rebase: Add wrapper for `git_rebase_inmemory_index()` (#900) (#905)

* rebase: Fix missing initialization of the repo pointer

While the `Rebase` structure has a pointer to the repository the rebase
is creatde in, this pointer isn't ever initialized. Fix this.

* rebase: Add wrapper for `git_rebase_inmemory_index()`

Add a new wrapper for `git_rebase_inmemory_index()`, which can be used
to retrieve the index for an in-memory rebase.

Co-authored-by: Patrick Steinhardt <psteinhardt@gitlab.com>
(cherry picked from commit e7d1b2b69f)

Co-authored-by: Patrick Steinhardt <ps@pks.im>

rebase.go

@@ -253,7 +253,7 @@ func (r *Repository) InitRebase(branch *AnnotatedCommit, upstream *AnnotatedComm
 		return nil, MakeGitError(ret)
 	}
 
-	return newRebaseFromC(ptr, cOpts), nil
+	return newRebaseFromC(ptr, r, cOpts), nil
 }
 
 // OpenRebase opens an existing rebase that was previously started by either an invocation of InitRebase or by another client.
@@ -275,7 +275,7 @@ func (r *Repository) OpenRebase(opts *RebaseOptions) (*Rebase, error) {
 		return nil, MakeGitError(ret)
 	}
 
-	return newRebaseFromC(ptr, cOpts), nil
+	return newRebaseFromC(ptr, r, cOpts), nil
 }
 
 // OperationAt gets the rebase operation specified by the given index.
@@ -327,6 +327,27 @@ func (rebase *Rebase) Next() (*RebaseOperation, error) {
 	return newRebaseOperationFromC(ptr), nil
 }
 
+// InmemoryIndex gets the index produced by the last operation, which is the
+// result of `Next()` and which will be committed by the next invocation of
+// `Commit()`. This is useful for resolving conflicts in an in-memory rebase
+// before committing them.
+//
+// This is only applicable for in-memory rebases; for rebases within a working
+// directory, the changes were applied to the repository's index.
+func (rebase *Rebase) InmemoryIndex() (*Index, error) {
+	runtime.LockOSThread()
+	defer runtime.UnlockOSThread()
+
+	var ptr *C.git_index
+	err := C.git_rebase_inmemory_index(&ptr, rebase.ptr)
+	runtime.KeepAlive(rebase)
+	if err < 0 {
+		return nil, MakeGitError(err)
+	}
+
+	return newIndexFromC(ptr, rebase.r), nil
+}
+
 // Commit commits the current patch.
 // You must have resolved any conflicts that were introduced during the patch application from the Next() invocation.
 func (rebase *Rebase) Commit(ID *Oid, author, committer *Signature, message string) error {
@@ -392,8 +413,8 @@ func (r *Rebase) Free() {
 	freeRebaseOptions(r.options)
 }
 
-func newRebaseFromC(ptr *C.git_rebase, opts *C.git_rebase_options) *Rebase {
+func newRebaseFromC(ptr *C.git_rebase, repo *Repository, opts *C.git_rebase_options) *Rebase {
-	rebase := &Rebase{ptr: ptr, options: opts}
+    rebase := &Rebase{ptr: ptr, r: repo, options: opts}
 	runtime.SetFinalizer(rebase, (*Rebase).Free)
 	return rebase
 }

rebase_test.go

@@ -14,6 +14,80 @@ import (
 
 // Tests
 
+func TestRebaseInMemoryWithConflict(t *testing.T) {
+	repo := createTestRepo(t)
+	defer cleanupTestRepo(t, repo)
+	seedTestRepo(t, repo)
+
+    // Create two branches with common history, where both modify "common-file"
+    // in a conflicting way.
+    _, err := commitSomething(repo, "common-file", "a\nb\nc\n", commitOptions{})
+    checkFatal(t, err)
+	checkFatal(t, createBranch(repo, "branch-a"))
+	checkFatal(t, createBranch(repo, "branch-b"))
+
+	checkFatal(t, repo.SetHead("refs/heads/branch-a"))
+    _, err = commitSomething(repo, "common-file", "1\nb\nc\n", commitOptions{})
+    checkFatal(t, err)
+
+	checkFatal(t, repo.SetHead("refs/heads/branch-b"))
+    _, err = commitSomething(repo, "common-file", "x\nb\nc\n", commitOptions{})
+    checkFatal(t, err)
+
+	branchA, err := repo.LookupBranch("branch-a", BranchLocal)
+    checkFatal(t, err)
+	onto, err := repo.AnnotatedCommitFromRef(branchA.Reference)
+    checkFatal(t, err)
+
+    // We then rebase "branch-b" onto "branch-a" in-memory, which should result
+    // in a conflict.
+    rebase, err := repo.InitRebase(nil, nil, onto, &RebaseOptions{InMemory: 1})
+    checkFatal(t, err)
+
+    _, err = rebase.Next()
+	checkFatal(t, err)
+
+    index, err := rebase.InmemoryIndex()
+	checkFatal(t, err)
+
+    // We simply resolve the conflict and commit the rebase.
+    if !index.HasConflicts() {
+        t.Fatal("expected index to have conflicts")
+    }
+
+    conflict, err := index.Conflict("common-file")
+    checkFatal(t, err)
+
+    resolvedBlobID, err := repo.CreateBlobFromBuffer([]byte("resolved contents"))
+    checkFatal(t, err)
+
+    resolvedEntry := *conflict.Our
+    resolvedEntry.Id = resolvedBlobID
+    checkFatal(t, index.Add(&resolvedEntry))
+    checkFatal(t, index.RemoveConflict("common-file"))
+
+    var commitID Oid
+    checkFatal(t, rebase.Commit(&commitID, signature(), signature(), "rebased message"))
+    checkFatal(t, rebase.Finish())
+
+    // And then assert that we can look up the new merge commit, and that the
+    // "common-file" has the expected contents.
+    commit, err := repo.LookupCommit(&commitID)
+    checkFatal(t, err)
+    if commit.Message() != "rebased message" {
+        t.Fatalf("unexpected commit message %q", commit.Message())
+    }
+
+    tree, err := commit.Tree()
+    checkFatal(t, err)
+
+    blob, err := repo.LookupBlob(tree.EntryByName("common-file").Id)
+    checkFatal(t, err)
+    if string(blob.Contents()) != "resolved contents" {
+        t.Fatalf("unexpected resolved blob contents %q", string(blob.Contents()))
+    }
+}
+
 func TestRebaseAbort(t *testing.T) {
 	// TEST DATA