simplified sparse checkout

This is the initial logic to support a simple sparse checkout where
directories to be included can be specified in CheckoutOptions.
This change doesn't fully support the sparse patterns, nor does this
change include the optimization to collapse flie entries in ithe index
that are excluded via the sparse checkout directory patterns included
under the parent directory.

1 files changed, 18 insertions, 7 deletions

diff --git a/worktree.go b/worktree.go
index 362d10e..c974aed 100644
--- a/worktree.go
+++ b/worktree.go
@@ -11,6 +11,8 @@ import (
 	"strings"
 	"sync"
 
+	"github.com/go-git/go-billy/v5"
+	"github.com/go-git/go-billy/v5/util"
 	"github.com/go-git/go-git/v5/config"
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/filemode"
@@ -20,9 +22,6 @@ import (
 	"github.com/go-git/go-git/v5/plumbing/storer"
 	"github.com/go-git/go-git/v5/utils/ioutil"
 	"github.com/go-git/go-git/v5/utils/merkletrie"
-
-	"github.com/go-git/go-billy/v5"
-	"github.com/go-git/go-billy/v5/util"
 )
 
 var (
@@ -183,6 +182,10 @@ func (w *Worktree) Checkout(opts *CheckoutOptions) error {
 		return err
 	}
 
+	if len(opts.SparseCheckoutDirectories) > 0 {
+		return w.ResetSparsely(ro, opts.SparseCheckoutDirectories)
+	}
+
 	return w.Reset(ro)
 }
 func (w *Worktree) createBranch(opts *CheckoutOptions) error {
@@ -263,8 +266,7 @@ func (w *Worktree) setHEADToBranch(branch plumbing.ReferenceName, commit plumbin
 	return w.r.Storer.SetReference(head)
 }
 
-// Reset the worktree to a specified state.
-func (w *Worktree) Reset(opts *ResetOptions) error {
+func (w *Worktree) ResetSparsely(opts *ResetOptions, dirs []string) error {
 	if err := opts.Validate(w.r); err != nil {
 		return err
 	}
@@ -294,7 +296,7 @@ func (w *Worktree) Reset(opts *ResetOptions) error {
 	}
 
 	if opts.Mode == MixedReset || opts.Mode == MergeReset || opts.Mode == HardReset {
-		if err := w.resetIndex(t); err != nil {
+		if err := w.resetIndex(t, dirs); err != nil {
 			return err
 		}
 	}
@@ -308,8 +310,17 @@ func (w *Worktree) Reset(opts *ResetOptions) error {
 	return nil
 }
 
-func (w *Worktree) resetIndex(t *object.Tree) error {
+// Reset the worktree to a specified state.
+func (w *Worktree) Reset(opts *ResetOptions) error {
+	return w.ResetSparsely(opts, nil)
+}
+
+func (w *Worktree) resetIndex(t *object.Tree, dirs []string) error {
 	idx, err := w.r.Storer.Index()
+	if len(dirs) > 0 {
+		idx.SkipUnless(dirs)
+	}
+
 	if err != nil {
 		return err
 	}