Inline Cargo.{toml,lock} checks in buildDepsOnly

lib/buildDepsOnly.nix

@@ -18,9 +18,24 @@ let
     "cargoExtraArgs"
     "cargoTestCommand"
   ];
+
+  throwMsg = throw ''
+    unable to find Cargo.toml and Cargo.lock at ${path}. please ensure one of the following:
+    - a Cargo.toml and Cargo.lock exists at the root of the source directory of the derivation
+    - set `cargoArtifacts = buildDepsOnly { src = ./some/path/to/cargo/root; }`
+    - set `cargoArtifacts = null` to skip reusing cargo artifacts altogether
+  '';
+
+  path = args.src or throwMsg;
+  cargoToml = path + /Cargo.toml;
+  cargoLock = path + /Cargo.lock;
+  dummySrc =
+    if builtins.pathExists cargoToml && builtins.pathExists cargoLock
+    then mkDummySrc args
+    else throwMsg;
 in
 mkCargoDerivation (cleanedArgs // {
-  src = mkDummySrc args;
+  src = dummySrc;
   pnameSuffix = "-deps";
   pname = args.pname or crateName.pname;
   version = args.version or crateName.version;

lib/cargoBuild.nix

@@ -3,26 +3,6 @@
 , mkCargoDerivation
 , vendorCargoDeps
 }:
-let
-  cargoArtifactsFromArgs = args:
-    if args ? src
-    then
-      let
-        path = args.src;
-        cargoToml = path + /Cargo.toml;
-        cargoLock = path + /Cargo.lock;
-      in
-      if builtins.pathExists cargoToml && builtins.pathExists cargoLock
-      then buildDepsOnly args
-      else
-        throw ''
-          unable to find Cargo.toml and Cargo.lock at ${path}. please ensure one of the following:
-          - a Cargo.toml and Cargo.lock exists at the root of the source directory of the derivation
-          - set `cargoArtifacts = buildDepsOnly { src = ./some/path/to/cargo/root; }`
-          - set `cargoArtifacts = null` to skip reusing cargo artifacts altogether
-        ''
-    else null;
-in
 
 { cargoBuildCommand ? "cargo build --workspace --release"
 , cargoTestCommand ? "cargo test --workspace --release"
@@ -55,7 +35,7 @@ mkCargoDerivation (cleanedArgs // memoizedArgs // {
   # at the start of the derivation. Useful for caching incremental cargo builds.
   # This can be inferred automatically if the `src` root has both a Cargo.toml
   # and Cargo.lock file.
-  cargoArtifacts = args.cargoArtifacts or (cargoArtifactsFromArgs args // memoizedArgs);
+  cargoArtifacts = args.cargoArtifacts or (buildDepsOnly args // memoizedArgs);
 
   buildPhaseCargoCommand = args.buildPhaseCargoCommand or ''
     ${cargoBuildCommand} ${cargoExtraArgs}