js_parser: keep @license and @preserve comments, and keep legal comments across import()

docs/bundler/minifier.mdx

@@ -757,17 +757,19 @@ foo&&bar||baz
 
 **Mode:** `--minify-whitespace`
 
-Removes comments except important license comments.
+Removes comments except legal comments. A legal comment starts with `/*!` or `//!`, or contains the word `@license` or `@preserve`. A longer word such as `@licensee` does not count.
 
 ```ts Input
 // This comment is removed
 /* So is this */
 /*! But this license comment is kept */
+/** @license MIT, and so is this one */
 function test() { /* inline comment */ }
 ```
 
 ```js Output
 /*! But this license comment is kept */
+/** @license MIT, and so is this one */
 function test(){}
 ```
 

src/js_parser/lexer.rs

@@ -150,7 +150,6 @@ pub struct LexerSnapshot<'a> {
     pub(crate) has_pure_comment_before: bool,
     pub(crate) has_react_hooks_suppression_before: bool,
     pub(crate) has_react_hooks_block_suppression: bool,
-    pub(crate) preserve_all_comments_before: bool,
     pub(crate) is_legacy_octal_literal: bool,
     pub(crate) is_log_disabled: bool,
     pub(crate) code_point: CodePoint,
@@ -219,7 +218,6 @@ pub struct Lexer<'a> {
     /// `eslint-disable` (no `-next-line` suffix). Never cleared by the
     /// parser, so it applies to every subsequent function in the file.
     pub(crate) has_react_hooks_block_suppression: bool,
-    pub(crate) preserve_all_comments_before: bool,
     pub(crate) is_legacy_octal_literal: bool,
     pub(crate) is_log_disabled: bool,
     pub(crate) comments_to_preserve_before: Vec<js_ast::G::Comment>,
@@ -335,7 +333,6 @@ impl<'a> Lexer<'a> {
             has_pure_comment_before: self.has_pure_comment_before,
             has_react_hooks_suppression_before: self.has_react_hooks_suppression_before,
             has_react_hooks_block_suppression: self.has_react_hooks_block_suppression,
-            preserve_all_comments_before: self.preserve_all_comments_before,
             is_legacy_octal_literal: self.is_legacy_octal_literal,
             is_log_disabled: self.is_log_disabled,
             code_point: self.code_point,
@@ -373,7 +370,6 @@ impl<'a> Lexer<'a> {
         self.has_pure_comment_before = original.has_pure_comment_before;
         self.has_react_hooks_suppression_before = original.has_react_hooks_suppression_before;
         self.has_react_hooks_block_suppression = original.has_react_hooks_block_suppression;
-        self.preserve_all_comments_before = original.preserve_all_comments_before;
         self.is_legacy_octal_literal = original.is_legacy_octal_literal;
         self.is_log_disabled = original.is_log_disabled;
         self.code_point = original.code_point;
@@ -1892,7 +1888,7 @@ impl<'a> Lexer<'a> {
 
     fn scan_comment_text(&mut self, for_pragma: bool) {
         let text = &self.contents[self.start..self.end];
-        let has_legal_annotation = text.len() > 2 && text[2] == b'!';
+        let has_legal_annotation = is_legal_comment(text);
         let is_multiline_comment = text.len() > 1 && text[1] == b'*';
 
         if self.track_comments {
@@ -1937,11 +1933,7 @@ impl<'a> Lexer<'a> {
             }
         }
 
-        if has_legal_annotation || self.preserve_all_comments_before {
-            if is_multiline_comment {
-                // text = lexer.removeMultilineCommentIndent(lexer.source.contents[0..lexer.start], text);
-            }
-
+        if has_legal_annotation {
             self.comments_to_preserve_before.push(js_ast::G::Comment {
                 text: text.into(),
                 loc: self.loc(),
@@ -2227,7 +2219,6 @@ impl<'a> Lexer<'a> {
             has_pure_comment_before: false,
             has_react_hooks_suppression_before: false,
             has_react_hooks_block_suppression: false,
-            preserve_all_comments_before: false,
             is_legacy_octal_literal: false,
             is_log_disabled: false,
             comments_to_preserve_before: Vec::new(),
@@ -3331,6 +3322,23 @@ pub(crate) fn is_whitespace(codepoint: CodePoint) -> bool {
         || strings::is_unicode_space_separator(codepoint as u32)
 }
 
+/// esbuild's rule: `/*! ... */`, `//! ...`, or the word `@license` / `@preserve` anywhere in the comment.
+pub(crate) fn is_legal_comment(text: &[u8]) -> bool {
+    if text.len() > 2 && text[2] == b'!' {
+        return true;
+    }
+    let mut rest = text;
+    while let Some(i) = strings::index_of_char_usize(rest, b'@') {
+        rest = &rest[i + 1..];
+        if strings::has_prefix_with_word_boundary(rest, b"license")
+            || strings::has_prefix_with_word_boundary(rest, b"preserve")
+        {
+            return true;
+        }
+    }
+    false
+}
+
 pub use bun_core::identifier::{is_identifier, is_identifier_utf16};
 
 pub fn range_of_identifier(source: &Source, loc: Loc) -> Range {

src/js_parser/p.rs

@@ -7379,8 +7379,7 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
     /// `lexer.is_log_disabled`. Lists are captured as lengths and truncated
     /// on restore; the attempt's arena allocations just become unreachable.
     /// The legal comments waiting for the next statement are moved out
-    /// instead: a block body or `import()` drains them, so a length cannot
-    /// restore them.
+    /// instead: a block body drains them, so a length cannot restore them.
     pub(crate) fn parser_snapshot(&mut self) -> ParserSnapshot<'a> {
         let comments_to_preserve_before =
             core::mem::take(&mut self.lexer.comments_to_preserve_before);

src/js_parser/parse/parse_import_export.rs

@@ -42,14 +42,8 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
         let old_allow_in = p.allow_in;
         p.allow_in = true;
 
-        p.lexer.preserve_all_comments_before = true;
         p.lexer.expect(T::TOpenParen)?;
 
-        // const comments = try p.lexer.comments_to_preserve_before.toOwnedSlice();
-        p.lexer.comments_to_preserve_before.clear();
-
-        p.lexer.preserve_all_comments_before = false;
-
         let mut value = p.parse_expr(Level::Comma)?;
 
         let mut import_options = Expr::EMPTY;
@@ -98,12 +92,9 @@ impl<'a, const TYPESCRIPT: bool, const SCAN_ONLY: bool> P<'a, TYPESCRIPT, SCAN_O
             }
         }
 
-        // _ = comments; // TODO: leading_interior comments
-
         Ok(p.new_expr(
             E::Import {
                 expr: value,
-                // .leading_interior_comments = comments,
                 import_record_index: u32::MAX,
                 options: import_options,
             },

test/bundler/bundler_bytecode_portable.test.ts

@@ -474,10 +474,10 @@ describe("bytecode cache portability", () => {
           "sha256": "2a5d62fb4ca9d107e3a5bb2abe6a73f3c859a6f1a91c6c3d77653cb8c2053361",
         },
         "bun build --bytecode --minify all.js": {
-          "js": "721d67b0c2135aad554c9962b4e4505a4d6856b50da537fee7566d43f6cfdbda",
+          "js": "02f69e5448f525a3f098f06e9da1565b887125621607fcf5ef3d6be4f2642d6f",
           "jsc": {
-            "bytes": 1998992,
-            "sha256": "f2631b3ba2b532e52183d5e6a44a7dbf5c0515b368d95fc692bf0e5ad15eb8f6",
+            "bytes": 1999024,
+            "sha256": "68d66351c6904f530efe9bb3d7d4bec29216cfca84ad0e592cf0f9cc2a6eab7a",
           },
         },
         "bun build --bytecode --minify features.js": {
@@ -502,10 +502,10 @@ describe("bytecode cache portability", () => {
           },
         },
         "bun build --bytecode all.js": {
-          "js": "a2f566b81700f852fef68247aef22af8b916858de30e4dc787846fd874c9e4d2",
+          "js": "3fed52509bcec75d9e29ae544e594c2bd0b656435391c4b25d93b77781e6875d",
           "jsc": {
-            "bytes": 2178656,
-            "sha256": "f743f4e9cff325bfd8d344f2dead6a8ba6b9933393a09c75334429ead924c480",
+            "bytes": 2178664,
+            "sha256": "7e1b891eeadd25c17d7cb0d0b2bbbd6f834c9460d1a52fc1ce80e362d806b919",
           },
         },
         "bun build --bytecode big.js": {
@@ -530,31 +530,31 @@ describe("bytecode cache portability", () => {
           },
         },
         "bun build --bytecode immutable/dist/immutable.es.js": {
-          "js": "c9a2ba9f6b6a662e6bdfd44128bc66284276f5eac2a8875adb4578472328dc9f",
+          "js": "05f0cde57bc6b435ac582d1dd835a4ca534e4463aece6cf8ab0ba804bada4b95",
           "jsc": {
-            "bytes": 280016,
-            "sha256": "2a99c33a2516e2d41187bc322ddd4523318530b51c60c3d9a8bd566d4f2929a1",
+            "bytes": 280032,
+            "sha256": "76e7397e6837de9932399628bf313864cb204fbf0cca6b9c01c8d919778084a6",
           },
         },
         "bun build --bytecode libraries.js": {
-          "js": "f9d0c270d3f41997b904689435104703b1f8b6b1c67ead48dff30e7354890cfd",
+          "js": "d07e6f6b8072d025b5dabc555ae1956f35eb93ae9949f4e28d3241d24454f860",
           "jsc": {
-            "bytes": 23806376,
-            "sha256": "1e2e31a113d8b5ca3e9cd73820d465e678756c0942023480569f785b15987dcf",
+            "bytes": 23806816,
+            "sha256": "b19fb12773cc11afa6e1fa4f2a2a67db4ae8dc9f9faa68f3fba178d9626e522e",
           },
         },
         "bun build --bytecode lodash/lodash.js": {
-          "js": "e372f1aec6b2bba20581abfce3b7273aae0ec4f593ed2aa4aa5c60c66836856d",
+          "js": "d848e69990c2f1f1de4cc4f085b82a68d4f9fe41dec935bc324c3446756638d1",
           "jsc": {
             "bytes": 347488,
-            "sha256": "531d6bb544c53641289a44e72ac096560b19d360c2ee19b77483987c367b9b5e",
+            "sha256": "c0a867e3d08d091010a748af6864b5080040ff6a1fd26450ece8b4e887ea6ba9",
           },
         },
         "bun build --bytecode react-dom/cjs/react-dom.development.js": {
-          "js": "e2cf34c8eb6f5952a33ca91e3949b28786349cf97ea3fbf0b3b8500dbccd4860",
+          "js": "0c1c056e3cf8c745148f5e60449707d9c997a9390ba8740e5d2d3371f9dbb8ae",
           "jsc": {
             "bytes": 980080,
-            "sha256": "32fa8492ad9fdf3ea31395756898d556df9dc6bdfbac9bba07bcafa748ab38ca",
+            "sha256": "1cd131e19ca8feff1cceb2dcbcada6a08656ef0653ad22c40e18f003fca7acf3",
           },
         },
         "bun build --bytecode records.js": {

test/bundler/bundler_comments.test.ts

@@ -430,3 +430,95 @@ describe("multi-line comments", () => {
     },
   });
 });
+
+describe("legal comments", () => {
+  // Like esbuild, keep a comment that contains the word "@license" or
+  // "@preserve", not only "/*!" and "//!". "@copyright" alone is not legal,
+  // and neither is a longer word such as "@licensee".
+  const legalForms = [
+    "/*! bang block */",
+    "//! bang line",
+    "/* @license MIT Copyright (c) Foo */",
+    "/** @license Apache-2.0 */",
+    "/* @preserve keep this */",
+    "// @license line form",
+    "// @preserve line form",
+    "/**\n * @license BSD-3-Clause\n * Copyright (c) Bar\n */",
+    "/* @license*/",
+    "/* see foo@license for the word boundary */",
+  ];
+  const droppedForms = [
+    "/* @copyright not legal */",
+    "/* plain comment */",
+    "/* the @licensee agrees */",
+    "/* @preserved for posterity */",
+    "// see the @licenses folder",
+    "/* @license_x */",
+    "/* @license9 */",
+  ];
+  const header = legalForms.join("\n") + "\n" + droppedForms.join("\n") + "\n";
+
+  function expectEachFormOnce(output: string) {
+    for (const form of legalForms) {
+      expect(output.split(form)).toHaveLength(2);
+    }
+    for (const form of droppedForms) {
+      expect(output).not.toContain(form);
+    }
+  }
+
+  for (const minify of [false, true]) {
+    itBundled(`@license and @preserve comments are kept ${minify ? "with" : "without"} minification`, {
+      files: {
+        "/entry.js": header + `console.log("hello");\n`,
+      },
+      minifyWhitespace: minify,
+      minifySyntax: minify,
+      minifyIdentifiers: minify,
+      run: {
+        stdout: "hello",
+      },
+      onAfterBundle(api) {
+        const output = api.readFile("/out.js");
+        expectEachFormOnce(output);
+        // The comments stay ahead of the statement they annotate.
+        expect(output.indexOf(legalForms.at(-1)!)).toBeLessThan(output.indexOf("console.log"));
+      },
+    });
+  }
+
+  itBundled("@license comments are kept when the file is transpiled without bundling", {
+    files: {
+      "/entry.ts": header + `export const x: number = 1;\n`,
+    },
+    bundling: false,
+    onAfterBundle(api) {
+      const output = api.readFile("/out.js");
+      expectEachFormOnce(output);
+      expect(output.indexOf(legalForms.at(-1)!)).toBeLessThan(output.indexOf("export const x"));
+    },
+  });
+
+  // Parsing "import(" used to clear every legal comment that was still waiting
+  // for the next statement boundary.
+  itBundled("a legal comment before import() is kept", {
+    files: {
+      "/entry.js": `
+        export const load = /*! before the arrow */ () => import("external-pkg");
+        export const load2 = () => import(/* @license inside the parens */ "external-pkg");
+        export const load3 = () => /* @preserve before import */ import("external-pkg");
+        console.log(typeof load, typeof load2, typeof load3);
+      `,
+    },
+    external: ["external-pkg"],
+    run: {
+      stdout: "function function function",
+    },
+    onAfterBundle(api) {
+      const output = api.readFile("/out.js");
+      expect(output.split("/*! before the arrow */")).toHaveLength(2);
+      expect(output.split("/* @license inside the parens */")).toHaveLength(2);
+      expect(output.split("/* @preserve before import */")).toHaveLength(2);
+    },
+  });
+});

test/bundler/bundler_npm.test.ts

@@ -55,17 +55,17 @@ describe("bundler", () => {
           "../entry.tsx",
         ],
         mappings: [
-          ["react.development.js:524:'getContextName'", "1:5623:at"],
-          ["react.development.js:2495:'actScopeDepth'", "23:4082:or++"],
-          ["react.development.js:696:''Component'", '1:7685:\'Component "%s"'],
-          ["entry.tsx:6:'\"Content-Type\"'", '100:18817:"Content-Type"'],
-          ["entry.tsx:11:'<html>'", "100:19071:void"],
-          ["entry.tsx:23:'await'", "100:19170:await"],
+          ["react.development.js:524:'getContextName'", "9:4156:at"],
+          ["react.development.js:2495:'actScopeDepth'", "31:4082:or++"],
+          ["react.development.js:696:''Component'", '9:6218:\'Component "%s"'],
+          ["entry.tsx:6:'\"Content-Type\"'", '132:18817:"Content-Type"'],
+          ["entry.tsx:11:'<html>'", "132:19071:void"],
+          ["entry.tsx:23:'await'", "132:19170:await"],
         ],
       },
     },
     expectExactFilesize: {
-      "out/entry.js": 221995,
+      "out/entry.js": 222988,
     },
     run: {
       stdout: "<!DOCTYPE html><html><body><h1>Hello World</h1><p>This is an example.</p></body></html>",