Add support for import assertions

Fixes #744 Fixes #566 In ESM mode, we parse import assertions and usually just pass them through to the output code, though TS import elision needs to know how to remove them as well. In CJS mode, we always remove import assertions since `require` can handle JSON files.
alangpierce · Sep 14, 2022 · 8e3f254 · 8e3f254
1 parent 0ae8d9b
commit 8e3f254
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Showing 12 changed files with 179 additions and 2 deletions.
diff --git a/generator/generateReadWordTree.ts b/generator/generateReadWordTree.ts
@@ -44,6 +44,7 @@ const CONTEXTUAL_KEYWORDS = [
   "abstract",
   "accessor",
   "as",
+  "assert",
   "asserts",
   "async",
   "await",

diff --git a/src/TokenProcessor.ts b/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}`);

diff --git a/src/parser/tokenizer/keywords.ts b/src/parser/tokenizer/keywords.ts
@@ -3,6 +3,7 @@ export enum ContextualKeyword {
   _abstract,
   _accessor,
   _as,
+  _assert,
   _asserts,
   _async,
   _await,

diff --git a/src/parser/tokenizer/readWordTree.ts b/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"

diff --git a/src/parser/traverser/statement.ts b/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);
+  }
+}
diff --git a/src/transformers/CJSImportTransformer.ts b/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();
     }

diff --git a/src/transformers/ESMImportTransformer.ts b/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();
       }

diff --git a/src/util/removeMaybeImportAssertion.ts b/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();
+  }
+}
diff --git a/test/imports-test.ts b/test/imports-test.ts
@@ -327,6 +327,23 @@ 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"};
+    `,
+      `"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);
+    `,
+    );
+  });
+
   it("allows an import statement with no import bindings", () => {
     assertResult(
       `

diff --git a/test/tokens-test.ts b/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);
   });

diff --git a/test/typescript-test.ts b/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"]},
+    );
+  });
 });
diff --git a/website/src/Worker.worker.ts b/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",
     );
   }