HasPreviousCommit causes recursive load of commits unnecessarily (#14598) (#14649)

This PR improves HasPreviousCommit to prevent the automatic and recursive loading
of previous commits using git merge-base --is-ancestor and git rev-list

Fix #13684

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: 6543 <6543@obermui.de>

modules/git/commit.go

@@ -9,6 +9,7 @@ import (
 	"bufio"
 	"bytes"
 	"container/list"
+	"errors"
 	"fmt"
 	"image"
 	"image/color"
@@ -17,6 +18,7 @@ import (
 	_ "image/png"  // for processing png images
 	"io"
 	"net/http"
+	"os/exec"
 	"strconv"
 	"strings"
 
@@ -309,23 +311,33 @@ func (c *Commit) CommitsBefore() (*list.List, error) {
 
 // HasPreviousCommit returns true if a given commitHash is contained in commit's parents
 func (c *Commit) HasPreviousCommit(commitHash SHA1) (bool, error) {
-	for i := 0; i < c.ParentCount(); i++ {
-		commit, err := c.Parent(i)
-		if err != nil {
-			return false, err
+	this := c.ID.String()
+	that := commitHash.String()
+
+	if this == that {
+		return false, nil
 	}
-		if commit.ID == commitHash {
+
+	if err := CheckGitVersionConstraint(">= 1.8.0"); err == nil {
+		_, err := NewCommand("merge-base", "--is-ancestor", that, this).RunInDir(c.repo.Path)
+		if err == nil {
 			return true, nil
 		}
-		commitInParentCommit, err := commit.HasPreviousCommit(commitHash)
-		if err != nil {
-			return false, err
+		var exitError *exec.ExitError
+		if errors.As(err, &exitError) {
+			if exitError.ProcessState.ExitCode() == 1 && len(exitError.Stderr) == 0 {
+				return false, nil
 			}
-		if commitInParentCommit {
-			return true, nil
 		}
+		return false, err
 	}
-	return false, nil
+
+	result, err := NewCommand("rev-list", "--ancestry-path", "-n1", that+".."+this, "--").RunInDir(c.repo.Path)
+	if err != nil {
+		return false, err
+	}
+
+	return len(strings.TrimSpace(result)) > 0, nil
 }
 
 // CommitsBeforeLimit returns num commits before current revision