fix: improve apps deploy error when APP_NAME is missing

cmd/apps/bundle_helpers.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"os"
+	"path/filepath"
 	"strings"
 	"time"
 
@@ -27,12 +29,49 @@ func makeArgsOptionalWithBundle(cmd *cobra.Command, usage string) {
 			return fmt.Errorf("accepts at most 1 arg(s), received %d", len(args))
 		}
 		if !hasBundleConfig() && len(args) != 1 {
-			return fmt.Errorf("accepts 1 arg(s), received %d", len(args))
+			return missingAppNameError()
 		}
 		return nil
 	}
 }
 
+// missingAppNameError returns an error message that explains what the positional
+// argument should be, and attempts to infer a suggestion from the local environment.
+func missingAppNameError() error {
+	hint := inferAppNameHint()
+	msg := `missing required argument: APP_NAME
+
+Usage: databricks apps <command> APP_NAME
+
+APP_NAME is the name of the Databricks app to operate on.
+Alternatively, run this command from a project directory containing
+databricks.yml to auto-detect the app name.`
+
+	if hint != "" {
+		msg += "\n\nDid you mean?\n  databricks apps deploy " + hint
+	}
+
+	return errors.New(msg)
+}
+
+// inferAppNameHint tries to suggest an app name from the local environment.
+// Only returns a hint if the current directory looks like a Databricks app
+// (contains app.yml or app.yaml), using the directory name as the suggestion.
+func inferAppNameHint() string {
+	wd, err := os.Getwd()
+	if err != nil {
+		return ""
+	}
+
+	for _, filename := range []string{"app.yml", "app.yaml"} {
+		if _, err := os.Stat(filepath.Join(wd, filename)); err == nil {
+			return filepath.Base(wd)
+		}
+	}
+
+	return ""
+}
+
 // getAppNameFromArgs returns the app name from args or detects it from the bundle.
 // Returns (appName, fromBundle, error).
 func getAppNameFromArgs(cmd *cobra.Command, args []string) (string, bool, error) {

cmd/apps/bundle_helpers_test.go

@@ -3,6 +3,8 @@ package apps
 import (
 	"context"
 	"errors"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/databricks/databricks-sdk-go/service/apps"
@@ -106,6 +108,72 @@ func TestFormatAppStatusMessage(t *testing.T) {
 	})
 }
 
+func TestInferAppNameHint(t *testing.T) {
+	t.Run("returns empty when no app config exists", func(t *testing.T) {
+		t.Chdir(t.TempDir())
+
+		assert.Equal(t, "", inferAppNameHint())
+	})
+
+	t.Run("returns dir name when app.yml exists", func(t *testing.T) {
+		dir := t.TempDir()
+		t.Chdir(dir)
+		err := os.WriteFile(filepath.Join(dir, "app.yml"), []byte("command: [\"python\"]"), 0o644)
+		assert.NoError(t, err)
+
+		assert.Equal(t, filepath.Base(dir), inferAppNameHint())
+	})
+
+	t.Run("returns dir name when app.yaml exists", func(t *testing.T) {
+		dir := t.TempDir()
+		t.Chdir(dir)
+		err := os.WriteFile(filepath.Join(dir, "app.yaml"), []byte("command: [\"python\"]"), 0o644)
+		assert.NoError(t, err)
+
+		assert.Equal(t, filepath.Base(dir), inferAppNameHint())
+	})
+
+	t.Run("returns empty when cwd has been deleted", func(t *testing.T) {
+		dir := t.TempDir()
+		t.Chdir(dir)
+		os.Remove(dir)
+
+		assert.Equal(t, "", inferAppNameHint())
+	})
+}
+
+func TestMissingAppNameError(t *testing.T) {
+	t.Run("includes APP_NAME and usage info", func(t *testing.T) {
+		t.Chdir(t.TempDir())
+
+		err := missingAppNameError()
+		assert.Contains(t, err.Error(), "APP_NAME")
+		assert.Contains(t, err.Error(), "databricks.yml")
+		assert.NotContains(t, err.Error(), "Did you mean")
+	})
+
+	t.Run("includes hint when app.yml exists", func(t *testing.T) {
+		dir := t.TempDir()
+		t.Chdir(dir)
+		writeErr := os.WriteFile(filepath.Join(dir, "app.yml"), []byte("command: [\"python\"]"), 0o644)
+		assert.NoError(t, writeErr)
+
+		err := missingAppNameError()
+		assert.Contains(t, err.Error(), "Did you mean")
+		assert.Contains(t, err.Error(), filepath.Base(dir))
+	})
+
+	t.Run("gracefully handles deleted cwd", func(t *testing.T) {
+		dir := t.TempDir()
+		t.Chdir(dir)
+		os.Remove(dir)
+
+		err := missingAppNameError()
+		assert.Contains(t, err.Error(), "APP_NAME")
+		assert.NotContains(t, err.Error(), "Did you mean")
+	})
+}
+
 func TestMakeArgsOptionalWithBundle(t *testing.T) {
 	t.Run("updates command usage", func(t *testing.T) {
 		cmd := &cobra.Command{}