feat(arborist)!: install optional peer dependencies

workspaces/arborist/lib/arborist/build-ideal-tree.js

@@ -1200,23 +1200,21 @@ This is a one-time fix-up, please be patient...
  return false
  }
 
+ // If the edge has no destination, that's a problem
+ if (!edge.to) {
+ return true
+ }
+
  // If it's already been logged as a load failure, skip it.
- if (edge.to && this[_loadFailures].has(edge.to)) {
+ if (this[_loadFailures].has(edge.to)) {
  return false
  }
 
  // If it's shrinkwrapped, we use what the shrinkwap wants.
- if (edge.to && edge.to.inShrinkwrap) {
+ if (edge.to.inShrinkwrap) {
  return false
  }
 
- // If the edge has no destination, that's a problem, unless
- // if it's peerOptional and not explicitly requested.
- if (!edge.to) {
- return edge.type !== 'peerOptional' ||
- this[_explicitRequests].has(edge)
- }
-
  // If the edge has an error, there's a problem.
  if (!edge.valid) {
  return true

workspaces/arborist/lib/place-dep.js

@@ -496,7 +496,27 @@ class PlaceDep {
  }
 
  get conflictOk () {
- return this.force || (!this.isMine && !this.strictPeerDeps)
+ if (this.force) {
+ return true
+ }
+
+ if (!this.isMine && !this.strictPeerDeps) {
+ return true
+ }
+
+ if (this.top.edge.type === 'peerOptional') {
+ return true
+ }
+
+ let fromIsOptional = !!this.top.edge.from.edgesIn.size
+ for (const edgeIn of this.top.edge.from.edgesIn.values()) {
+ if (edgeIn.type !== 'peerOptional') {
+ fromIsOptional = false
+ break
+ }
+ }
+
+ return fromIsOptional
  }
 
  get isMine () {