fix: ignore existence of commits for force pushes (#9262)

- Because we wish to show the status of the old and new commit of a force push, ignore that the commit doesn't exist and return a commit with only its ID filled. This is enough to still show the CI status of this commit although the commit itself is no longer reachable.
- Add unit test.
- Add integration test.
- Resolves forgejo/forgejo#9250

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/9262
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Gusted <postmaster@gusted.xyz>
Co-committed-by: Gusted <postmaster@gusted.xyz>

modules/git/repo_commit.go

@@ -458,14 +458,28 @@ func (repo *Repository) getBranches(commit *Commit, limit int) ([]string, error)
 	return branches, nil
 }
 
-// GetCommitsFromIDs get commits from commit IDs
-func (repo *Repository) GetCommitsFromIDs(commitIDs []string) []*Commit {
+// GetCommitsFromIDs get commits from commit IDs. If ignoreExistence is
+// specified, then commits that no longer exists are still returned but
+// without any information except the ID.
+func (repo *Repository) GetCommitsFromIDs(commitIDs []string, ignoreExistence bool) []*Commit {
 	commits := make([]*Commit, 0, len(commitIDs))
 
 	for _, commitID := range commitIDs {
 		commit, err := repo.GetCommit(commitID)
 		if err == nil && commit != nil {
 			commits = append(commits, commit)
+		} else if ignoreExistence && IsErrNotExist(err) {
+			// It's entirely possible the commit no longer exists, we only care
+			// about the status and verification. Verification is no longer possible,
+			// but getting the status is still possible with just the ID. We do have
+			// to assumme the commitID is not shortened, we cannot recover the full
+			// commitID.
+			id, err := NewIDFromString(commitID)
+			if err == nil {
+				commits = append(commits, &Commit{
+					ID: id,
+				})
+			}
 		}
 	}