Speed up app loading and checks

* We were loading an applet by walking its entire source FS, but
  skipping any files outside of the root directory. Instead, just list
  and process the files in the root directory explicitly.

* Move buildifier-based checks to the end of `pixlet check`, since they
  walk the entire directory tree. This means they won't run if there are
  any other errors, which are quicker to find.

cmd/check.go

@@ -59,34 +59,6 @@ func checkCmd(cmd *cobra.Command, args []string) error {
 			baseDir = filepath.Dir(path)
 		}
 
-		// run format and lint on *.star files in the fs
-		fs.WalkDir(fsys, ".", func(p string, d fs.DirEntry, err error) error {
-			if err != nil {
-				return err
-			}
-
-			if d.IsDir() || !strings.HasSuffix(p, ".star") {
-				return nil
-			}
-
-			realPath := filepath.Join(baseDir, p)
-
-			dryRunFlag = true
-			if err := formatCmd(cmd, []string{realPath}); err != nil {
-				foundIssue = true
-				failure(p, fmt.Errorf("app is not formatted correctly: %w", err), fmt.Sprintf("try `pixlet format %s`", realPath))
-			}
-
-			outputFormat = "off"
-			err = lintCmd(cmd, []string{realPath})
-			if err != nil {
-				foundIssue = true
-				failure(p, fmt.Errorf("app has lint warnings: %w", err), fmt.Sprintf("try `pixlet lint --fix %s`", realPath))
-			}
-
-			return nil
-		})
-
 		// Check if an app can load.
 		err = community.LoadApp(cmd, []string{path})
 		if err != nil {
@@ -152,6 +124,34 @@ func checkCmd(cmd *cobra.Command, args []string) error {
 			continue
 		}
 
+		// run format and lint on *.star files in the fs
+		fs.WalkDir(fsys, ".", func(p string, d fs.DirEntry, err error) error {
+			if err != nil {
+				return err
+			}
+
+			if d.IsDir() || !strings.HasSuffix(p, ".star") {
+				return nil
+			}
+
+			realPath := filepath.Join(baseDir, p)
+
+			dryRunFlag = true
+			if err := formatCmd(cmd, []string{realPath}); err != nil {
+				foundIssue = true
+				failure(p, fmt.Errorf("app is not formatted correctly: %w", err), fmt.Sprintf("try `pixlet format %s`", realPath))
+			}
+
+			outputFormat = "off"
+			err = lintCmd(cmd, []string{realPath})
+			if err != nil {
+				foundIssue = true
+				failure(p, fmt.Errorf("app has lint warnings: %w", err), fmt.Sprintf("try `pixlet lint --fix %s`", realPath))
+			}
+
+			return nil
+		})
+
 		// If we're here, the app and manifest are good to go!
 		success(path)
 	}

runtime/applet.go

@@ -11,9 +11,9 @@ import (
 	"testing"
 	"testing/fstest"
 
+	starlibbsoup "github.com/qri-io/starlib/bsoup"
 	starlibgzip "github.com/qri-io/starlib/compress/gzip"
 	starlibbase64 "github.com/qri-io/starlib/encoding/base64"
-	starlibbsoup "github.com/qri-io/starlib/bsoup"
 	starlibcsv "github.com/qri-io/starlib/encoding/csv"
 	starlibhash "github.com/qri-io/starlib/hash"
 	starlibhtml "github.com/qri-io/starlib/html"
@@ -311,24 +311,21 @@ func (a *Applet) PathsForBundle() []string {
 }
 
 func (a *Applet) load(fsys fs.FS) (err error) {
-	if err := fs.WalkDir(fsys, ".", func(pathToLoad string, d fs.DirEntry, walkDirErr error) error {
-		if walkDirErr != nil {
-			return walkDirErr
-		}
+	// list files in the root directory of fsys
+	rootDir, err := fs.ReadDir(fsys, ".")
+	if err != nil {
+		return fmt.Errorf("reading root directory: %v", err)
+	}
 
-		if d.IsDir() || path.Dir(pathToLoad) != "." {
-			// only process files in the root directory
-			return nil
+	for _, d := range rootDir {
+		if d.IsDir() || !strings.HasSuffix(d.Name(), ".star") {
+			// only process Starlark files
+			continue
 		}
 
-		if !strings.HasSuffix(pathToLoad, ".star") {
-			// not a starlark file
-			return nil
+		if err := a.ensureLoaded(fsys, d.Name()); err != nil {
+			return err
 		}
-
-		return a.ensureLoaded(fsys, pathToLoad)
-	}); err != nil {
-		return err
 	}
 
 	if a.mainFun == nil {