Add cargoFmt

README.md

@@ -242,6 +242,43 @@ environment variables during the build, you can bring them back via
 `.overrideAttrs`.
 * `cargoClippyExtraArgs`
 
+### `lib.cargoFmt`
+
+`cargoFmt :: set -> drv`
+
+Create a derivation which will run a `cargo fmt` invocation in a cargo
+workspace.
+
+Except where noted below, all derivation attributes are delegated to
+`cargoBuild`, and can be used to influence its behavior.
+* `cargoArtifacts` is disabled/cleared
+* `cargoBuildCommand` will be set to run `cargo fmt` for all targets in the
+  workspace.
+* `cargoExtraArgs` will have `rustFmtExtraArgs` appended to it
+  - Default value: `""`
+* `cargoVendorDir` is disabled/cleared
+* `doCheck` is disabled
+* `doInstallCargoArtifacts` is disabled
+* `doRemapSourcePathPrefix` is disabled
+* `pnameSuffix` will be set to `"-fmt"`
+
+#### Optional attributes
+* `rustFmtExtraArgs`: additional flags to be passed in the rustfmt invocation
+  - Default value: `""`
+* `cargoExtraArgs`: additional flags to be passed in the cargo invocation
+  - Default value: `""`
+
+#### Native build dependencies
+The `rustfmt` package is automatically appended as a native build input to any
+other `nativeBuildInputs` specified by the caller.
+
+#### Remove attributes
+The following attributes will be removed before being lowered to
+`cargoBuild`. If you absolutely need these attributes present as
+environment variables during the build, you can bring them back via
+`.overrideAttrs`.
+* `rustFmtExtraArgs`
+
 ### `lib.cleanCargoToml`
 
 `cleanCargoToml :: set -> set`

checks/default.nix

@@ -15,6 +15,10 @@ onlyDrvs (lib.makeScope myLib.newScope (self:
 
     clippy = callPackage ./clippy { };
 
+    cargoFmt = myLib.cargoFmt {
+      src = ./simple;
+    };
+
     compilesFresh = callPackage ./compilesFresh.nix { };
     compilesFreshSimple = self.compilesFresh ./simple "simple" { };
     compilesFreshOverlappingTargets = self.compilesFresh

examples/custom-toolchain/flake.nix

@@ -36,6 +36,7 @@
         craneLib = (crane.mkLib pkgs).overrideScope' (final: prev: {
           rustc = rustWithWasiTarget;
           cargo = rustWithWasiTarget;
+          rustfmt = rustWithWasiTarget;
         });
 
         my-crate = craneLib.buildPackage {

lib/cargoFmt.nix

@@ -0,0 +1,24 @@
+{ cargoBuild
+, rustfmt
+}:
+
+{ cargoExtraArgs ? ""
+, rustFmtExtraArgs ? ""
+, ...
+}@origArgs:
+let
+  args = builtins.removeAttrs origArgs [ "rustFmtExtraArgs" ];
+in
+cargoBuild (args // {
+  cargoArtifacts = null;
+  cargoVendorDir = null;
+  doCheck = false;
+  doInstallCargoArtifacts = false;
+  doRemapSourcePathPrefix = false;
+  pnameSuffix = "-fmt";
+
+  cargoBuildCommand = "cargo fmt";
+  cargoExtraArgs = "${cargoExtraArgs} -- --check ${rustFmtExtraArgs}";
+
+  nativeBuildInputs = (args.nativeBuildInputs or [ ]) ++ [ rustfmt ];
+})

lib/default.nix

@@ -16,6 +16,7 @@ lib.makeScope newScope (self:
     buildPackage = callPackage ./buildPackage.nix { };
     cargoBuild = callPackage ./cargoBuild.nix { };
     cargoClippy = callPackage ./cargoClippy.nix { };
+    cargoFmt = callPackage ./cargoFmt.nix { };
     cleanCargoToml = callPackage ./cleanCargoToml.nix { };
     crateNameFromCargoToml = callPackage ./crateNameFromCargoToml.nix { };
     downloadCargoPackage = callPackage ./downloadCargoPackage.nix { };