Jest: The original function name gets lost in the Jest error stack

[gaearon]

test('hello world', () => {
 function BadCode() {
    throw new Error('noo')
  }

  function run(fn) {
    fn()
  }

  run(BadCode)
});

I expect to see BadCode in the stack because it's a named function. But it shows up as fn instead:

      at fn (sum.test.js:3:11)
      at run (sum.test.js:7:5)
      at Object.<anonymous> (sum.test.js:10:3)

Same with error.stack property.

Isn't this just a Node issue?

Nope, try it in Node REPL and see BadCode:

Uncaught Error: noo
    at BadCode (repl:2:11)
    at run (repl:2:5)

Also works correctly in Chrome.

I've done both locally so I used the same Node version (12.18.3). So it's Jest-specific.

I can also reproduce this on Repl.it: https://repl.it/repls/SecondaryItchyGui

I've tried vm.runInContext locally but that did not trigger the issue. I also verified I'm not transpiling anything. So I have no idea what is the cause of this. The underlying bug is probably in Node or V8 but we need to figure out what is special about Jest that is triggering it.

Why fix this?

This affects the new React component stack printing strategy so it would be unfortunate for this to stay unfixed very long.

[flozender]

Would love to give it a shot!

[SimenB]

Go for it 🙂

[SimenB]

Hmm, maybe not. @gaearon did you test with latest version of Jest? Repl.it is on 24 by default This is what I'm seeing running your example in [email protected] (node 12.19.0)

  ✕ hello world (3 ms)

  ● hello world

    noo

      1 | test('hello world', () => {
      2 |   function BadCode() {
    > 3 |     throw new Error('noo');
        |           ^
      4 |   }
      5 |
      6 |   function run(fn) {

      at BadCode (test.js:3:11)
      at fn (test.js:7:5)
      at Object.run (test.js:10:3)

[gaearon]

No, I didn't test with a different Jest version. This looks better! Although I'm still confused about why fn even exists in the stack..

[flozender]

@SimenB I tried the same and got fn:

  ✕ hello world (2 ms)

  ● hello world

    noo

      1 | test("hello world", () => {
      2 |   function BadCode() {
    > 3 |     throw new Error("noo");
        |           ^
      4 |   }
      5 | 
      6 |   function run(fn) {

      at fn (__tests__/index.test.js:3:11)
      at run (__tests__/index.test.js:7:5)
      at Object.<anonymous> (__tests__/index.test.js:10:3)

Node: v12.19.0
Jest: v26.5.3

[SimenB]

Interesting! It doesn't reproduce in the Jest repo or the project at work.

[flozender]

Oh, yeah! Jest repo gives me BadCode:

  ● hello world

    noo

      1 | test('hello world', () => {
      2 |   function BadCode() {
    > 3 |     throw new Error('noo');
        |           ^
      4 |   }
      5 | 
      6 |   function run(fn) {

      at BadCode (index.test.js:3:11)
      at fn (index.test.js:7:5)
      at Object.run (index.test.js:10:3)

[SimenB]

do you have a repository that reproduces?

[gaearon]

React repo does.

[gaearon]

(but with the old version)

[flozender]

You could also try this: https://github.com/flozender/jest-fnName/

[SimenB]

React repo doesn't reproduce for me 🙈

[gaearon]

Hmm. Actually sorry I created some confusion here — it reproed in a separate setup unrelated to our main Jest config. My mind blanked.

[gaearon]

This is where I could repro it. https://github.com/facebook/react/tree/master/fixtures/legacy-jsx-runtimes
Run yarn && yarn test in that directory.

[SimenB]

@flozender's repo works (or doesn't... It reproduces the bug, is what I'm trying to say)

[SimenB]

This "fixes" the reproduction

diff --git i/yarn.lock w/yarn.lock
index 3d75ffc..d290b3c 100644
--- i/yarn.lock
+++ w/yarn.lock
@@ -3019,9 +3019,9 @@ source-map-resolve@^0.5.0:
     urix "^0.1.0"

 source-map-support@^0.5.6:
-  version "0.5.19"
-  resolved "https://registry.yarnpkg.com/source-map-support/-/source-map-support-0.5.19.tgz#a98b62f86dcaf4f67399648c085291ab9e8fed61"
-  integrity sha512-Wonm7zOCIJzBGQdB+thsPar0kYuCIzYvxZwlBa87yi/Mdjv7Tip2cyVbLj5o0cFPN4EVkuTwb3GDDyUx2DGnGw==
+  version "0.5.13"
+  resolved "https://registry.yarnpkg.com/source-map-support/-/source-map-support-0.5.13.tgz#31b24a9c2e73c2de85066c0feb7d44767ed52932"
+  integrity sha512-SHSKFHadjVA5oR4PPqhtAVdcBWwRYVd6g6cAXnIbRiIwc2EhPrTuKUBdSLvlEKyIP3GCf89fltvcZiP9MMFA1w==
   dependencies:
     buffer-from "^1.0.0"
     source-map "^0.6.0"

So related to #9147 somehow is my guess

Adding "jest": {"transform": {}} to package.json also "fixes" it, fwiw