Print errors to stderr

changes/errors.yml

@@ -0,0 +1,3 @@
+---
+changed:
+  - Errors are outputted to stderr instead of stdout

internal/pkg/conflictless/check.go

@@ -1,6 +1,7 @@
 package conflictless
 
-func check(cfg *Config) {
+// Check checks the validity of the change files.
+func Check(cfg *Config) {
 	combined, err := scanDir(*cfg.Flags.Directory)
 	if err != nil {
 		PrintErrorAndExit(err.Error(), func() {})

internal/pkg/conflictless/check_test.go

@@ -0,0 +1,69 @@
+package conflictless_test
+
+import (
+	"errors"
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/ypjama/conflictless-keepachangelog/internal/pkg/conflictless"
+)
+
+//nolint:paralleltest // this test is not parallel because it modifies os.Stdout.
+func TestCheck(t *testing.T) {
+	cfg := new(conflictless.Config)
+
+	changesDir, err := os.MkdirTemp(os.TempDir(), "changes")
+	assert.NoError(t, err)
+
+	defer os.RemoveAll(changesDir)
+
+	changesFile := createFile(t, changesDir, "test-check.json")
+	defer os.Remove(changesFile.Name())
+
+	stdOutFile := createTempFile(t, os.TempDir(), "stdout-test-check")
+	defer os.Remove(stdOutFile.Name())
+
+	writeDataToFile(t, []byte(`{"fixed":["foo"]}`), changesFile)
+
+	cfg.Flags.Directory = &changesDir
+
+	os.Stdout = stdOutFile
+
+	conflictless.Check(cfg)
+
+	data, err := os.ReadFile(stdOutFile.Name())
+
+	assert.NoError(t, err)
+	assert.Equal(t, "Change files are valid!\n", string(data))
+}
+
+func TestCheckWhenDirectoryDoesNotExist(t *testing.T) {
+	t.Parallel()
+
+	if os.Getenv("TEST_CHECK_WHEN_ERROR") == "1" {
+		cfg := new(conflictless.Config)
+
+		nonExistentDir := os.TempDir() + "/foo/bar"
+		cfg.Flags.Directory = &nonExistentDir
+
+		conflictless.Check(cfg)
+
+		return
+	}
+
+	//nolint:gosec // this is a test package so G204 doesn't really matter here.
+	cmd := exec.Command(os.Args[0], "-test.run=^TestCheckWhenDirectoryDoesNotExist$")
+
+	cmd.Env = append(os.Environ(), "TEST_CHECK_WHEN_ERROR=1")
+	err := cmd.Run()
+
+	exitErr := new(*exec.ExitError)
+	errors.As(err, exitErr)
+
+	expectedCode := 2
+	exitCode := (*exitErr).ExitCode()
+
+	assert.Equal(t, expectedCode, exitCode, "process exited with %d, want exit status %d", expectedCode, exitCode)
+}

internal/pkg/conflictless/cli.go

@@ -40,13 +40,13 @@ func CLI() {
 
 	switch cfg.Flags.Command {
 	case commandCheck:
-		check(&cfg)
+		Check(&cfg)
 	case commandGen:
 		Generate(&cfg)
 	case commandHelp:
 		help()
 	default:
-		PrintErrorAndExit(fmt.Sprintf("invalid command: '%s'", cfg.Flags.Command), usage)
+		PrintErrorAndExit(fmt.Sprintf("invalid command: '%s'", cfg.Flags.Command), usageOnError)
 	}
 }
 
@@ -62,17 +62,17 @@ func parseCLIFlags(cfg *Config) {
 	switch cfg.Flags.Command {
 	case commandHelp:
 		cmd = flag.NewFlagSet(commandHelp, flag.ExitOnError)
-		cmd.Usage = usage
+		cmd.Usage = usageOnError
 	case commandGen:
 		cmd = flag.NewFlagSet(commandGen, flag.ExitOnError)
-		cmd.Usage = usageGenerate
+		cmd.Usage = usageGenerateOnError
 
 		defineBumpFlags(cfg, cmd)
 		defineDirFlags(cfg, cmd)
 		defineSkipFlags(cfg, cmd)
 	case commandCheck:
 		cmd = flag.NewFlagSet(commandCheck, flag.ExitOnError)
-		cmd.Usage = usageCheck
+		cmd.Usage = usageCheckOnError
 
 		defineDirFlags(cfg, cmd)
 	}

internal/pkg/conflictless/conflictless_test.go

@@ -0,0 +1,42 @@
+package conflictless_test
+
+import (
+	"os"
+	"testing"
+)
+
+const (
+	mkdirFileMode = 0o755
+	writeFileMode = 0o644
+)
+
+func writeDataToFile(t *testing.T, data []byte, file *os.File) {
+	t.Helper()
+
+	err := os.WriteFile(file.Name(), data, writeFileMode)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func createFile(t *testing.T, dir, name string) *os.File {
+	t.Helper()
+
+	file, err := os.Create(dir + "/" + name)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return file
+}
+
+func createTempFile(t *testing.T, dir, pattern string) *os.File {
+	t.Helper()
+
+	file, err := os.CreateTemp(dir, pattern)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return file
+}

internal/pkg/conflictless/generate.go

@@ -12,7 +12,7 @@ import (
 func Generate(cfg *Config) {
 	err := cfg.SetBumpFromFlags()
 	if err != nil {
-		PrintErrorAndExit(err.Error(), usageGenerate)
+		PrintErrorAndExit(err.Error(), usageGenerateOnError)
 	}
 
 	cfg.Changelog, err = ReadChangelog(cfg)

internal/pkg/conflictless/generate_test.go

@@ -8,42 +8,6 @@ import (
 	"github.com/ypjama/conflictless-keepachangelog/internal/pkg/conflictless"
 )
 
-const (
-	mkdirFileMode = 0o755
-	writeFileMode = 0o644
-)
-
-func writeDataToFile(t *testing.T, data []byte, file *os.File) {
-	t.Helper()
-
-	err := os.WriteFile(file.Name(), data, writeFileMode)
-	if err != nil {
-		t.Fatal(err)
-	}
-}
-
-func createFile(t *testing.T, dir, name string) *os.File {
-	t.Helper()
-
-	file, err := os.Create(dir + "/" + name)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	return file
-}
-
-func createTempFile(t *testing.T, dir, pattern string) *os.File {
-	t.Helper()
-
-	file, err := os.CreateTemp(dir, pattern)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	return file
-}
-
 func TestGenerate(t *testing.T) {
 	t.Parallel()
 
@@ -54,13 +18,13 @@ func TestGenerate(t *testing.T) {
 
 	os.TempDir()
 
-	changesFile := createFile(t, changesDir, "1-foo.json")
+	changesFile := createFile(t, changesDir, "test-generate.json")
 	defer os.Remove(changesFile.Name())
 
-	changelogFile := createTempFile(t, os.TempDir(), "CHANGELOG.md")
+	changelogFile := createTempFile(t, os.TempDir(), "test-generate-CHANGELOG.md")
 	defer os.Remove(changelogFile.Name())
 
-	gitConfigFile := createTempFile(t, os.TempDir(), ".gitconfig")
+	gitConfigFile := createTempFile(t, os.TempDir(), "test-generate.gitconfig")
 	defer os.Remove(gitConfigFile.Name())
 
 	writeDataToFile(t, []byte(`{"fixed":["foo"]}`), changesFile)

internal/pkg/conflictless/print.go

@@ -8,7 +8,7 @@ import (
 // PrintUsageAndExit prints the usage and exits.
 func PrintUsageAndExit(cfg *Config) {
 	if cfg.Flags.Command == "" {
-		PrintErrorAndExit("", usage)
+		PrintErrorAndExit("", usageOnError)
 	}
 
 	switch cfg.Flags.Command {
@@ -26,8 +26,7 @@ func PrintUsageAndExit(cfg *Config) {
 // PrintErrorAndExit prints an error message and exits.
 func PrintErrorAndExit(msg string, usageFunc func()) {
 	if msg != "" {
-		//nolint:forbidigo
-		fmt.Printf("Error: %s\n\n", msg)
+		fmt.Fprintf(os.Stderr, "Error: %s\n\n", msg)
 	}
 
 	usageFunc()

internal/pkg/conflictless/print_test.go

@@ -2,6 +2,7 @@ package conflictless_test
 
 import (
 	"errors"
+	"net/url"
 	"os"
 	"os/exec"
 	"testing"
@@ -79,9 +80,8 @@ func TestPrintUsageAndExit(t *testing.T) {
 	}
 }
 
+//nolint:paralleltest // this test is not parallel because it modifies os.Stdout.
 func TestPrintCheckSuccess(t *testing.T) {
-	t.Parallel()
-
 	for _, testCase := range []struct {
 		description string
 		noContent   bool
@@ -94,9 +94,7 @@ func TestPrintCheckSuccess(t *testing.T) {
 		testCase := testCase
 
 		t.Run("", func(t *testing.T) {
-			t.Parallel()
-
-			file := createTempFile(t, os.TempDir(), "test-stdout")
+			file := createTempFile(t, os.TempDir(), "stdout-"+url.QueryEscape(testCase.description))
 			defer os.Remove(file.Name())
 
 			os.Stdout = file

internal/pkg/conflictless/usage.go

@@ -1,6 +1,9 @@
 package conflictless
 
-import "fmt"
+import (
+	"fmt"
+	"os"
+)
 
 const (
 	flagIndentation            = "\t"
@@ -19,9 +22,8 @@ const (
 		"Skip version links in changelog file (default: false)"
 )
 
-func usage() {
-	//nolint:forbidigo
-	fmt.Print(`Usage: conflictless <command> [flags]
+func usageText() string {
+	return `Usage: conflictless <command> [flags]
 
 The commands are:
 
@@ -31,27 +33,55 @@ The commands are:
 
 Use "conflictless help <topic>" for more information about that topic.
 
-`)
+`
 }
 
-func usageCheck() {
-	//nolint:forbidigo
-	fmt.Printf(`Usage: conflictless check [flags]
+func usageTextForGenerate() string {
+	return fmt.Sprintf(`Usage: conflictless generate [flags]
 
 The flags are:
 
 %s
-`, flagDescriptionDir)
+%s
+%s
+`,
+		flagDescriptionBump,
+		flagDescriptionDir,
+		flagDescriptionSkipVersionLinks,
+	)
 }
 
-func usageGenerate() {
-	//nolint:forbidigo
-	fmt.Printf(`Usage: conflictless generate [flags]
+func usageTextForCheck() string {
+	return fmt.Sprintf(`Usage: conflictless check [flags]
 
 The flags are:
 
 %s
-%s
-%s
-`, flagDescriptionBump, flagDescriptionDir, flagDescriptionSkipVersionLinks)
+`,
+		flagDescriptionDir,
+	)
+}
+
+func usage() {
+	fmt.Fprint(os.Stdout, usageText())
+}
+
+func usageOnError() {
+	fmt.Fprint(os.Stderr, usageText())
+}
+
+func usageCheck() {
+	fmt.Fprint(os.Stdout, usageTextForCheck())
+}
+
+func usageCheckOnError() {
+	fmt.Fprint(os.Stderr, usageTextForCheck())
+}
+
+func usageGenerate() {
+	fmt.Fprint(os.Stdout, usageTextForGenerate())
+}
+
+func usageGenerateOnError() {
+	fmt.Fprint(os.Stderr, usageTextForGenerate())
 }