[BUG] ERESOLVE peer dep conflict reported when no conflict exists

[ljharb]

Current Behavior:

in eslint-plugin-react's repo, on master, i ran npx npm@7 install --save-dev @types/eslint @types/node eslint-plugin-eslint-plugin@3 semver sinon typescript typescript-eslint-parser.

I got https://gist.github.com/ljharb/dc643e6f094d5dfc912633a5e55637ab as output. Note:

npm ERR! Conflicting peer dependency: eslint@7.24.0
npm ERR! node_modules/eslint
npm ERR!   peer eslint@"^7.0.0" from eslint-plugin-eslint-plugin@3.0.2

Expected Behavior:

It should have installed and saved these dev deps. ^7.0.0 is compatible with v7.24.0.

Steps To Reproduce:

Clone the repo, run npm install, then run the above command.

Environment:

• OS: Mac
• Node: 15.14.0
• npm: 7.11.0 and v7.10.0

(this does _ not_ appear to be the same issue as #3113 or #2823)

[darcyclarke]

@ljharb can you reproduce on latest? (ie. 7.17.0) I know we've made numerous changes/bug fixes since 7.10.0

[ljharb]

@darcyclarke yes, i can reproduce it on latest npm:

code ERESOLVE
ERESOLVE unable to resolve dependency tree

Found: eslint-plugin-eslint-plugin@2.3.0
node_modules/eslint-plugin-eslint-plugin
  dev eslint-plugin-eslint-plugin@"3" from the root project

Could not resolve dependency:
dev eslint-plugin-eslint-plugin@"3" from the root project

Conflicting peer dependency: eslint@7.28.0
node_modules/eslint
  peer eslint@"^7.0.0" from eslint-plugin-eslint-plugin@3.0.3
  node_modules/eslint-plugin-eslint-plugin
    dev eslint-plugin-eslint-plugin@"3" from the root project

`eresolve-report.txt`:

# npm resolution error report

2021-06-12T07:00:59.767Z

Found: eslint-plugin-eslint-plugin@2.3.0
node_modules/eslint-plugin-eslint-plugin
  dev eslint-plugin-eslint-plugin@"3" from the root project

Could not resolve dependency:
dev eslint-plugin-eslint-plugin@"3" from the root project

Conflicting peer dependency: eslint@7.28.0
node_modules/eslint
  peer eslint@"^7.0.0" from eslint-plugin-eslint-plugin@3.0.3
  node_modules/eslint-plugin-eslint-plugin
    dev eslint-plugin-eslint-plugin@"3" from the root project

Fix the upstream dependency conflict, or retry
this command with --force, or --legacy-peer-deps
to accept an incorrect (and potentially broken) dependency resolution.

Raw JSON explanation object:

{
  "code": "ERESOLVE",
  "current": {
    "name": "eslint-plugin-eslint-plugin",
    "version": "2.3.0",
    "location": "node_modules/eslint-plugin-eslint-plugin",
    "isWorkspace": false,
    "dependents": [
      {
        "type": "dev",
        "name": "eslint-plugin-eslint-plugin",
        "spec": "3",
        "error": "INVALID",
        "from": {
          "location": "$PWD"
        }
      }
    ]
  },
  "currentEdge": null,
  "edge": {
    "type": "dev",
    "name": "eslint-plugin-eslint-plugin",
    "spec": "3",
    "error": "INVALID",
    "from": {
      "location": "$PWD"
    }
  },
  "peerConflict": {
    "name": "eslint",
    "version": "7.28.0",
    "whileInstalling": {
      "name": "eslint-plugin-react",
      "version": "7.24.0",
      "path": "$PWD"
    },
    "location": "node_modules/eslint",
    "isWorkspace": false,
    "dependents": [
      {
        "type": "peer",
        "name": "eslint",
        "spec": "^7.0.0",
        "from": {
          "name": "eslint-plugin-eslint-plugin",
          "version": "3.0.3",
          "whileInstalling": {
            "name": "eslint-plugin-react",
            "version": "7.24.0",
            "path": "$PWD"
          },
          "location": "node_modules/eslint-plugin-eslint-plugin",
          "isWorkspace": false,
          "dependents": [
            {
              "type": "dev",
              "name": "eslint-plugin-eslint-plugin",
              "spec": "3",
              "from": {
                "location": "$PWD"
              }
            }
          ]
        }
      }
    ]
  },
  "strictPeerDeps": false,
  "force": false
}

[isaacs]

This is a reporting error.

$ npm view @typescript-eslint/parser@"^2.34.0" peerDependencies
{ eslint: '^5.0.0 || ^6.0.0' }

$ npm view eslint-plugin-eslint-plugin@3 peerDependencies
eslint-plugin-eslint-plugin@3.0.0 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.0.1 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.0.2 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.0.3 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.1.0 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.2.0 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.3.0 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.4.0 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.5.0 { eslint: '^7.0.0' }
eslint-plugin-eslint-plugin@3.5.1 { eslint: '^7.0.0' }

You're trying to use @typescript-eslint/parser@"^2.34.0" alongside eslint-plugin-eslint-plugin@3, but these two have incompatible peer deps.

So the ERESOLVE is the correct outcome, but the reporting here leaves much to be desired.

I'm in the midst of upgrading the cli to @npmcli/arborist@2.8.0, and the report got even more broken. 😅 So I'm going to dig into that now.

[isaacs]

Ok, the error was easy to work around. Caused by the ERESOLVE explanations getting a bit more useful in arborist 2.8, ironically enough, but no longer squishing a direct conflict in with the extended peerDep conflict, which was losing some information.

Fixed report looks like this, and I'm going to call this a by-design crash, with a reporting error that'll be fixed on the next release:

$ npm i --save-dev @types/eslint @types/node eslint-plugin-eslint-plugin@3 semver sinon typescript typescript-eslint-parser
npm ERR! code ERESOLVE
npm ERR! ERESOLVE could not resolve
npm ERR!
npm ERR! While resolving: eslint-plugin-react@7.24.0
npm ERR! Found: eslint@6.8.0
npm ERR! node_modules/eslint
npm ERR!   dev eslint@"^3 || ^4 || ^5 || ^6 || ^7" from the root project
npm ERR!   peer eslint@"^5.0.0 || ^6.0.0" from @typescript-eslint/parser@2.34.0
npm ERR!   node_modules/@typescript-eslint/parser
npm ERR!     dev @typescript-eslint/parser@"^2.34.0" from the root project
npm ERR!   2 more (eslint-config-airbnb-base, eslint-plugin-import)
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! dev eslint-plugin-eslint-plugin@"3" from the root project
npm ERR!
npm ERR! Conflicting peer dependency: eslint@7.31.0
npm ERR! node_modules/eslint
npm ERR!   peer eslint@"^7.0.0" from eslint-plugin-eslint-plugin@3.5.1
npm ERR!   node_modules/eslint-plugin-eslint-plugin
npm ERR!     dev eslint-plugin-eslint-plugin@"3" from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
npm ERR!
npm ERR! See /Users/isaacs/.npm/eresolve-report.txt for a full report.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/isaacs/.npm/_logs/2021-07-27T23_10_48_034Z-debug.log

[ljharb]

I see the conflict, thanks.