Refactor git command stdio pipe (#36422)

Most potential deadlock problems should have been fixed, and new code is
unlikely to cause new problems with the new design.

Also raise the minimum Git version required to 2.6.0 (released in 2015)

modules/git/pipeline/revlist.go

@@ -6,52 +6,25 @@ package pipeline
 import (
 	"bufio"
 	"context"
-	"fmt"
 	"io"
 	"strings"
-	"sync"
 
 	"code.gitea.io/gitea/modules/git/gitcmd"
 )
 
-// RevListAllObjects runs rev-list --objects --all and writes to a pipewriter
-func RevListAllObjects(ctx context.Context, revListWriter *io.PipeWriter, wg *sync.WaitGroup, basePath string, errChan chan<- error) {
-	defer wg.Done()
-	defer revListWriter.Close()
-
-	cmd := gitcmd.NewCommand("rev-list", "--objects", "--all")
-	if err := cmd.WithDir(basePath).
-		WithStdout(revListWriter).
-		RunWithStderr(ctx); err != nil {
-		_ = revListWriter.CloseWithError(fmt.Errorf("git rev-list --objects --all [%s]: %w", basePath, err))
-		errChan <- err
-	}
-}
-
 // RevListObjects run rev-list --objects from headSHA to baseSHA
-func RevListObjects(ctx context.Context, revListWriter *io.PipeWriter, wg *sync.WaitGroup, tmpBasePath, headSHA, baseSHA string, errChan chan<- error) {
-	defer wg.Done()
-	defer revListWriter.Close()
-
-	cmd := gitcmd.NewCommand("rev-list", "--objects").AddDynamicArguments(headSHA)
+func RevListObjects(ctx context.Context, cmd *gitcmd.Command, tmpBasePath, headSHA, baseSHA string) error {
+	cmd.AddArguments("rev-list", "--objects").AddDynamicArguments(headSHA)
 	if baseSHA != "" {
 		cmd = cmd.AddArguments("--not").AddDynamicArguments(baseSHA)
 	}
-	if err := cmd.WithDir(tmpBasePath).
-		WithStdout(revListWriter).
-		RunWithStderr(ctx); err != nil {
-		errChan <- fmt.Errorf("git rev-list [%s]: %w", tmpBasePath, err)
-	}
+	return cmd.WithDir(tmpBasePath).RunWithStderr(ctx)
 }
 
 // BlobsFromRevListObjects reads a RevListAllObjects and only selects blobs
-func BlobsFromRevListObjects(revListReader *io.PipeReader, shasToCheckWriter *io.PipeWriter, wg *sync.WaitGroup) {
-	defer wg.Done()
-	defer revListReader.Close()
-	scanner := bufio.NewScanner(revListReader)
-	defer func() {
-		_ = shasToCheckWriter.CloseWithError(scanner.Err())
-	}()
+func BlobsFromRevListObjects(in io.ReadCloser, out io.WriteCloser) error {
+	defer out.Close()
+	scanner := bufio.NewScanner(in)
 	for scanner.Scan() {
 		line := scanner.Text()
 		if len(line) == 0 {
@@ -63,12 +36,12 @@ func BlobsFromRevListObjects(revListReader *io.PipeReader, shasToCheckWriter *io
 		}
 		toWrite := []byte(fields[0] + "\n")
 		for len(toWrite) > 0 {
-			n, err := shasToCheckWriter.Write(toWrite)
+			n, err := out.Write(toWrite)
 			if err != nil {
-				_ = revListReader.CloseWithError(err)
-				break
+				return err
 			}
 			toWrite = toWrite[n:]
 		}
 	}
+	return scanner.Err()
 }