Implement Export{Default,Namespace}Specifier parsing ourselves.

lib/parsers/acorn-extensions.js

@@ -0,0 +1,169 @@
+"use strict";
+
+const tt = require("acorn").tokTypes;
+
+exports.enableAll = function (parser) {
+  exports.enableTolerance(parser);
+  exports.enableExportExtensions(parser);
+};
+
+exports.enableTolerance = function (parser) {
+  // It's not Reify's job to enforce strictness.
+  parser.strict = false;
+
+  // Tolerate recoverable parse errors.
+  parser.raiseRecoverable = noopRaiseRecoverable;
+};
+
+function noopRaiseRecoverable() {}
+
+exports.enableExportExtensions = function (parser) {
+  // Our custom lookahead method.
+  parser.withLookAhead = withLookAhead;
+
+  // Export-related modifications.
+  parser.parseExport = parseExport;
+  parser.isExportDefaultSpecifier = isExportDefaultSpecifier;
+  parser.parseExportSpecifiersMaybe = parseExportSpecifiersMaybe;
+  parser.parseExportFrom = parseExportFrom;
+  parser.shouldParseExportDeclaration = shouldParseExportDeclaration;
+};
+
+function parseExport(node, exports) {
+  this.next();
+  if (this.type === tt.star) {
+    const specifier = this.startNode();
+    this.next();
+    if (this.eatContextual("as")) {
+      // export * as ns from '...'
+      specifier.exported = this.parseIdent(true);
+      node.specifiers = [
+        this.finishNode(specifier, "ExportNamespaceSpecifier")
+      ];
+      this.parseExportSpecifiersMaybe(node);
+      this.parseExportFrom(node, exports);
+    } else {
+      // export * from '...'
+      this.parseExportFrom(node, exports);
+      return this.finishNode(node, "ExportAllDeclaration");
+    }
+  } else if (this.isExportDefaultSpecifier()) {
+    // export def from '...'
+    const specifier = this.startNode();
+    specifier.exported = this.parseIdent(true);
+    node.specifiers = [
+      this.finishNode(specifier, "ExportDefaultSpecifier")
+    ];
+    if (this.type === tt.comma &&
+        peekNextType(this) === tt.star) {
+      // export def, * as ns from '...'
+      this.expect(tt.comma);
+      const specifier = this.startNode();
+      this.expect(tt.star);
+      this.expectContextual("as");
+      specifier.exported = this.parseIdent(true);
+      node.specifiers.push(
+        this.finishNode(specifier, "ExportNamespaceSpecifier")
+      );
+    } else {
+      // export def, { x, y as z } from '...'
+      this.parseExportSpecifiersMaybe(node);
+    }
+    this.parseExportFrom(node, exports);
+  } else if (this.eat(tt._default)) {
+    // export default ...
+    exports.default = true;
+    let isAsync;
+    if (this.type === tt._function || (isAsync = this.isAsyncFunction())) {
+      let fNode = this.startNode();
+      this.next();
+      if (isAsync) this.next();
+      node.declaration = this.parseFunction(fNode, "nullableID", false, isAsync);
+    } else if (this.type === tt._class) {
+      let cNode = this.startNode();
+      node.declaration = this.parseClass(cNode, "nullableID");
+    } else {
+      node.declaration = this.parseMaybeAssign();
+      this.semicolon();
+    }
+    return this.finishNode(node, "ExportDefaultDeclaration");
+  } else if (this.shouldParseExportDeclaration()) {
+    // export var|const|let|function|class ...
+    node.declaration = this.parseStatement(true);
+    if (node.declaration.type === "VariableDeclaration") {
+      this.checkVariableExport(exports, node.declaration.declarations);
+    } else {
+      exports[node.declaration.id.name] = true;
+    }
+    node.specifiers = [];
+    node.source = null;
+  } else {
+    // export { x, y as z } [from '...']
+    node.declaration = null;
+    node.specifiers = this.parseExportSpecifiers(exports);
+    this.parseExportFrom(node, exports);
+  }
+  return this.finishNode(node, "ExportNamedDeclaration");
+}
+
+// Calls the given callback with the state of the parser temporarily
+// advanced by calling this.nextToken() n times, then rolls the parser
+// back to its original state and returns whatever the callback returned.
+function withLookAhead(n, callback) {
+  const old = Object.assign(Object.create(null), this);
+  while (n-- > 0) this.nextToken();
+  try {
+    return callback.call(this);
+  } finally {
+    Object.assign(this, old);
+  }
+}
+
+function peekNextType(parser) {
+  return parser.withLookAhead(1, () => parser.type);
+}
+
+function isExportDefaultSpecifier() {
+  return this.type === tt.name &&
+    this.withLookAhead(1, isCommaOrFrom);
+}
+
+function isCommaOrFrom() {
+  // Note: `this` should be the parser object.
+  return this.type === tt.comma ||
+    (this.type === tt.name &&
+     this.value === "from");
+}
+
+function parseExportSpecifiersMaybe(node) {
+  if (this.eat(tt.comma)) {
+    node.specifiers.push.apply(
+      node.specifiers,
+      this.parseExportSpecifiers()
+    );
+  }
+}
+
+function parseExportFrom(node, exports) {
+  const hasFrom = this.eatContextual("from") && this.type === tt.string;
+  node.source = hasFrom ? this.parseExprAtom() : null;
+
+  if (node.specifiers) {
+    for (let i = 0; i < node.specifiers.length; i++) {
+      const s = node.specifiers[i];
+      const exported = s.exported;
+      exports[exported.name] = true;
+    }
+  }
+
+  this.semicolon();
+}
+
+function shouldParseExportDeclaration() {
+  return this.type.keyword === "var" ||
+    this.type.keyword === "const" ||
+    this.type.keyword === "class" ||
+    this.type.keyword === "function" ||
+    this.isLet() ||
+    this.isAsyncFunction();
+}

lib/parsers/acorn.js

@@ -1,6 +1,7 @@
 "use strict";
 
-const acorn = require("acorn");
+let acorn = null;
+let acornExtensions = null;
 
 exports.options = {
   ecmaVersion: 8,
@@ -11,17 +12,19 @@ exports.options = {
 };
 
 function acornParse(code) {
-  const parser = new acorn.Parser(exports.options, code);
+  if (acorn === null) {
+    acorn = require("acorn");
+  }
+
+  if (acornExtensions === null) {
+    acornExtensions = require("./acorn-extensions.js");
+  }
 
-  // It's not Reify's job to enforce strictness.
-  parser.strict = false;
+  const parser = new acorn.Parser(exports.options, code);
 
-  // Tolerate recoverable parse errors.
-  parser.raiseRecoverable = noopRaiseRecoverable;
+  acornExtensions.enableAll(parser);
 
   return parser.parse();
 }
 
-function noopRaiseRecoverable() {}
-
 exports.parse = acornParse;

lib/parsers/top-level.js

@@ -1,6 +1,7 @@
 "use strict";
 
-const acorn = require("acorn");
+let acorn = null;
+let acornExtensions = null;
 
 exports.options = {
   ecmaVersion: 8,
@@ -25,20 +26,22 @@ function quickParseBlock() {
 }
 
 function topLevelParse(code) {
+  if (acorn === null) {
+    acorn = require("acorn");
+  }
+
+  if (acornExtensions === null) {
+    acornExtensions = require("./acorn-extensions.js");
+  }
+
   const parser = new acorn.Parser(exports.options, code);
 
+  acornExtensions.enableAll(parser);
+
   // Override the Parser's parseBlock method.
   parser.parseBlock = quickParseBlock;
 
-  // It's not Reify's job to enforce strictness.
-  parser.strict = false;
-
-  // Tolerate recoverable parse errors.
-  parser.raiseRecoverable = noopRaiseRecoverable;
-
   return parser.parse();
 }
 
-function noopRaiseRecoverable() {}
-
 exports.parse = topLevelParse;

test/export-tests.js

@@ -1,6 +1,4 @@
 const assert = require("assert");
-const parserSupportsExportFromExtensions =
-  process.env.REIFY_PARSER === "babylon";
 
 describe("export declarations", () => {
   it("should allow * exports", () => {
@@ -206,8 +204,7 @@ describe("export declarations", () => {
     });
   });
 
-  (parserSupportsExportFromExtensions ? it : xit
-  )("should support export-from extensions", () => {
+  it("should support export-from extensions", () => {
     import {
       def1, def2, def3,
       ns1, ns2, ns3,