add ability to credential range of change commits

---
type: change
message: |-
  add ability to credential range of change commits

  previously it wasn't possible to generate a credential for the changes of a
  range of commits, which was not super helpful. Now it is!
change_hash: AG8eGxGH30bZYieD7uYtiUtpQL7u357SKPE0rvbk8LpR
credentials:
- type: pgp_signature
  pub_key_id: 95C46FA6A41148AC
  body: 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
  account: mediocregopher

cmd/dehub/cmd_commit.go

@@ -102,23 +102,38 @@ func cmdCommit(ctx context.Context, cmd *dcmd.Cmd) {
 	cmd.SubCmd("credential", "Commit credential of a different commit",
 		func(ctx context.Context, cmd *dcmd.Cmd) {
 			flag := cmd.FlagSet()
-			rev := flag.String("rev", "", "Revision of commit to accredit")
+			startRev := flag.String("start", "", "Revision of the starting commit to accredit (when accrediting a range of changes)")
+			endRev := flag.String("end", "HEAD", "Revision of the ending commit to accredit (when accrediting a range of changes)")
+			rev := flag.String("rev", "", "Revision of commit to accredit (when accrediting a single commit)")
 			cmd.Run(func() (context.Context, error) {
-				if *rev == "" {
+				if *rev == "" && *startRev == "" {
-					return nil, errors.New("-rev is required")
+					return nil, errors.New("-rev or -start is required")
 				} else if hasStaged {
 					return nil, errors.New("credential commit cannot have any files changed")
 				}
 
+				var credCommit dehub.Commit
+				if *rev != "" {
 					gitCommit, err := repo.GetGitRevision(plumbing.Revision(*rev))
 					if err != nil {
 						return nil, fmt.Errorf("resolving revision %q: %w", *rev, err)
+					} else if credCommit, err = repo.NewCommitCredential(gitCommit.Interface.GetHash()); err != nil {
+						return nil, fmt.Errorf("constructing credential commit: %w", err)
+					}
+				} else {
+					gitCommits, err := repo.GetGitRevisionRange(
+						plumbing.Revision(*startRev),
+						plumbing.Revision(*endRev),
+					)
+					if err != nil {
+						return nil, fmt.Errorf("resolving revisions %q to %q: %w",
+							*startRev, *endRev, err)
+					} else if credCommit, err = repo.NewCommitCredentialFromChanges(gitCommits); err != nil {
+						return nil, fmt.Errorf("constructing credential commit: %w", err)
+					}
 				}
 
-				credCommit, err := repo.NewCommitCredential(gitCommit.Interface.GetHash())
+				if err := accreditAndCommit(credCommit); err != nil {
-				if err != nil {
-					return nil, fmt.Errorf("constructing credential commit: %w", err)
-				} else if err := accreditAndCommit(credCommit); err != nil {
 					return nil, err
 				}
 				return nil, nil

commit.go

@@ -439,3 +439,46 @@ func (r *Repo) verifyCommit(branch plumbing.ReferenceName, gitCommit GitCommit,
 
 	return nil
 }
+
+type changeRangeInfo struct {
+	lastChangeCommit   GitCommit
+	authors            map[string]struct{}
+	msg                string
+	startTree, endTree *object.Tree
+	changeHash         []byte
+}
+
+// changeRangeInfo returns various pieces of information about a range of
+// commits' changes.
+func (r *Repo) changeRangeInfo(commits []GitCommit) (changeRangeInfo, error) {
+	info := changeRangeInfo{
+		authors: map[string]struct{}{},
+	}
+
+	var lastChangeCommitOk bool
+	for _, commit := range commits {
+		if _, ok := commit.Interface.(*CommitChange); ok {
+			info.lastChangeCommit = commit
+			lastChangeCommitOk = true
+			for _, cred := range commit.Commit.Common.Credentials {
+				info.authors[cred.AccountID] = struct{}{}
+			}
+		}
+	}
+	if !lastChangeCommitOk {
+		return changeRangeInfo{}, errors.New("no change commits found")
+	}
+
+	// startTree has to be the tree of the parent of the first commit, which
+	// isn't included in commits. Determine it the hard way.
+	var err error
+	if info.startTree, err = r.parentTree(commits[0].GitCommit); err != nil {
+		return changeRangeInfo{}, fmt.Errorf("getting tree of parent of %q: %w",
+			commits[0].GitCommit.Hash, err)
+	}
+
+	info.msg = info.lastChangeCommit.Commit.Change.Message
+	info.endTree = info.lastChangeCommit.GitTree
+	info.changeHash = genChangeHash(nil, info.msg, info.startTree, info.endTree)
+	return info, nil
+}

commit_change.go

@@ -74,40 +74,17 @@ func (cc CommitChange) GetHash() []byte {
 // start/end will be different than the one which needs to be accredited in
 // onto/end.
 func (r *Repo) CombineCommitChanges(commits []GitCommit, onto plumbing.ReferenceName) (GitCommit, error) {
-	authorsSet := map[string]struct{}{}
+	info, err := r.changeRangeInfo(commits)
-	var lastChangeCommit GitCommit
+	if err != nil {
-	var lastChangeCommitOk bool
+		return GitCommit{}, err
-	for _, commit := range commits {
-		if _, ok := commit.Interface.(*CommitChange); ok {
-			lastChangeCommit = commit
-			lastChangeCommitOk = true
-			for _, cred := range commit.Commit.Common.Credentials {
-				authorsSet[cred.AccountID] = struct{}{}
-			}
-		}
-	}
-	if !lastChangeCommitOk {
-		return GitCommit{}, errors.New("no change commits in range")
 	}
 
-	authors := make([]string, 0, len(authorsSet))
+	authors := make([]string, 0, len(info.authors))
-	for author := range authorsSet {
+	for author := range info.authors {
 		authors = append(authors, author)
 	}
 	sort.Strings(authors)
 
-	// startTree has to be the tree of startRev, which isn't included in
-	// commits. Determine it the hard way.
-	startTree, err := r.parentTree(commits[0].GitCommit)
-	if err != nil {
-		return GitCommit{}, fmt.Errorf("getting tree of parent of %q: %w",
-			commits[0].GitCommit.Hash, err)
-	}
-
-	msg := lastChangeCommit.Commit.Change.Message
-	endTree := lastChangeCommit.GitTree
-	changeHash := genChangeHash(nil, msg, startTree, endTree)
-
 	ontoBranchName, err := r.ReferenceToBranchName(onto)
 	if err != nil {
 		return GitCommit{}, fmt.Errorf("resolving %q into a branch name: %w", onto, err)
@@ -120,8 +97,8 @@ func (r *Repo) CombineCommitChanges(commits []GitCommit, onto plumbing.Reference
 		return GitCommit{}, fmt.Errorf("resolving revision %q: %w", onto, err)
 	}
 	ontoTree := ontoCommit.GitTree
-	ontoEndChangeHash := genChangeHash(nil, msg, ontoTree, endTree)
+	ontoEndChangeHash := genChangeHash(nil, info.msg, ontoTree, info.endTree)
-	if !bytes.Equal(ontoEndChangeHash, changeHash) {
+	if !bytes.Equal(ontoEndChangeHash, info.changeHash) {
 		// TODO figure out what files to show as being the "problem files" in
 		// the error message
 		return GitCommit{}, fmt.Errorf("rebasing onto %q would cause the change hash to change, aborting combine", onto)
@@ -129,7 +106,7 @@ func (r *Repo) CombineCommitChanges(commits []GitCommit, onto plumbing.Reference
 
 	var creds []sigcred.Credential
 	for _, commit := range commits {
-		if bytes.Equal(commit.Interface.GetHash(), changeHash) {
+		if bytes.Equal(commit.Interface.GetHash(), info.changeHash) {
 			creds = append(creds, commit.Commit.Common.Credentials...)
 		}
 	}
@@ -141,8 +118,8 @@ func (r *Repo) CombineCommitChanges(commits []GitCommit, onto plumbing.Reference
 
 	commit := Commit{
 		Change: &CommitChange{
-			Message:    msg,
+			Message:    info.msg,
-			ChangeHash: changeHash,
+			ChangeHash: info.changeHash,
 		},
 		Common: CommitCommon{Credentials: creds},
 	}
@@ -151,7 +128,7 @@ func (r *Repo) CombineCommitChanges(commits []GitCommit, onto plumbing.Reference
 		Commit:     commit,
 		Author:     strings.Join(authors, ","),
 		ParentHash: ontoCommit.GitCommit.Hash,
-		GitTree:    endTree,
+		GitTree:    info.endTree,
 	})
 	if err != nil {
 		return GitCommit{}, fmt.Errorf("storing commit: %w", err)

commit_credential.go

@@ -27,6 +27,18 @@ func (r *Repo) NewCommitCredential(hash []byte) (Commit, error) {
 	}, nil
 }
 
+// NewCommitCredentialFromChanges constructs and returns a Comit populated with
+// a CommitCredential for all changes in the given range of GitCommits. The
+// message of the last change commit in the range is used when generating the
+// hash.
+func (r *Repo) NewCommitCredentialFromChanges(commits []GitCommit) (Commit, error) {
+	info, err := r.changeRangeInfo(commits)
+	if err != nil {
+		return Commit{}, err
+	}
+	return r.NewCommitCredential(info.changeHash)
+}
+
 // MessageHead implements the method for the CommitInterface interface.
 func (cc CommitCredential) MessageHead(common CommitCommon) (string, error) {
 	hash64 := base64.StdEncoding.EncodeToString(cc.CredentialedHash)