Rust: Implement UnusedValue.ql

Author: hvitved

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

@@ -9,7 +9,16 @@
  */
 
 import rust
+import codeql.rust.dataflow.Ssa
+import codeql.rust.dataflow.internal.SsaImpl
+import UnusedVariable
 
-from Locatable e
-where none() // TODO: implement query
-select e, "Variable is assigned a value that is never used."
+from AstNode write, Ssa::Variable v
+where
+  variableWrite(write, v) and
+  // SSA definitions are only created for live writes
+  not write = any(Ssa::WriteDefinition def).getWriteAccess().getAstNode() and
+  // avoid overlap with the unused variable query
+  not isUnused(v) and
+  not v instanceof DiscardVariable
+select write, "Variable is assigned a value that is never used."

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

@@ -9,11 +9,8 @@
  */
 
 import rust
+import UnusedVariable
 
 from Variable v
-where
-  not exists(v.getAnAccess()) and
-  not exists(v.getInitializer()) and
-  not v.getName().charAt(0) = "_" and
-  exists(File f | f.getBaseName() = "main.rs" | v.getLocation().getFile() = f) // temporarily severely limit results
+where isUnused(v)
 select v, "Variable is not used."

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

@@ -0,0 +1,14 @@
+import rust
+
+/** A deliberately unused variable. */
+class DiscardVariable extends Variable {
+  DiscardVariable() { this.getName().charAt(0) = "_" }
+}
+
+/** Holds if variable `v` is unused. */
+predicate isUnused(Variable v) {
+  not exists(v.getAnAccess()) and
+  not exists(v.getInitializer()) and
+  not v instanceof DiscardVariable and
+  exists(File f | f.getBaseName() = "main.rs" | v.getLocation().getFile() = f) // temporarily severely limit results
+}

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

@@ -0,0 +1,16 @@
+| main.rs:6:9:6:9 | a | Variable is assigned a value that is never used. |
+| main.rs:9:9:9:9 | d | Variable is assigned a value that is never used. |
+| main.rs:35:5:35:5 | b | Variable is assigned a value that is never used. |
+| main.rs:37:5:37:5 | c | Variable is assigned a value that is never used. |
+| main.rs:40:5:40:5 | c | Variable is assigned a value that is never used. |
+| main.rs:44:9:44:9 | d | Variable is assigned a value that is never used. |
+| main.rs:50:5:50:5 | e | Variable is assigned a value that is never used. |
+| main.rs:61:5:61:5 | f | Variable is assigned a value that is never used. |
+| main.rs:63:5:63:5 | f | Variable is assigned a value that is never used. |
+| main.rs:65:5:65:5 | g | Variable is assigned a value that is never used. |
+| main.rs:87:9:87:9 | a | Variable is assigned a value that is never used. |
+| main.rs:108:9:108:10 | is | Variable is assigned a value that is never used. |
+| main.rs:133:13:133:17 | total | Variable is assigned a value that is never used. |
+| main.rs:232:13:232:17 | total | Variable is assigned a value that is never used. |
+| main.rs:301:9:301:9 | x | Variable is assigned a value that is never used. |
+| main.rs:309:17:309:17 | x | Variable is assigned a value that is never used. |

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

@@ -20,3 +20,16 @@
 | main.rs:386:21:386:21 | y | Variable is not used. |
 | main.rs:434:27:434:29 | val | Variable is not used. |
 | main.rs:437:22:437:24 | acc | Variable is not used. |
+| main.rs:164:9:164:9 | x | Variable is not used. |
+| main.rs:202:17:202:17 | a | Variable is not used. |
+| main.rs:210:20:210:22 | val | Variable is not used. |
+| main.rs:224:14:224:16 | val | Variable is not used. |
+| main.rs:239:22:239:24 | val | Variable is not used. |
+| main.rs:246:24:246:26 | val | Variable is not used. |
+| main.rs:254:13:254:15 | num | Variable is not used. |
+| main.rs:269:12:269:12 | j | Variable is not used. |
+| main.rs:289:25:289:25 | y | Variable is not used. |
+| main.rs:292:28:292:28 | a | Variable is not used. |
+| main.rs:295:9:295:9 | p | Variable is not used. |
+| main.rs:302:13:302:13 | y | Variable is not used. |
+| main.rs:310:21:310:21 | y | Variable is not used. |

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

@@ -3,10 +3,10 @@
 // --- locals ---
 
 fn locals_1() {
-    let a = 1; // BAD: unused value [NOT DETECTED]
+    let a = 1; // BAD: unused value
     let b = 1;
     let c = 1;
-    let d = String::from("a"); // BAD: unused value [NOT DETECTED]
+    let d = String::from("a"); // BAD: unused value
     let e = String::from("b");
     let f = 1;
     let _ = 1; // (deliberately unused)
@@ -32,22 +32,22 @@ fn locals_2() {
     let h: i32;
     let i: i32;
 
-    b = 1; // BAD: unused value [NOT DETECTED]
+    b = 1; // BAD: unused value
 
-    c = 1; // BAD: unused value [NOT DETECTED]
+    c = 1; // BAD: unused value
     c = 2;
     println!("use {}", c);
-    c = 3; // BAD: unused value [NOT DETECTED]
+    c = 3; // BAD: unused value
 
     d = 1;
     if cond() {
-        d = 2; // BAD: unused value [NOT DETECTED]
+        d = 2; // BAD: unused value
         d = 3;
     } else {
     }
     println!("use {}", d);
 
-    e = 1; // BAD: unused value [NOT DETECTED]
+    e = 1; // BAD: unused value
     if cond() {
         e = 2;
     } else {
@@ -58,16 +58,16 @@ fn locals_2() {
     f = 1;
     f += 1;
     println!("use {}", f);
-    f += 1; // BAD: unused value [NOT DETECTED]
+    f += 1; // BAD: unused value
     f = 1;
-    f += 1; // BAD: unused value [NOT DETECTED]
+    f += 1; // BAD: unused value
 
-    g = if cond() { 1 } else { 2 }; // BAD: unused value (x2) [NOT DETECTED]
+    g = if cond() { 1 } else { 2 }; // BAD: unused value
     h = if cond() { 3 } else { 4 };
     i = if cond() { h } else { 5 };
     println!("use {}", i);
 
-    _ = 1; // (deliberately unused) [NOT DETECTED]
+    _ = 1; // GOOD (deliberately unused)
 }
 
 // --- structs ---
@@ -84,7 +84,7 @@ impl MyStruct {
 }
 
 fn structs() {
-    let a = MyStruct { val: 1 }; // BAD: unused value [NOT DETECTED]
+    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
@@ -105,7 +105,7 @@ fn structs() {
 // --- arrays ---
 
 fn arrays() {
-    let is = [1, 2, 3]; // BAD: unused values (x3) [NOT DETECTED]
+    let is = [1, 2, 3]; // BAD: unused values (x3)
     let js = [1, 2, 3];
     let ks = [1, 2, 3];
 
@@ -130,7 +130,7 @@ fn statics() {
     static mut STAT4: i32 = 0; // BAD: unused value [NOT DETECTED]
 
     unsafe {
-        let total = CON1 + STAT1 + STAT3;
+        let total = CON1 + STAT1 + STAT3; // BAD: unused value
     }
 }
 
@@ -237,7 +237,7 @@ enum YesOrNo {
     No,
 }
 
-use YesOrNo::{Yes, No}; // allows `Yes`, `No` to be accessed without qualifiers.
+use YesOrNo::{No, Yes}; // allows `Yes`, `No` to be accessed without qualifiers.
 
 struct MyPoint {
     x: i64,
@@ -255,7 +255,8 @@ fn if_lets_matches() {
     }
 
     let mut next = Some(30);
-    while let Some(val) = next // BAD: unused variable
+    while let Some(val) = // BAD: unused variable
+        next
     {
         next = None;
     }
@@ -270,25 +271,22 @@ fn if_lets_matches() {
     match c {
         Some(val) => { // BAD: unused variable
         }
-        None => {
-        }
+        None => {}
     }
 
     let d = Some(70);
     match d {
         Some(val) => {
-            total += val;
-        }
-        None => {
+            total += val; // BAD: unused value
         }
+        None => {}
     }
 
     let e = Option::Some(80);
     match e {
         Option::Some(val) => { // BAD: unused variable
         }
-        Option::None => {
-        }
+        Option::None => {}
     }
 
     let f = MyOption::Some(90);
@@ -298,10 +296,9 @@ fn if_lets_matches() {
         MyOption::None => {}
     }
 
-    let g : Result<i64, i64> = Ok(100);
+    let g: Result<i64, i64> = Ok(100);
     match g {
-        Ok(_) => {
-        }
+        Ok(_) => {}
         Err(num) => {} // BAD: unused variable
     }
 
@@ -327,8 +324,7 @@ fn if_lets_matches() {
     }
 
     let l = Yes;
-    if let Yes = l {
-    }
+    if let Yes = l {}
 
     match 1 {
         1 => {}
@@ -337,16 +333,13 @@ fn if_lets_matches() {
 
     let p1 = MyPoint { x: 1, y: 2 };
     match p1 {
-        MyPoint { x: 0, y: 0 } => {
-        }
+        MyPoint { x: 0, y: 0 } => {}
         MyPoint { x: 1, y } => { // BAD: unused variable
         }
-        MyPoint { x: 2, y: _ } => {
-        }
+        MyPoint { x: 2, y: _ } => {}
         MyPoint { x: 3, y: a } => { // BAD: unused variable
         }
-        MyPoint { x: 4, .. } => {
-        }
+        MyPoint { x: 4, .. } => {}
         p => { // BAD: unused variable
         }
     }
@@ -374,15 +367,15 @@ fn if_lets_matches() {
 }
 
 fn shadowing() -> i32 {
-    let x = 1; // BAD: unused value [NOT DETECTED]
+    let x = 1; // BAD: unused value
     let mut y: i32; // BAD: unused variable
 
     {
         let x = 2;
         let mut y: i32;
 
         {
-            let x = 3; // BAD: unused value [NOT DETECTED]
+            let x = 3; // BAD: unused value
             let mut y: i32; // BAD: unused variable
         }
 
@@ -449,16 +442,16 @@ fn main() {
     structs();
     arrays();
     statics();
-	println!("lets use result {}", parameters(1, 2, 3));
+    println!("lets use result {}", parameters(1, 2, 3));
     loops();
     if_lets_matches();
     shadowing();
     func_ptrs();
     folds_and_closures();
 
-	unreachable_if();
-	unreachable_panic();
-	unreachable_match();
-	unreachable_loop();
-	unreachable_paren();
+    unreachable_if();
+    unreachable_panic();
+    unreachable_match();
+    unreachable_loop();
+    unreachable_paren();
 }