[init] init config should return error if already exists (#2346)

## Summary

This fixes a NPE in autodetect. Previously when initializing a config
with a directory that already contained a config we would return `(nil,
nil)` but this is a mistake and a bit inconsistent with typical go. This
changes it so that if config already exists we return an error instead.

IMO this also provides better UX displaying a message indicating config
already exists.

This does have a minor backward compatibility issue. If users where used
to calling `devbox init` and having it not fail they would now need to
first test if devbox.json already exists.

## How was it tested?

Author: mikeland73

internal/boxcli/global.go

@@ -63,7 +63,7 @@ func ensureGlobalConfig() (string, error) {
 	if err != nil {
 		return "", err
 	}
-	err = devbox.InitConfig(globalConfigPath)
+	err = devbox.EnsureConfig(globalConfigPath)
 	if err != nil {
 		return "", err
 	}

internal/boxcli/init.go

@@ -5,11 +5,13 @@ package boxcli
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/pkg/errors"
 	"github.com/spf13/cobra"
 
 	"go.jetpack.io/devbox/internal/devbox"
+	"go.jetpack.io/devbox/internal/ux"
 	"go.jetpack.io/devbox/pkg/autodetect"
 )
 
@@ -28,7 +30,16 @@ func initCmd() *cobra.Command {
 			"You can then add packages using `devbox add`",
 		Args: cobra.MaximumNArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
-			return runInitCmd(cmd, args, flags)
+			err := runInitCmd(cmd, args, flags)
+			if errors.Is(err, os.ErrExist) {
+				path := pathArg(args)
+				if path == "" || path == "." {
+					path, _ = os.Getwd()
+				}
+				ux.Fwarningf(cmd.ErrOrStderr(), "devbox.json already exists in %q.", path)
+				err = nil
+			}
+			return err
 		},
 	}
 

internal/devbox/devbox.go

@@ -76,6 +76,14 @@ func InitConfig(dir string) error {
 	return err
 }
 
+func EnsureConfig(dir string) error {
+	err := InitConfig(dir)
+	if err != nil && !errors.Is(err, os.ErrExist) {
+		return err
+	}
+	return nil
+}
+
 func Open(opts *devopt.Opts) (*Devbox, error) {
 	var cfg *devconfig.Config
 	var err error

internal/devbox/util.go

@@ -55,7 +55,7 @@ func ensureDevboxUtilityConfig() (string, error) {
 		return "", err
 	}
 
-	err = InitConfig(path)
+	err = EnsureConfig(path)
 	if err != nil {
 		return "", err
 	}

internal/devconfig/init.go

@@ -4,7 +4,6 @@
 package devconfig
 
 import (
-	"errors"
 	"os"
 	"path/filepath"
 
@@ -17,11 +16,6 @@ func Init(dir string) (*Config, error) {
 		os.O_RDWR|os.O_CREATE|os.O_EXCL,
 		0o644,
 	)
-	if errors.Is(err, os.ErrExist) {
-		// TODO: Should we return an error here?
-		// If we do, it breaks a bunch of tests, but it's likely the correct behavior
-		return nil, nil
-	}
 	if err != nil {
 		return nil, err
 	}

testscripts/init/empty.test.txt

@@ -6,8 +6,9 @@ exists devbox.json
 
 json.superset devbox.json expected.json
 
-# Second init should be a no-op.
+# Second init should be a no-op with a warning
 exec devbox init
+stderr 'devbox.json already exists in'
 
 -- expected.json --
 {