Allow --force to override conflicted peerOptional

With a dependency graph like this:

```
root -> (a, b@1)
a -> PEEROPTIONAL(b@2)
```

We do not install the peerOptional dependency by default, so even though
`b@2` is included in the peerSet of `a`, it is not added to the tree.

Then, the `b@1` dependency is added to satisfy root's direct dependency
on it, causing the `a -> b@2` edge to become invalid.

We then try to resolve the `a -> b@2` edge, and find that we cannot
place it anywhere, causing an `ERESOLVE` error.

However, because `b@2` is no longer a part of a peerSet sourced on the
`root` node, we miss the chance to detect that it should be overridden,
resulting in an `ERESOLVE` failure even when `--force` is used.

This commit adds the check for `this[_force]` prior to crashing with
ERESOLVE, so that cases that avoid our earlier heuristics still accept
the invalid resolution when `--force` is in effect.

Fix: #226
Fix: npm/cli#2504

lib/arborist/build-ideal-tree.js

@@ -805,6 +805,7 @@ This is a one-time fix-up, please be patient...
       // a virtual root of whatever brought in THIS node.
       // so we VR the node itself if the edge is not a peer
       const source = edge.peer ? peerSource : node
+
       const virtualRoot = this[_virtualRoot](source, true)
       // reuse virtual root if we already have one, but don't
       // try to do the override ahead of time, since we MAY be able
@@ -826,8 +827,7 @@ This is a one-time fix-up, please be patient...
       // +-- z@1
       // But if x and y are loaded in the same virtual root, then they will
       // be forced to agree on a version of z.
-      const required = edge.type === 'peerOptional' ? new Set()
-        : new Set([edge.from])
+      const required = new Set([edge.from])
       const parent = edge.peer ? virtualRoot : null
       const dep = vrDep && vrDep.satisfies(edge) ? vrDep
         : await this[_nodeFromEdge](edge, parent, null, required)
@@ -1217,8 +1217,25 @@ This is a one-time fix-up, please be patient...
         break
     }
 
-    if (!target)
-      this[_failPeerConflict](edge)
+    // if we can't find a target, that means that the last placed checked
+    // (and all the places before it) had a copy already.  if we're in
+    // --force mode, then the user has explicitly said that they're ok
+    // with conflicts.  This can only occur in --force mode in the case
+    // when a node was added to the tree with a peerOptional dep that we
+    // ignored, and then later, that edge became invalid, and we fail to
+    // resolve it.  We will warn about it in a moment.
+    if (!target) {
+      if (this[_force]) {
+        // we know that there is a dep (not the root) which is the target
+        // of this edge, or else it wouldn't have been a conflict.
+        target = edge.to.resolveParent
+        canPlace = KEEP
+      } else
+        this[_failPeerConflict](edge)
+    } else {
+      // it worked, so we clearly have no peer conflicts at this point.
+      this[_peerConflict] = null
+    }
 
     this.log.silly(
       'placeDep',
@@ -1229,9 +1246,6 @@ This is a one-time fix-up, please be patient...
       `want: ${edge.spec || '*'}`
     )
 
-    // it worked, so we clearly have no peer conflicts at this point.
-    this[_peerConflict] = null
-
     // Can only get KEEP here if the original edge was valid,
     // and we're checking for an update but it's already up to date.
     if (canPlace === KEEP) {
@@ -1417,6 +1431,7 @@ This is a one-time fix-up, please be patient...
     })
     const entryEdge = peerEntryEdge || edge
     const source = this[_peerSetSource].get(dep)
+
     isSource = isSource || target === source
     // if we're overriding the source, then we care if the *target* is
     // ours, even if it wasn't actually the original source, since we

test/arborist/build-ideal-tree.js

@@ -1545,6 +1545,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: true,
     },
+
     'prod dep directly on conflicted peer, older': {
       pkg: {
         dependencies: {
@@ -1554,6 +1555,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: true,
     },
+
     'prod dep directly on conflicted peer, full peer set, newer': {
       pkg: {
         dependencies: {
@@ -1566,6 +1568,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: true,
     },
+
     'prod dep directly on conflicted peer, full peer set, older': {
       pkg: {
         dependencies: {
@@ -1578,6 +1581,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: true,
     },
+
     'prod dep directly on conflicted peer, meta peer set, older': {
       pkg: {
         dependencies: {
@@ -1589,6 +1593,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: true,
     },
+
     'dep indirectly on conflicted peer': {
       pkg: {
         dependencies: {
@@ -1598,6 +1603,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: true,
     },
+
     'collision forcing duplication, order 1': {
       pkg: {
         dependencies: {
@@ -1608,6 +1614,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'collision forcing duplication, order 2': {
       pkg: {
         dependencies: {
@@ -1618,6 +1625,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'collision forcing duplication via add, order 1': {
       pkg: {
         dependencies: {
@@ -1628,6 +1636,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'collision forcing duplication via add, order 2': {
       pkg: {
         dependencies: {
@@ -1638,6 +1647,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'collision forcing metadep duplication, order 1': {
       pkg: {
         dependencies: {
@@ -1648,6 +1658,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'collision forcing metadep duplication, order 2': {
       pkg: {
         dependencies: {
@@ -1658,6 +1669,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'direct collision forcing metadep duplication, order 1': {
       pkg: {
         dependencies: {
@@ -1668,6 +1680,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'direct collision forcing metadep duplication, order 2': {
       pkg: {
         dependencies: {
@@ -1678,6 +1691,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: true,
     },
+
     'dep with conflicting peers': {
       pkg: {
         dependencies: {
@@ -1688,6 +1702,7 @@ t.test('more peer dep conflicts', t => {
       // but it is a conflict in a peerSet that the root is sourcing.
       error: true,
     },
+
     'metadeps with conflicting peers': {
       pkg: {
         dependencies: {
@@ -1696,6 +1711,7 @@ t.test('more peer dep conflicts', t => {
       },
       error: false,
     },
+
     'metadep conflict that warns because source is target': {
       pkg: {
         dependencies: {
@@ -1706,6 +1722,7 @@ t.test('more peer dep conflicts', t => {
       error: false,
       resolvable: false,
     },
+
     'metadep conflict triggering the peerConflict code path': {
       pkg: {
         dependencies: {
@@ -1717,6 +1734,7 @@ t.test('more peer dep conflicts', t => {
       resolvable: false,
     },
   })
+
   t.jobs = cases.length
   t.plan(cases.length)
 
@@ -2468,3 +2486,90 @@ t.test('do not ERESOLVE on peerOptionals that are ignored anyway', t => {
     })
   }
 })
+
+t.test('allow ERESOLVE to be forced when not in the source', async t => {
+  const types = [
+    'peerDependencies',
+    'optionalDependencies',
+    'devDependencies',
+    'dependencies',
+  ]
+
+  // in these tests, the deps are both of the same type.  b has a peerOptional
+  // dep on peer, and peer is a direct dependency of the root.
+  t.test('both direct and peer of the same type', t => {
+    t.plan(types.length)
+    const pj = type => ({
+      name: '@isaacs/conflicted-peer-optional-from-dev-dep',
+      version: '1.2.3',
+      [type]: {
+        '@isaacs/conflicted-peer-optional-from-dev-dep-peer': '1',
+        '@isaacs/conflicted-peer-optional-from-dev-dep-b': '',
+      },
+    })
+
+    for (const type of types) {
+      t.test(type, async t => {
+        const path = t.testdir({
+          'package.json': JSON.stringify(pj(type)),
+        })
+        t.matchSnapshot(await printIdeal(path, { force: true }), 'use the force')
+        t.rejects(printIdeal(path), { code: 'ERESOLVE' }, 'no force')
+      })
+    }
+  })
+
+  // in these, the peer is a peer dep of the root, and b is a different type
+  t.test('peer is peer, b is some other type', t => {
+    t.plan(types.length - 1)
+    const pj = type => ({
+      name: '@isaacs/conflicted-peer-optional-from-dev-dep',
+      version: '1.2.3',
+      peerDependencies: {
+        '@isaacs/conflicted-peer-optional-from-dev-dep-b': '',
+      },
+      [type]: {
+        '@isaacs/conflicted-peer-optional-from-dev-dep-peer': '1',
+      },
+    })
+    for (const type of types) {
+      if (type === 'peerDependencies')
+        continue
+      t.test(type, async t => {
+        const path = t.testdir({
+          'package.json': JSON.stringify(pj(type)),
+        })
+        t.matchSnapshot(await printIdeal(path, { force: true }), 'use the force')
+        t.rejects(printIdeal(path), { code: 'ERESOLVE' }, 'no force')
+      })
+    }
+  })
+
+  // in these, b is a peer dep, and peer is some other type
+  t.test('peer is peer, b is some other type', t => {
+    t.plan(types.length - 1)
+    const pj = type => ({
+      name: '@isaacs/conflicted-peer-optional-from-dev-dep',
+      version: '1.2.3',
+      peerDependencies: {
+        '@isaacs/conflicted-peer-optional-from-dev-dep-peer': '1',
+      },
+      [type]: {
+        '@isaacs/conflicted-peer-optional-from-dev-dep-b': '',
+      },
+    })
+    for (const type of types) {
+      if (type === 'peerDependencies')
+        continue
+      t.test(type, async t => {
+        const path = t.testdir({
+          'package.json': JSON.stringify(pj(type)),
+        })
+        t.matchSnapshot(await printIdeal(path, { force: true }), 'use the force')
+        t.rejects(printIdeal(path), { code: 'ERESOLVE' }, 'no force')
+      })
+    }
+  })
+
+  t.end()
+})

test/fixtures/conflicted-peer-optional-from-dev-dep/b/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "@isaacs/conflicted-peer-optional-from-dev-dep-b",
+  "version": "1.0.0",
+  "peerDependencies": {
+    "@isaacs/conflicted-peer-optional-from-dev-dep-peer": "2"
+  },
+  "peerDependenciesMeta": {
+    "@isaacs/conflicted-peer-optional-from-dev-dep-peer": {
+      "optional": true
+    }
+  }
+}

test/fixtures/conflicted-peer-optional-from-dev-dep/peer/1/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "@isaacs/conflicted-peer-optional-from-dev-dep-peer",
+  "version": "1.0.0"
+}

test/fixtures/conflicted-peer-optional-from-dev-dep/peer/2/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "@isaacs/conflicted-peer-optional-from-dev-dep-peer",
+  "version": "2.0.0"
+}

test/fixtures/registry-mocks/content/isaacs/conflicted-peer-optional-from-dev-dep-b.json

@@ -0,0 +1,61 @@
+{
+  "_id": "@isaacs/conflicted-peer-optional-from-dev-dep-b",
+  "name": "@isaacs/conflicted-peer-optional-from-dev-dep-b",
+  "dist-tags": {
+    "latest": "1.0.0"
+  },
+  "versions": {
+    "1.0.0": {
+      "name": "@isaacs/conflicted-peer-optional-from-dev-dep-b",
+      "version": "1.0.0",
+      "peerDependencies": {
+        "@isaacs/conflicted-peer-optional-from-dev-dep-peer": "2"
+      },
+      "peerDependenciesMeta": {
+        "@isaacs/conflicted-peer-optional-from-dev-dep-peer": {
+          "optional": true
+        }
+      },
+      "_id": "@isaacs/conflicted-peer-optional-from-dev-dep-b@1.0.0",
+      "_nodeVersion": "15.3.0",
+      "_npmVersion": "7.5.3",
+      "dist": {
+        "integrity": "sha512-2rStqBkn1QSXBjweS4lHUPH9jt4ToFqkw2nUbWA4fZBxOaYS1nkS/ST70xRlQxRW+3UdTFGc+5xk187sHlMT/A==",
+        "shasum": "63f188dba7ec8a3e23b09540230ba8014ee760d2",
+        "tarball": "https://registry.npmjs.org/@isaacs/conflicted-peer-optional-from-dev-dep-b/-/conflicted-peer-optional-from-dev-dep-b-1.0.0.tgz",
+        "fileCount": 1,
+        "unpackedSize": 299,
+        "npm-signature": "-----BEGIN PGP SIGNATURE-----\r\nVersion: OpenPGP.js v3.0.13\r\nComment: https://openpgpjs.org\r\n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\nHGT/\r\n=wnoR\r\n-----END PGP SIGNATURE-----\r\n"
+      },
+      "_npmUser": {
+        "name": "isaacs",
+        "email": "i@izs.me"
+      },
+      "directories": {},
+      "maintainers": [
+        {
+          "name": "isaacs",
+          "email": "i@izs.me"
+        }
+      ],
+      "_npmOperationalInternal": {
+        "host": "s3://npm-registry-packages",
+        "tmp": "tmp/conflicted-peer-optional-from-dev-dep-b_1.0.0_1613008191679_0.24514239505031288"
+      },
+      "_hasShrinkwrap": false
+    }
+  },
+  "time": {
+    "created": "2021-02-11T01:49:51.620Z",
+    "1.0.0": "2021-02-11T01:49:51.832Z",
+    "modified": "2021-02-11T01:49:54.757Z"
+  },
+  "maintainers": [
+    {
+      "name": "isaacs",
+      "email": "i@izs.me"
+    }
+  ],
+  "readme": "ERROR: No README data found!",
+  "readmeFilename": ""
+}