Fix build of legacy packages and add CI tests

.github/workflows/ci.yaml

@@ -105,6 +105,12 @@ jobs:
         exclude:
           - os: macos-latest
             nixpkgs-channel: nixos-21.11
+        include:
+          # The legacy package, used by compatible functions.
+          - os: ubuntu-latest
+            rust-channel: stable
+            profile: rust
+            nixpkgs-channel: nixpkgs-unstable
     runs-on: ${{ matrix.os }}
     env:
       NIX_SHELL_CMD: nix-shell --pure --argstr channel ${{ matrix.rust-channel }} --argstr profile ${{ matrix.profile }}
@@ -135,13 +141,13 @@ jobs:
         [[ "$(< out)" == *"Hello, world!"* ]]
 
     - name: Test cargo fmt
-      if: matrix.profile == 'default'
+      if: matrix.profile == 'default' || matrix.profile == 'rust'
       run: |
         cd examples/hello-world
         $NIX_SHELL_CMD --command "cargo fmt -- --check"
 
     - name: Test cargo clippy
-      if: matrix.profile == 'default'
+      if: matrix.profile == 'default' || matrix.profile == 'rust'
       run: |
         cd examples/hello-world
         set -o pipefail

mk-component-set.nix

@@ -36,7 +36,7 @@ let
         optional (hostPlatform.isDarwin && linksToRustc) bintools;
 
       buildInputs =
-        optional (elem pname [ "rustc" "cargo" "llvm-tools-preview" ]) zlib ++
+        optional (elem pname [ "rustc" "cargo" "llvm-tools-preview" "rust" ]) zlib ++
         optional linksToRustc self.rustc;
 
       # Nightly `rustc` since 2022-02-17 links to `libstdc++.so.6` on Linux.