From b718196f79c89c76dc638864305e1ce51ec7aebe Mon Sep 17 00:00:00 2001
From: Paul Campbell <pcampbell@kemitix.net>
Date: Sun, 15 Aug 2021 08:15:01 +0100
Subject: [PATCH] Add AvoidDoubleBraceInitialization

commit-id:c25380aa
---
 builder/src/main/resources/application.yml    |  7 +++++
 .../rules/AvoidDoubleBraceInitialization.md   | 31 +++++++++++++++++++
 2 files changed, 38 insertions(+)
 create mode 100644 builder/src/main/resources/rules/AvoidDoubleBraceInitialization.md

diff --git a/builder/src/main/resources/application.yml b/builder/src/main/resources/application.yml
index c9ce6aa..c37c3fb 100644
--- a/builder/src/main/resources/application.yml
+++ b/builder/src/main/resources/application.yml
@@ -1580,3 +1580,10 @@ rules:
         enabled: true
         source: CHECKSTYLE
         uri: https://checkstyle.sourceforge.io/config_coding.html#UnnecessarySemicolonAfterOuterTypeDeclaration
+    -
+        name: AvoidDoubleBraceInitialization
+        parent: TREEWALKER
+        level: LAYOUT
+        enabled: true
+        source: CHECKSTYLE
+        uri: https://checkstyle.sourceforge.io/config_coding.html#AvoidDoubleBraceInitialization
diff --git a/builder/src/main/resources/rules/AvoidDoubleBraceInitialization.md b/builder/src/main/resources/rules/AvoidDoubleBraceInitialization.md
new file mode 100644
index 0000000..4c755d8
--- /dev/null
+++ b/builder/src/main/resources/rules/AvoidDoubleBraceInitialization.md
@@ -0,0 +1,31 @@
+
+Detects double brace initialization.
+
+Rationale: Double brace initialization (set of Instance Initializers in class
+body) may look cool, but it is considered as anti-pattern and should be avoided.
+This is also can lead to a hard-to-detect memory leak, if the anonymous class
+instance is returned outside and other object(s) hold reference to it. Created
+anonymous class is not static, it holds an implicit reference to the outer class
+instance. See this
+[blog post](https://blog.jooq.org/2014/12/08/dont-be-clever-the-double-curly-braces-anti-pattern/)
+and
+[article](https://www.baeldung.com/java-double-brace-initialization)
+for more details. Check ignores any comments and semicolons in class body.
+
+Invalid:
+````java
+class MyClass {
+    List<Integer> list1 = new ArrayList<>() { // violation
+        {
+            add(1);
+        }
+    };
+    List<String> list2 = new ArrayList<>() { // violation
+        ;
+        // comments and semicolons are ignored
+        {
+            add("foo");
+        }
+    };
+}
+````