From edc6e7eba84d19a04c6c2b91f411cba714c935c4 Mon Sep 17 00:00:00 2001
From: Tom Hvitved <hvitved@github.com>
Date: Wed, 27 Jan 2021 10:47:42 +0100
Subject: [PATCH] Add `UnusedParameter.ql` query

---
 ql/src/queries/variables/UnusedParameter.ql | 27 +++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 ql/src/queries/variables/UnusedParameter.ql

diff --git a/ql/src/queries/variables/UnusedParameter.ql b/ql/src/queries/variables/UnusedParameter.ql
new file mode 100644
index 00000000000..afad3df545b
--- /dev/null
+++ b/ql/src/queries/variables/UnusedParameter.ql
@@ -0,0 +1,27 @@
+/**
+ * @name Unused parameter.
+ * @description A parameter that is not used later on, or whose value is always overwritten,
+ *              can be removed.
+ * @kind problem
+ * @problem.severity warning
+ * @id rb/unused-parameter
+ * @tags maintainability
+ *       external/cwe/cwe-563
+ * @precision low
+ */
+
+import ruby
+import codeql_ruby.dataflow.SSA
+
+class RelevantParameterVariable extends LocalVariable {
+  RelevantParameterVariable() {
+    exists(Parameter p |
+      this = p.getAVariable() and
+      not this.getName().charAt(0) = "_"
+    )
+  }
+}
+
+from RelevantParameterVariable v
+where not exists(Ssa::WriteDefinition def | def.getWriteAccess() = v.getDefiningAccess())
+select v, "Unused parameter."