Fixes #2942

src/bundler/bundle_v2.zig

@@ -7397,7 +7397,20 @@ const LinkerContext = struct {
                             var clone = std.ArrayList(G.Decl).initCapacity(allocator, before.decls.len + after.decls.len) catch unreachable;
                             clone.appendSliceAssumeCapacity(before.decls.slice());
                             clone.appendSliceAssumeCapacity(after.decls.slice());
-                            before.decls.update(clone);
+                            // we must clone instead of overwrite in-place incase the same S.Local is used across threads
+                            // https://github.com/oven-sh/bun/issues/2942
+                            stmts.items[end - 1] = Stmt.allocate(
+                                allocator,
+                                S.Local,
+                                S.Local{
+                                    .decls = BabyList(G.Decl).fromList(clone),
+                                    .is_export = before.is_export,
+                                    .was_commonjs_export = before.was_commonjs_export,
+                                    .was_ts_import_equals = before.was_ts_import_equals,
+                                    .kind = before.kind,
+                                },
+                                stmts.items[end - 1].loc,
+                            );
                         }
                         continue;
                     }

test/bundler/bundler_regressions.test.ts

@@ -0,0 +1,140 @@
+import assert from "assert";
+import dedent from "dedent";
+import { itBundled, testForFile } from "./expectBundled";
+var { describe, test, expect } = testForFile(import.meta.path);
+
+describe("bundler", () => {
+  itBundled("regression/MergeAdjacentDecl#2942", {
+    files: {
+      "/shared.js": `
+      // Current version.
+      export var VERSION = '1.13.6';
+
+      // Establish the root object, \`window\` (\`self\`) in the browser, \`global\`
+      // on the server, or \`this\` in some virtual machines. We use \`self\`
+      // instead of \`window\` for \`WebWorker\` support.
+      export var root = (typeof self == 'object' && self.self === self && self) ||
+                (typeof global == 'object' && global.global === global && global) ||
+                Function('return this')() ||
+                {};
+
+      // Save bytes in the minified (but not gzipped) version:
+      export var ArrayProto = Array.prototype, ObjProto = Object.prototype;
+      export var SymbolProto = typeof Symbol !== 'undefined' ? Symbol.prototype : null;
+
+      // Create quick reference variables for speed access to core prototypes.
+      export var push = ArrayProto.push,
+          slice = ArrayProto.slice,
+          toString = ObjProto.toString,
+          hasOwnProperty = ObjProto.hasOwnProperty;
+
+      // Modern feature detection.
+      export var supportsArrayBuffer = typeof ArrayBuffer !== 'undefined',
+          supportsDataView = typeof DataView !== 'undefined';
+
+      // All **ECMAScript 5+** native function implementations that we hope to use
+      // are declared here.
+      export var nativeIsArray = Array.isArray,
+          nativeKeys = Object.keys,
+          nativeCreate = Object.create,
+          nativeIsView = supportsArrayBuffer && ArrayBuffer.isView;
+
+      // Create references to these builtin functions because we override them.
+      export var _isNaN = isNaN,
+          _isFinite = isFinite;
+
+      // Keys in IE < 9 that won't be iterated by \`for key in ...\` and thus missed.
+      export var hasEnumBug = !{toString: null}.propertyIsEnumerable('toString');
+      export var nonEnumerableProps = ['valueOf', 'isPrototypeOf', 'toString',
+        'propertyIsEnumerable', 'hasOwnProperty', 'toLocaleString'];
+
+      // The largest integer that can be represented exactly.
+      export var MAX_ARRAY_INDEX = Math.pow(2, 53) - 1;
+
+      `,
+      // This was a race condition, so we want to add a lot of files to maximize the chances of hitting it
+      "/a.js": "import * as ABC from './shared.js';; console.log(ABC);",
+      "/b.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/c.js": "import * as ABC from './shared.js';; console.log(ABC);",
+      "/d.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/e.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/g.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/h.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/i.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/j.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/k.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/l.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/m.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/n.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_1.js": "import * as ABC from './shared.js';; console.log(ABC);",
+      "/a_2.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_3.js": "import * as ABC from './shared.js';; console.log(ABC);",
+      "/a_4.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_5.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_6.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_7.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_8.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_9.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_10.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_11.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_12.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/a_13.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_1.js": "import * as ABC from './shared.js';; console.log(ABC);",
+      "/b_2.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_3.js": "import * as ABC from './shared.js';; console.log(ABC);",
+      "/b_4.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_5.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_6.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_7.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_8.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_9.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_10.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_11.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_12.js": "import * as ABC from './shared.js'; console.log(ABC);",
+      "/b_13.js": "import * as ABC from './shared.js'; console.log(ABC);",
+    },
+    minifySyntax: true,
+
+    entryPoints: [
+      "/a.js",
+      "/b.js",
+      "/c.js",
+      "/d.js",
+      "/e.js",
+      "/g.js",
+      "/h.js",
+      "/i.js",
+      "/j.js",
+      "/k.js",
+      "/l.js",
+      "/m.js",
+      "/n.js",
+      "/a_1.js",
+      "/a_2.js",
+      "/a_3.js",
+      "/a_4.js",
+      "/a_5.js",
+      "/a_6.js",
+      "/a_7.js",
+      "/a_8.js",
+      "/a_9.js",
+      "/a_10.js",
+      "/a_11.js",
+      "/a_12.js",
+      "/a_13.js",
+      "/b_1.js",
+      "/b_2.js",
+      "/b_3.js",
+      "/b_4.js",
+      "/b_5.js",
+      "/b_6.js",
+      "/b_7.js",
+      "/b_8.js",
+      "/b_9.js",
+      "/b_10.js",
+      "/b_11.js",
+      "/b_12.js",
+      "/b_13.js",
+    ],
+  });
+});