1 files changed, 145 insertions, 0 deletions
diff --git a/internal/testgit/packobjects.go b/internal/testgit/packobjects.go
new file mode 100644
index 00000000..62f86963
--- /dev/null
+++ b/internal/testgit/packobjects.go
@@ -0,0 +1,145 @@
+package testgit
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"lindenii.org/go/furgit/object/id"
+)
+
+// ErrInvalidPackObjectsOptions reports an inconsistent
+// combination of pack-objects options.
+var ErrInvalidPackObjectsOptions = errors.New("internal/testgit: invalid pack-objects options")
+
+// PackObjectsOptions controls one on-disk pack-objects invocation.
+type PackObjectsOptions struct {
+	// RevIndex requests writing a .rev reverse index alongside the pack.
+	RevIndex bool
+
+	// Revs changes how the input is interpreted.
+	//
+	// When false, each include is one object name,
+	// and exactly those objects are packed.
+	//
+	// When true, each include is a revision argument,
+	// and pack-objects packs the closure of objects
+	// reachable from the includes but not from the excludes,
+	// the same walk git rev-list --objects performs.
+	Revs bool
+
+	// Exclude lists objects to omit by reachability,
+	// fed as "^<oid>" revision arguments.
+	// A non-nil Exclude requires Revs.
+	Exclude []id.ObjectID
+}
+
+// PackObjects packs the include objects with git pack-objects
+// into a temporary directory,
+// and returns the artifact path prefix "<dir>/pack-<hash>",
+// to which ".pack", ".idx", and ".rev" suffixes apply.
+func (repo *Repo) PackObjects(tb testing.TB, include []id.ObjectID, opts PackObjectsOptions) (string, error) {
+	tb.Helper()
+
+	if opts.Exclude != nil && !opts.Revs {
+		return "", fmt.Errorf("%w: Exclude requires Revs", ErrInvalidPackObjectsOptions)
+	}
+
+	dir := tb.TempDir()
+
+	revIndex := "false"
+	if opts.RevIndex {
+		revIndex = "true"
+	}
+
+	args := []string{"-c", "pack.writeReverseIndex=" + revIndex, "pack-objects"}
+	if opts.Revs {
+		args = append(args, "--revs")
+	}
+
+	args = append(args, "--end-of-options", filepath.Join(dir, "pack"))
+
+	out, err := repo.run(tb, packObjectsStdin(include, opts.Exclude), "git", args...)
+	if err != nil {
+		return "", err
+	}
+
+	return filepath.Join(dir, "pack-"+strings.TrimSpace(string(out))), nil
+}
+
+// PackObjectsStdoutOptions controls one streamed pack-objects invocation.
+type PackObjectsStdoutOptions struct {
+	// Revs changes how the input is interpreted.
+	//
+	// When false, each include is one object name,
+	// and exactly those objects are packed.
+	//
+	// When true, each include is a revision argument,
+	// and pack-objects packs the closure of objects
+	// reachable from the includes but not from the excludes,
+	// the same walk git rev-list --objects performs.
+	Revs bool
+
+	// Thin omits excluded base objects from the pack,
+	// producing a thin pack that must be completed before use.
+	// Thin requires Revs.
+	Thin bool
+
+	// Exclude lists objects to omit by reachability,
+	// fed as "^<oid>" revision arguments.
+	// A non-nil Exclude requires Revs.
+	Exclude []id.ObjectID
+}
+
+// PackObjectsStdout packs the include objects with git pack-objects
+// and returns the pack stream written to standard output.
+func (repo *Repo) PackObjectsStdout(tb testing.TB, include []id.ObjectID, opts PackObjectsStdoutOptions) ([]byte, error) {
+	tb.Helper()
+
+	if opts.Exclude != nil && !opts.Revs {
+		return nil, fmt.Errorf("%w: Exclude requires Revs", ErrInvalidPackObjectsOptions)
+	}
+
+	if opts.Thin && !opts.Revs {
+		return nil, fmt.Errorf("%w: Thin requires Revs", ErrInvalidPackObjectsOptions)
+	}
+
+	args := []string{"pack-objects", "--stdout"}
+	if opts.Revs {
+		args = append(args, "--revs")
+	}
+
+	if opts.Thin {
+		args = append(args, "--thin")
+	}
+
+	out, err := repo.run(tb, packObjectsStdin(include, opts.Exclude), "git", args...)
+	if err != nil {
+		return nil, err
+	}
+
+	return out, nil
+}
+
+// packObjectsStdin builds the pack-objects standard input:
+// the include object IDs,
+// followed by the exclude object IDs as "^<oid>" lines.
+func packObjectsStdin(include, exclude []id.ObjectID) *bytes.Buffer {
+	var stdin bytes.Buffer
+
+	for _, oid := range include {
+		stdin.WriteString(oid.String())
+		stdin.WriteByte('\n')
+	}
+
+	for _, oid := range exclude {
+		stdin.WriteByte('^')
+		stdin.WriteString(oid.String())
+		stdin.WriteByte('\n')
+	}
+
+	return &stdin
+}