From 3d1b950e85b9d668d830bca68f5ab154a6f06aee Mon Sep 17 00:00:00 2001
From: Phlosioneer <mattmdrr2@gmail.com>
Date: Sun, 1 Apr 2018 06:08:40 -0400
Subject: [PATCH] Implement size_hint for some iterators

This PR implements size_hints for Deps, DepsNotReplaced, and Members.
These size_hints are used extensively by cargo to allocate Vecs.

Deps, DepsNotReplaced, and RcVecIter also now implement ExactSizeIterator.
---
 src/cargo/core/resolver/resolve.rs | 22 ++++++++++++++++++++++
 src/cargo/core/workspace.rs        |  5 +++++
 2 files changed, 27 insertions(+)

diff --git a/src/cargo/core/resolver/resolve.rs b/src/cargo/core/resolver/resolve.rs
index 08805eba2..73d30b159 100644
--- a/src/cargo/core/resolver/resolve.rs
+++ b/src/cargo/core/resolver/resolve.rs
@@ -203,8 +203,19 @@ impl<'a> Iterator for Deps<'a> {
             .and_then(|e| e.next())
             .map(|id| self.resolve.replacement(id).unwrap_or(id))
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self.edges {
+            // Note: Edges is actually a std::collections::hash_set::Iter, which
+            // is an ExactSizeIterator.
+            Some(ref iter) => iter.size_hint(),
+            None => (0, Some(0))
+        }
+    }
 }
 
+impl<'a> ExactSizeIterator for Deps<'a> {}
+
 pub struct DepsNotReplaced<'a> {
     edges: Option<Edges<'a, PackageId>>,
 }
@@ -215,4 +226,15 @@ impl<'a> Iterator for DepsNotReplaced<'a> {
     fn next(&mut self) -> Option<&'a PackageId> {
         self.edges.as_mut().and_then(|e| e.next())
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        match self.edges {
+            // Note: Edges is actually a std::collections::hash_set::Iter, which
+            // is an ExactSizeIterator.
+            Some(ref iter) => iter.size_hint(),
+            None => (0, Some(0))
+        }
+    }
 }
+
+impl<'a> ExactSizeIterator for DepsNotReplaced<'a> {}
diff --git a/src/cargo/core/workspace.rs b/src/cargo/core/workspace.rs
index 9377b185c..0c20f63e6 100644
--- a/src/cargo/core/workspace.rs
+++ b/src/cargo/core/workspace.rs
@@ -776,6 +776,11 @@ impl<'a, 'cfg> Iterator for Members<'a, 'cfg> {
             }
         }
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.iter.size_hint();
+        (0, upper)
+    }
 }
 
 impl MaybePackage {
-- 
2.30.2