Rust: Placeholder queries for unused variable, unused value

rust/ql/src/queries/unusedentities/UnusedValue.qhelp

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+<!DOCTYPE qhelp PUBLIC
+  "-//Semmle//qhelp//EN"
+  "qhelp.dtd">
+<qhelp>
+
+<overview>
+<p>This rule finds values that are assigned to variables but never used. Unused values should be removed to increase readability and avoid confusion.</p>
+</overview>
+
+<recommendation>
+<p>Remove any unused values. Also remove any variables that only hold unused values.</p>
+</recommendation>
+
+<example>
+<p>In the following example, there is a variable <code>average</code> that is initialized to <code>0</code>, but that value is never used:</p>
+<sample src="UnusedValueBad.rs" />
+<p>The problem can be fixed by removing the value and the variable that contains it:</p>
+<sample src="UnusedValueGood.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>

rust/ql/src/queries/unusedentities/UnusedValue.ql

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+/**
+ * @name Unused value
+ * @description Unused values may be an indication that the code is incomplete or has a typo.
+ * @kind problem
+ * @problem.severity recommendation
+ * @precision high
+ * @id rust/unused-value
+ * @tags maintainability
+ */
+
+select 1, "Variable is assigned a value that is never used."

rust/ql/src/queries/unusedentities/UnusedValueBad.rs

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+fn get_sum(values:&[i32]) -> i32 {
+	let mut sum = 0;
+	let mut average = 0; // BAD: unused value
+
+	for v in values {
+		sum += v;
+	}
+
+	return sum;
+}

rust/ql/src/queries/unusedentities/UnusedValueGood.rs

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+fn get_sum(values:&[i32]) -> i32 {
+	let mut sum = 0;
+
+	for v in values {
+		sum += v;
+	}
+
+	return sum;
+}

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>

rust/ql/src/queries/unusedentities/UnusedVariable.ql

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+/**
+ * @name Unused variable
+ * @description Unused variables may be an indication that the code is incomplete or has a typo.
+ * @kind problem
+ * @problem.severity recommendation
+ * @precision high
+ * @id rust/unused-variable
+ * @tags maintainability
+ */
+
+select 1, "Variable is not used."

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;
+}

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;
+}

rust/ql/test/query-tests/unusedentities/UnusedValue.expected

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+| 1 | Variable is assigned a value that is never used. |

rust/ql/test/query-tests/unusedentities/UnusedValue.qlref

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+queries/unusedentities/UnusedValue.ql

rust/ql/test/query-tests/unusedentities/UnusedVariable.expected

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+| 1 | Variable is not used. |

rust/ql/test/query-tests/unusedentities/UnusedVariable.qlref

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+queries/unusedentities/UnusedVariable.ql

rust/ql/test/query-tests/unusedentities/main.rs

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+
+//fn cond() -> bool;
+
+// --- locals ---
+
+fn locals_1() {
+	let a = 1; // BAD: unused value
+	let b = 1;
+	let c = 1;
+	let d = String::from("a"); // BAD: unused value
+	let e = String::from("b");
+	let _ = 1; // (deliberately unused)
+
+	println!("use {}", b);
+
+	if cond() {
+		println!("use {}", c);
+	}
+
+	println!("use {}", e);
+}
+
+fn locals_2() {
+	let a: i32;
+	let b: i32; // BAD: unused variable
+	let mut c: i32;
+	let mut d: i32;
+	let mut e: i32;
+	let mut f: i32;
+	let g: i32;
+	let h: i32;
+	let i: i32;
+
+	b = 1; // BAD: unused value
+
+	c = 1; // BAD: unused value
+	c = 2;
+	println!("use {}", c);
+	c = 3; // BAD: unused value
+
+	d = 1;
+	if cond() {
+		d = 2; // BAD: unused value
+		d = 3;
+	} else {
+	}
+	println!("use {}", d);
+
+	e = 1; // BAD: unused value
+	if cond() {
+		e = 2;
+	} else {
+		e = 3;
+	}
+	println!("use {}", e);
+
+	f = 1;
+	f += 1;
+	println!("use {}", f);
+	f += 1; // BAD: unused value
+	f = 1;
+	f += 1; // BAD: unused value
+
+	g = if cond() { 1 } else { 2 }; // BAD: unused value (x2)
+	h = if cond() { 3 } else { 4 };
+	i = if cond() { h } else { 5 };
+	println!("use {}", i);
+
+	_ = 1; // (deliberately unused)
+}
+
+// --- structs ---
+
+#[derive(Debug)]
+struct MyStruct {
+	val: i64
+}
+
+impl MyStruct {
+	fn my_get(&mut self) -> i64 {
+		return self.val;
+	}
+}
+
+fn structs() {
+	let a = MyStruct {val : 1 }; // BAD: unused value
+	let b = MyStruct {val : 2 };
+	let c = MyStruct {val : 3 };
+	let mut d : MyStruct; // BAD: unused variable
+	let mut e : MyStruct;
+	let mut f : MyStruct;
+
+	println!("lets use {:?} and {}", b, c.val);
+
+	e = MyStruct {val : 4 };
+	println!("lets use {}", e.my_get());
+	e.val = 5;
+	println!("lets use {}", e.my_get());
+
+	f = MyStruct {val : 6 }; // BAD: unused value
+	f.val = 7; // BAD: unused value
+}
+
+// --- arrays ---
+
+fn arrays() {
+	let is = [1, 2, 3]; // BAD: unused values (x3)
+	let js = [1, 2, 3];
+	let ks = [1, 2, 3];
+
+	println!("lets use {:?}", js);
+
+	for k in ks {
+		println!("lets use {}", k);
+	}
+}
+
+// --- constants and statics ---
+
+const CON1: i32 = 1;
+const CON2: i32 = 2; // BAD: unused value
+static mut STAT1: i32 = 1;
+static mut STAT2: i32 = 2; // BAD: unused value
+
+fn statics() {
+	static mut STAT3: i32 = 0;
+	static mut STAT4: i32 = 0; // BAD: unused value
+
+	unsafe
+	{
+		let total = CON1 + STAT1 + STAT3;
+	}
+}
+
+// --- parameters ---
+
+fn parameters(
+		x: i32,
+		y: i32, // BAD: unused variable
+		_z: i32 // (`_` is asking the compiler, and by extension us, to not warn that this is unused)
+	) -> i32 {
+	return x;
+}
+
+fn main() {
+	locals_1();
+	locals_2();
+	structs();
+	arrays();
+	statics();
+	println!("lets use result {}", parameters(1, 2, 3));
+}