short hash support

---
type: change
message: short hash support
change_hash: AAgqKEF108rXJcNRh8iYiusJfKurEPZaPABTuJyHXnY9
credentials:
- type: pgp_signature
  pub_key_id: 95C46FA6A41148AC
  body: 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
  account: mediocregopher

ROADMAP.md

@@ -12,7 +12,6 @@ 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.
-* Support short hash names
 * 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
   config.

repo.go

@@ -3,11 +3,13 @@ package dehub
 
 import (
 	"bytes"
+	"encoding/hex"
 	"errors"
 	"fmt"
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"dehub.dev/src/dehub.git/fs"
 
@@ -354,21 +356,6 @@ func (r *Repo) GetGitCommit(h plumbing.Hash) (gc GitCommit, err error) {
 	return
 }
 
-// GetGitRevision resolves the revision and returns the GitCommit it references.
-func (r *Repo) GetGitRevision(rev plumbing.Revision) (GitCommit, error) {
-	// This returns a pointer for some reason, not sure why.
-	h, err := r.GitRepo.ResolveRevision(rev)
-	if err != nil {
-		return GitCommit{}, fmt.Errorf("resolving revision: %w", err)
-	}
-
-	gc, err := r.GetGitCommit(*h)
-	if err != nil {
-		return GitCommit{}, fmt.Errorf("getting commit %q: %w", *h, err)
-	}
-	return gc, nil
-}
-
 // ErrHeadIsZero is used to indicate that HEAD resolves to the zero hash. An
 // example of when this can happen is if the repo was just initialized and has
 // no commits, or if an orphan branch is checked out.
@@ -436,10 +423,85 @@ func (r *Repo) GetGitCommitRange(start, end plumbing.Hash) ([]GitCommit, error)
 	return commits, nil
 }
 
+var (
+	hashLen    = len(plumbing.ZeroHash)
+	hashStrLen = len(plumbing.ZeroHash.String())
+	errNotHex  = errors.New("not a valid hex string")
+)
+
+func (r *Repo) findCommitByShortHash(hashStr string) (plumbing.Hash, error) {
+	paddedHashStr := hashStr
+	if len(hashStr)%2 > 0 {
+		paddedHashStr += "0"
+	}
+
+	if hashB, err := hex.DecodeString(paddedHashStr); err != nil {
+		return plumbing.ZeroHash, errNotHex
+	} else if len(hashStr) == hashStrLen {
+		var hash plumbing.Hash
+		copy(hash[:], hashB)
+		return hash, nil
+	} else if len(hashStr) < 2 {
+		return plumbing.ZeroHash, errors.New("hash string must be 2 characters long or more")
+	}
+
+	for i := 2; i < hashStrLen; i++ {
+		hashPrefix, hashTail := hashStr[:i], hashStr[i:]
+		path := filepath.Join("objects", hashPrefix)
+		fileInfos, err := r.GitDirFS.ReadDir(path)
+		if err != nil {
+			return plumbing.ZeroHash, fmt.Errorf("listing files in %q: %w", path, err)
+		}
+
+		var matchedHash plumbing.Hash
+		for _, fileInfo := range fileInfos {
+			objFileName := fileInfo.Name()
+			if !strings.HasPrefix(objFileName, hashTail) {
+				continue
+			}
+
+			objHash := plumbing.NewHash(hashPrefix + objFileName)
+			obj, err := r.GitRepo.Storer.EncodedObject(plumbing.AnyObject, objHash)
+			if err != nil {
+				return plumbing.ZeroHash, fmt.Errorf("reading object %q off disk: %w", objHash, err)
+			} else if obj.Type() != plumbing.CommitObject {
+				continue
+
+			} else if matchedHash == plumbing.ZeroHash {
+				matchedHash = objHash
+				continue
+			}
+
+			return plumbing.ZeroHash, fmt.Errorf("both %q and %q match", matchedHash, objHash)
+		}
+
+		if matchedHash != plumbing.ZeroHash {
+			return matchedHash, nil
+		}
+	}
+
+	return plumbing.ZeroHash, errors.New("failed to find a commit object with a matching prefix")
+}
+
 func (r *Repo) resolveRev(rev plumbing.Revision) (plumbing.Hash, error) {
 	if rev == plumbing.Revision(plumbing.ZeroHash.String()) {
 		return plumbing.ZeroHash, nil
 	}
+
+	{
+		// pretend the revision is a short hash until proven otherwise
+		shortHash := string(rev)
+		hash, err := r.findCommitByShortHash(shortHash)
+		if errors.Is(err, errNotHex) {
+			// ok, continue
+		} else if err != nil {
+			return plumbing.ZeroHash, fmt.Errorf("resolving as short hash: %w", err)
+		} else {
+			// guess it _is_ a short hash, knew it!
+			return hash, nil
+		}
+	}
+
 	h, err := r.GitRepo.ResolveRevision(rev)
 	if err != nil {
 		return plumbing.ZeroHash, fmt.Errorf("resolving revision %q: %w", rev, err)
@@ -447,6 +509,20 @@ func (r *Repo) resolveRev(rev plumbing.Revision) (plumbing.Hash, error) {
 	return *h, nil
 }
 
+// GetGitRevision resolves the revision and returns the GitCommit it references.
+func (r *Repo) GetGitRevision(rev plumbing.Revision) (GitCommit, error) {
+	hash, err := r.resolveRev(rev)
+	if err != nil {
+		return GitCommit{}, err
+	}
+
+	gc, err := r.GetGitCommit(hash)
+	if err != nil {
+		return GitCommit{}, fmt.Errorf("getting commit %q: %w", hash, err)
+	}
+	return gc, nil
+}
+
 // GetGitRevisionRange is like GetGitCommitRange, first resolving the given
 // revisions into hashes before continuing with GetGitCommitRange's behavior.
 func (r *Repo) GetGitRevisionRange(startRev, endRev plumbing.Revision) ([]GitCommit, error) {

repo_test.go

@@ -309,3 +309,22 @@ func TestThisRepoStillVerifies(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestShortHashResolving(t *testing.T) {
+	// TODO ideally this test would test the conflicting hashes are noticed, but
+	// that's hard...
+	h := newHarness(t)
+	hash := h.changeCommit("first commit", h.cfg.Accounts[0].ID, h.sig).GitCommit.Hash
+	hashStr := hash.String()
+	t.Log(hashStr)
+
+	for i := 2; i < len(hashStr); i++ {
+		gotCommit, err := h.repo.GetGitRevision(plumbing.Revision(hashStr[:i]))
+		if err != nil {
+			t.Fatalf("resolving %q: %v", hashStr[:i], err)
+		} else if gotCommit.GitCommit.Hash != hash {
+			t.Fatalf("expected hash %q but got %q",
+				gotCommit.GitCommit.Hash, hash)
+		}
+	}
+}