Add support for import assertions

generator/generateReadWordTree.ts

@@ -44,6 +44,7 @@ const CONTEXTUAL_KEYWORDS = [
   "abstract",
   "accessor",
   "as",
+  "assert",
   "asserts",
   "async",
   "await",

src/TokenProcessor.ts

@@ -189,6 +189,24 @@ export default class TokenProcessor {
     this.replaceTokenTrimmingLeftWhitespace("");
   }
 
+  /**
+   * Remove all code until the next }, accounting for balanced braces.
+   */
+  removeBalancedCode(): void {
+    let braceDepth = 0;
+    while (!this.isAtEnd()) {
+      if (this.matches1(tt.braceL)) {
+        braceDepth++;
+      } else if (this.matches1(tt.braceR)) {
+        if (braceDepth === 0) {
+          return;
+        }
+        braceDepth--;
+      }
+      this.removeToken();
+    }
+  }
+
   copyExpectedToken(tokenType: TokenType): void {
     if (this.tokens[this.tokenIndex].type !== tokenType) {
       throw new Error(`Expected token ${tokenType}`);

src/parser/tokenizer/keywords.ts

@@ -3,6 +3,7 @@ export enum ContextualKeyword {
   _abstract,
   _accessor,
   _as,
+  _assert,
   _asserts,
   _async,
   _await,

src/parser/tokenizer/readWordTree.ts

@@ -45,7 +45,7 @@ export const READ_WORD_TREE = new Int32Array([
   // "asser"
   -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 540, -1, -1, -1, -1, -1, -1,
   // "assert"
-  -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 567, -1, -1, -1, -1, -1, -1, -1,
+  ContextualKeyword._assert << 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 567, -1, -1, -1, -1, -1, -1, -1,
   // "asserts"
   ContextualKeyword._asserts << 1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
   // "asy"

src/parser/traverser/statement.ts

@@ -64,6 +64,7 @@ import {
   parseIdentifier,
   parseMaybeAssign,
   parseMethod,
+  parseObj,
   parseParenExpression,
   parsePropertyName,
 } from "./expression";
@@ -78,6 +79,7 @@ import {
   eatContextual,
   expect,
   expectContextual,
+  hasPrecedingLineBreak,
   isContextual,
   isLineTerminator,
   semicolon,
@@ -996,6 +998,7 @@ function parseExportSpecifiersMaybe(): void {
 export function parseExportFrom(): void {
   if (eatContextual(ContextualKeyword._from)) {
     parseExprAtom();
+    maybeParseImportAssertions();
   }
   semicolon();
 }
@@ -1118,6 +1121,7 @@ export function parseImport(): void {
     expectContextual(ContextualKeyword._from);
     parseExprAtom();
   }
+  maybeParseImportAssertions();
   semicolon();
 }
 
@@ -1191,3 +1195,16 @@ function parseImportSpecifier(): void {
     parseImportedIdentifier();
   }
 }
+
+/**
+ * Parse import assertions like `assert {type: "json"}`.
+ *
+ * Import assertions technically have their own syntax, but are always parseable
+ * as a plain JS object, so just do that for simplicity.
+ */
+function maybeParseImportAssertions(): void {
+  if (isContextual(ContextualKeyword._assert) && !hasPrecedingLineBreak()) {
+    next();
+    parseObj(false, false);
+  }
+}

src/transformers/CJSImportTransformer.ts

@@ -10,6 +10,7 @@ import getDeclarationInfo, {
   EMPTY_DECLARATION_INFO,
 } from "../util/getDeclarationInfo";
 import getImportExportSpecifierInfo from "../util/getImportExportSpecifierInfo";
+import {removeMaybeImportAssertion} from "../util/removeMaybeImportAssertion";
 import shouldElideDefaultExport from "../util/shouldElideDefaultExport";
 import type ReactHotLoaderTransformer from "./ReactHotLoaderTransformer";
 import type RootTransformer from "./RootTransformer";
@@ -143,6 +144,7 @@ export default class CJSImportTransformer extends Transformer {
       this.tokens.replaceTokenTrimmingLeftWhitespace(this.importProcessor.claimImportCode(path));
       this.tokens.appendCode(this.importProcessor.claimImportCode(path));
     }
+    removeMaybeImportAssertion(this.tokens);
     if (this.tokens.matches1(tt.semi)) {
       this.tokens.removeToken();
     }
@@ -330,6 +332,7 @@ export default class CJSImportTransformer extends Transformer {
       ) {
         this.tokens.removeToken();
         this.tokens.removeToken();
+        removeMaybeImportAssertion(this.tokens);
       }
       return true;
     } else {
@@ -781,6 +784,7 @@ export default class CJSImportTransformer extends Transformer {
       this.tokens.removeToken();
       const path = this.tokens.stringValue();
       this.tokens.replaceTokenTrimmingLeftWhitespace(this.importProcessor.claimImportCode(path));
+      removeMaybeImportAssertion(this.tokens);
     } else {
       // This is a normal named export, so use that.
       this.tokens.appendCode(exportStatements.join(" "));
@@ -798,6 +802,7 @@ export default class CJSImportTransformer extends Transformer {
     }
     const path = this.tokens.stringValue();
     this.tokens.replaceTokenTrimmingLeftWhitespace(this.importProcessor.claimImportCode(path));
+    removeMaybeImportAssertion(this.tokens);
     if (this.tokens.matches1(tt.semi)) {
       this.tokens.removeToken();
     }

src/transformers/ESMImportTransformer.ts

@@ -11,6 +11,7 @@ import getDeclarationInfo, {
 } from "../util/getDeclarationInfo";
 import getImportExportSpecifierInfo from "../util/getImportExportSpecifierInfo";
 import {getNonTypeIdentifiers} from "../util/getNonTypeIdentifiers";
+import {removeMaybeImportAssertion} from "../util/removeMaybeImportAssertion";
 import shouldElideDefaultExport from "../util/shouldElideDefaultExport";
 import type ReactHotLoaderTransformer from "./ReactHotLoaderTransformer";
 import Transformer from "./Transformer";
@@ -102,6 +103,7 @@ export default class ESMImportTransformer extends Transformer {
       ) {
         this.tokens.removeToken();
         this.tokens.removeToken();
+        removeMaybeImportAssertion(this.tokens);
       }
       return true;
     }
@@ -145,6 +147,7 @@ export default class ESMImportTransformer extends Transformer {
         this.tokens.removeToken();
       }
       this.tokens.removeToken();
+      removeMaybeImportAssertion(this.tokens);
       if (this.tokens.matches1(tt.semi)) {
         this.tokens.removeToken();
       }

src/util/removeMaybeImportAssertion.ts

@@ -0,0 +1,19 @@
+import {ContextualKeyword} from "../parser/tokenizer/keywords";
+import {TokenType as tt} from "../parser/tokenizer/types";
+import type TokenProcessor from "../TokenProcessor";
+
+/**
+ * Starting at a potential `assert` token remove the import assertion if there
+ * is one.
+ */
+export function removeMaybeImportAssertion(tokens: TokenProcessor): void {
+  if (tokens.matches2(tt.name, tt.braceL) && tokens.matchesContextual(ContextualKeyword._assert)) {
+    // assert
+    tokens.removeToken();
+    // {
+    tokens.removeToken();
+    tokens.removeBalancedCode();
+    // }
+    tokens.removeToken();
+  }
+}

test/imports-test.ts

@@ -327,6 +327,29 @@ return obj && obj.__esModule ? obj : { default: obj }; }
     );
   });
 
+  it("removes import assertions", () => {
+    assertResult(
+      `
+      import DefaultName from 'module1' assert {type: "json"};
+      import {namedName} from 'module2' assert {type: "json"};
+      import "module3" assert {type: "json"};
+      export * from "module4" assert {type: "json"};
+      // Arbitrary expressions like these aren't actually allowed right now, but
+      // exercise the ability to detect matching braces.
+      import test from "module5" assert {type: {foo: "test"}};
+    `,
+      `"use strict";${ESMODULE_PREFIX}${IMPORT_DEFAULT_PREFIX}${CREATE_STAR_EXPORT_PREFIX}
+      var _module1 = require('module1'); var _module12 = _interopRequireDefault(_module1);
+      var _module2 = require('module2');
+      require('module3');
+      var _module4 = require('module4'); _createStarExport(_module4);
+      // Arbitrary expressions like these aren't actually allowed right now, but
+      // exercise the ability to detect matching braces.
+      var _module5 = require('module5'); var _module52 = _interopRequireDefault(_module5);
+    `,
+    );
+  });
+
   it("allows an import statement with no import bindings", () => {
     assertResult(
       `

test/tokens-test.ts

@@ -15,7 +15,17 @@ function assertTokens(
 ): void {
   const tokens: Array<SimpleToken> = parse(code, true, !isFlow, isFlow).tokens;
   const helpMessage = `Tokens did not match. Starting point with just token types: [${tokens
-    .map((t) => `{type: tt.${tt[t.type]}}`)
+    .map((t) => {
+      let tokenCode = "{";
+      tokenCode += `type: tt.${tt[t.type]}`;
+      if (t.contextualKeyword) {
+        tokenCode += `, contextualKeyword: ContextualKeyword.${
+          ContextualKeyword[t.contextualKeyword]
+        }`;
+      }
+      tokenCode += "}";
+      return tokenCode;
+    })
     .join(", ")}]`;
   assert.strictEqual(tokens.length, expectedTokens.length, helpMessage);
   const projectedTokens = tokens.map((token, i) => {
@@ -506,6 +516,42 @@ describe("tokens", () => {
     );
   });
 
+  it("parses import assertions", () => {
+    assertTokens(
+      `
+      import foo from "./foo.json" assert {type: "json"};
+      export {val} from './foo.js' assert {type: "javascript"};
+    `,
+      [
+        {type: tt._import},
+        {type: tt.name},
+        {type: tt.name, contextualKeyword: ContextualKeyword._from},
+        {type: tt.string},
+        {type: tt.name, contextualKeyword: ContextualKeyword._assert},
+        {type: tt.braceL},
+        {type: tt.name, contextualKeyword: ContextualKeyword._type},
+        {type: tt.colon},
+        {type: tt.string},
+        {type: tt.braceR},
+        {type: tt.semi},
+        {type: tt._export},
+        {type: tt.braceL},
+        {type: tt.name},
+        {type: tt.braceR},
+        {type: tt.name, contextualKeyword: ContextualKeyword._from},
+        {type: tt.string},
+        {type: tt.name, contextualKeyword: ContextualKeyword._assert},
+        {type: tt.braceL},
+        {type: tt.name, contextualKeyword: ContextualKeyword._type},
+        {type: tt.colon},
+        {type: tt.string},
+        {type: tt.braceR},
+        {type: tt.semi},
+        {type: tt.eof},
+      ],
+    );
+  });
+
   it("treats single-child JSX as non-static", () => {
     assertFirstJSXRole("const elem = <div>Hello</div>;", JSXRole.OneChild);
   });

test/typescript-test.ts

@@ -1,5 +1,6 @@
 import type {Options} from "../src/Options";
 import {
+  CREATE_NAMED_EXPORT_FROM_PREFIX,
   CREATE_REQUIRE_PREFIX,
   CREATE_STAR_EXPORT_PREFIX,
   ESMODULE_PREFIX,
@@ -3413,4 +3414,52 @@ describe("typescript transform", () => {
       {transforms: ["typescript", "jsx"]},
     );
   });
+
+  it("allows and preserves import assertions when targeting ESM", () => {
+    assertResult(
+      `
+      import jsonValue from "./file1.json" assert {type: "json"};
+      import implicitlyElidedImport from "./file2.json" assert {type: "json"};
+      import type explicitlyElidedImport from "./file3.json" assert {type: "json"};
+      import "./file4.json" assert {type: "json"};
+      export {val} from './file5.json' assert {type: "json"};
+      export type {val} from './file6.json' assert {type: "json"};
+      console.log(jsonValue);
+    `,
+      `
+      import jsonValue from "./file1.json" assert {type: "json"};
+
+
+      import "./file4.json" assert {type: "json"};
+      export {val} from './file5.json' assert {type: "json"};
+      ;
+      console.log(jsonValue);
+    `,
+      {transforms: ["typescript"]},
+    );
+  });
+
+  it("removes import assertions when targeting CJS", () => {
+    assertResult(
+      `
+      import jsonValue from "./file1.json" assert {type: "json"};
+      import implicitlyElidedImport from "./file2.json" assert {type: "json"};
+      import type explicitlyElidedImport from "./file3.json" assert {type: "json"};
+      import "./file4.json" assert {type: "json"};
+      export {val} from './file5.json' assert {type: "json"};
+      export type {val} from './file6.json' assert {type: "json"};
+      console.log(jsonValue);
+    `,
+      `"use strict";${ESMODULE_PREFIX}${IMPORT_DEFAULT_PREFIX}${CREATE_NAMED_EXPORT_FROM_PREFIX}
+      var _file1json = require('./file1.json'); var _file1json2 = _interopRequireDefault(_file1json);
+
+
+      require('./file4.json');
+      var _file5json = require('./file5.json'); _createNamedExportFrom(_file5json, 'val', 'val');
+      ;
+      console.log(_file1json2.default);
+    `,
+      {transforms: ["typescript", "imports"]},
+    );
+  });
 });

website/src/Worker.worker.ts

@@ -154,6 +154,7 @@ function runBabel(): {code: string; time: number | null} {
       "proposal-optional-catch-binding",
       "proposal-nullish-coalescing-operator",
       "proposal-optional-chaining",
+      "syntax-import-assertions",
     );
   }