBuild
 , makeRustPlatform
-}: rec {
-  # https://doc.rust-lang.org/reference/conditional-compilation.html#target_arch
-  toTargetArch = platform:
-    if platform.isAarch32 then "arm"
-    else platform.parsed.cpu.name;
+}:
 
-  # https://doc.rust-lang.org/reference/conditional-compilation.html#target_os
-  toTargetOs = platform:
-    if platform.isDarwin then "macos"
-    else platform.parsed.kernel.name;
+let
+  # Use `import` to make sure no packages sneak in here.
+  lib' = import ../../../build-support/rust/lib { inherit lib; };
+in
+{
+  lib = lib';
 
-  # Returns the name of the rust target, even if it is custom. Adjustments are
-  # because rust has slightly different naming conventions than we do.
-  toRustTarget = platform: with platform.parsed; let
-    cpu_ = platform.rustc.platform.arch or {
-      "armv7a" = "armv7";
-      "armv7l" = "armv7";
-      "armv6l" = "arm";
-      "armv5tel" = "armv5te";
-    }.${cpu.name} or cpu.name;
-    vendor_ = platform.rustc.platform.vendor or {
-      "w64" = "pc";
-    }.${vendor.name} or vendor.name;
-  in platform.rustc.config
-    or "${cpu_}-${vendor_}-${kernel.name}${lib.optionalString (abi.name != "unknown") "-${abi.name}"}";
-
-  # Returns the name of the rust target if it is standard, or the json file
-  # containing the custom target spec.
-  toRustTargetSpec = platform:
-    if (platform.rustc or {}) ? platform
-    then builtins.toFile (toRustTarget platform + ".json") (builtins.toJSON platform.rustc.platform)
-    else toRustTarget platform;
+  # Backwards compat before `lib` was factored out.
+  inherit (lib') toTargetArch toTargetOs toRustTarget toRustTargetSpec;
 
   # This just contains tools for now. But it would conceivably contain
   # libraries too, say if we picked some default/recommended versions from

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

@@ -7,11 +7,11 @@ rec {
     inherit rustc cargo;
   };
 
-  fetchCargoTarball = buildPackages.callPackage ../../../build-support/rust/fetchCargoTarball.nix {
+  fetchCargoTarball = buildPackages.callPackage ../../../build-support/rust/fetch-cargo-tarball {
     inherit cargo;
   };
 
-  buildRustPackage = callPackage ../../../build-support/rust {
+  buildRustPackage = callPackage ../../../build-support/rust/build-rust-package {
     inherit cargoBuildHook cargoCheckHook cargoInstallHook cargoSetupHook
       fetchCargoTarball rustc;
   };