Memoize completed native link dependencies

internal/engine/filesystem_links.go

@@ -126,6 +126,69 @@ type importLinkFrame struct {
 	link    string
 }
 
+type importLinkOperations struct {
+	lstat           func(string) (fs.FileInfo, error)
+	readlink        func(string) (string, error)
+	normalizeTarget func(string, string) (string, error)
+}
+
+func resolveImportLinkPath(name string, operations importLinkOperations) (string, error) {
+	frames := []importLinkFrame{{pending: strings.Split(name, "/")}}
+	resolved := ""
+	active := make(map[string]struct{})
+	completed := make(map[string]string)
+	for len(frames) > 0 {
+		frame := &frames[len(frames)-1]
+		if len(frame.pending) == 0 {
+			if frame.link != "" {
+				if resolved == "" {
+					resolved = "."
+				}
+				completed[frame.link] = resolved
+				delete(active, frame.link)
+			}
+			frames = frames[:len(frames)-1]
+			continue
+		}
+		segment := frame.pending[0]
+		frame.pending = frame.pending[1:]
+		candidate := path.Join(resolved, segment)
+		if candidate == "" {
+			candidate = "."
+		}
+		info, err := operations.lstat(candidate)
+		if err != nil {
+			return "", err
+		}
+		if info.Mode()&fs.ModeSymlink == 0 {
+			resolved = candidate
+			continue
+		}
+		if target, ok := completed[candidate]; ok {
+			resolved = target
+			continue
+		}
+		if _, exists := active[candidate]; exists {
+			return "", errImportDirectoryLinkCycle
+		}
+		target, err := operations.readlink(candidate)
+		if err != nil {
+			return "", err
+		}
+		targetPath, err := operations.normalizeTarget(candidate, target)
+		if err != nil {
+			return "", err
+		}
+		active[candidate] = struct{}{}
+		frames = append(frames, importLinkFrame{pending: strings.Split(targetPath, "/"), link: candidate})
+		resolved = ""
+	}
+	if resolved == "" {
+		resolved = "."
+	}
+	return resolved, nil
+}
+
 func resolveHostImportPath(access *filesystemAccess, name string) (string, error) {
 	frames := []importLinkFrame{{pending: strings.Split(filepath.ToSlash(name), "/")}}
 	resolved := ""
@@ -189,57 +252,27 @@ func resolveNativeImportPath(access *filesystemAccess, filesystem fs.ReadLinkFS,
 	if !fs.ValidPath(name) || !access.contains(name) {
 		return "", fs.ErrInvalid
 	}
-	frames := []importLinkFrame{{pending: strings.Split(name, "/")}}
-	resolved := ""
-	activeLinks := make(map[string]struct{})
-	for len(frames) > 0 {
-		frame := &frames[len(frames)-1]
-		if len(frame.pending) == 0 {
-			delete(activeLinks, frame.link)
-			frames = frames[:len(frames)-1]
-			continue
-		}
-		segment := frame.pending[0]
-		frame.pending = frame.pending[1:]
-		candidate := path.Join(resolved, segment)
-		if candidate == "" {
-			candidate = "."
-		}
-		// Ancestors of a multi-component root are resolution prefixes, not
-		// selected targets. Complete paths and link targets remain contained.
-		if !access.contains(candidate) && !strings.HasPrefix(access.rootPath, candidate+"/") {
-			return "", errImportPathOutsideRoot
-		}
-		info, err := filesystem.Lstat(candidate)
-		if err != nil {
-			return "", err
-		}
-		if info.Mode()&fs.ModeSymlink == 0 {
-			resolved = candidate
-			continue
-		}
-		if _, exists := activeLinks[candidate]; exists {
-			return "", errImportDirectoryLinkCycle
-		}
-		activeLinks[candidate] = struct{}{}
-		target, err := filesystem.ReadLink(candidate)
-		if err != nil {
-			return "", err
-		}
-		if target == "" || strings.HasPrefix(target, "/") {
-			return "", errImportPathOutsideRoot
-		}
-		targetPath := path.Clean(path.Join(path.Dir(candidate), target))
-		if !fs.ValidPath(targetPath) || !access.contains(targetPath) {
-			return "", errImportPathOutsideRoot
-		}
-		frames = append(frames, importLinkFrame{pending: strings.Split(targetPath, "/"), link: candidate})
-		resolved = ""
-	}
-	if resolved == "" {
-		resolved = "."
-	}
-	return resolved, nil
+	return resolveImportLinkPath(name, importLinkOperations{
+		lstat: func(candidate string) (fs.FileInfo, error) {
+			// Ancestors of a multi-component root are resolution prefixes, not
+			// selected targets. Complete paths and link targets remain contained.
+			if !access.contains(candidate) && !strings.HasPrefix(access.rootPath, candidate+"/") {
+				return nil, errImportPathOutsideRoot
+			}
+			return filesystem.Lstat(candidate)
+		},
+		readlink: filesystem.ReadLink,
+		normalizeTarget: func(candidate, target string) (string, error) {
+			if target == "" || strings.HasPrefix(target, "/") {
+				return "", errImportPathOutsideRoot
+			}
+			targetPath := path.Clean(path.Join(path.Dir(candidate), target))
+			if !fs.ValidPath(targetPath) || !access.contains(targetPath) {
+				return "", errImportPathOutsideRoot
+			}
+			return targetPath, nil
+		},
+	})
 }
 
 func isImportLinkCycle(err error) bool {