Migrated Repository will show modifications when possible (#17191)

* Read patches to get history

1 files changed, 39 insertions, 1 deletions

diff --git a/routers/web/repo/pull.go b/routers/web/repo/pull.go
index bf80a7e5df..ba775d761b 100644
--- a/routers/web/repo/pull.go
+++ b/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