From 0100cdd24496b28212cb2bcda3397db303dc5f49 Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Thu, 13 Dec 2018 04:50:08 -0500
Subject: [PATCH] More comment on the plugin dependency stuff.

---
 .../proxy/plugin/VelocityPluginManager.java           |  6 ++++++
 .../proxy/plugin/util/PluginDependencyUtils.java      | 11 ++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java b/proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java
index 83e9b69bd..02f3391d2 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java
@@ -17,6 +17,7 @@ import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.Comparator;
 import java.util.HashMap;
 import java.util.IdentityHashMap;
 import java.util.List;
@@ -68,6 +69,11 @@ public class VelocityPluginManager implements PluginManager {
       return;
     }
 
+    // Sort the loaded plugins twice. First, sort the already-loaded plugins by their IDs, so as
+    // to make the topographic sort deterministic (since the order will differ depending on the
+    // first node chosen in the graph, which is the first plugin we found). Afterwards, we execute
+    // a depth-first search over the loaded plugins.
+    found.sort(Comparator.comparing(PluginDescription::getId));
     List<PluginDescription> sortedPlugins = PluginDependencyUtils.sortCandidates(found);
 
     // Now load the plugins
diff --git a/proxy/src/main/java/com/velocitypowered/proxy/plugin/util/PluginDependencyUtils.java b/proxy/src/main/java/com/velocitypowered/proxy/plugin/util/PluginDependencyUtils.java
index 93c5b341d..5fb735afb 100644
--- a/proxy/src/main/java/com/velocitypowered/proxy/plugin/util/PluginDependencyUtils.java
+++ b/proxy/src/main/java/com/velocitypowered/proxy/plugin/util/PluginDependencyUtils.java
@@ -26,12 +26,16 @@ public class PluginDependencyUtils {
    * @throws IllegalStateException if there is a circular loop in the dependency graph
    */
   public static List<PluginDescription> sortCandidates(List<PluginDescription> candidates) {
-    // Create our graph, we're going to be using this for Kahn's algorithm.
-    MutableGraph<PluginDescription> graph = GraphBuilder.directed().allowsSelfLoops(false).build();
+    // Create a graph and populate it with plugin dependencies. Specifically, each graph has plugin
+    // nodes, and edges that represent the dependencies that plugin relies on. Non-existent plugins
+    // are ignored.
+    MutableGraph<PluginDescription> graph = GraphBuilder.directed()
+        .allowsSelfLoops(false)
+        .expectedNodeCount(candidates.size())
+        .build();
     Map<String, PluginDescription> candidateMap = Maps
         .uniqueIndex(candidates, d -> d == null ? null : d.getId());
 
-    // Add edges
     for (PluginDescription description : candidates) {
       graph.addNode(description);
 
@@ -44,6 +48,7 @@ public class PluginDependencyUtils {
       }
     }
 
+    // Now we do the depth-first search.
     List<PluginDescription> sorted = new ArrayList<>();
     Map<PluginDescription, Mark> marks = new HashMap<>();