[BUG] 'npm update' results in unclear error on peer-dep mismatch

[KilianKilmister]

Companion issue posted in arborist

Current Behavior:

npm update results in arborist thowing an Error on mismatched peer-dep

the resulting error message doesn't point at what caused the error:

npm ERR! code ERESOLVE
npm ERR! unable to resolve dependency tree

npm ERR! A complete log of this run can be found in:
npm ERR! /Users/kilianhefti/.npm/_logs/2020-08-16T01_03_09_094Z-debug.log
Waiting for the debugger to disconnect...

Expected Behavior:

Concise error message (and a way of strong-arming a match as no dev-/preview/-whatever-version will ever be compatible) RRFC about current peer-dep behaviour

Steps To Reproduce:

have unmatched peer-dep (eg. ts-node and typescript@4.0.0-dev)

Environment:

final log entries: dist, node-v and npm-v are highlited

1001 timing command:update Completed in 20505ms
1002 verbose type peer
1003 verbose stack Error: unable to resolve dependency tree
1003 verbose stack at Arborist.[placeDep] (/Users/kilianhefti/.npm-packages/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:771:27)
1003 verbose stack at /Users/kilianhefti/.npm-packages/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:588:46
1003 verbose stack at Array.map ()
1003 verbose stack at Arborist.[buildDepStep] (/Users/kilianhefti/.npm-packages/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:588:8)
1003 verbose stack at async Arborist.buildIdealTree (/Users/kilianhefti/.npm-packages/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:160:7)
1003 verbose stack at async Promise.all (index 1)
1003 verbose stack at async Arborist.reify (/Users/kilianhefti/.npm-packages/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/reify.js:126:5)
1003 verbose stack at async update (/Users/kilianhefti/.npm-packages/lib/node_modules/npm/lib/update.js:34:3)
1004 verbose cwd /Users/kilianhefti/dev/cmd-repo
1005 verbose Darwin 19.6.0
1006 verbose argv "/usr/local/bin/node" "/Users/kilianhefti/.npm-packages/bin/npm" "update"
1007 verbose node v14.8.0
1008 verbose npm v7.0.0-beta.4
1009 error code ERESOLVE
1010 error unable to resolve dependency tree
1011 verbose exit [ 1, true ]

Note

I will file a propper RFC about strong-arming the peer-dep stuff (Link to come)
RRFC about current peer-dep behaviour
But having had to debug dependency resolution to discover the issue, I have to say, there is some real nice code in the npm-repos. well commented, clean, smart. v7 is looking good.
And i've been experimenting with npm-workspaces: the linking works like a charm and everything looks really clean. there should be some beta documentation on them tho. i only descovered that it was working while i debugged Arborists tree-building.

[ruyadorno]

hi @KilianKilmister thanks for taking the time to report 😊 as you have been following along the story around peer dependencies has been evolving a lot and quite quickly during the beta period, since you reported this the ERESOLVE has been expanded to contain a human-readable explanation for the conflict and with this week's pre-release (v7.0.0-beta.12) we flipped the switch and the default behavior for npm install is to be more resilient and only WARN in cases where the install tree can still be constructed (the previous more strict behavior is now behind a --strict-peer-deps flag).

We would love to see more feedback and bug reports if you get some time to give it another try to the beta. Thanks again for all the help!

[KilianKilmister]

@ruyadorno Apologies on the late reply, I've been having way too much on my plate. While i did read it just after i got the notification, writing the reply got drowned out by other things.

I did update npm right after you posted the reply and it works as advertised.
I've been using the beta as my main npm-client (updating at each prerelease) since it was opened and i must say i'm very happy with both its initial state and the in-beta progress. v7 adresses many of the criticisms i had of npm as a tool and the new features have new allowed me to use mono-repos as the prefered structure for new projects. With this change, the last major problem i had with v7 has now been solved aswell.

I invested a lot of work on the topic of peer-deps over at the RFC repo in the weeks after i opened this issue and after a last minute removal from the task list of an openRFC meeting and not Having gotten a reply on the followup of that, I was sure that my efforts have been in vain.
I am really, really glad that parts of it seem to have stuck around non-the-less and i was very relieved when i saw this change.

Thanks a lot.