Use TS3.7 when possible for @babel/type dts (#12317)

Makefile

@@ -49,6 +49,7 @@ build-flow-typings:
 
 build-typescript-typings:
 	$(NODE) packages/babel-types/scripts/generators/typescript.js > packages/babel-types/lib/index.d.ts
+	$(NODE) packages/babel-types/scripts/generators/typescript.js --ts3.7 > packages/babel-types/lib/index-ts3.7.d.ts
 
 build-standalone: build-babel-standalone
 

packages/babel-types/package.json

@@ -15,6 +15,13 @@
   },
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
+  "typesVersions": {
+    ">=3.7": {
+      "lib/index.d.ts": [
+        "lib/index-ts3.7.d.ts"
+      ]
+    }
+  },
   "dependencies": {
     "@babel/helper-validator-identifier": "workspace:^7.10.4",
     "lodash": "^4.17.19",

packages/babel-types/scripts/generators/typescript.js

@@ -4,6 +4,15 @@ const t = require("../../");
 const stringifyValidator = require("../utils/stringifyValidator");
 const toFunctionName = require("../utils/toFunctionName");
 
+// For backward compat, we cannot use TS 3.7 syntax in published packages
+const ts3_7 = process.argv.includes("--ts3.7")
+  ? (code, ...substitutions) => template(code, substitutions)
+  : () => "";
+const template = (strings, substitutions) =>
+  strings
+    .slice(1)
+    .reduce((res, str, i) => res + substitutions[i] + str, strings[0]);
+
 let code = `// NOTE: This file is autogenerated. Do not modify.
 // See packages/babel-types/scripts/generators/typescript.js for script used.
 
@@ -130,7 +139,7 @@ for (const typeName of t.TYPES) {
     `export function is${typeName}(node: object | null | undefined, opts?: object | null): ${result};`,
     // TypeScript 3.7: https://github.com/microsoft/TypeScript/pull/32695 will allow assert declarations
     // eslint-disable-next-line max-len
-    `// export function assert${typeName}(node: object | null | undefined, opts?: object | null): asserts ${
+    ts3_7`export function assert${typeName}(node: object | null | undefined, opts?: object | null): asserts ${
       result === "boolean" ? "node" : result
     };`
   );
@@ -138,8 +147,7 @@ for (const typeName of t.TYPES) {
 
 lines.push(
   // assert/
-  // Commented out as this declaration requires TypeScript 3.7 (what do?)
+  ts3_7`export function assertNode(obj: any): asserts obj is Node`,
-  `// export function assertNode(obj: any): asserts obj is Node`,
 
   // builders/
   // eslint-disable-next-line max-len