Share link dependency evaluation with host access

internal/engine/filesystem_links.go

@@ -119,8 +119,8 @@ func (a *filesystemAccess) importEntryTarget(name string, entry fs.DirEntry, fol
 	return importEntryTarget{symlink: symlink, dir: info.IsDir(), identity: name}, nil
 }
 
-// A link stays active until its target has resolved, not until the entire
-// original pathname has resolved. Remaining segments may reuse a finished link.
+// A link remains active until its own target resolves. Completed targets can be
+// reused while the caller continues resolving its remaining components.
 type importLinkFrame struct {
 	pending []string
 	link    string
@@ -190,58 +190,34 @@ func resolveImportLinkPath(name string, operations importLinkOperations) (string
 }
 
 func resolveHostImportPath(access *filesystemAccess, name string) (string, error) {
-	frames := []importLinkFrame{{pending: strings.Split(filepath.ToSlash(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 = "."
-		}
-		info, err := access.root.Lstat(filepath.FromSlash(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 := access.root.Readlink(filepath.FromSlash(candidate))
-		if err != nil {
-			return "", err
-		}
-		var targetPath string
-		if filepath.IsAbs(target) {
-			relative, err := filepath.Rel(access.rootPath, filepath.Clean(target))
-			if err != nil {
+	return resolveImportLinkPath(filepath.ToSlash(name), hostImportLinkOperations(access))
+}
+
+func hostImportLinkOperations(access *filesystemAccess) importLinkOperations {
+	return importLinkOperations{
+		lstat: func(candidate string) (fs.FileInfo, error) {
+			return access.root.Lstat(filepath.FromSlash(candidate))
+		},
+		readlink: func(candidate string) (string, error) {
+			return access.root.Readlink(filepath.FromSlash(candidate))
+		},
+		normalizeTarget: func(candidate, target string) (string, error) {
+			var targetPath string
+			if filepath.IsAbs(target) {
+				relative, err := filepath.Rel(access.rootPath, filepath.Clean(target))
+				if err != nil {
+					return "", errImportPathOutsideRoot
+				}
+				targetPath = path.Clean(filepath.ToSlash(relative))
+			} else {
+				targetPath = path.Clean(path.Join(path.Dir(candidate), filepath.ToSlash(target)))
+			}
+			if !withinPortableRoot(targetPath) {
 				return "", errImportPathOutsideRoot
 			}
-			targetPath = path.Clean(filepath.ToSlash(relative))
-		} else {
-			targetPath = path.Clean(path.Join(path.Dir(candidate), filepath.ToSlash(target)))
-		}
-		if !withinPortableRoot(targetPath) {
-			return "", errImportPathOutsideRoot
-		}
-		frames = append(frames, importLinkFrame{pending: strings.Split(targetPath, "/"), link: candidate})
-		resolved = ""
+			return targetPath, nil
+		},
 	}
-	if resolved == "" {
-		resolved = "."
-	}
-	return resolved, nil
 }
 
 func withinPortableRoot(name string) bool {