bump ts to 4.0, ensure no new type syntax

package-lock.json

@@ -5,6 +5,7 @@
   "requires": true,
   "packages": {
     "": {
+      "name": "svelte",
       "version": "3.43.0",
       "license": "MIT",
       "devDependencies": {
@@ -45,7 +46,7 @@
         "sourcemap-codec": "^1.4.8",
         "tiny-glob": "^0.2.6",
         "tslib": "^2.0.3",
-        "typescript": "^3.7.5"
+        "typescript": "~4.0.0"
       },
       "engines": {
         "node": ">= 8"
@@ -5543,9 +5544,9 @@
       "dev": true
     },
     "node_modules/typescript": {
-      "version": "3.7.5",
+      "version": "4.0.8",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.7.5.tgz",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.0.8.tgz",
-      "integrity": "sha512-/P5lkRXkWHNAbcJIiHPfRoKqyd7bsyCma1hZNUGfn20qm64T6ZBlrzprymeu918H+mB/0rIg2gGK/BXkhhYgBw==",
+      "integrity": "sha512-oz1765PN+imfz1MlZzSZPtC/tqcwsCyIYA8L47EkRnRW97ztRk83SzMiWLrnChC0vqoYxSU1fcFUDA5gV/ZiPg==",
       "dev": true,
       "bin": {
         "tsc": "bin/tsc",
@@ -10298,9 +10299,9 @@
       "dev": true
     },
     "typescript": {
-      "version": "3.7.5",
+      "version": "4.0.8",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.7.5.tgz",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-4.0.8.tgz",
-      "integrity": "sha512-/P5lkRXkWHNAbcJIiHPfRoKqyd7bsyCma1hZNUGfn20qm64T6ZBlrzprymeu918H+mB/0rIg2gGK/BXkhhYgBw==",
+      "integrity": "sha512-oz1765PN+imfz1MlZzSZPtC/tqcwsCyIYA8L47EkRnRW97ztRk83SzMiWLrnChC0vqoYxSU1fcFUDA5gV/ZiPg==",
       "dev": true
     },
     "unbox-primitive": {

package.json

@@ -83,7 +83,7 @@
     "pretest": "npm run build",
     "posttest": "agadoo internal/index.mjs",
     "prepublishOnly": "node check_publish_env.js && npm run lint && npm test",
-    "tsd": "tsc -p src/compiler --emitDeclarationOnly && tsc -p src/runtime --emitDeclarationOnly",
+    "tsd": "tsc -p src/compiler --emitDeclarationOnly && tsc -p src/runtime --emitDeclarationOnly && node ./post-typegen.js",
     "lint": "eslint \"{src,test}/**/*.{ts,js}\""
   },
   "repository": {
@@ -140,7 +140,7 @@
     "sourcemap-codec": "^1.4.8",
     "tiny-glob": "^0.2.6",
     "tslib": "^2.0.3",
-    "typescript": "^3.7.5"
+    "typescript": "~4.0.0"
   },
   "nyc": {
     "include": [

post-typegen.js

@@ -0,0 +1,14 @@
+// Svelte 3 types are generated using TS 3.7 . Using newer type syntax is therefore technically a breaking change.
+// `export type` / `import type` was introduced later, and needed now in one of the files.
+// Replace `export type` with `export` in the `d.ts` file as it doesn't make a difference in `d.ts` files.
+// This keeps backwards-compatibility
+
+const fs = require('fs');
+
+const path = 'types/runtime/index.d.ts';
+const content = fs.readFileSync(path, 'utf8');
+const replaced = content.replace('export type', 'export');
+if (content === replaced) {
+    throw new Error('types/runtime/index.d.ts changed. Update post-typegen.js')
+}
+fs.writeFileSync(path, replaced);