Bring back Graph::sort so we can use it in tests

This reverts commit a26676a

Author: Eh2406

src/cargo/core/resolver/resolve.rs

@@ -171,6 +171,10 @@ unable to verify that `{0}` is the same as when the lockfile was generated
         self.graph.contains(k)
     }
 
+    pub fn sort(&self) -> Vec<PackageId> {
+        self.graph.sort()
+    }
+
     pub fn iter(&self) -> impl Iterator<Item = &PackageId> {
         self.graph.iter()
     }

src/cargo/util/graph.rs

@@ -1,5 +1,5 @@
 use std::borrow::Borrow;
-use std::collections::hash_map::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::fmt;
 use std::hash::Hash;
 
@@ -42,6 +42,30 @@ impl<N: Eq + Hash + Clone, E: Default> Graph<N, E> {
         self.nodes.get(from).into_iter().flat_map(|x| x.iter())
     }
 
+    /// A topological sort of the `Graph`
+    pub fn sort(&self) -> Vec<N> {
+        let mut ret = Vec::new();
+        let mut marks = HashSet::new();
+
+        for node in self.nodes.keys() {
+            self.sort_inner_visit(node, &mut ret, &mut marks);
+        }
+
+        ret
+    }
+
+    fn sort_inner_visit(&self, node: &N, dst: &mut Vec<N>, marks: &mut HashSet<N>) {
+        if !marks.insert(node.clone()) {
+            return;
+        }
+
+        for child in self.nodes[node].keys() {
+            self.sort_inner_visit(child, dst, marks);
+        }
+
+        dst.push(node.clone());
+    }
+
     pub fn iter(&self) -> impl Iterator<Item = &N> {
         self.nodes.keys()
     }

tests/testsuite/support/resolver.rs

@@ -50,7 +50,7 @@ pub fn resolve_and_validated(
             }));
         }
     }
-    let out: Vec<PackageId> = resolve.iter().cloned().collect();
+    let out = resolve.sort();
     assert_eq!(out.len(), used.len());
     Ok(out)
 }
@@ -62,8 +62,7 @@ pub fn resolve_with_config(
     config: Option<&Config>,
 ) -> CargoResult<Vec<PackageId>> {
     let resolve = resolve_with_config_raw(pkg, deps, registry, config)?;
-    let out: Vec<PackageId> = resolve.iter().cloned().collect();
-    Ok(out)
+    Ok(resolve.sort())
 }
 
 pub fn resolve_with_config_raw(