Memoize completed native link dependencies

internal/engine/filesystem_links_test.go

@@ -2,6 +2,7 @@ package engine
 
 import (
 	"errors"
+	"fmt"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -45,3 +46,147 @@ func TestImportLinkResolutionTracksActiveExpansions(t *testing.T) {
 		})
 	}
 }
+
+func TestNativeLinkResolutionMemoizesCompletedDependencies(t *testing.T) {
+	// The small graph stays within host symlink-depth limits while exceeding the
+	// bounded linear operation allowance without completed-target reuse.
+	const linkCount = 5
+	root := t.TempDir()
+	configurationRoot := filepath.Join(root, "workspace", "config")
+	for _, directory := range []string{
+		filepath.Join(configurationRoot, "graph"),
+		filepath.Join(configurationRoot, "selected"),
+	} {
+		if err := os.MkdirAll(directory, 0o700); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for index := 0; index < linkCount; index++ {
+		name := fmt.Sprintf("s%02d", index)
+		target := "."
+		if index > 0 {
+			previous := fmt.Sprintf("s%02d", index-1)
+			target = previous + "/" + previous
+		}
+		if err := os.Symlink(target, filepath.Join(configurationRoot, "graph", name)); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+	}
+	if err := os.WriteFile(filepath.Join(configurationRoot, "graph", "item.yml"), []byte("value: linked\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Symlink(fmt.Sprintf("../graph/s%02d", linkCount-1), filepath.Join(configurationRoot, "selected", "entry")); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+
+	for _, selector := range []string{"directory", "glob"} {
+		t.Run(selector, func(t *testing.T) {
+			base := os.DirFS(root)
+			if _, ok := base.(fs.ReadLinkFS); !ok {
+				t.Skip("host directory filesystem does not expose link inspection")
+			}
+			filesystem := newCountingReadLinkFS(base, linkCount*20+40)
+			access := newNativeAccess(filesystem, "workspace/config", &namespaceToken{})
+			if _, err := access.canonical("workspace/config/selected"); err != nil {
+				t.Fatalf("selected directory canonicalization failed before selection: %v", err)
+			}
+			var diagnostics []Diagnostic
+			if selector == "directory" {
+				_, diagnostics = selectDirectoryWithDiagnostics(t, access, "workspace/config", "    - dir: selected\n      follow: true\n")
+			} else {
+				_, diagnostics = selectGlobForTestWithDiagnostics(t, access, "workspace/config", "    - glob: 'selected/*/*.yml'\n      follow: true\n")
+			}
+			if len(diagnostics) != 0 {
+				t.Fatalf("selection diagnostics = %#v after %d link operations", diagnostics, filesystem.operations)
+			}
+			if filesystem.operations == 0 || filesystem.operations > filesystem.limit {
+				t.Fatalf("link-resolution operations = %d, want 1..%d", filesystem.operations, filesystem.limit)
+			}
+			if filesystem.readLinks < linkCount {
+				t.Fatalf("link reads = %d, want the selector to resolve the repeated dependency graph", filesystem.readLinks)
+			}
+		})
+	}
+}
+
+func TestNativeLinkResolutionRejectsEscapesAndSkipsWhenFollowingIsDisabled(t *testing.T) {
+	root := t.TempDir()
+	configurationRoot := filepath.Join(root, "workspace", "config")
+	selected := filepath.Join(configurationRoot, "selected")
+	if err := os.MkdirAll(selected, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Symlink("../../../outside", filepath.Join(selected, "escape")); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+	base := os.DirFS(root)
+	if _, ok := base.(fs.ReadLinkFS); !ok {
+		t.Skip("host directory filesystem does not expose link inspection")
+	}
+	filesystem := newCountingReadLinkFS(base, 100)
+	access := newNativeAccess(filesystem, "workspace/config", &namespaceToken{})
+	if _, err := resolveNativeImportPath(access, filesystem.links, "workspace/config/selected/escape"); !errors.Is(err, errImportPathOutsideRoot) {
+		t.Fatalf("escaping native link error = %v, want outside-root rejection", err)
+	}
+
+	filesystem.readLinks = 0
+	_, diagnostics := selectDirectoryWithDiagnostics(t, access, "workspace/config", "    - dir: selected\n      follow: false\n")
+	if len(diagnostics) != 0 || filesystem.readLinks != 0 {
+		t.Fatalf("follow-disabled selection diagnostics=%#v readlink calls=%d", diagnostics, filesystem.readLinks)
+	}
+}
+
+type countingReadLinkFS struct {
+	filesystem fs.FS
+	links      fs.ReadLinkFS
+	operations int
+	readLinks  int
+	limit      int
+}
+
+func newCountingReadLinkFS(filesystem fs.FS, limit int) *countingReadLinkFS {
+	links, ok := filesystem.(fs.ReadLinkFS)
+	if !ok {
+		panic("test filesystem does not support link inspection")
+	}
+	return &countingReadLinkFS{filesystem: filesystem, links: links, limit: limit}
+}
+
+func (f *countingReadLinkFS) Open(name string) (fs.File, error) { return f.filesystem.Open(name) }
+
+func (f *countingReadLinkFS) Stat(name string) (fs.FileInfo, error) {
+	if statter, ok := f.filesystem.(fs.StatFS); ok {
+		return statter.Stat(name)
+	}
+	return fs.Stat(f.filesystem, name)
+}
+
+func (f *countingReadLinkFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	if reader, ok := f.filesystem.(fs.ReadDirFS); ok {
+		return reader.ReadDir(name)
+	}
+	return fs.ReadDir(f.filesystem, name)
+}
+
+func (f *countingReadLinkFS) count() error {
+	f.operations++
+	if f.operations > f.limit {
+		return errors.New("native link operation limit exceeded")
+	}
+	return nil
+}
+
+func (f *countingReadLinkFS) Lstat(name string) (fs.FileInfo, error) {
+	if err := f.count(); err != nil {
+		return nil, err
+	}
+	return f.links.Lstat(name)
+}
+
+func (f *countingReadLinkFS) ReadLink(name string) (string, error) {
+	if err := f.count(); err != nil {
+		return "", err
+	}
+	f.readLinks++
+	return f.links.ReadLink(name)
+}