Back parser state exportedIdentifiers by set (#13406)

packages/babel-parser/benchmark/many-named-export/1-length.bench.mjs

@@ -0,0 +1,34 @@
+import Benchmark from "benchmark";
+import baseline from "@babel-baseline/parser";
+import current from "../../lib/index.js";
+import { report } from "../util.mjs";
+
+const suite = new Benchmark.Suite();
+// All codepoints in [0x4e00, 0x9ffc] are valid identifier name per Unicode 13
+function createInput(length) {
+  if (length > 0x9ffc - 0x4e00) {
+    throw new Error(
+      `Length greater than ${
+        0x9ffc - 0x4e00
+      } is not supported! Consider modify the \`createInput\`.`
+    );
+  }
+  let source = "export { ";
+  for (let i = 0; i < length; i++) {
+    source += String.fromCharCode(0x4e00 + i) + ",";
+  }
+  return source + " } from './foo'";
+}
+function benchCases(name, implementation, options) {
+  for (const length of [256, 512, 1024, 2048]) {
+    const input = createInput(length);
+    suite.add(`${name} ${length} length-1 named export`, () => {
+      implementation.parse(input, options);
+    });
+  }
+}
+
+benchCases("baseline", baseline, { sourceType: "module" });
+benchCases("current", current, { sourceType: "module" });
+
+suite.on("cycle", report).run();

packages/babel-parser/package.json

@@ -33,7 +33,7 @@
     "node": ">=6.0.0"
   },
   "devDependencies": {
-    "@babel-baseline/parser": "npm:@babel/parser@^7.14.0",
+    "@babel-baseline/parser": "npm:@babel/parser@^7.14.4",
     "@babel/code-frame": "workspace:*",
     "@babel/helper-fixtures": "workspace:*",
     "@babel/helper-validator-identifier": "workspace:*",

packages/babel-parser/src/parser/base.js

@@ -18,6 +18,9 @@ export default class BaseParser {
   declare expressionScope: ExpressionScopeHandler;
   declare plugins: PluginsMap;
   declare filename: ?string;
+  // Names of exports store. `default` is stored as a name for both
+  // `export default foo;` and `export { foo as default };`.
+  declare exportedIdentifiers: Set<string>;
   sawUnambiguousESM: boolean = false;
   ambiguousScriptDifferentAst: boolean = false;
 

packages/babel-parser/src/parser/statement.js

@@ -2114,7 +2114,7 @@ export default class StatementParser extends ExpressionParser {
       | N.ExportDefaultSpecifier,
     name: string,
   ): void {
-    if (this.state.exportedIdentifiers.indexOf(name) > -1) {
+    if (this.exportedIdentifiers.has(name)) {
       this.raise(
         node.start,
         name === "default"
@@ -2123,7 +2123,7 @@ export default class StatementParser extends ExpressionParser {
         name,
       );
     }
-    this.state.exportedIdentifiers.push(name);
+    this.exportedIdentifiers.add(name);
   }
 
   // Parses a comma-separated list of module exports.

packages/babel-parser/src/parser/util.js

@@ -349,8 +349,8 @@ export default class UtilParser extends Tokenizer {
     const oldLabels = this.state.labels;
     this.state.labels = [];
 
-    const oldExportedIdentifiers = this.state.exportedIdentifiers;
-    this.state.exportedIdentifiers = [];
+    const oldExportedIdentifiers = this.exportedIdentifiers;
+    this.exportedIdentifiers = new Set();
 
     // initialize scopes
     const oldInModule = this.inModule;
@@ -372,7 +372,7 @@ export default class UtilParser extends Tokenizer {
     return () => {
       // Revert state
       this.state.labels = oldLabels;
-      this.state.exportedIdentifiers = oldExportedIdentifiers;
+      this.exportedIdentifiers = oldExportedIdentifiers;
 
       // Revert scopes
       this.inModule = oldInModule;

packages/babel-parser/src/tokenizer/state.js

@@ -148,10 +148,6 @@ export default class State {
   // after a non-directive is parsed
   strictErrors: Map<number, ErrorTemplate> = new Map();
 
-  // Names of exports store. `default` is stored as a name for both
-  // `export default foo;` and `export { foo as default };`.
-  exportedIdentifiers: Array<string> = [];
-
   // Tokens length in token store
   tokensLength: number = 0;