Share link dependency evaluation with host access

internal/engine/filesystem_links_test.go

@@ -136,6 +136,129 @@ func TestNativeLinkResolutionRejectsEscapesAndSkipsWhenFollowingIsDisabled(t *te
 	}
 }
 
+func TestHostLinkResolutionMemoizesCompletedDependencies(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")
+	graph := filepath.Join(configurationRoot, "graph")
+	selected := filepath.Join(configurationRoot, "selected")
+	for _, directory := range []string{graph, 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(graph, name)); err != nil {
+			t.Skipf("symlinks unavailable: %v", err)
+		}
+	}
+	if err := os.WriteFile(filepath.Join(graph, "item.yml"), []byte("value: linked\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	aliasTarget := fmt.Sprintf("../graph/s%02d", linkCount-1)
+	if err := os.Symlink(aliasTarget, filepath.Join(selected, "entry")); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+	containedAbsolute := filepath.Join(graph, "s00")
+	if err := os.Symlink(containedAbsolute, filepath.Join(selected, "absolute")); err != nil {
+		t.Skipf("absolute symlinks unavailable: %v", err)
+	}
+	outside := t.TempDir()
+	if err := os.Symlink(outside, filepath.Join(selected, "escape")); err != nil {
+		t.Skipf("symlinks unavailable: %v", err)
+	}
+
+	access, err := openHostAccess(root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer access.close()
+	name := filepath.ToSlash(filepath.Join("workspace", "config", "selected", "entry"))
+	operations := hostImportLinkOperations(access)
+	var operationCount int
+	lstat := operations.lstat
+	readlink := operations.readlink
+	operations.lstat = func(candidate string) (fs.FileInfo, error) {
+		operationCount++
+		if operationCount > linkCount*20+40 {
+			return nil, errors.New("host link operation limit exceeded")
+		}
+		return lstat(candidate)
+	}
+	operations.readlink = func(candidate string) (string, error) {
+		operationCount++
+		if operationCount > linkCount*20+40 {
+			return "", errors.New("host link operation limit exceeded")
+		}
+		return readlink(candidate)
+	}
+	resolved, err := resolveImportLinkPath(name, operations)
+	if err != nil || resolved != filepath.ToSlash(filepath.Join("workspace", "config", "graph")) {
+		t.Fatalf("host repeated-link resolution = %q, %v", resolved, err)
+	}
+	if operationCount == 0 || operationCount > linkCount*20+40 {
+		t.Fatalf("host link operations = %d, want 1..%d", operationCount, linkCount*20+40)
+	}
+
+	contained, err := resolveHostImportPath(access, filepath.Join("workspace", "config", "selected", "absolute"))
+	if err != nil || contained != filepath.ToSlash(filepath.Join("workspace", "config", "graph")) {
+		t.Fatalf("contained absolute link = %q, %v", contained, err)
+	}
+	if _, err := resolveHostImportPath(access, filepath.Join("workspace", "config", "selected", "escape")); !errors.Is(err, errImportPathOutsideRoot) {
+		t.Fatalf("escaping absolute link error = %v, want outside-root rejection", err)
+	}
+
+	for _, selector := range []string{"directory", "glob"} {
+		t.Run(selector, func(t *testing.T) {
+			var diagnostics []Diagnostic
+			if selector == "directory" {
+				_, diagnostics = selectDirectoryWithDiagnostics(t, access, root, "    - dir: workspace/config/selected/entry\n      follow: true\n")
+			} else {
+				_, diagnostics = selectGlobForTestWithDiagnostics(t, access, root, "    - glob: 'workspace/config/selected/entry/*.yml'\n      follow: true\n")
+			}
+			if len(diagnostics) != 0 {
+				t.Fatalf("host selector diagnostics = %#v", diagnostics)
+			}
+		})
+	}
+}
+
+func TestHostLinkResolutionKeepsNamespacesIndependent(t *testing.T) {
+	for _, test := range []struct {
+		name   string
+		target string
+	}{
+		{name: "left", target: "left-target"},
+		{name: "right", target: "right-target"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			root := t.TempDir()
+			if err := os.Mkdir(filepath.Join(root, test.target), 0o700); err != nil {
+				t.Fatal(err)
+			}
+			if err := os.Symlink(test.target, filepath.Join(root, "alias")); err != nil {
+				t.Skipf("symlinks unavailable: %v", err)
+			}
+			access, err := openHostAccess(root)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer access.close()
+			if got, err := resolveHostImportPath(access, "alias"); err != nil || got != test.target {
+				t.Fatalf("namespace link = %q, %v; want %q", got, err, test.target)
+			}
+		})
+	}
+}
+
 type countingReadLinkFS struct {
 	filesystem fs.FS
 	links      fs.ReadLinkFS