Refactor git command stderr handling (#36402)

And clean up legacy fragile & incorrect logic

modules/git/grep.go

@@ -5,11 +5,10 @@ package git
 
 import (
 	"bufio"
-	"bytes"
 	"context"
 	"errors"
 	"fmt"
-	"os"
+	"io"
 	"slices"
 	"strconv"
 	"strings"
@@ -42,15 +41,6 @@ type GrepOptions struct {
 }
 
 func GrepSearch(ctx context.Context, repo *Repository, search string, opts GrepOptions) ([]*GrepResult, error) {
-	stdoutReader, stdoutWriter, err := os.Pipe()
-	if err != nil {
-		return nil, fmt.Errorf("unable to create os pipe to grep: %w", err)
-	}
-	defer func() {
-		_ = stdoutReader.Close()
-		_ = stdoutWriter.Close()
-	}()
-
 	/*
 	 The output is like this ( "^@" means \x00):
 
@@ -83,12 +73,11 @@ func GrepSearch(ctx context.Context, repo *Repository, search string, opts GrepO
 	cmd.AddDynamicArguments(util.IfZero(opts.RefName, "HEAD"))
 	cmd.AddDashesAndList(opts.PathspecList...)
 	opts.MaxResultLimit = util.IfZero(opts.MaxResultLimit, 50)
-	stderr := bytes.Buffer{}
-	err = cmd.WithDir(repo.Path).
-		WithStdout(stdoutWriter).
-		WithStderr(&stderr).
+
+	var stdoutReader io.ReadCloser
+	err := cmd.WithDir(repo.Path).
+		WithStdoutReader(&stdoutReader).
 		WithPipelineFunc(func(ctx context.Context, cancel context.CancelFunc) error {
-			_ = stdoutWriter.Close()
 			defer stdoutReader.Close()
 
 			isInBlock := false
@@ -133,17 +122,17 @@ func GrepSearch(ctx context.Context, repo *Repository, search string, opts GrepO
 			}
 			return nil
 		}).
-		Run(ctx)
+		RunWithStderr(ctx)
 	// git grep exits by cancel (killed), usually it is caused by the limit of results
-	if gitcmd.IsErrorExitCode(err, -1) && stderr.Len() == 0 {
+	if gitcmd.IsErrorExitCode(err, -1) && err.Stderr() == "" {
 		return results, nil
 	}
 	// git grep exits with 1 if no results are found
-	if gitcmd.IsErrorExitCode(err, 1) && stderr.Len() == 0 {
+	if gitcmd.IsErrorExitCode(err, 1) && err.Stderr() == "" {
 		return nil, nil
 	}
 	if err != nil && !errors.Is(err, context.Canceled) {
-		return nil, fmt.Errorf("unable to run git grep: %w, stderr: %s", err, stderr.String())
+		return nil, fmt.Errorf("unable to run git grep: %w", err)
 	}
 	return results, nil
 }