feat: add cpu profile flag

cli/cli.go

@@ -24,6 +24,8 @@ type Format struct {
 
 	Paths []string `name:"paths" arg:"" type:"path" optional:"" help:"Paths to format. Defaults to formatting the whole tree."`
 	Stdin bool     `help:"Format the context passed in via stdin"`
+
+	CpuProfile string `optional:"" help:"file into which a cpu profile will be written"`
 }
 
 func ConfigureLogging() {

cli/format.go

@@ -9,6 +9,7 @@ import (
 	"os/signal"
 	"path/filepath"
 	"runtime"
+	"runtime/pprof"
 	"strings"
 	"syscall"
 
@@ -39,6 +40,25 @@ var (
 )
 
 func (f *Format) Run() (err error) {
+	// cpu profiling
+	if Cli.CpuProfile != "" {
+		// it is not recommended to go over 500 hz, but anything less wasn't producing meaningful samples
+		runtime.SetCPUProfileRate(500)
+
+		cpuProfile, err := os.Create(Cli.CpuProfile)
+		if err != nil {
+			return fmt.Errorf("failed to open file for writing cpu profile: %w", err)
+		} else if err = pprof.StartCPUProfile(cpuProfile); err != nil {
+			return fmt.Errorf("failed to start cpu profile: %w", err)
+		}
+		defer func() {
+			pprof.StopCPUProfile()
+			if err := cpuProfile.Close(); err != nil {
+				log.Errorf("failed to close cpu profile: %v", err)
+			}
+		}()
+	}
+
 	// create a prefixed logger
 	l := log.WithPrefix("format")
 

cli/format_test.go

@@ -21,6 +21,27 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestCpuProfile(t *testing.T) {
+	as := require.New(t)
+	tempDir := test.TempExamples(t)
+
+	// capture current cwd, so we can replace it after the test is finished
+	cwd, err := os.Getwd()
+	as.NoError(err)
+
+	t.Cleanup(func() {
+		// return to the previous working directory
+		as.NoError(os.Chdir(cwd))
+	})
+
+	_, err = cmd(t, "-C", tempDir, "--allow-missing-formatter", "--cpu-profile", "cpu.pprof")
+	as.NoError(err)
+	as.FileExists(filepath.Join(tempDir, "cpu.pprof"))
+	file, err := os.Stat(filepath.Join(tempDir, "cpu.pprof"))
+	as.NoError(err)
+	as.False(file.Size() == 0)
+}
+
 func TestAllowMissingFormatter(t *testing.T) {
 	as := require.New(t)
 

go.mod

@@ -46,10 +46,8 @@ require (
 	github.com/xanzy/ssh-agent v0.3.3 // indirect
 	golang.org/x/crypto v0.22.0 // indirect
 	golang.org/x/exp v0.0.0-20240416160154-fe59bbe5cc7f // indirect
-	golang.org/x/mod v0.17.0 // indirect
 	golang.org/x/net v0.24.0 // indirect
 	golang.org/x/sys v0.19.0 // indirect
-	golang.org/x/tools v0.20.0 // indirect
 	gopkg.in/warnings.v0 v0.1.2 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )

gomod2nix.toml

@@ -118,9 +118,6 @@ schema = 3
   [mod."golang.org/x/exp"]
     version = "v0.0.0-20240416160154-fe59bbe5cc7f"
     hash = "sha256-168CD9hlLJaQ7stQk/ztlP3zgaWXUMbIHa38gAeRRs4="
-  [mod."golang.org/x/mod"]
-    version = "v0.17.0"
-    hash = "sha256-CLaPeF6uTFuRDv4oHwOQE6MCMvrzkUjWN3NuyywZjKU="
   [mod."golang.org/x/net"]
     version = "v0.24.0"
     hash = "sha256-w1c21ljta5wNIyel9CSIn/crPzwOCRofNKhqmfs4aEQ="
@@ -130,9 +127,6 @@ schema = 3
   [mod."golang.org/x/sys"]
     version = "v0.19.0"
     hash = "sha256-cmuL31TYLJmDm/fDnI2Sn0wB88cpdOHV1+urorsJWx4="
-  [mod."golang.org/x/tools"]
-    version = "v0.20.0"
-    hash = "sha256-g5T5FrNPO/cf2W1lc+/93FcFB3HftPjqI72FueD9Wt8="
   [mod."gopkg.in/warnings.v0"]
     version = "v0.1.2"
     hash = "sha256-ATVL9yEmgYbkJ1DkltDGRn/auGAjqGOfjQyBYyUo8s8="

nix/devshell.nix

@@ -25,6 +25,7 @@
           # golang
           go
           delve
+          pprof
           graphviz
         ]
         ++