[BUG] specific diff3 conflict is not parsed

Is there an existing issue for this?

• I have searched the existing issues

This issue exists in the latest npm version

• I am using the latest npm

Current Behavior

When package-lock.json is conflicted, I believe npm has some functionality to automatically resolve the conflicts when you npm install. However, this doesn't work consistently when git is configured to use diff3 conflict markers – here I get a "must provide string spec" error, much like #2117:

$ npm i
npm ERR! must provide string spec

npm ERR! A complete log of this run can be found in: /Users/ah37/.npm/_logs/2023-11-13T16_41_08_559Z-debug-0.log

That log contains the following stack trace:

35 verbose stack TypeError: must provide string spec
35 verbose stack     at new Edge (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/edge.js:68:13)
35 verbose stack     at #loadDepType (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/node.js:896:9)
35 verbose stack     at [Arborist.Node._loadDeps] (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/node.js:874:22)
35 verbose stack     at new Node (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/node.js:260:20)
35 verbose stack     at #loadNode (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/load-virtual.js:261:18)
35 verbose stack     at #resolveNodes (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/load-virtual.js:190:43)
35 verbose stack     at #loadFromShrinkwrap (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/load-virtual.js:90:48)
35 verbose stack     at Arborist.loadVirtual (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/load-virtual.js:63:35)
35 verbose stack     at async Arborist.buildIdealTree (/nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/lib/node_modules/npm/node_modules/@npmcli/arborist/lib/arborist/build-ideal-tree.js:193:7)
35 verbose stack     at async Promise.all (index 1)

Expected Behavior

I'd hoped that npm would be able to understand both regular conflict markers and the (more useful) diff3 markers.

The error can, however, be worked around via git checkout --conflict=merge package-lock.json.

Steps To Reproduce

1. Get into a state where your package-lock.json contains a merge conflict
2. Run git checkout --conflict=diff3 package-lock.json to make sure it uses diff3 markers
3. Run npm i
4. See "must provide string spec" error

Environment

• npm: 9.8.1
• Node.js: 18.18.2
• OS Name: macOS Ventura 13.6.1
• System Model Name: MacBook Pro
• npm config:

; node bin location = /nix/store/fwgfw6i5q1hv49bgfl96bmzv72l98khy-nodejs-18.18.2/bin/node
; node version = v18.18.2
; npm local prefix = /Users/ah37
; npm version = 9.8.1
; cwd = /Users/ah37
; HOME = /Users/ah37
; Run `npm config ls -l` to show all defaults.

Reproduce with a conflicted package-lock.json using git checkout --conflict=diff3, then run npm i; inspect the stack's @npmcli/arborist files, especially lib/edge.js and lib/node.js. Done means npm accepts diff3 conflict markers as well as regular markers without the "must provide string spec" error.