change the priority in witch we build crates

[Eh2406]

On my windows 4 core, this made clean builds (of 3596cb8) go from 257-223s to 210-205s. So that looks like an improvement.

[rust-highfive]

r? @nrc

(rust_highfive has picked a reviewer for you, use r? to override)

[alexcrichton]

Instead of assert_ne could this change to just asserting that the set is nonempty?

[alexcrichton]

I think the .into_iter here can be elided

[alexcrichton]

Could this perhaps avoid .clone() by returning &HashSet<N> inside the HashMap itself?

[alexcrichton]

as in, depth returns a &HashSet<N>

[Eh2406]

WIth witch lifetime? I tried 'results, but it did not go well. Is there something else worth trying? Is it worth Rc<HashSet<N>>?

[alexcrichton]

I was thinking of a diff like:

diff --git a/src/cargo/util/dependency_queue.rs b/src/cargo/util/dependency_queue.rs
index 21886c0ee..946549507 100644
--- a/src/cargo/util/dependency_queue.rs
+++ b/src/cargo/util/dependency_queue.rs
@@ -88,14 +88,15 @@ impl<N: Hash + Eq + Clone, E: Eq + Hash + Clone, V> DependencyQueue<N, E, V> {
         }
         self.priority = out.into_iter().map(|(n, set)| (n, set.len())).collect();
 
-        fn depth<N: Hash + Eq + Clone, E: Hash + Eq + Clone>(
+        fn depth<'a, N: Hash + Eq + Clone, E: Hash + Eq + Clone>(
             key: &N,
             map: &HashMap<N, HashMap<E, HashSet<N>>>,
-            results: &mut HashMap<N, HashSet<N>>,
-        ) -> HashSet<N> {
-            if let Some(depth) = results.get(key) {
+            results: &'a mut HashMap<N, HashSet<N>>,
+        ) -> &'a HashSet<N> {
+            if results.contains_key(key) {
+                let depth = &results[key];
                 assert!(!depth.is_empty(), "cycle in DependencyQueue");
-                return depth.clone();
+                return depth;
             }
             results.insert(key.clone(), HashSet::new());
 
@@ -108,12 +109,12 @@ impl<N: Hash + Eq + Clone, E: Eq + Hash + Clone, V> DependencyQueue<N, E, V> {
                 .flat_map(|it| it.values())
                 .flat_map(|set| set)
             {
-                set.extend(depth(dep, map, results))
+                set.extend(depth(dep, map, results).iter().cloned())
             }
 
-            *results.get_mut(key).unwrap() = set.clone();
-
-            set
+            let slot = results.get_mut(key).unwrap();
+            *slot = set;
+            return &*slot;
         }
     }

if that feels to complicated though it's definitely too minor to use Rc, so we can just go w/ what's here as-is.

[Eh2406]

You are a wizard! Hat's off!

[alexcrichton]

@bors: r+

[bors]

📌 Commit 384056e has been approved by alexcrichton

[bors]

⌛ Testing commit 384056e with merge b6c6f68...

[bors]

☀️ Test successful - checks-azure
Approved by: alexcrichton
Pushing b6c6f68 to master...