implement amend flag for change and comment commit types

---
type: change
message: |-
  implement amend flag for change and comment commit types

  This involved a custom implementation of soft reset, since go-git's doesn't
  correctly handle the behavior around the initial commit of a repo. There is also
  a small fix to HasStagedChanges, since it wasn't properly handling untracked
  files.
change_hash: AJxjg7EN6l2UBcqGXLAqS4HGCfMgD3xCmQ7uZMSOScBc
credentials:
- type: pgp_signature
  pub_key_id: 95C46FA6A41148AC
  body: 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
  account: mediocregopher

ROADMAP.md

@@ -10,7 +10,6 @@ Must be able to feel good about showing the project publicly, as well as be able
 to accept help from people asking to help.
 
 * Fast-forward perms on branches (so they can be deleted)
-* Ammending commits.
 * Figure out commit range syntax, use that everywhere.
 * Ability to specify a pgp key manually, even if it's not in the project.
 * Ability to require _any_ signature on a commit, even if it's not in the
@@ -65,6 +64,9 @@ to accept help from people asking to help.
 These tasks aren't necessarily scheduled for any particular milestone, but they
 are things that could use doing anyway.
 
+* Config validation. Every interface used by the config should have a
+  `Validate() error` method, and Config itself should as well.
+
 * Maybe coalesce the `accessctl`, `fs`, and `sigcred` packages back into the
   root "dehub" package.
 

cmd/dehub/cmd_commit.go

@@ -78,14 +78,24 @@ func cmdCommit(ctx context.Context, cmd *dcmd.Cmd) {
 		func(ctx context.Context, cmd *dcmd.Cmd) {
 			flag := cmd.FlagSet()
 			msg := flag.String("msg", "", "Commit message")
+			amend := flag.Bool("amend", false, "Add changes to HEAD commit, amend its message, and re-accredit it")
 			cmd.Run(func() (context.Context, error) {
-				if !hasStaged {
+				if !hasStaged && !*amend {
 					return nil, errors.New("no changes have been staged for commit")
 				}
 
+				var prevMsg string
+				if *amend {
+					oldHead, err := repo.softReset("change")
+					if err != nil {
+						return nil, err
+					}
+					prevMsg = oldHead.Commit.Change.Message
+				}
+
 				if *msg == "" {
 					var err error
-					if *msg, err = tmpFileMsg(); err != nil {
+					if *msg, err = tmpFileMsg(defaultCommitFileMsgTpl, prevMsg); err != nil {
 						return nil, fmt.Errorf("error collecting commit message from user: %w", err)
 
 					} else if *msg == "" {
@@ -115,7 +125,7 @@ func cmdCommit(ctx context.Context, cmd *dcmd.Cmd) {
 				if *rev == "" && *startRev == "" {
 					return nil, errors.New("-rev or -start is required")
 				} else if hasStaged {
-					return nil, errors.New("credential commit cannot have any files changed")
+					return nil, errors.New("credential commit cannot have staged changes")
 				}
 
 				var credCommit dehub.Commit
@@ -154,10 +164,24 @@ func cmdCommit(ctx context.Context, cmd *dcmd.Cmd) {
 		func(ctx context.Context, cmd *dcmd.Cmd) {
 			flag := cmd.FlagSet()
 			msg := flag.String("msg", "", "Comment message")
+			amend := flag.Bool("amend", false, "Amend the comment message currently in HEAD")
 			cmd.Run(func() (context.Context, error) {
+				if hasStaged {
+					return nil, errors.New("comment commit cannot have staged changes")
+				}
+
+				var prevMsg string
+				if *amend {
+					oldHead, err := repo.softReset("comment")
+					if err != nil {
+						return nil, err
+					}
+					prevMsg = oldHead.Commit.Comment.Message
+				}
+
 				if *msg == "" {
 					var err error
-					if *msg, err = tmpFileMsg(); err != nil {
+					if *msg, err = tmpFileMsg(defaultCommitFileMsgTpl, prevMsg); err != nil {
 						return nil, fmt.Errorf("collecting comment message from user: %w", err)
 
 					} else if *msg == "" {

cmd/dehub/cmd_util.go

@@ -1,11 +1,13 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"os"
 
 	"dehub.dev/src/dehub.git"
+	"gopkg.in/src-d/go-git.v4/plumbing"
 )
 
 type repo struct {
@@ -26,3 +28,50 @@ func (r *repo) openRepo() error {
 	}
 	return nil
 }
+
+// softReset resets to HEAD^ (or to an orphaned index, if HEAD has no parents),
+// returning the old HEAD.
+func (r *repo) softReset(expType string) (dehub.GitCommit, error) {
+	head, err := r.GetGitHead()
+	if err != nil {
+		return head, fmt.Errorf("getting HEAD commit: %w", err)
+	} else if typ, err := head.Commit.Type(); err != nil {
+		return head, fmt.Errorf("determining commit type of HEAD:% w", err)
+	} else if expType != "" && typ != expType {
+		return head, fmt.Errorf("expected HEAD to be a %q commit, but found %q",
+			expType, typ)
+	}
+
+	branchName, branchErr := r.ReferenceToBranchName(plumbing.HEAD)
+	numParents := head.GitCommit.NumParents()
+	if numParents > 1 {
+		return head, errors.New("cannot reset to parent of a commit with multiple parents")
+
+	} else if numParents == 0 {
+		// if there are no parents then HEAD is the only commit in the branch.
+		// Don't handle ErrNoBranchReference because there's not really anything
+		// which can be done for that; we can't set head to "no commit".
+		// Otherwise, just remove the branch reference, HEAD will still point to
+		// it and all of HEAD's changes will be in the index.
+		if branchErr != nil {
+			return head, branchErr
+		} else if err := r.GitRepo.Storer.RemoveReference(branchName); err != nil {
+			return head, fmt.Errorf("removing reference %q: %w", branchName, err)
+		}
+		return head, nil
+	}
+
+	refName := branchName
+	if errors.Is(branchErr, dehub.ErrNoBranchReference) {
+		refName = plumbing.HEAD
+	} else if err != nil {
+		return head, fmt.Errorf("resolving HEAD: %w", err)
+	}
+
+	parentHash := head.GitCommit.ParentHashes[0]
+	newHeadRef := plumbing.NewHashReference(refName, parentHash)
+	if err := r.GitRepo.Storer.SetReference(newHeadRef); err != nil {
+		return head, fmt.Errorf("storing reference %q: %w", newHeadRef, err)
+	}
+	return head, nil
+}

cmd/dehub/tmp_file.go

@@ -12,7 +12,12 @@ import (
 	"strings"
 )
 
-func tmpFileMsg() (string, error) {
+const defaultCommitFileMsgTpl = `%s
+
+# Please enter the commit message for your commit. Lines starting
+# with '#' will be ignored, and an empty message aborts the commit.`
+
+func tmpFileMsg(tpl string, args ...interface{}) (string, error) {
 	editor := os.Getenv("EDITOR")
 	if editor == "" {
 		return "", errors.New("EDITOR not set, please set it or use -msg in order to create your commit message")
@@ -27,10 +32,7 @@ func tmpFileMsg() (string, error) {
 	tmpfName := tmpf.Name()
 	defer os.Remove(tmpfName)
 
-	tmpBody := bytes.NewBufferString(`
-
-# Please enter the commit message for your commit. Lines starting
-# with '#' will be ignored, and an empty message aborts the commit.`)
+	tmpBody := bytes.NewBufferString(fmt.Sprintf(tpl, args...))
 
 	_, err = io.Copy(tmpf, tmpBody)
 	tmpf.Close()

commit.go

@@ -281,7 +281,8 @@ func (r *Repo) HasStagedChanges() (bool, error) {
 
 	var any bool
 	for _, fileStatus := range status {
-		if fileStatus.Staging != git.Unmodified {
+		if fileStatus.Staging != git.Unmodified &&
+			fileStatus.Staging != git.Untracked {
 			any = true
 			break
 		}

repo.go

@@ -267,9 +267,13 @@ func (r *Repo) TraverseReferenceChain(refName plumbing.ReferenceName, pred func(
 	}
 }
 
+// ErrNoBranchReference is returned from ReferenceToBranchName if no reference
+// in the reference chain is for a branch.
+var ErrNoBranchReference = errors.New("no branch reference found")
+
 // ReferenceToBranchName traverses a chain of references looking for the first
-// branch reference, and returns that name, or returns an error if no branch
-// reference is part of the chain.
+// branch reference, and returns that name, or returns ErrNoBranchReference if
+// no branch reference is part of the chain.
 func (r *Repo) ReferenceToBranchName(refName plumbing.ReferenceName) (plumbing.ReferenceName, error) {
 	// first check if the given refName is a branch, if so just return that.
 	if refName.IsBranch() {
@@ -280,7 +284,7 @@ func (r *Repo) ReferenceToBranchName(refName plumbing.ReferenceName) (plumbing.R
 		return ref.Target().IsBranch()
 	})
 	if errors.Is(err, errTraverseRefNoMatch) {
-		return "", errors.New("no branch in reference chain")
+		return "", ErrNoBranchReference
 	} else if err != nil {
 		return "", fmt.Errorf("traversing reference chain: %w", err)
 	}