feat: Re-introduce support for TS 3.9

Closes #1362.

Co-Authored-By: Constantine Dergachev <13132449+Dergash@users.noreply.github.com>

package.json

@@ -28,11 +28,12 @@
     "marked": "^1.1.1",
     "minimatch": "^3.0.0",
     "progress": "^2.0.3",
+    "semver": "^7.3.2",
     "shelljs": "^0.8.4",
     "typedoc-default-themes": "^0.11.1"
   },
   "peerDependencies": {
-    "typescript": ">=4.0.2"
+    "typescript": "3.9.x || 4.0.x"
   },
   "devDependencies": {
     "@types/fs-extra": "^9.0.1",

scripts/replace_application_version.js

@@ -1,16 +1,29 @@
 // @ts-check
 
-const fs = require('fs-extra');
-const { join } = require('path');
+const fs = require("fs-extra");
+const { join } = require("path");
 
-const file = join(__dirname, '../dist/lib/application.js');
+const file = join(__dirname, "../dist/lib/application.js");
 
-Promise.all([
-    fs.readJson(join(__dirname, '../package.json')).then(({ version }) => version),
-    fs.readFile(file, { encoding: 'utf-8' })
-]).then(([version, text]) => {
-    return fs.writeFile(file, text.replace(/{{ VERSION }}/g, version));
-}).catch(reason => {
+async function main() {
+    const [package, text] = await Promise.all([
+        fs.readJson(join(__dirname, "../package.json")),
+        fs.readFile(file, { encoding: "utf-8" }),
+    ]);
+
+    const replacements = {
+        VERSION: package.version,
+        SUPPORTED: package.peerDependencies.typescript,
+    };
+
+    const replaced = text.replace(/{{ (VERSION|SUPPORTED) }}/g, (_, match) => {
+        return replacements[match];
+    });
+
+    await fs.writeFile(file, replaced);
+}
+
+main().catch((reason) => {
     console.error(reason);
     process.exit(1);
 });

src/lib/application.ts

@@ -9,6 +9,7 @@
 import * as Path from 'path';
 import * as FS from 'fs';
 import * as typescript from 'typescript';
+import * as semver from 'semver';
 
 import { Converter } from './converter/index';
 import { Renderer } from './output/renderer';
@@ -92,6 +93,11 @@ export class Application extends ChildableComponent<
      */
     static VERSION = '{{ VERSION }}';
 
+    /**
+     * The supported TypeScript version.
+     */
+    static SUPPORTED_TS_VERSION = '{{ SUPPORTED }}';
+
     /**
      * Create a new TypeDoc application instance.
      *
@@ -184,6 +190,10 @@ export class Application extends ChildableComponent<
             this.getTypeScriptPath()
         );
 
+        if (!semver.satisfies(typescript.version, Application.SUPPORTED_TS_VERSION)) {
+            this.logger.warn(`You are running in an unsupported TypeScript version! TypeDoc supports ${Application.SUPPORTED_TS_VERSION}`);
+        }
+
         const result = this.converter.convert(src);
         if (result.errors && result.errors.length) {
             this.logger.diagnostics(result.errors);

src/lib/converter/types/tuple.ts

@@ -47,7 +47,9 @@ export class TupleConverter extends ConverterTypeComponent implements TypeConver
      * @returns The type reflection representing the given tuple type node.
      */
     convertNode(context: Context, node: ts.TupleTypeNode): TupleType {
-        const elements: Type[] = this.owner.convertTypes(context, node.elements);
+        // TS 3.9 support
+        const elementTypes = node.elements ?? (node as any).elementTypes;
+        const elements: Type[] = this.owner.convertTypes(context, elementTypes);
         return new TupleType(elements);
     }
 
@@ -74,7 +76,8 @@ export class TupleConverter extends ConverterTypeComponent implements TypeConver
 @Component({ name: 'type:named-tuple-member' })
 export class NamedTupleMemberConverter extends ConverterTypeComponent implements TypeNodeConverter<ts.Type, ts.NamedTupleMember> {
     supportsNode(_context: Context, node: ts.Node) {
-        return ts.isNamedTupleMember(node);
+        // TS 3.9 support
+        return ts.isNamedTupleMember && ts.isNamedTupleMember(node);
     }
 
     convertNode(context: Context, node: ts.NamedTupleMember): NamedTupleMember | undefined {