Read patches to get history

modules/git/repo_compare.go

@@ -6,9 +6,14 @@
 package git
 
 import (
+	"bufio"
 	"bytes"
+	"errors"
 	"fmt"
 	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"regexp"
 	"strconv"
 	"strings"
@@ -188,6 +193,8 @@ func GetDiffShortStat(repoPath string, args ...string) (numFiles, totalAdditions
 var shortStatFormat = regexp.MustCompile(
 	`\s*(\d+) files? changed(?:, (\d+) insertions?\(\+\))?(?:, (\d+) deletions?\(-\))?`)
 
+var patchCommits = regexp.MustCompile(`^From\s(\w+)\s`)
+
 func parseDiffStat(stdout string) (numFiles, totalAdditions, totalDeletions int, err error) {
 	if len(stdout) == 0 || stdout == "\n" {
 		return 0, 0, 0, nil
@@ -267,3 +274,57 @@ func (repo *Repository) GetDiffFromMergeBase(base, head string, w io.Writer) err
 	}
 	return err
 }
+
+// ReadPullHead will fetch a pull ref if possible or return an error
+func (repo *Repository) ReadPullHead(prID int64) (commitSHA string, err error) {
+	headPath := fmt.Sprintf("refs/pull/%d/head", prID)
+	fullHeadPath := filepath.Join(repo.Path, headPath)
+	loadHead, err := os.Open(fullHeadPath)
+	if err != nil {
+		return "", err
+	}
+	defer loadHead.Close()
+	// Read only the first line of the patch - usually it contains the first commit made in patch
+	scanner := bufio.NewScanner(loadHead)
+	scanner.Scan()
+	commitHead := scanner.Text()
+	if len(commitHead) != 40 {
+		return "", errors.New("head file doesn't contain valid commit ID")
+	}
+	return commitHead, nil
+}
+
+// ReadPatchCommit will check if a diff patch exists and return stats
+func (repo *Repository) ReadPatchCommit(prID int64) (commitSHA string, err error) {
+	// Migrated repositories download patches to "pulls" location
+	patchFile := fmt.Sprintf("pulls/%d.patch", prID)
+	loadPatch, err := os.Open(filepath.Join(repo.Path, patchFile))
+	if err != nil {
+		return "", err
+	}
+	defer loadPatch.Close()
+	// Read only the first line of the patch - usually it contains the first commit made in patch
+	scanner := bufio.NewScanner(loadPatch)
+	scanner.Scan()
+	// Parse the Patch stats, sometimes Migration returns a 404 for the patch file
+	commitSHAGroups := patchCommits.FindStringSubmatch(scanner.Text())
+	if len(commitSHAGroups) != 0 {
+		commitSHA = commitSHAGroups[1]
+	} else {
+		return "", errors.New("patch file doesn't contain valid commit ID")
+	}
+	return commitSHA, nil
+}
+
+// WritePullHead will populate a PR head retrieved from patch file
+func (repo *Repository) WritePullHead(prID int64, commitSHA string) error {
+	headPath := fmt.Sprintf("refs/pull/%d", prID)
+	fullHeadPath := filepath.Join(repo.Path, headPath)
+	// Create missing directory just in case
+	if err := os.MkdirAll(fullHeadPath, os.ModePerm); err != nil {
+		return err
+	}
+	commitBytes := []byte(commitSHA)
+	pullPath := filepath.Join(fullHeadPath, "head")
+	return ioutil.WriteFile(pullPath, commitBytes, os.ModePerm)
+}

routers/web/repo/pull.go

@@ -320,8 +320,46 @@ func PrepareMergedViewPullInfo(ctx *context.Context, issue *models.Issue) *git.C
 	setMergeTarget(ctx, pull)
 	ctx.Data["HasMerged"] = true
 
+	var baseCommit string
+	// Some migrated PR won't have any Base SHA and lose history, try to get one
+	if pull.MergeBase == "" {
+		var commitSHA, parentCommit string
+		// If there is a head or a patch file, and it is readable, grab info
+		commitSHA, err := ctx.Repo.GitRepo.ReadPullHead(pull.Index)
+		if err != nil {
+			// Head File does not exist, try the patch
+			commitSHA, err = ctx.Repo.GitRepo.ReadPatchCommit(pull.Index)
+			if err == nil {
+				// Recreate pull head in files for next time
+				if err := ctx.Repo.GitRepo.WritePullHead(pull.Index, commitSHA); err != nil {
+					log.Error("Could not write head file", err)
+				}
+			} else {
+				// There is no history available
+				log.Trace("No history file available for PR %d", pull.Index)
+			}
+		}
+		if commitSHA != "" {
+			// Get immediate parent of the first commit in the patch, grab history back
+			parentCommit, err = git.NewCommandContext(ctx, "rev-list", "-1", "--skip=1", commitSHA).RunInDir(ctx.Repo.GitRepo.Path)
+			if err == nil {
+				parentCommit = strings.TrimSpace(parentCommit)
+			}
+			// Special case on Git < 2.25 that doesn't fail on immediate empty history
+			if err != nil || parentCommit == "" {
+				log.Info("No known parent commit for PR %d, error: %v", pull.Index, err)
+				// bring at least partial history if it can work
+				parentCommit = commitSHA
+			}
+		}
+		baseCommit = parentCommit
+	} else {
+		// Keep an empty history or original commit
+		baseCommit = pull.MergeBase
+	}
+
 	compareInfo, err := ctx.Repo.GitRepo.GetCompareInfo(ctx.Repo.Repository.RepoPath(),
-		pull.MergeBase, pull.GetGitRefName(), true, false)
+		baseCommit, pull.GetGitRefName(), true, false)
 	if err != nil {
 		if strings.Contains(err.Error(), "fatal: Not a valid object name") || strings.Contains(err.Error(), "unknown revision or path not in the working tree") {
 			ctx.Data["IsPullRequestBroken"] = true