I also found that falsy causes are not inspected, but that can be fixed in a separate PR.

@targos how would you handle undefined and null? I would at least skip those?

I would always inspect if Object.hasOwn(err, 'cause') === true with no exception.

@targos I added another commit to also inspect falsy values besides undefined. Undefined is used in argument default values as "does not exist" and I would handle it here identically.

@targos I added another commit to also inspect falsy values besides undefined. Undefined is used in argument default values as "does not exist" and I would handle it here identically.

Okay, I don't have a strong opinion, but new Error('message', { cause: undefined }) creates the property while just new Error('message') doesn't.

CI: https://ci.nodejs.org/job/node-test-pull-request/41399/

@nodejs/util PTAL. This should ideally land before the next release.

- Loading data for nodejs/node/pull/41097
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----------------------------------- PR info ------------------------------------
Title      util: make sure error causes of any type may be inspected (#41097)
Author     Ruben Bridgewater  (@BridgeAR)
Branch     BridgeAR:fix-non-error-cause-inspection -> nodejs:master
Labels     util, author ready, needs-ci
Commits    2
 - util: make sure error causes of any type may be inspected
 - util: serialize falsy cause values while inspecting errors
Committers 1
 - Ruben Bridgewater 
PR-URL: https://github.com/nodejs/node/pull/41097
Fixes: https://github.com/nodejs/node/issues/41096
Reviewed-By: Michaël Zasso 
Reviewed-By: James M Snell 
------------------------------ Generated metadata ------------------------------
PR-URL: https://github.com/nodejs/node/pull/41097
Fixes: https://github.com/nodejs/node/issues/41096
Reviewed-By: Michaël Zasso 
Reviewed-By: James M Snell 
--------------------------------------------------------------------------------
   ℹ  This PR was created on Mon, 06 Dec 2021 13:34:46 GMT
   ✔  Approvals: 2
   ✔  - Michaël Zasso (@targos) (TSC): https://github.com/nodejs/node/pull/41097#pullrequestreview-824046654
   ✔  - James M Snell (@jasnell) (TSC): https://github.com/nodejs/node/pull/41097#pullrequestreview-826822688
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   ℹ  Last Full PR CI on 2021-12-07T19:10:46Z: https://ci.nodejs.org/job/node-test-pull-request/41399/
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Auto-merging lib/internal/util/inspect.js
[master 12b79bd4f5] util: make sure error causes of any type may be inspected
 Author: Ruben Bridgewater 
 Date: Mon Dec 6 14:22:30 2021 +0100
 3 files changed, 39 insertions(+), 1 deletion(-)
Auto-merging lib/internal/util/inspect.js
Auto-merging test/parallel/test-util-inspect.js
[master 1272d9fe5a] util: serialize falsy cause values while inspecting errors
 Author: Ruben Bridgewater 
 Date: Mon Dec 6 15:25:42 2021 +0100
 2 files changed, 12 insertions(+), 1 deletion(-)
   ✔  Patches applied
There are 2 commits in the PR. Attempting autorebase.
Rebasing (2/4)
Executing: git node land --amend --yes

⚠  Found Fixes: #41096, skipping..

--------------------------------- New Message ----------------------------------

util: make sure error causes of any type may be inspected
An error cause may be of any type. Handle all of them, no matter

if they are an error or not.
Fixes: #41096
Signed-off-by: Ruben Bridgewater ruben@bridgewater.de
PR-URL: #41097

Reviewed-By: Michaël Zasso targos@protonmail.com

Reviewed-By: James M Snell jasnell@gmail.com
[detached HEAD b95b3f5eb4] util: make sure error causes of any type may be inspected

Author: Ruben Bridgewater ruben@bridgewater.de

Date: Mon Dec 6 14:22:30 2021 +0100

3 files changed, 39 insertions(+), 1 deletion(-)

Rebasing (3/4)

Rebasing (4/4)
Executing: git node land --amend --yes

--------------------------------- New Message ----------------------------------

util: serialize falsy cause values while inspecting errors
Signed-off-by: Ruben Bridgewater ruben@bridgewater.de
PR-URL: #41097

Fixes: #41096

Reviewed-By: Michaël Zasso targos@protonmail.com

Reviewed-By: James M Snell jasnell@gmail.com
[detached HEAD 3d14b8d6bb] util: serialize falsy cause values while inspecting errors

Author: Ruben Bridgewater ruben@bridgewater.de

Date: Mon Dec 6 15:25:42 2021 +0100

2 files changed, 12 insertions(+), 1 deletion(-)
Successfully rebased and updated refs/heads/master.
ℹ  Use --fixupAll option, squash the PR manually or land the PR from the command line.

@BridgeAR this didn't land cleanly into the release, can you backport this to v17.x-staging?

@danielleadams this should land cleanly on top of #41002.

@BridgeAR the spec for error cause very intentionally differentiates between an absent property, and a present undefined, so it's critically important that util.inspect differentiate between these two.

@ljharb I am fine if you like to also visualize an undefined cause. Please feel free to open another PR.