From f93fd7cd6b8ddc68d8773123c6b173cde66938a1 Mon Sep 17 00:00:00 2001
From: Geoffrey White <40627776+geoffw0@users.noreply.github.com>
Date: Tue, 17 Sep 2024 15:40:11 +0100
Subject: [PATCH] Rust: Add qhelp and example for the unused variable query.

---
 .../unusedentities/UnusedVariable.qhelp       | 24 +++++++++++++++++++
 .../unusedentities/UnusedVariableBad.rs       | 10 ++++++++
 .../unusedentities/UnusedVariableGood.rs      |  9 +++++++
 3 files changed, 43 insertions(+)
 create mode 100644 rust/ql/src/queries/unusedentities/UnusedVariable.qhelp
 create mode 100644 rust/ql/src/queries/unusedentities/UnusedVariableBad.rs
 create mode 100644 rust/ql/src/queries/unusedentities/UnusedVariableGood.rs

diff --git a/rust/ql/src/queries/unusedentities/UnusedVariable.qhelp b/rust/ql/src/queries/unusedentities/UnusedVariable.qhelp
new file mode 100644
index 000000000000..c34283962f62
--- /dev/null
+++ b/rust/ql/src/queries/unusedentities/UnusedVariable.qhelp
@@ -0,0 +1,24 @@
+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+
+<overview>
+<p>This rule finds variables that are never accessed. Unused variables should be removed to increase readability and avoid confusion.</p>
+</overview>
+
+<recommendation>
+<p>Remove any unused variables.</p>
+</recommendation>
+
+<example>
+<p>In the following example, there is an unused variable <code>average</code> that is never used:</p>
+<sample src="UnusedVariableBad.rs" />
+<p>The problem can be fixed simply by removing the variable:</p>
+<sample src="UnusedVariableGood.rs" />
+</example>
+
+<references>
+<li>GeeksforGeeks: <a href="https://www.geeksforgeeks.org/how-to-avoid-unused-variable-warning-in-rust/">How to avoid unused Variable warning in Rust?</a></li>
+</references>
+</qhelp>
diff --git a/rust/ql/src/queries/unusedentities/UnusedVariableBad.rs b/rust/ql/src/queries/unusedentities/UnusedVariableBad.rs
new file mode 100644
index 000000000000..e968ea6d80e7
--- /dev/null
+++ b/rust/ql/src/queries/unusedentities/UnusedVariableBad.rs
@@ -0,0 +1,10 @@
+fn get_sum(values:&[i32]) -> i32 {
+	let mut sum = 0;
+	let mut average; // BAD: unused variable
+
+	for v in values {
+		sum += v;
+	}
+
+	return sum;
+}
diff --git a/rust/ql/src/queries/unusedentities/UnusedVariableGood.rs b/rust/ql/src/queries/unusedentities/UnusedVariableGood.rs
new file mode 100644
index 000000000000..1b502ea29156
--- /dev/null
+++ b/rust/ql/src/queries/unusedentities/UnusedVariableGood.rs
@@ -0,0 +1,9 @@
+fn get_sum(values:&[i32]) -> i32 {
+	let mut sum = 0;
+
+	for v in values {
+		sum += v;
+	}
+
+	return sum;
+}