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, 0 deletions

diff --git a/plumbing/format/index/index.go b/plumbing/format/index/index.go
index 649416a..f4c7647 100644
--- a/plumbing/format/index/index.go
+++ b/plumbing/format/index/index.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/go-git/go-git/v5/plumbing"
@@ -211,3 +212,20 @@ type EndOfIndexEntry struct {
 	//	their contents).
 	Hash plumbing.Hash
 }
+
+// SkipUnless applies patterns in the form of A, A/B, A/B/C
+// to the index to prevent the files from being checked out
+func (i *Index) SkipUnless(patterns []string) {
+	for _, e := range i.Entries {
+		var include bool
+		for _, pattern := range patterns {
+			if strings.HasPrefix(e.Name, pattern) {
+				include = true
+				break
+			}
+		}
+		if !include {
+			e.SkipWorktree = true
+		}
+	}
+}