profiletool merge: Support walking through directories of profiles.

This allows the tool to recursively merge a directory full of N profiles,
as opposed to needing each profile to be explicitly listed on the command
line.

The intent is to run this as part of the build system for PGO builds, such
that individual profiles can exist in the repo but get merged at compile
time.

PiperOrigin-RevId: 650441896

tools/profiletool/profiletool.go

@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"path/filepath"
 
 	"github.com/google/pprof/profile"
 	"gvisor.dev/gvisor/pkg/log"
@@ -61,9 +62,30 @@ func mergeProfiles() error {
 	if err := mergeCmd.Parse(os.Args[2:]); err != nil {
 		return fmt.Errorf("invalid flags: %w", err)
 	}
-	profilePaths := mergeCmd.Args()
-	if len(profilePaths) < 2 {
-		return errors.New("must provide at least 2 profiles as positional arguments")
+	argPaths := mergeCmd.Args()
+	var profilePaths []string
+	for _, argPath := range argPaths {
+		st, err := os.Stat(argPath)
+		if err != nil {
+			return fmt.Errorf("cannot stat %q: %w", argPath, err)
+		}
+		if st.IsDir() {
+			filepath.Walk(argPath, func(path string, info os.FileInfo, err error) error {
+				if err != nil {
+					return fmt.Errorf("cannot walk %q: %w", path, err)
+				}
+				if info.IsDir() {
+					return nil
+				}
+				profilePaths = append(profilePaths, path)
+				return nil
+			})
+		} else {
+			profilePaths = append(profilePaths, argPath)
+		}
+	}
+	if len(profilePaths) == 0 {
+		return errors.New("no profiles (or directories containing profiles) specified as positional arguments")
 	}
 	profiles := make([]*profile.Profile, len(profilePaths))
 	for i, profilePath := range profilePaths {
@@ -73,7 +95,7 @@ func mergeProfiles() error {
 		}
 		prof, err := profile.Parse(profileFile)
 		if err != nil {
-			return fmt.Errorf("cannot parse %q: %w", profilePath, err)
+			return fmt.Errorf("cannot parse %q as a profile: %w", profilePath, err)
 		}
 		profileFile.Close()
 		profiles[i] = prof