Let downlevel-dts do most of the heavy lifting

.gitignore

@@ -137,7 +137,6 @@ typings/
 
 ### Project
 /dist/
+!/dist/types/ts3.6/polyfill.d.ts
 /lib/
 /temp/
-/types/ponyfill.d.ts
-/types/tsdoc-metadata.json

api-extractor.json

@@ -195,7 +195,7 @@
      * SUPPORTED TOKENS: <projectFolder>, <packageName>, <unscopedPackageName>
      * DEFAULT VALUE: "<projectFolder>/dist/<unscopedPackageName>.d.ts"
      */
-    "untrimmedFilePath": "<projectFolder>/types/ponyfill.d.ts",
+    "untrimmedFilePath": "<projectFolder>/dist/types/ts3.6/ponyfill.d.ts",
 
     /**
      * Specifies the output path for a .d.ts rollup file to be generated with trimming for a "beta" release.
@@ -242,7 +242,7 @@
      *
      * DEFAULT VALUE: true
      */
-    // "enabled": true,
+    "enabled": true,
     /**
      * Specifies where the TSDoc metadata file should be written.
      *
@@ -256,9 +256,8 @@
      * SUPPORTED TOKENS: <projectFolder>, <packageName>, <unscopedPackageName>
      * DEFAULT VALUE: "<lookup>"
      */
-    // "tsdocMetadataFilePath": "<projectFolder>/dist/tsdoc-metadata.json"
+    "tsdocMetadataFilePath": "<projectFolder>/dist/types/tsdoc-metadata.json"
   },
-
   /**
    * Specifies what type of newlines API Extractor should use when writing output files.  By default, the output files
    * will be written with Windows-style newlines.  To use POSIX-style newlines, specify "lf" instead.

build/downlevel-dts.js

@@ -1,64 +1,19 @@
 // Based on downlevel-dts (MIT licensed) by Nathan Shively-Sanders
 // https://github.com/sandersn/downlevel-dts/blob/e7d1cb5aced5686826fe8aac4d4af2f745a9ef60/index.js
 
-const { Project, ts } = require('ts-morph');
+const { Project } = require('ts-morph');
 const path = require('path');
 
 const project = new Project();
-const inputDir = project.addDirectoryAtPath(path.join(__dirname, '../types/'));
-const outputDir = project.createDirectory(path.join(__dirname, '../dist/types/'));
-
-// Create output directory
-const ts36Dir = outputDir.createDirectory('ts3.6');
-project.saveSync();
+const inputDir = project.addDirectoryAtPath(path.join(__dirname, '../dist/types/'));
 
 // Down-level all *.d.ts files in input directory
 const files = inputDir.addSourceFilesAtPaths('*.d.ts');
-for (const originalFile of files) {
-  // Create copy for TypeScript 3.6 and higher
-  originalFile.copyToDirectory(ts36Dir, { overwrite: true });
-  // Downlevel and create copy for TypeScript 3.6 and lower
-  const downlevelFile = originalFile.copyToDirectory(outputDir, { overwrite: true });
-  downlevelTS36(downlevelFile);
-  downlevelTS34(downlevelFile);
+for (const file of files) {
+  downlevelTS34(file);
 }
 project.saveSync();
 
-/**
- * Down-level TypeScript 3.6 types in the given source file
- */
-function downlevelTS36(f) {
-  // Replace get/set accessors with (read-only) properties
-  const gs = f.getDescendantsOfKind(ts.SyntaxKind.GetAccessor);
-  for (const g of gs) {
-    const s = g.getSetAccessor();
-    const returnTypeNode = g.getReturnTypeNode();
-    const returnType = returnTypeNode ? returnTypeNode.getText() : 'any';
-    g.getParent().insertProperty(g.getChildIndex(), Object.assign({}, g.getStructure(), {
-      type: returnType,
-      isReadonly: !s
-    }));
-    g.remove();
-    if (s) {
-      s.remove();
-    }
-  }
-  const ss = f.getDescendantsOfKind(ts.SyntaxKind.SetAccessor);
-  for (const s of ss) {
-    const g = s.getGetAccessor();
-    if (!g) {
-      const firstParam = s.getParameters()[0];
-      const firstParamTypeNode = firstParam && firstParam.getTypeNode();
-      const firstParamType = firstParamTypeNode ? firstParamTypeNode.getText() : 'any';
-      s.getParent().insertProperty(s.getChildIndex(), Object.assign({}, s.getStructure(), {
-        type: firstParamType,
-        isReadonly: false
-      }));
-      s.remove();
-    }
-  }
-}
-
 /**
  * Down-level TypeScript 3.4 types in the given source file
  */

package.json

@@ -24,16 +24,16 @@
     "lint": "eslint \"src/**/*.ts\"",
     "build": "npm run build:bundle && npm run build:types",
     "build:bundle": "rollup -c",
-    "build:types": "tsc --project . --emitDeclarationOnly --declarationDir ./lib && api-extractor run && node ./build/downlevel-dts.js",
-    "accept:types": "tsc --project . --emitDeclarationOnly --declarationDir ./lib && api-extractor run --local && node ./build/downlevel-dts.js",
+    "build:types": "tsc --project . --emitDeclarationOnly --declarationDir ./lib && api-extractor run",
+    "accept:types": "npm run build:types -- --local",
+    "postbuild:types": "downlevel-dts ./dist/types/ts3.6/ ./dist/types/ --to=3.5 && node ./build/downlevel-dts.js",
     "prepare": "npm run build"
   },
   "files": [
     "dist",
     "es6",
     "es2018",
-    "ponyfill",
-    "types"
+    "ponyfill"
   ],
   "engines": {
     "node": ">= 8"
@@ -61,12 +61,13 @@
     "@rollup/plugin-inject": "^5.0.5",
     "@rollup/plugin-replace": "^5.0.5",
     "@rollup/plugin-strip": "^3.0.4",
-    "@rollup/plugin-typescript": "^11.1.5",
     "@rollup/plugin-terser": "^0.4.4",
+    "@rollup/plugin-typescript": "^11.1.5",
     "@types/node": "^18.19.4",
     "@typescript-eslint/eslint-plugin": "^6.17.0",
     "@typescript-eslint/parser": "^6.17.0",
     "@ungap/promise-all-settled": "^1.1.2",
+    "downlevel-dts": "^0.11.0",
     "eslint": "^8.56.0",
     "jasmine": "^5.1.0",
     "micromatch": "^4.0.5",

test/types/polyfill.ts

@@ -1,7 +1,7 @@
 /*
  * This test verifies that the polyfill's type definitions correctly augment TypeScript's built-in DOM types.
  */
-import '../../types/polyfill';
+import '../../dist/types/ts3.6/polyfill';
 
 const readable = new ReadableStream<Uint8Array>({
   // TODO Figure out a way to augment the type of "declare var ReadableStream"?