bun build transforms modules.exports.now to exports.now - breaks date-format and log4js packages

[GeoffWilliams]

What version of Bun is running?

1.1.8+89d25807f

What platform is your computer?

Linux 6.1.0-17-amd64 x86_64 unknown

What steps can reproduce the bug?

When using bun build with date-format, modules.exports is getting transpiled to exports which causes runtime errors.

This testcase demonstrates the error - I was also getting a similar error from log4js

create project

bun init
bun add date-format

index.ts

import dateFormat from "date-format";
console.log(dateFormat.asString(new Date().toISOString()));

build

bun build --outdir build index.ts --target=bun

run testcase

bun ./build/index.js

What is the expected behavior?

Should print the current date to console, no errors. Eg:

2024-05-19T03:47:19.008Z

What do you see instead?

Bun reports error because exports.now is undefined:

40 |     if (typeof format !== "string") {
41 |       date = format;
42 |       format = exports.ISO8601_FORMAT;
43 |     }
44 |     if (!date) {
45 |       date = exports.now();
                  ^
TypeError: exports.now is not a function. (In 'exports.now()', 'exports.now' is undefined)
      at asString (/home/geoff/tmp/expr/testcase/build/index.js:45:14)
      at /home/geoff/tmp/expr/testcase/build/index.js:184:13

Bun v1.1.8 (Linux x64)

If we look in the source codes of date-format package, we see module.exports.now() - bun removed the module. qualification which breaks the library:

// from node_modules/date-format/lib/index.js
function asString(format, date) {
  if (typeof format !== "string") {
    date = format;
    format = module.exports.ISO8601_FORMAT;
  }
  if (!date) {
    date = module.exports.now();
  }

If I edit build/index.js and change back to module.exports.now the codes works as expected.

Additional information

I originally found this because log4js was erroring when using bun build and bun build --compile:

914 |     }
915 |     var vDay = addZero(date.getDate());
916 |     var vMonth = addZero(date.getMonth() + 1);
917 |     var vYearLong = addZero(date.getFullYear());
918 |     var vYearShort = addZero(vYearLong.substring(2, 4));
919 |     var vYear = format.indexOf("yyyy") > -1 ? vYearLong : vYearShort;
                      ^
TypeError: undefined is not an object (evaluating 'format.indexOf')
      at asString (/home/geoff/tmp/expr/testcase/build/index.js:919:17)
      at timestampLevelAndCategory (/home/geoff/tmp/expr/testcase/build/index.js:1062:52)
      at colouredLayout (/home/geoff/tmp/expr/testcase/build/index.js:1068:12)
      at /home/geoff/tmp/expr/testcase/build/index.js:1813:31
      at /home/geoff/tmp/expr/testcase/build/index.js:6044:7
      at forEach (:1:21)
      at sendLogEventToAppender (/home/geoff/tmp/expr/testcase/build/index.js:6043:5)
      at forEach (:1:21)
      at sendToListeners (/home/geoff/tmp/expr/testcase/build/index.js:1680:5)
      at send (/home/geoff/tmp/expr/testcase/build/index.js:1731:9)

Bun v1.1.8 (Linux x64)

Workaround

1. Build with --external=date-format
2. node_modules/date-format resolvable

Found via: #7024