Split out buildWithCargo into a lower level mkCargoDerivation

* The intention here is to split up different "responsibilities" into
  smaller parts which can be composed as a DAG rather than mutually
  recursive functions. Specifically:
* `mkCargoDerivation` represents a lower-level thin wrapper around
  `stdenv.mkDerivation` which will
  - set up hooks
  - require the caller to define the variables needed by the hooks (like
    vendor dir, or artifacts to inherit)
  - ensure that build/check/install phases can be configured by the
    caller without having them remember to call pre/post hooks
* This allows `buildDepsOnly` to only focus on setting some default
  values (like good default commands to build all artifacts, setting the
  derivation name, etc.) and delegating the rest to `mkCargoDerivation`
* Lastly, the responsibility of `buildWithCargo` ends up ensuring that
  `cargoArtifacts` and `cargoVendorDir` are defined if the caller does
  not pass them in

lib/buildDepsOnly.nix

@@ -1,36 +1,46 @@
-{ buildWithCargo
-, crateNameFromCargoToml
+{ crateNameFromCargoToml
+, mkCargoDerivation
 , mkDummySrc
+, vendorCargoDeps
 }:
 
-args:
+{ cargoExtraArgs ? ""
+, cargoCheckCommand ? "cargo check --workspace --release"
+, cargoBuildCommand ? "cargo build --workspace --release"
+, cargoTestCommand ? "cargo test --workspace --release"
+, ...
+}@args:
 let
   crateName = crateNameFromCargoToml args;
-  defaults = {
-    inherit (crateName) version;
-    pname = "${crateName.pname}-deps";
-
-    buildPhase = ''
-      runHook preBuild
-      cargo check --workspace --release
-      cargo build --workspace --release
-      runHook postBuild
-    '';
-
-    # Don't install anything by default, but let the caller set their own if they wish
-    installPhase = ''
-      runHook preInstall
-      mkdir -p $out
-      runHook postInstall
-    '';
-  };
-
-  forced = {
-    # Prevent infinite recursion, we are the root of all artifacts
-    cargoArtifacts = null;
-    # No point in building this if not for the cargo artifacts
-    doCopyTargetToOutput = true;
-    src = mkDummySrc args;
-  };
 in
-buildWithCargo (defaults // args // forced)
+mkCargoDerivation (args // {
+  src = mkDummySrc args;
+  pname = args.pname or "${crateName.pname}-deps";
+  version = args.version or crateName.version;
+
+  cargoArtifacts = null;
+
+  cargoVendorDir = args.cargoVendorDir or vendorCargoDeps {
+    cargoLock = args.src + /Cargo.lock;
+  };
+
+  # First we run `cargo check` to cache cargo's internal artifacts, fingerprints, etc. for all deps.
+  # Then we run `cargo build` to actually compile the deps and cache the results
+  buildPhaseCargoCommand = args.buildPhaseCargoCommand or ''
+    ${cargoCheckCommand} ${cargoExtraArgs}
+    ${cargoBuildCommand} ${cargoExtraArgs}
+  '';
+
+  checkPhaseCargoCommand = args.checkPhaseCargoCommand or ''
+    ${cargoTestCommand} ${cargoExtraArgs}
+  '';
+
+  # No point in building this if not for the cargo artifacts
+  doCopyTargetToOutput = true;
+
+  # By default, don't install anything (else, besides the cargo target directory),
+  # but let the caller set their own if they wish
+  installPhaseCargoCommand = args.installPhaseCargoCommand or ''
+    mkdir -p $out
+  '';
+})

lib/buildWithCargo.nix

@@ -1,14 +1,7 @@
 { buildDepsOnly
-, cargo
-, configureCargoCommonVarsHook
-, configureCargoVendoredDepsHook
-, copyCargoTargetToOutputHook
 , crateNameFromCargoToml
-, inheritCargoArtifactsHook
 , installFromCargoArtifactsHook
-, lib
-, remapSourcePathPrefixHook
-, stdenv
+, mkCargoDerivation
 , vendorCargoDeps
 }:
 let
@@ -60,47 +53,36 @@ in
   # access. Directory structure should basically follow the output of `cargo vendor`.
   # This can be inferred automatically if the `src` root has a Cargo.lock file.
 , cargoVendorDir ? vendorCargoDepsFromArgs args
-  # Controls whether cargo's `target` directory should be copied as an output
-, doCopyTargetToOutput ? true
-  # Controls instructing rustc to remap the path prefix of any sources it
-  # captures (for example, this can include file names in panic info). This is
-  # useful to omit any references to `/nix/store/...` from the final binary,
-  # as including them will make Nix pull in all sources when installing any binaries.
-, doRemapSourcePathPrefix ? true
-, nativeBuildInputs ? [ ]
+, cargoBuildCommand ? "cargo build --workspace --release"
+, cargoTestCommand ? "cargo test --workspace --release"
+, cargoExtraArgs ? ""
 , ...
 }@args:
 let
-  defaultValues = (crateNameFromCargoToml args) // {
-    inherit
-      cargoArtifacts
-      cargoVendorDir
-      doCopyTargetToOutput
-      doRemapSourcePathPrefix;
-
-    buildPhase = ''
-      runHook preBuild
-      cargo build --workspace --release
-      runHook postBuild
-    '';
-
-    checkPhase = ''
-      runHook preCheck
-      cargo test --workspace --release
-      runHook postCheck
-    '';
-  };
-
-  additions = {
-    nativeBuildInputs = nativeBuildInputs ++ [
-      cargo
-      configureCargoCommonVarsHook
-      configureCargoVendoredDepsHook
-      copyCargoTargetToOutputHook
-      inheritCargoArtifactsHook
-      installFromCargoArtifactsHook
-      remapSourcePathPrefixHook
-    ];
-  };
+  crateName = crateNameFromCargoToml args;
 in
-stdenv.mkDerivation (defaultValues // args // additions)
+mkCargoDerivation (args // {
+  pname = args.pname or crateName.pname;
+  version = args.version or crateName.version;
+
+  inherit cargoArtifacts cargoVendorDir;
+
+  # Don't copy target dir by default since we are going to be installing bins/libs
+  doCopyTargetToOutput = args.doCopyTargetToOutput ? false;
+
+  nativeBuildInputs = (args.nativeBuildInputs or [ ]) ++ [
+    installFromCargoArtifactsHook
+  ];
+
+  buildPhaseCargoCommand = args.buildPhaseCargoCommand or ''
+    ${cargoBuildCommand} ${cargoExtraArgs}
+  '';
+
+  checkPhaseCargoCommand = args.checkPhaseCargoCommand or ''
+    ${cargoTestCommand} ${cargoExtraArgs}
+  '';
+
+  installPhaseCargoCommand = args.installPhaseCargoCommand or ''
+    installFromCargoArtifacts
+  '';
+})

lib/default.nix

@@ -17,6 +17,7 @@ lib.makeScope newScope (self:
     cleanCargoToml = callPackage ./cleanCargoToml.nix { };
     crateNameFromCargoToml = callPackage ./crateNameFromCargoToml.nix { };
     downloadCargoPackage = callPackage ./downloadCargoPackage.nix { };
+    mkCargoDerivation = callPackage ./mkCargoDerivation.nix { };
     mkDummySrc = callPackage ./mkDummySrc.nix { };
     urlForCargoPackage = callPackage ./urlForCargoPackage.nix { };
     vendorCargoDeps = callPackage ./vendorCargoDeps.nix { };

lib/mkCargoDerivation.nix

@@ -0,0 +1,64 @@
+{ cargo
+, configureCargoCommonVarsHook
+, configureCargoVendoredDepsHook
+, copyCargoTargetToOutputHook
+, inheritCargoArtifactsHook
+, remapSourcePathPrefixHook
+, stdenv
+}:
+
+args@{
+  # A directory to an existing cargo `target` directory, which will be reused
+  # at the start of the derivation. Useful for caching incremental cargo builds.
+  cargoArtifacts
+  # A directory of vendored cargo sources which can be consumed without network
+  # access. Directory structure should basically follow the output of `cargo vendor`.
+, cargoVendorDir
+  # A command (likely a cargo invocation) to run during the derivation's build
+  # phase. Pre and post build hooks will automatically be run.
+, buildPhaseCargoCommand
+  # A command (likely a cargo invocation) to run during the derivation's check
+  # phase. Pre and post check hooks will automatically be run.
+, checkPhaseCargoCommand
+  # A command (likely a cargo invocation) to run during the derivation's install
+  # phase. Pre and post install hooks will automatically be run.
+, installPhaseCargoCommand
+, ...
+}:
+stdenv.mkDerivation (args // {
+  # Controls whether cargo's `target` directory should be copied as an output
+  doCopyTargetToOutput = args.doCopyTargetToOutput or true;
+
+  # Controls instructing rustc to remap the path prefix of any sources it
+  # captures (for example, this can include file names in panic info). This is
+  # useful to omit any references to `/nix/store/...` from the final binary,
+  # as including them will make Nix pull in all sources when installing any binaries.
+  doRemapSourcePathPrefix = args.doRemapSourcePathPrefix or true;
+
+  nativeBuildInputs = (args.nativeBuildInputs or [ ]) ++ [
+    cargo
+    configureCargoCommonVarsHook
+    configureCargoVendoredDepsHook
+    copyCargoTargetToOutputHook
+    inheritCargoArtifactsHook
+    remapSourcePathPrefixHook
+  ];
+
+  buildPhase = args.buildPhase or ''
+    runHook preBuild
+    ${buildPhaseCargoCommand}
+    runHook postBuild
+  '';
+
+  checkPhase = args.checkPhase or ''
+    runHook preCheck
+    ${checkPhaseCargoCommand}
+    runHook postCheck
+  '';
+
+  installPhase = args.installPhase or ''
+    runHook preInstall
+    ${installPhaseCargoCommand}
+    runHook postInstall
+  '';
+})