From a616acac9e93c0633a77f3f83328e95c0a88ba1b Mon Sep 17 00:00:00 2001
From: Joakim Erdfelt <joakim.erdfelt@gmail.com>
Date: Wed, 12 Jun 2024 13:21:56 -0500
Subject: [PATCH] Issue #11909 - duplicate --modules=<name> can trigger
 ConcurrentModificationException

+ Reworked tracking of enabled modules to not
  trigger change in "sources" Set if the module
  is already enabled.
---
 .../org/eclipse/jetty/start/StartArgs.java    |  8 ++++---
 .../org/eclipse/jetty/start/MainTest.java     | 24 +++++++++++++++++++
 .../src/test/resources/dist-home/start.ini    |  1 -
 .../resources/jetty-logging.properties        |  0
 .../overdeclared-modules/start.d/config.ini   |  1 +
 5 files changed, 30 insertions(+), 4 deletions(-)
 delete mode 100644 jetty-core/jetty-start/src/test/resources/dist-home/start.ini
 create mode 100644 jetty-core/jetty-start/src/test/resources/overdeclared-modules/resources/jetty-logging.properties
 create mode 100644 jetty-core/jetty-start/src/test/resources/overdeclared-modules/start.d/config.ini

diff --git a/jetty-core/jetty-start/src/main/java/org/eclipse/jetty/start/StartArgs.java b/jetty-core/jetty-start/src/main/java/org/eclipse/jetty/start/StartArgs.java
index 083c87cb5f39..d9f54b049842 100644
--- a/jetty-core/jetty-start/src/main/java/org/eclipse/jetty/start/StartArgs.java
+++ b/jetty-core/jetty-start/src/main/java/org/eclipse/jetty/start/StartArgs.java
@@ -1426,9 +1426,11 @@ private void selectModules(String source, List<String> moduleNames)
     {
         for (String moduleName : moduleNames)
         {
-            modules.add(moduleName);
-            Set<String> set = sources.computeIfAbsent(moduleName, k -> new HashSet<>());
-            set.add(source);
+            if (modules.add(moduleName))
+            {
+                Set<String> set = sources.computeIfAbsent(moduleName, k -> new HashSet<>());
+                set.add(source);
+            }
         }
     }
 
diff --git a/jetty-core/jetty-start/src/test/java/org/eclipse/jetty/start/MainTest.java b/jetty-core/jetty-start/src/test/java/org/eclipse/jetty/start/MainTest.java
index 98051e391eb8..2b8d29468773 100644
--- a/jetty-core/jetty-start/src/test/java/org/eclipse/jetty/start/MainTest.java
+++ b/jetty-core/jetty-start/src/test/java/org/eclipse/jetty/start/MainTest.java
@@ -30,6 +30,7 @@
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsString;
+import static org.hamcrest.Matchers.hasItem;
 import static org.hamcrest.Matchers.is;
 import static org.hamcrest.Matchers.not;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -183,4 +184,27 @@ public void testJvmArgExpansion() throws Exception
         );
         assertThat(commandLine, containsString(expectedExpansion));
     }
+
+    @Test
+    public void testModulesDeclaredTwice() throws Exception
+    {
+        List<String> cmdLineArgs = new ArrayList<>();
+
+        Path homePath = MavenPaths.findTestResourceDir("dist-home");
+        Path basePath = MavenPaths.findTestResourceDir("overdeclared-modules");
+        cmdLineArgs.add("jetty.home=" + homePath);
+        cmdLineArgs.add("user.dir=" + basePath);
+
+        Main main = new Main();
+
+        cmdLineArgs.add("--module=main");
+
+        // The "main" module is enabled in both ...
+        // 1) overdeclared-modules/start.d/config.ini
+        // 2) command-line
+        // This shouldn't result in an error
+        StartArgs args = main.processCommandLine(cmdLineArgs.toArray(new String[0]));
+
+        assertThat(args.getSelectedModules(), hasItem("main"));
+    }
 }
diff --git a/jetty-core/jetty-start/src/test/resources/dist-home/start.ini b/jetty-core/jetty-start/src/test/resources/dist-home/start.ini
deleted file mode 100644
index 4cae2dd2f88f..000000000000
--- a/jetty-core/jetty-start/src/test/resources/dist-home/start.ini
+++ /dev/null
@@ -1 +0,0 @@
---module=main
diff --git a/jetty-core/jetty-start/src/test/resources/overdeclared-modules/resources/jetty-logging.properties b/jetty-core/jetty-start/src/test/resources/overdeclared-modules/resources/jetty-logging.properties
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/jetty-core/jetty-start/src/test/resources/overdeclared-modules/start.d/config.ini b/jetty-core/jetty-start/src/test/resources/overdeclared-modules/start.d/config.ini
new file mode 100644
index 000000000000..32c205126083
--- /dev/null
+++ b/jetty-core/jetty-start/src/test/resources/overdeclared-modules/start.d/config.ini
@@ -0,0 +1 @@
+--modules=main
\ No newline at end of file