Support "Discard Bindings" proposal (#17708)

Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>

changelog_unreleased/javascript/17708.md

@@ -0,0 +1,10 @@
+#### Add support for "Discard Bindings" proposal (#17708 by @fisker)
+
+The Stage 2 proposal ["Discard Bindings"](https://github.com/tc39/proposal-discard-binding) is now supported via Babel. Also keep in mind our [policy on non-standardized syntax](https://prettier.io/docs/en/rationale.html#disclaimer-about-non-standard-syntax) before using this proposed syntax feature with Prettier.
+
+<!-- prettier-ignore -->
+```jsx
+const [void] = x;
+
+const {x:void} = x;
+```

src/language-js/parse/babel.js

@@ -49,6 +49,7 @@ const parseOptions = {
     "sourcePhaseImports",
     "deferredImportEvaluation",
     ["optionalChainingAssign", { version: "2023-07" }],
+    ["discardBinding", { syntaxType: "void" }],
   ],
   tokens: false,
   // Ranges not available on comments, so we use `Node#{start,end}` instead

src/language-js/print/estree.js

@@ -648,6 +648,9 @@ function printEstree(path, options, print, args) {
     case "ModuleExpression":
       return ["module ", print("body")];
 
+    case "VoidPattern":
+      return "void";
+
     case "InterpreterDirective": // Printed as comment
     default:
       /* c8 ignore next */

src/language-js/traverse/visitor-keys.evaluate.js

@@ -66,10 +66,6 @@ const excludeNodeTypes = new Set([
   "DecimalLiteral",
   // Babel, Won't exist since we use `createImportExpressions` when parsing with babel
   "Import",
-
-  // Babel v7.28.0
-  // https://github.com/prettier/prettier/pull/17696
-  "VoidPattern",
 ]);
 
 const visitorKeys = Object.fromEntries(

tests/format/js/babel-plugins/__snapshots__/format.test.js.snap

@@ -690,6 +690,51 @@ class Foo {
 ================================================================================
 `;
 
+exports[`discard-binding.js [acorn] format 1`] = `
+"Unexpected keyword 'void' (1:11)
+> 1 | const [a, void] = iter;
+    |           ^
+  2 |
+Cause: Unexpected keyword 'void' (1:10)"
+`;
+
+exports[`discard-binding.js [espree] format 1`] = `
+"Unexpected keyword 'void' (1:11)
+> 1 | const [a, void] = iter;
+    |           ^
+  2 |
+Cause: Unexpected keyword 'void'"
+`;
+
+exports[`discard-binding.js [meriyah] format 1`] = `
+"Unexpected token: ']' (1:15)
+> 1 | const [a, void] = iter;
+    |               ^
+  2 |
+Cause: [1:14-1:15]: Unexpected token: ']'"
+`;
+
+exports[`discard-binding.js [oxc] format 1`] = `
+"Identifier expected. 'void' is a reserved word that cannot be used here. (1:11)
+> 1 | const [a, void] = iter;
+    |           ^^^^
+  2 |"
+`;
+
+exports[`discard-binding.js format 1`] = `
+====================================options=====================================
+parsers: ["babel", "babel-ts", "babel-flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+const [a, void] = iter;
+
+=====================================output=====================================
+const [a, void] = iter;
+
+================================================================================
+`;
+
 exports[`do-expressions.js [acorn] format 1`] = `
 "Unexpected token (3:9)
   1 | // https://babeljs.io/docs/babel-plugin-proposal-do-expressions

tests/format/js/babel-plugins/discard-binding.js

@@ -0,0 +1 @@
+const [a, void] = iter;

tests/format/js/babel-plugins/format.test.js

@@ -25,6 +25,7 @@ runFormatTest(import.meta, ["babel", "babel-ts", "babel-flow"], {
       "source-phase-imports.js",
       "deferred-import-evaluation.js",
       "optional-chaining-assignment.js",
+      "discard-binding.js",
     ],
     espree: [
       "decorators.js",
@@ -48,6 +49,7 @@ runFormatTest(import.meta, ["babel", "babel-ts", "babel-flow"], {
       "source-phase-imports.js",
       "deferred-import-evaluation.js",
       "optional-chaining-assignment.js",
+      "discard-binding.js",
     ],
     meriyah: [
       "do-expressions.js",
@@ -73,6 +75,7 @@ runFormatTest(import.meta, ["babel", "babel-ts", "babel-flow"], {
       "source-phase-imports.js",
       "deferred-import-evaluation.js",
       "optional-chaining-assignment.js",
+      "discard-binding.js",
     ],
     oxc: [
       "async-do-expressions.js",
@@ -91,6 +94,7 @@ runFormatTest(import.meta, ["babel", "babel-ts", "babel-flow"], {
       "throw-expressions.js",
       "typescript.js",
       "v8intrinsic.js",
+      "discard-binding.js",
     ],
     "oxc-ts": [
       "async-do-expressions.js",
@@ -109,6 +113,7 @@ runFormatTest(import.meta, ["babel", "babel-ts", "babel-flow"], {
       "throw-expressions.js",
       "typescript.js",
       "v8intrinsic.js",
+      "discard-binding.js",
     ],
     babel: ["flow.js", "typescript.js"],
     __babel_estree: ["flow.js", "typescript.js"],

tests/format/js/discard-binding/array-pattern.js

@@ -0,0 +1,36 @@
+{
+  // destructuring binding
+  const [, void, ] = value;
+}
+{
+  // for-of destructuring binding
+  for (const [void] of []);
+}
+{
+  // destructuring assignment
+  [void] = [];
+}
+{
+  // for-of destructuring assignment;
+  for ([void] of []);
+}
+{
+  // function param;
+  function f([[[void], void, ], void]) {}
+}
+{
+  // arrow function param
+  ([[[void], void, ], void]) => {}
+}
+{
+  // async arrow function param
+  async ([[[void], void, ], void]) => {}
+}
+{
+  // destructuring assignment in async call";
+  async([void] = []);
+}
+{
+  // catch param
+  try {} catch ([void]) {}
+}

tests/format/js/discard-binding/basic.js

@@ -0,0 +1,7 @@
+const [void] = [,void] = [void,] = [];
+
+function f(void, { p: void }, [ void ]) {}
+
+(void, { p: void }, [ void ]) => {}
+
+async (void, { p: void }, [ void ]) => {}

tests/format/js/discard-binding/discard-binding-arrow-params.js

@@ -0,0 +1 @@
+(void) => {}

tests/format/js/discard-binding/discard-binding-assignment.js

@@ -0,0 +1 @@
+([void] = []);

tests/format/js/discard-binding/discard-binding-async-arrow-params.js

@@ -0,0 +1 @@
+async (void) => {}

tests/format/js/discard-binding/discard-binding-bindings.js

@@ -0,0 +1 @@
+const { p: void } = {};

tests/format/js/discard-binding/discard-binding-for-await-using-binding.js

@@ -0,0 +1,3 @@
+async () => {
+  for(await using void of []);
+}

tests/format/js/discard-binding/discard-binding-for-bindings.js

@@ -0,0 +1 @@
+for(const { p: void } of []);

tests/format/js/discard-binding/discard-binding-for-lhs.js

@@ -0,0 +1 @@
+for({ p: void } of []);

tests/format/js/discard-binding/discard-binding-for-using-binding.js

@@ -0,0 +1,3 @@
+{
+  for(using void of []);
+}

tests/format/js/discard-binding/format.test.js

@@ -0,0 +1,12 @@
+runFormatTest(import.meta, ["babel", "flow", "typescript"], {
+  errors: {
+    flow: true,
+    typescript: true,
+    acorn: true,
+    espree: true,
+    meriyah: true,
+    oxc: true,
+    "oxc-ts": true,
+    hermes: true,
+  },
+});

tests/format/js/discard-binding/function-parameter.js

@@ -0,0 +1,20 @@
+{
+  // function parameter
+  function f(void) {}
+}
+{
+  // arrow function parameter
+  (x, void) => {}
+}
+{
+  // async arrow function parameter
+  async (void, x) => {}
+}
+{
+  // object method parameter
+  ({ f(x, void, y) {} });
+}
+{
+  // class method parameter
+  class C { m(void,) {} }
+}

tests/format/js/discard-binding/object-pattern.js

@@ -0,0 +1,36 @@
+{
+  // destructuring binding
+  const { void: void } = value;
+}
+{
+  // for-of destructuring binding
+  for (const { p: void } of []);
+}
+{
+  // destructuring assignment
+  ({ p: void } = {});
+}
+{
+  // for-of destructuring assignment
+  for ({ p: void } of []);
+}
+{
+  // function param
+  function f({ q: { q: { p: void }, p: void }, p: void }) {}
+}
+{
+  // arrow function param
+  ({ q: { q: { p: void }, p: void }, p: void }) => {}
+}
+{
+  // async arrow function param
+  async ({ q: { q: { p: void }, p: void }, p: void }) => {}
+}
+{
+  // destructuring assignment in async call
+  async({ p: void } = {});
+}
+{
+  // catch param
+  try {} catch ({ p: void }) {}
+}

tests/format/js/discard-binding/unary-expression-void.js

@@ -0,0 +1,16 @@
+// expr
+void [
+  // pattern
+  [ void ] = [{
+    // expr
+    [ void [] ]:
+    // pattern
+    [ void ] =
+    // expr
+    void [
+      // pattern
+      ([void]) => []
+    ]
+    // expr
+  }] = [void []]
+]

tests/format/js/discard-binding/using-variable-declarator.js

@@ -0,0 +1,34 @@
+{
+  // using 1 declarator
+  using void = f();
+}
+{
+  // using 2 declarators
+  using void = f(), void = g();
+}
+{
+  // using void declarator and normal declarator
+  using void = f(), x = g();
+}
+{
+  // using declarator in for-of
+  for(using void of []);
+}
+async () => {
+  {
+    // await using 1 declarator
+    await using void = f();
+  }
+  {
+    // await using 2 declarators
+    await using void = f(), void = g();
+  }
+  {
+    // await using void declarator and normal declarator
+    await using void = f(), x = g();
+  }
+  {
+    // await using declarator in for-of
+    for(await using void of []);
+  }
+}

tests/format/js/discard-binding/using.js

@@ -0,0 +1,6 @@
+{
+  using void = f();
+}
+async (void) => {
+  await using void = f();
+}

tests/format/misc/errors/js/discard-binding/format.test.js

@@ -0,0 +1,10 @@
+runFormatTest(import.meta, [
+  "babel",
+  "typescript",
+  "acorn",
+  "espree",
+  "meriyah",
+  "oxc",
+  "oxc-ts",
+  "hermes",
+]);

tests/format/misc/errors/js/discard-binding/invalid-array-expression.js

@@ -0,0 +1,9 @@
+([[[void], x, ], y]);
+
+([[[x], void, ], y]);
+
+([[[x], y, ], void]);
+
+([void, x = 0]);
+
+async([void, x = 0]);

tests/format/misc/errors/js/discard-binding/invalid-assignment-expression.js

@@ -0,0 +1 @@
+void = 0;

tests/format/misc/errors/js/discard-binding/invalid-assignment-for.js

@@ -0,0 +1 @@
+for (void of []);

tests/format/misc/errors/js/discard-binding/invalid-assignment-pattern.js

@@ -0,0 +1,69 @@
+{
+  // function parameter
+  function f(void = 0) {}
+}
+{
+  // arrow function parameter
+  (void = 0) => {}
+}
+{
+  // async arrow function parameter
+  async (void = 0) => {}
+}
+{
+  // nested array pattern: function parameter
+  function f([void = 0]) {}
+}
+{
+  // nested array pattern: arrow function parameter
+  ([void = 0]) => {}
+}
+{
+  // nested array pattern: async arrow function parameter
+  async ([void = 0]) => {}
+}
+{
+  // nested object pattern: function parameter
+  function f({ p: void = 0 }) {}
+}
+{
+  // nested object pattern: arrow function parameter
+  ({ p: void = 0 }) => {}
+}
+{
+  // nested object pattern: async arrow function parameter
+  async ({ p: void = 0 }) => {}
+}
+
+{
+  // nested array pattern: destructuring binding
+  let [void = 0] = [];
+}
+{
+  // nested object pattern: destructuring binding
+  let { p: void = 0 } = {};
+}
+{
+  // nested array pattern: for-of destructuring binding
+  for (let [void = 0] of []);
+}
+{
+  // nested object pattern: for-of destructuring binding
+  for (let { p: void = 0 } of [{}]);
+}
+{
+  // nested array pattern: destructuring assignment
+  ([void = 0] = []);
+}
+{
+  // nested object pattern: destructuring assignment
+  ({ p: void = 0 } = {});
+}
+{
+  // nested array pattern: for-of destructuring assignment
+  for ([void = 0] of []);
+}
+{
+  // nested object pattern: for-of destructuring assignment
+  for ({ p: void = 0 } of [{}]);
+}

tests/format/misc/errors/js/discard-binding/invalid-async-call-argument.js

@@ -0,0 +1,5 @@
+async(void, x);
+
+async(x, void);
+
+async(void, () => {});

tests/format/misc/errors/js/discard-binding/invalid-catch-parameter.js

@@ -0,0 +1 @@
+try {} catch (void) {}

tests/format/misc/errors/js/discard-binding/invalid-lone-arrow-function-parameter.js

@@ -0,0 +1 @@
+void => {}

tests/format/misc/errors/js/discard-binding/invalid-lone-async-arrow-function-parameter.js

@@ -0,0 +1 @@
+async void => {}

tests/format/misc/errors/js/discard-binding/invalid-object-expression.js

@@ -0,0 +1,9 @@
+({ p: { p: { p: void }, x, }, y});
+
+({ p: { x: { x }, p: void, }, y});
+
+({ y: { x: { x }, y, }, p: void });
+
+({ p: void, x: x = 0 });
+
+async({ p: void, x: x = 0 });

tests/format/misc/errors/js/discard-binding/invalid-parenthesized-assignment.js

@@ -0,0 +1 @@
+[(void)] = [];

tests/format/misc/errors/js/discard-binding/invalid-parenthesized-binding.js

@@ -0,0 +1 @@
+const [, (void), ] = value;

tests/format/misc/errors/js/discard-binding/invalid-rest-element-array-pattern-for-lhs.js

@@ -0,0 +1 @@
+for ([ ...void ] of []);

tests/format/misc/errors/js/discard-binding/invalid-rest-element-array-pattern-lhs.js

@@ -0,0 +1 @@
+([ ...void ] = []);

tests/format/misc/errors/js/discard-binding/invalid-rest-element-array-pattern.js

@@ -0,0 +1,6 @@
+{
+  var [ ...void ] = [];
+}
+{
+  for (var [...void] of [[]]);
+}

tests/format/misc/errors/js/discard-binding/invalid-rest-element-object-pattern-for-lhs.js

@@ -0,0 +1 @@
+for ({ ...void } of []);

tests/format/misc/errors/js/discard-binding/invalid-rest-element-object-pattern-lhs.js

@@ -0,0 +1 @@
+({ ...void } = {});

tests/format/misc/errors/js/discard-binding/invalid-rest-element-object-pattern.js

@@ -0,0 +1,6 @@
+{
+  var { ...void } = {};
+}
+{
+  for (var { ...void } of [{}]);
+}

tests/format/misc/errors/js/discard-binding/invalid-sequence-expression.js

@@ -0,0 +1,5 @@
+(void, x);
+
+(x, void);
+
+(void, () => {});

tests/format/misc/errors/js/discard-binding/invalid-variable-declarator.js

@@ -0,0 +1,9 @@
+{
+  var void = f();
+}
+{
+  let void = f(), void = g();
+}
+{
+  const void = f(), x = g();
+}

tests/unit/__snapshots__/visitor-keys.js.snap

@@ -1170,6 +1170,7 @@ exports[`visitor keys estree 1`] = `
     "init",
   ],
   "Variance": [],
+  "VoidPattern": [],
   "VoidTypeAnnotation": [],
   "WhileStatement": [
     "body",