use ReadonlyArray for DocumentSelector (#10070)

fixes #10025

Author: smart-bo

packages/plugin-ext/src/common/arrays.ts

@@ -44,3 +44,11 @@ export interface Splice<T> {
     readonly deleteCount: number;
     readonly toInsert: T[];
 }
+
+/**
+ * @returns 'true' if the 'arg' is a 'ReadonlyArray'.
+ */
+export function isReadonlyArray(arg: unknown): arg is readonly unknown[] {
+    // Since Typescript does not properly narrow down typings for 'ReadonlyArray' we need to help it.
+    return Array.isArray(arg);
+}

packages/plugin-ext/src/plugin/languages.ts

@@ -90,6 +90,7 @@ import { DeclarationAdapter } from './languages/declaration';
 import { CallHierarchyAdapter } from './languages/call-hierarchy';
 import { BinaryBuffer } from '@theia/core/lib/common/buffer';
 import { DocumentSemanticTokensAdapter, DocumentRangeSemanticTokensAdapter } from './languages/semantic-highlighting';
+import { isReadonlyArray } from '../common/arrays';
 
 type Adapter = CompletionAdapter |
     SignatureHelpAdapter |
@@ -204,7 +205,7 @@ export class LanguagesExtImpl implements LanguagesExt {
     }
 
     private transformDocumentSelector(selector: theia.DocumentSelector): SerializedDocumentFilter[] {
-        if (Array.isArray(selector)) {
+        if (isReadonlyArray(selector)) {
             return selector.map(sel => this.doTransformDocumentSelector(sel)!);
         }
 

packages/plugin-ext/src/plugin/type-converters.ts

@@ -27,6 +27,7 @@ import { isMarkdownString, MarkdownString } from './markdown-string';
 import * as types from './types-impl';
 import { UriComponents } from '../common/uri-components';
 import { TaskGroup } from './types-impl';
+import { isReadonlyArray } from '../common/arrays';
 
 const SIDE_GROUP = -2;
 const ACTIVE_GROUP = -1;
@@ -169,9 +170,9 @@ export function fromRangeOrRangeWithMessage(ranges: theia.Range[] | theia.Decora
         });
     } else {
         return ranges.map((r): DecorationOptions =>
-            ({
-                range: fromRange(r)!
-            }));
+        ({
+            range: fromRange(r)!
+        }));
     }
 }
 
@@ -213,7 +214,7 @@ export function toMarkdown(value: model.MarkdownString): MarkdownString {
 export function fromDocumentSelector(selector: theia.DocumentSelector | undefined): LanguageSelector | undefined {
     if (!selector) {
         return undefined;
-    } else if (Array.isArray(selector)) {
+    } else if (isReadonlyArray(selector)) {
         return <LanguageSelector>selector.map(fromDocumentSelector);
     } else if (typeof selector === 'string') {
         return selector;

packages/plugin/src/theia.d.ts

@@ -6154,7 +6154,7 @@ declare module '@theia/plugin' {
      *
      * @sample `let sel:DocumentSelector = { scheme: 'file', language: 'typescript' }`;
      */
-    export type DocumentSelector = DocumentFilter | string | Array<DocumentFilter | string>;
+    export type DocumentSelector = DocumentFilter | string | ReadonlyArray<DocumentFilter | string>;
 
     /**
      * A tuple of two characters, like a pair of