git: add DeleteBranches method

CHANGELOG.md

@@ -9,16 +9,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
--  There are several new `git.RefMutation` constructors: `SetRef`,
-   `SetRefIfMatches`, and `CreateRef`.
--  `git.RefMutation` has a new `IsNoop` method to make it easier to check for
-   the zero value.
--  `git.CommitOptions` and `git.AmendOptions` have a new field: `SkipHooks`.
+- There are several new `git.RefMutation` constructors: `SetRef`,
+  `SetRefIfMatches`, and `CreateRef`.
+- `git.RefMutation` has a new `IsNoop` method to make it easier to check for
+  the zero value.
+- `git.CommitOptions` and `git.AmendOptions` have a new field: `SkipHooks`.
+- New method `Git.DeleteBranches`.
 
 ### Changed
 
--  `*client.PullStream.ListRefs` and `*client.PushStream.Refs` now return a map
-   of refs instead of a slice.
+- `*client.PullStream.ListRefs` and `*client.PushStream.Refs` now return a map
+  of refs instead of a slice.
 
 ## [0.9.0][] - 2021-01-26
 

api.go

@@ -1021,6 +1021,36 @@ func (g *Git) NewBranch(ctx context.Context, name string, opts BranchOptions) er
 	return g.run(ctx, errPrefix, args)
 }
 
+// DeleteBranchOptions specifies options for a new branch.
+type DeleteBranchOptions struct {
+	// If Force is true, then the branch will be deleted
+	// even if the branch has not been merged
+	// or if the branch does not point to a valid commit.
+	Force bool
+}
+
+// DeleteBranches deletes zero or more branches.
+// If names is empty, then DeleteBranches returns nil without running Git.
+func (g *Git) DeleteBranches(ctx context.Context, names []string, opts DeleteBranchOptions) error {
+	if len(names) == 0 {
+		return nil
+	}
+	errPrefix := "git branch --delete " + strings.Join(names, " ")
+	for _, name := range names {
+		if err := validateBranch(name); err != nil {
+			return fmt.Errorf("%s: %w", errPrefix, err)
+		}
+	}
+	args := make([]string, 0, len(names)+4)
+	args = append(args, "branch", "--delete")
+	if opts.Force {
+		args = append(args, "--force")
+	}
+	args = append(args, "--")
+	args = append(args, names...)
+	return g.run(ctx, errPrefix, args)
+}
+
 // NullTreeHash computes the hash of an empty tree and adds it to the
 // repository. This is sometimes useful as a diff comparison target.
 func (g *Git) NullTreeHash(ctx context.Context) (Hash, error) {

branch_test.go

@@ -295,3 +295,49 @@ func TestNewBranch(t *testing.T) {
 		})
 	}
 }
+
+func TestDeleteBranches(t *testing.T) {
+	ctx := context.Background()
+	gitPath, err := findGit()
+	if err != nil {
+		t.Skip("git not found:", err)
+	}
+	env, err := newTestEnv(ctx, gitPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer env.cleanup()
+
+	// Create a repository with a commit and a branch "foo".
+	if err := env.g.Init(ctx, "."); err != nil {
+		t.Fatal(err)
+	}
+	const content = "Hello, World!\n"
+	if err := env.root.Apply(filesystem.Write("file.txt", content)); err != nil {
+		t.Fatal(err)
+	}
+	if err := env.g.Add(ctx, []Pathspec{"file.txt"}, AddOptions{}); err != nil {
+		t.Fatal(err)
+	}
+	if err := env.g.Commit(ctx, dummyContent, CommitOptions{}); err != nil {
+		t.Fatal(err)
+	}
+	if err := env.g.NewBranch(ctx, "foo", BranchOptions{}); err != nil {
+		t.Fatal(err)
+	}
+
+	// Delete the branch "foo".
+	if err := env.g.DeleteBranches(ctx, []string{"foo"}, DeleteBranchOptions{}); err != nil {
+		t.Error(err)
+	}
+
+	// Verify that "foo" no longer exists.
+	refs, err := env.g.ListRefs(ctx)
+	if err != nil {
+		t.Fatal(err)
+	}
+	const fooRef = Ref("refs/heads/foo")
+	if hash, ok := refs[fooRef]; ok {
+		t.Errorf("%s = %v; want missing", fooRef, hash)
+	}
+}