Update eachmodule to stream output when not running concurrently (#893)

Updates the eachmodule utility to stream the invoked command output and
error to stdout when the utility is run without concurrency. This allows
better viewing of the command output being invoked. When invoked with
concurrency, the utility falls back to the old behavior of buffering the
output.

internal/repotools/cmd/eachmodule/cmd.go

@@ -20,11 +20,11 @@ type Work struct {
 type WorkLog struct {
 	Path, Cmd string
 	Err       error
-	Output    *bytes.Buffer
+	Output    io.Reader
 }
 
 // CommandWorker provides a consumer of work jobs and posts results to the worklog
-func CommandWorker(ctx context.Context, jobs <-chan Work, results chan<- WorkLog) {
+func CommandWorker(ctx context.Context, jobs <-chan Work, results chan<- WorkLog, outWriter io.ReadWriter) {
 	for {
 		var result WorkLog
 
@@ -35,12 +35,15 @@ func CommandWorker(ctx context.Context, jobs <-chan Work, results chan<- WorkLog
 			if !ok {
 				return
 			}
-			output := bytes.NewBuffer(nil)
+			if outWriter == nil {
+				outWriter = bytes.NewBuffer(nil)
+				result.Output = outWriter
+			}
+
 			result.Path = w.Path
 			result.Cmd = w.Cmd
-			result.Output = output
 
-			cmd, err := NewCommand(ctx, output, output, w.Path, w.Cmd)
+			cmd, err := NewCommand(ctx, outWriter, outWriter, w.Path, w.Cmd)
 			if err != nil {
 				result.Err = fmt.Errorf("failed to build command, %w", err)
 				break

internal/repotools/cmd/eachmodule/main.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"log"
 	"os"
 	"os/signal"
@@ -135,13 +137,23 @@ func run() (err error) {
 				relPath = result.Path
 			}
 
+			var output string
+			if result.Output != nil {
+				b, err := ioutil.ReadAll(result.Output)
+				if err != nil {
+					log.Printf("%s: %s => failed to read result output, %v",
+						relPath, result.Cmd, err)
+				}
+				output = string(b)
+			}
+
 			if result.Err != nil {
 				log.Printf("%s: %s => error: %v\n%s",
-					relPath, result.Cmd, result.Err, result.Output.String())
+					relPath, result.Cmd, result.Err, output)
 				failed = true
 			} else {
 				log.Printf("%s: %s =>\n%s",
-					relPath, result.Cmd, result.Output.String())
+					relPath, result.Cmd, output)
 			}
 
 			//  Terminate early as soon as any command fails.
@@ -158,7 +170,11 @@ func run() (err error) {
 	for i := 0; i < atOnce; i++ {
 		go func() {
 			defer jobWG.Done()
-			CommandWorker(ctx, jobs, results)
+			var output io.ReadWriter
+			if atOnce == 1 {
+				output = os.Stdout
+			}
+			CommandWorker(ctx, jobs, results, output)
 		}()
 	}