feat: option to auto-format Nix output using nixfmt

.github/workflows/test.yml

@@ -20,9 +20,26 @@ jobs:
         go-version: '>=1.21'
     - run: go version
     - name: Test
-      run: go test -v -covermode=count -coverprofile=coverage.out
+      run: make coverage
     - name: Upload coverage
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
+      with:
+        fail_ci_if_error: true
+        files: coverage.out
+        token: ${{ secrets.CODECOV_TOKEN }}
+  linux-test-with-nixfmt:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v22
+      with:
+        github_access_token: ${{ secrets.GITHUB_TOKEN }}
+        nix_path: nixpkgs=channel:nixos-unstable
+    - uses: DeterminateSystems/magic-nix-cache-action@main
+    - name: Run tests with nixfmt
+      run: nix develop --command make coverage
+    - name: Upload coverage
+      uses: codecov/codecov-action@v4
       with:
         fail_ci_if_error: true
         files: coverage.out
@@ -37,3 +54,4 @@ jobs:
         nix_path: nixpkgs=channel:nixos-unstable
     - uses: DeterminateSystems/magic-nix-cache-action@main
     - run: make flake
+

.gitignore

@@ -5,3 +5,4 @@ out.nix*
 *.env
 result
 .pre-commit-config.yaml
+coverage.out

Makefile

@@ -5,7 +5,7 @@ test:
 	go test -v
 
 coverage:
-	go test -v -covermode=count
+	go test -v -covermode=count -coverprofile=coverage.out
 
 flake:
 	nix build -L .#packages.x86_64-linux.default

README.md

@@ -209,46 +209,48 @@ Discussion: https://github.com/aksiksi/compose2nix/issues/24
 ```
 $ compose2nix -h
 Usage of compose2nix:
+  -auto_format
+    	if true, Nix output will be formatted using "nixfmt" (must be present in $PATH).
   -auto_start
-        auto-start setting for generated service(s). this applies to all services, not just containers. (default true)
+    	auto-start setting for generated service(s). this applies to all services, not just containers. (default true)
   -check_systemd_mounts
-        if set, volume paths will be checked against systemd mount paths on the current machine and marked as container dependencies.
+    	if set, volume paths will be checked against systemd mount paths on the current machine and marked as container dependencies.
   -create_root_target
-        if set, a root systemd target will be created, which when stopped tears down all resources. (default true)
+    	if set, a root systemd target will be created, which when stopped tears down all resources. (default true)
   -default_stop_timeout duration
-        default stop timeout for generated container services. (default 1m30s)
+    	default stop timeout for generated container services. (default 1m30s)
   -env_files string
-        one or more comma-separated paths to .env file(s).
+    	one or more comma-separated paths to .env file(s).
   -env_files_only
-        only use env file(s) in the NixOS container definitions.
+    	only use env file(s) in the NixOS container definitions.
   -generate_unused_resources
-        if set, unused resources (e.g., networks) will be generated even if no containers use them.
+    	if set, unused resources (e.g., networks) will be generated even if no containers use them.
   -ignore_missing_env_files
-        if set, missing env files will be ignored.
+    	if set, missing env files will be ignored.
   -include_env_files
-        include env files in the NixOS container definition.
+    	include env files in the NixOS container definition.
   -inputs string
-        one or more comma-separated path(s) to Compose file(s). (default "docker-compose.yml")
+    	one or more comma-separated path(s) to Compose file(s). (default "docker-compose.yml")
   -output string
-        path to output Nix file. (default "docker-compose.nix")
+    	path to output Nix file. (default "docker-compose.nix")
   -project string
-        project name used as a prefix for generated resources. this overrides any top-level "name" set in the Compose file(s).
+    	project name used as a prefix for generated resources. this overrides any top-level "name" set in the Compose file(s).
   -remove_volumes
-        if set, volumes will be removed on systemd service stop.
+    	if set, volumes will be removed on systemd service stop.
   -root_path string
-        root path to use for any relative paths in the Compose file (e.g., volumes). if unset, the current working directory will be used.
+    	root path to use for any relative paths in the Compose file (e.g., volumes). if unset, the current working directory will be used.
   -runtime string
-        one of: ["podman", "docker"]. (default "podman")
+    	one of: ["podman", "docker"]. (default "podman")
   -service_include string
-        regex pattern for services to include.
+    	regex pattern for services to include.
   -use_compose_log_driver
-        if set, always use the Docker Compose log driver.
+    	if set, always use the Docker Compose log driver.
   -use_upheld_by
-        if set, upheldBy will be used for service dependencies (NixOS 24.05+).
+    	if set, upheldBy will be used for service dependencies (NixOS 24.05+).
   -version
-        display version and exit
+    	display version and exit
   -write_nix_setup
-        if true, Nix setup code is written to output (runtime, DNS, autoprune, etc.) (default true)
+    	if true, Nix setup code is written to output (runtime, DNS, autoprune, etc.) (default true)
 ```
 
 ### Supported Docker Compose Features

compose.go

@@ -80,6 +80,7 @@ type Generator struct {
 	UseUpheldBy             bool
 	RemoveVolumes           bool
 	NoCreateRootTarget      bool
+	AutoFormat              bool
 	WriteHeader             bool
 	NoWriteNixSetup         bool
 	DefaultStopTimeout      time.Duration
@@ -164,6 +165,7 @@ func (g *Generator) Run(ctx context.Context) (*NixContainerConfig, error) {
 		CreateRootTarget: !g.NoCreateRootTarget,
 		AutoStart:        g.AutoStart,
 		WriteNixSetup:    !g.NoWriteNixSetup,
+		AutoFormat:       g.AutoFormat,
 	}, nil
 }
 

flake.nix

@@ -36,7 +36,7 @@
     devShells = forAllSystems (system:
       let pkgs = pkgsFor system; in {
         default = pkgs.mkShell {
-          buildInputs = [ pkgs.go pkgs.gopls ];
+          buildInputs = [ pkgs.go pkgs.gopls pkgs.nixfmt-rfc-style ];
           # Add a Git pre-commit hook.
           shellHook = onchg.shellHook.${system};
         };

helpers.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"os/exec"
 	"slices"
 	"strings"
 )
@@ -61,3 +62,37 @@ func ReadEnvFiles(envFiles []string, mergeWithEnv, ignoreMissing bool) (env []st
 
 	return env, nil
 }
+
+// formatNixCode will format Nix code by calling 'nixfmt' and passing in the
+// given code via stdin.
+func formatNixCode(contents []byte) ([]byte, error) {
+	// Check for existence of 'nixfmt' in $PATH.
+	nixfmtPath, err := exec.LookPath("nixfmt")
+	if err != nil {
+		return nil, fmt.Errorf("'nixfmt' not found in $PATH: %w", err)
+	}
+
+	cmd := exec.Command(nixfmtPath)
+
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return nil, fmt.Errorf("failed to setup stdin pipe: %w", err)
+	}
+	if err := func() error {
+		defer stdin.Close()
+		if _, err := stdin.Write(contents); err != nil {
+			return fmt.Errorf("failed to write content to stdin: %w", err)
+		}
+		return nil
+	}(); err != nil {
+		return nil, err
+	}
+
+	// Overwrite contents with formatted output.
+	contents, err = cmd.Output()
+	if err != nil {
+		return nil, fmt.Errorf("failed to run 'nixfmt' on contents: %w", err)
+	}
+
+	return contents, nil
+}

main.go

@@ -38,6 +38,7 @@ var removeVolumes = flag.Bool("remove_volumes", false, "if set, volumes will be
 var createRootTarget = flag.Bool("create_root_target", true, "if set, a root systemd target will be created, which when stopped tears down all resources.")
 var defaultStopTimeout = flag.Duration("default_stop_timeout", defaultSystemdStopTimeout, "default stop timeout for generated container services.")
 var writeNixSetup = flag.Bool("write_nix_setup", true, "if true, Nix setup code is written to output (runtime, DNS, autoprune, etc.)")
+var autoFormat = flag.Bool("auto_format", false, `if true, Nix output will be formatted using "nixfmt" (must be present in $PATH).`)
 var version = flag.Bool("version", false, "display version and exit")
 
 func main() {
@@ -47,6 +48,9 @@ func main() {
 		fmt.Printf("compose2nix v%s\n", appVersion)
 		return
 	}
+	if *output == "" {
+		log.Fatal("No output path specified.")
+	}
 
 	ctx := context.Background()
 
@@ -95,6 +99,7 @@ func main() {
 		NoCreateRootTarget:      !*createRootTarget,
 		WriteHeader:             true,
 		NoWriteNixSetup:         !*writeNixSetup,
+		AutoFormat:              *autoFormat,
 		DefaultStopTimeout:      *defaultStopTimeout,
 	}
 	containerConfig, err := g.Run(ctx)
@@ -103,14 +108,16 @@ func main() {
 	}
 	fmt.Printf("Generated NixOS config in %v\n", time.Since(start))
 
-	if *output != "" {
-		dir := path.Dir(*output)
-		if _, err := os.Stat(dir); err != nil {
-			log.Fatalf("Directory %q does not exist", dir)
-		}
-		if err := os.WriteFile(*output, []byte(containerConfig.String()), 0644); err != nil {
-			log.Fatal(err)
-		}
-		fmt.Printf("Wrote NixOS config to %s\n", *output)
+	dir := path.Dir(*output)
+	if _, err := os.Stat(dir); err != nil {
+		log.Fatalf("Directory %q does not exist: %v", dir, err)
+	}
+	f, err := os.Create(*output)
+	if err != nil {
+		log.Fatalf("Failed to create file %q: %v", *output, err)
+	}
+	if err := containerConfig.Write(f); err != nil {
+		log.Fatal(err)
 	}
+	fmt.Printf("Wrote NixOS config to %s\n", *output)
 }

nix.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"io"
 	"strings"
 	"text/template"
 )
@@ -203,6 +204,7 @@ type NixContainerConfig struct {
 	Volumes          []*NixVolume
 	CreateRootTarget bool
 	WriteNixSetup    bool
+	AutoFormat       bool
 	AutoStart        bool
 }
 
@@ -221,6 +223,29 @@ func (c *NixContainerConfig) String() string {
 	return s.String()
 }
 
+// Write writes out the Nix config to the provided Writer.
+//
+// If the AutoFormat option on this struct is set to "true", this method will
+// attempt to format the Nix config by calling "nixfmt" and passing in the
+// fully built config via stdin.
+func (c *NixContainerConfig) Write(out io.Writer) error {
+	config := []byte(c.String())
+
+	if c.AutoFormat {
+		formatted, err := formatNixCode(config)
+		if err != nil {
+			return err
+		}
+		config = formatted
+	}
+
+	if _, err := out.Write(config); err != nil {
+		return fmt.Errorf("failed to write Nix code: %w", err)
+	}
+
+	return nil
+}
+
 func rootTarget(runtime ContainerRuntime, project *Project) string {
 	return fmt.Sprintf("%s-compose-%s", runtime, project.With("root"))
 }

nix_test.go

@@ -1,10 +1,12 @@
 package main
 
 import (
+	"bytes"
 	"context"
 	"flag"
 	"fmt"
 	"os"
+	"os/exec"
 	"path"
 	"strings"
 	"testing"
@@ -39,7 +41,11 @@ func runSubtestsWithGenerator(t *testing.T, g *Generator) {
 			if err != nil {
 				t.Fatal(err)
 			}
-			got := c.String()
+			gotBuf := new(bytes.Buffer)
+			if err := c.Write(gotBuf); err != nil {
+				t.Fatal(err)
+			}
+			got := gotBuf.String()
 			if *update {
 				if err := os.WriteFile(outFilePath, []byte(got), 0644); err != nil {
 					t.Fatal(err)
@@ -68,6 +74,21 @@ func TestBasic(t *testing.T) {
 	runSubtestsWithGenerator(t, g)
 }
 
+func TestBasicAutoFormat(t *testing.T) {
+	if _, err := exec.LookPath("nixfmt"); err != nil {
+		t.Skip()
+	}
+	composePath, envFilePath := getPaths(t, true)
+	g := &Generator{
+		Inputs:                  []string{composePath},
+		EnvFiles:                []string{envFilePath},
+		AutoStart:               true,
+		GenerateUnusedResources: true,
+		AutoFormat:              true,
+	}
+	runSubtestsWithGenerator(t, g)
+}
+
 func TestProject(t *testing.T) {
 	composePath, envFilePath := getPaths(t, true)
 	g := &Generator{