fix(core): fix performance of hashing external dependencies up front

packages/nx/src/hasher/__snapshots__/task-hasher.spec.ts.snap

@@ -63,7 +63,7 @@ exports[`TaskHasher hashTarget should hash entire subtree of dependencies 1`] =
     },
     "runtime": {},
   },
-  "value": "17607022607820563118",
+  "value": "14419327228911184578",
 }
 `;
 

packages/nx/src/hasher/task-hasher.ts

@@ -186,9 +186,9 @@ class TaskHasherImpl {
   private runtimeHashes: {
     [runtime: string]: Promise<PartialHash>;
   } = {};
-  private externalDependencyHashes: Map<string, PartialHash> = new Map<
+  private externalDependencyHashes: Map<string, PartialHash[]> = new Map<
     string,
-    PartialHash
+    PartialHash[]
   >();
   private allExternalDependenciesHash: PartialHash;
   private projectRootMappings = createProjectRootMappings(
@@ -416,22 +416,23 @@ class TaskHasherImpl {
   }
 
   private getExternalDependencyHash(externalNodeName: string) {
-    return this.externalDependencyHashes.get(externalNodeName);
+    return this.combinePartialHashes(
+      this.externalDependencyHashes.get(externalNodeName)
+    );
   }
 
   private hashExternalDependency(
     externalNodeName: string,
     visited: Set<string>
-  ): PartialHash {
+  ): PartialHash[] {
     // try to retrieve the hash from cache
     if (this.externalDependencyHashes.has(externalNodeName)) {
       return this.externalDependencyHashes.get(externalNodeName);
     }
     visited.add(externalNodeName);
     const node = this.projectGraph.externalNodes[externalNodeName];
-    let partialHash: PartialHash;
+    const partialHashes: PartialHash[] = [];
     if (node) {
-      const partialHashes: PartialHash[] = [];
       if (node.data.hash) {
         // we already know the hash of this dependency
         partialHashes.push({
@@ -453,25 +454,26 @@ class TaskHasherImpl {
       if (this.projectGraph.dependencies[externalNodeName]) {
         this.projectGraph.dependencies[externalNodeName].forEach((d) => {
           if (!visited.has(d.target)) {
-            partialHashes.push(this.hashExternalDependency(d.target, visited));
+            partialHashes.push(
+              ...this.hashExternalDependency(d.target, visited)
+            );
           }
         });
       }
-      partialHash = this.combinePartialHashes(partialHashes);
     } else {
       // unknown dependency
       // this may occur if dependency is not an npm package
       // but rather symlinked in node_modules or it's pointing to a remote git repo
       // in this case we have no information about the versioning of the given package
-      partialHash = {
+      partialHashes.push({
         value: `__${externalNodeName}__`,
         details: {
           [externalNodeName]: `__${externalNodeName}__`,
         },
-      };
+      });
     }
-    this.externalDependencyHashes.set(externalNodeName, partialHash);
-    return partialHash;
+    this.externalDependencyHashes.set(externalNodeName, partialHashes);
+    return partialHashes;
   }
 
   private hashTarget(