Partial support for TypeScript 3.8 (private fields, import/export type modifier) (#7631)

* support TypeScript 3.8

* Update standard_private_fields.ts

* improve tests for import/export type modifier

* temporary hacks for private fields

* comment out some tests, update snapshots

* add changelog entry

changelog_unreleased/typescript/pr-7631.md

@@ -0,0 +1,9 @@
+#### TypeScript 3.8 ([#7631](https://github.com/prettier/prettier/pull/7631) by [@thorn0](https://github.com/thorn0))
+
+Prettier doesn't yet fully support the new syntax added in TypeScript 3.8:
+
+| Syntax                                                                                                                          | `typescript` parser | `babel-ts` parser |
+| ------------------------------------------------------------------------------------------------------------------------------- | ------------------- | ----------------- |
+| [Type-Only Imports and Exports](https://devblogs.microsoft.com/typescript/announcing-typescript-3-8/#type-only-imports-exports) | ✔️                  | ❌                |
+| [ECMAScript Private Fields](https://devblogs.microsoft.com/typescript/announcing-typescript-3-8/#ecmascript-private-fields)     | ✔️                  | ✔️                |
+| [`export * as ns`](https://devblogs.microsoft.com/typescript/announcing-typescript-3-8/#export-star-as-namespace-syntax)        | ❌                  | ❌                |

src/language-js/postprocess.js

@@ -1,6 +1,9 @@
 "use strict";
 
-const { getLast } = require("../common/util");
+const {
+  getLast,
+  getNextNonSpaceNonCommentCharacter
+} = require("../common/util");
 const { composeLoc, locEnd } = require("./loc");
 
 function postprocess(ast, options) {
@@ -48,6 +51,20 @@ function postprocess(ast, options) {
           node.end = getLast(node.expressions).end;
         }
         break;
+      case "ClassProperty":
+        // TODO: Temporary auto-generated node type. To remove when typescript-estree has proper support for private fields.
+        if (
+          node.key &&
+          node.key.type === "TSPrivateIdentifier" &&
+          getNextNonSpaceNonCommentCharacter(
+            options.originalText,
+            node.key,
+            locEnd
+          ) === "?"
+        ) {
+          node.optional = true;
+        }
+        break;
     }
   });
 

src/language-js/printer-estree.js

@@ -3521,6 +3521,10 @@ function printPathNoParens(path, options, print, args) {
     case "PrivateName":
       return concat(["#", path.call(print, "id")]);
 
+    // TODO: Temporary auto-generated node type. To remove when typescript-estree has proper support for private fields.
+    case "TSPrivateIdentifier":
+      return n.escapedText;
+
     case "TSConditionalType":
       return printTernaryOperator(path, options, print, {
         beforeParts: () => [

tests/typescript_class/__snapshots__/jsfmt.spec.js.snap

@@ -253,3 +253,57 @@ class User {
 
 ================================================================================
 `;
+
+exports[`standard_private_fields.ts 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+class Square {
+    #sideLength: number;
+    readonly #area: number;
+    #unit?: string;
+
+    constructor(sideLength: number, unit?: string) {
+        this.#sideLength = sideLength;
+        this.#area = this.#sideLength ** 2;
+        if (unit) {
+          this.#unit = unit;
+        }
+    }
+
+    equals(other: any) {
+        return this.#sideLength === other.#sideLength;
+    }
+
+    getArea() {
+      return this.#area + (this.#unit ?? 'px') + '²';
+    }
+}
+
+=====================================output=====================================
+class Square {
+  #sideLength: number;
+  readonly #area: number;
+  #unit?: string;
+
+  constructor(sideLength: number, unit?: string) {
+    this.#sideLength = sideLength;
+    this.#area = this.#sideLength ** 2;
+    if (unit) {
+      this.#unit = unit;
+    }
+  }
+
+  equals(other: any) {
+    return this.#sideLength === other.#sideLength;
+  }
+
+  getArea() {
+    return this.#area + (this.#unit ?? "px") + "²";
+  }
+}
+
+================================================================================
+`;

tests/typescript_class/standard_private_fields.ts

@@ -0,0 +1,21 @@
+class Square {
+    #sideLength: number;
+    readonly #area: number;
+    #unit?: string;
+
+    constructor(sideLength: number, unit?: string) {
+        this.#sideLength = sideLength;
+        this.#area = this.#sideLength ** 2;
+        if (unit) {
+          this.#unit = unit;
+        }
+    }
+
+    equals(other: any) {
+        return this.#sideLength === other.#sideLength;
+    }
+
+    getArea() {
+      return this.#area + (this.#unit ?? 'px') + '²';
+    }
+}

tests/typescript_export/__snapshots__/jsfmt.spec.js.snap

@@ -60,6 +60,22 @@ declare module "hello" {
 ================================================================================
 `;
 
+exports[`export-as-ns.ts 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+// TODO: uncomment when typescript-estree gets support for this syntax
+// export * as utilities from "./utilities.js";
+
+=====================================output=====================================
+// TODO: uncomment when typescript-estree gets support for this syntax
+// export * as utilities from "./utilities.js";
+
+================================================================================
+`;
+
 exports[`export-class.js 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]

tests/typescript_export/export-as-ns.ts

@@ -0,0 +1,2 @@
+// TODO: uncomment when typescript-estree gets support for this syntax
+// export * as utilities from "./utilities.js";

tests/typescript_import_export/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,45 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`type-modifier.ts 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+export type { SomeThing };
+export type { A as B };
+export type { B as C } from './a';
+export type { foo } from 'bar';
+export type * from 'bar';
+export type { foo };
+
+// this should be treated as a normal import statement
+import type from './foo';
+
+import type { SomeThing } from "./some-module.js";
+import type { foo, bar } from 'baz';
+import type { foo as bar } from 'baz';
+import type * as foo from './bar';
+import type foo from 'bar';
+import type foo, { bar } from 'bar';
+
+=====================================output=====================================
+export type { SomeThing };
+export type { A as B };
+export type { B as C } from "./a";
+export type { foo } from "bar";
+export type * from "bar";
+export type { foo };
+
+// this should be treated as a normal import statement
+import type from "./foo";
+
+import type { SomeThing } from "./some-module.js";
+import type { foo, bar } from "baz";
+import type { foo as bar } from "baz";
+import type * as foo from "./bar";
+import type foo from "bar";
+import type foo, { bar } from "bar";
+
+================================================================================
+`;

tests/typescript_import_export/jsfmt.spec.js

@@ -0,0 +1,2 @@
+// TODO: remove disableBabelTS when Babel's TS plugin gets support for import/export `type` modifier
+run_spec(__dirname, ["typescript"], { disableBabelTS: true });

tests/typescript_import_export/type-modifier.ts

@@ -0,0 +1,16 @@
+export type { SomeThing };
+export type { A as B };
+export type { B as C } from './a';
+export type { foo } from 'bar';
+export type * from 'bar';
+export type { foo };
+
+// this should be treated as a normal import statement
+import type from './foo';
+
+import type { SomeThing } from "./some-module.js";
+import type { foo, bar } from 'baz';
+import type { foo as bar } from 'baz';
+import type * as foo from './bar';
+import type foo from 'bar';
+import type foo, { bar } from 'bar';