Add attachComment parser option to disable comment attachment

benchmark/babel-parser/many-empty-statements/attachComment-false.bench.mjs

@@ -7,13 +7,14 @@ const suite = new Benchmark.Suite();
 
 function benchCases(name, implementation, options) {
   for (const length of [256, 512, 1024, 2048]) {
+    const input = ";".repeat(length);
     suite.add(`${name} ${length} empty statement`, () => {
-      implementation.parse(";".repeat(length), options);
+      implementation.parse(input, options);
     });
   }
 }
 
-benchCases("baseline", baseline);
+benchCases("baseline", baseline, { attachComment: true });
 benchCases("current + attachComment: false", current, { attachComment: false });
 
 suite.on("cycle", report).run();

benchmark/babel-parser/many-leading-trailing-comments/attachComment-false.bench.mjs

@@ -0,0 +1,28 @@
+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();
+
+function createInput(length) {
+  return "\n// c\na".repeat(length);
+}
+
+function benchCases(name, implementation, options) {
+  for (const length of [256, 512, 1024, 2048]) {
+    const input = createInput(length);
+    const { parse } = implementation;
+    suite.add(
+      `${name} ${length} leading comments + ${length - 1} trailing comments`,
+      () => {
+        parse(input, options);
+      }
+    );
+  }
+}
+
+benchCases("baseline", baseline, { attachComment: true });
+benchCases("current + attachComment: false", current, { attachComment: false });
+
+suite.on("cycle", report).run();

benchmark/babel-parser/many-leading-trailing-comments/bench.mjs

@@ -7,7 +7,7 @@ const suite = new Benchmark.Suite();
 function createInput(length) {
   return "\n// c\na".repeat(length);
 }
-current.parse(createInput(256), {});
+
 function benchCases(name, implementation, options) {
   for (const length of [128, 256, 512, 1024]) {
     const input = createInput(length);

eslint/babel-eslint-parser/src/worker/configuration.cjs

@@ -31,6 +31,8 @@ function normalizeParserOptions(options) {
       allowSuperOutsideMethod: true,
       ...options.babelOptions.parserOpts,
       plugins: getParserPlugins(options.babelOptions),
+      // skip comment attaching for parsing performance
+      attachComment: false,
       ranges: true,
       tokens: true,
     },

packages/babel-parser/src/options.js

@@ -22,6 +22,7 @@ export type Options = {
   tokens: boolean,
   createParenthesizedExpressions: boolean,
   errorRecovery: boolean,
+  attachComment: boolean,
 };
 
 export const defaultOptions: Options = {
@@ -66,6 +67,11 @@ export const defaultOptions: Options = {
   // When enabled, errors are attached to the AST instead of being directly thrown.
   // Some errors will still throw, because @babel/parser can't always recover.
   errorRecovery: false,
+  // When enabled, comments will be attached to adjacent AST nodes as one of
+  // `leadingComments`, `trailingComments` and `innerComments`. The comment attachment
+  // is vital to preserve comments after transform. If you don't print AST back,
+  // consider set this option to `false` for performance
+  attachComment: true,
 };
 
 // Interpret and default an options object

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

@@ -9,23 +9,22 @@ import type { Comment, Node as NodeType, NodeBase } from "../types";
 
 class Node implements NodeBase {
   constructor(parser: Parser, pos: number, loc: Position) {
-    this.type = "";
     this.start = pos;
     this.end = 0;
     this.loc = new SourceLocation(loc);
     if (parser?.options.ranges) this.range = [pos, 0];
     if (parser?.filename) this.loc.filename = parser.filename;
   }
 
-  type: string;
-  start: number;
-  end: number;
-  loc: SourceLocation;
-  range: [number, number];
-  leadingComments: Array<Comment>;
-  trailingComments: Array<Comment>;
-  innerComments: Array<Comment>;
-  extra: { [key: string]: any };
+  type: string = "";
+  declare start: number;
+  declare end: number;
+  declare loc: SourceLocation;
+  declare range: [number, number];
+  declare leadingComments: Array<Comment>;
+  declare trailingComments: Array<Comment>;
+  declare innerComments: Array<Comment>;
+  declare extra: { [key: string]: any };
 }
 const NodePrototype = Node.prototype;
 
@@ -135,7 +134,7 @@ export class NodeUtils extends UtilParser {
     node.end = pos;
     node.loc.end = loc;
     if (this.options.ranges) node.range[1] = pos;
-    this.processComment(node);
+    if (this.options.attachComment) this.processComment(node);
     return node;
   }
 

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

@@ -403,7 +403,7 @@ export default class Tokenizer extends ParserErrors {
               const comment = this.skipBlockComment();
               if (comment !== undefined) {
                 this.addComment(comment);
-                comments.push(comment);
+                if (this.options.attachComment) comments.push(comment);
               }
               break;
             }
@@ -412,7 +412,7 @@ export default class Tokenizer extends ParserErrors {
               const comment = this.skipLineComment(2);
               if (comment !== undefined) {
                 this.addComment(comment);
-                comments.push(comment);
+                if (this.options.attachComment) comments.push(comment);
               }
               break;
             }
@@ -436,7 +436,7 @@ export default class Tokenizer extends ParserErrors {
               const comment = this.skipLineComment(3);
               if (comment !== undefined) {
                 this.addComment(comment);
-                comments.push(comment);
+                if (this.options.attachComment) comments.push(comment);
               }
             } else {
               break loop;
@@ -452,7 +452,7 @@ export default class Tokenizer extends ParserErrors {
               const comment = this.skipLineComment(4);
               if (comment !== undefined) {
                 this.addComment(comment);
-                comments.push(comment);
+                if (this.options.attachComment) comments.push(comment);
               }
             } else {
               break loop;

packages/babel-parser/test/attachComment-false.js

@@ -0,0 +1,12 @@
+import path from "path";
+import { runFixtureTestsWithoutExactASTMatch } from "./helpers/runFixtureTests";
+import { parseExpression } from "../lib";
+import { fileURLToPath } from "url";
+
+runFixtureTestsWithoutExactASTMatch(
+  path.join(path.dirname(fileURLToPath(import.meta.url)), "expressions"),
+  (input, options = {}) => {
+    options.attachComment = false;
+    return parseExpression(input, options);
+  },
+);

packages/babel-parser/test/fixtures/comments/attachComment-false/array-expression-trailing-comma/input.js

@@ -0,0 +1,18 @@
+const nonTrailing = [
+  "One", // One
+   // Two
+  "Two" // Three
+  // Four
+]
+
+const trailingAfterComma = [
+  "One", // One
+   // Two
+  "Two", // Three
+  // Four
+]
+
+const trailingAfterArray = [
+  "One", // One
+   // Two
+] // Three

packages/babel-parser/test/fixtures/comments/attachComment-false/array-expression-trailing-comma/output.json

@@ -0,0 +1,187 @@
+{
+  "type": "File",
+  "start":0,"end":229,"loc":{"start":{"line":1,"column":0},"end":{"line":18,"column":10}},
+  "program": {
+    "type": "Program",
+    "start":0,"end":229,"loc":{"start":{"line":1,"column":0},"end":{"line":18,"column":10}},
+    "sourceType": "script",
+    "interpreter": null,
+    "body": [
+      {
+        "type": "VariableDeclaration",
+        "start":0,"end":76,"loc":{"start":{"line":1,"column":0},"end":{"line":6,"column":1}},
+        "declarations": [
+          {
+            "type": "VariableDeclarator",
+            "start":6,"end":76,"loc":{"start":{"line":1,"column":6},"end":{"line":6,"column":1}},
+            "id": {
+              "type": "Identifier",
+              "start":6,"end":17,"loc":{"start":{"line":1,"column":6},"end":{"line":1,"column":17},"identifierName":"nonTrailing"},
+              "name": "nonTrailing"
+            },
+            "init": {
+              "type": "ArrayExpression",
+              "start":20,"end":76,"loc":{"start":{"line":1,"column":20},"end":{"line":6,"column":1}},
+              "elements": [
+                {
+                  "type": "StringLiteral",
+                  "start":24,"end":29,"loc":{"start":{"line":2,"column":2},"end":{"line":2,"column":7}},
+                  "extra": {
+                    "rawValue": "One",
+                    "raw": "\"One\""
+                  },
+                  "value": "One"
+                },
+                {
+                  "type": "StringLiteral",
+                  "start":50,"end":55,"loc":{"start":{"line":4,"column":2},"end":{"line":4,"column":7}},
+                  "extra": {
+                    "rawValue": "Two",
+                    "raw": "\"Two\""
+                  },
+                  "value": "Two"
+                }
+              ]
+            }
+          }
+        ],
+        "kind": "const"
+      },
+      {
+        "type": "VariableDeclaration",
+        "start":78,"end":162,"loc":{"start":{"line":8,"column":0},"end":{"line":13,"column":1}},
+        "declarations": [
+          {
+            "type": "VariableDeclarator",
+            "start":84,"end":162,"loc":{"start":{"line":8,"column":6},"end":{"line":13,"column":1}},
+            "id": {
+              "type": "Identifier",
+              "start":84,"end":102,"loc":{"start":{"line":8,"column":6},"end":{"line":8,"column":24},"identifierName":"trailingAfterComma"},
+              "name": "trailingAfterComma"
+            },
+            "init": {
+              "type": "ArrayExpression",
+              "start":105,"end":162,"loc":{"start":{"line":8,"column":27},"end":{"line":13,"column":1}},
+              "extra": {
+                "trailingComma": 140
+              },
+              "elements": [
+                {
+                  "type": "StringLiteral",
+                  "start":109,"end":114,"loc":{"start":{"line":9,"column":2},"end":{"line":9,"column":7}},
+                  "extra": {
+                    "rawValue": "One",
+                    "raw": "\"One\""
+                  },
+                  "value": "One"
+                },
+                {
+                  "type": "StringLiteral",
+                  "start":135,"end":140,"loc":{"start":{"line":11,"column":2},"end":{"line":11,"column":7}},
+                  "extra": {
+                    "rawValue": "Two",
+                    "raw": "\"Two\""
+                  },
+                  "value": "Two"
+                }
+              ]
+            }
+          }
+        ],
+        "kind": "const"
+      },
+      {
+        "type": "VariableDeclaration",
+        "start":164,"end":220,"loc":{"start":{"line":15,"column":0},"end":{"line":18,"column":1}},
+        "declarations": [
+          {
+            "type": "VariableDeclarator",
+            "start":170,"end":220,"loc":{"start":{"line":15,"column":6},"end":{"line":18,"column":1}},
+            "id": {
+              "type": "Identifier",
+              "start":170,"end":188,"loc":{"start":{"line":15,"column":6},"end":{"line":15,"column":24},"identifierName":"trailingAfterArray"},
+              "name": "trailingAfterArray"
+            },
+            "init": {
+              "type": "ArrayExpression",
+              "start":191,"end":220,"loc":{"start":{"line":15,"column":27},"end":{"line":18,"column":1}},
+              "extra": {
+                "trailingComma": 200
+              },
+              "elements": [
+                {
+                  "type": "StringLiteral",
+                  "start":195,"end":200,"loc":{"start":{"line":16,"column":2},"end":{"line":16,"column":7}},
+                  "extra": {
+                    "rawValue": "One",
+                    "raw": "\"One\""
+                  },
+                  "value": "One"
+                }
+              ]
+            }
+          }
+        ],
+        "kind": "const"
+      }
+    ],
+    "directives": []
+  },
+  "comments": [
+    {
+      "type": "CommentLine",
+      "value": " One",
+      "start":31,"end":37,"loc":{"start":{"line":2,"column":9},"end":{"line":2,"column":15}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Two",
+      "start":41,"end":47,"loc":{"start":{"line":3,"column":3},"end":{"line":3,"column":9}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Three",
+      "start":56,"end":64,"loc":{"start":{"line":4,"column":8},"end":{"line":4,"column":16}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Four",
+      "start":67,"end":74,"loc":{"start":{"line":5,"column":2},"end":{"line":5,"column":9}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " One",
+      "start":116,"end":122,"loc":{"start":{"line":9,"column":9},"end":{"line":9,"column":15}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Two",
+      "start":126,"end":132,"loc":{"start":{"line":10,"column":3},"end":{"line":10,"column":9}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Three",
+      "start":142,"end":150,"loc":{"start":{"line":11,"column":9},"end":{"line":11,"column":17}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Four",
+      "start":153,"end":160,"loc":{"start":{"line":12,"column":2},"end":{"line":12,"column":9}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " One",
+      "start":202,"end":208,"loc":{"start":{"line":16,"column":9},"end":{"line":16,"column":15}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Two",
+      "start":212,"end":218,"loc":{"start":{"line":17,"column":3},"end":{"line":17,"column":9}}
+    },
+    {
+      "type": "CommentLine",
+      "value": " Three",
+      "start":221,"end":229,"loc":{"start":{"line":18,"column":2},"end":{"line":18,"column":10}}
+    }
+  ]
+}

packages/babel-parser/test/fixtures/comments/attachComment-false/options.json

@@ -0,0 +1,3 @@
+{
+  "attachComment": false
+}