Rust: Don't consider parameters in trait method definitions without bodies as variables

Author: paldepind

rust/ql/lib/codeql/rust/elements/internal/VariableImpl.qll

@@ -84,7 +84,10 @@ module Impl {
     // an enum constant (e.g. `None`). This excludes static and constant variables (UPPERCASE),
     // which we don't appear to recognize yet anyway. This also assumes programmers follow the
     // naming guidelines, which they generally do, but they're not enforced.
-    not name.charAt(0).isUppercase()
+    not name.charAt(0).isUppercase() and
+    // exclude parameters from functions without a bodies as these are trait method declarations
+    // without implementations
+    not exists(Function f | not f.hasBody() and f.getParamList().getAParam().getPat() = p)
   }
 
   /** A variable. */

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

@@ -19,8 +19,6 @@
 | main.rs:370:9:370:9 | x | Variable is assigned a value that is never used. |
 | main.rs:378:17:378:17 | x | Variable is assigned a value that is never used. |
 | main.rs:432:9:432:10 | i6 | Variable is assigned a value that is never used. |
-| more.rs:4:23:4:25 | val | Variable is assigned a value that is never used. |
-| more.rs:8:19:8:21 | val | Variable is assigned a value that is never used. |
 | more.rs:24:9:24:11 | val | Variable is assigned a value that is never used. |
 | more.rs:46:9:46:14 | a_ptr4 | Variable is assigned a value that is never used. |
 | more.rs:61:9:61:13 | d_ptr | Variable is assigned a value that is never used. |

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

@@ -18,6 +18,4 @@
 | main.rs:379:21:379:21 | y | Variable is not used. |
 | main.rs:427:27:427:29 | val | Variable is not used. |
 | main.rs:430:22:430:24 | acc | Variable is not used. |
-| main.rs:442:9:442:13 | times | Variable is not used. |
-| main.rs:443:9:443:14 | unused | Variable is not used. |
 | main.rs:455:9:455:14 | unused | Variable is not used. |

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

@@ -439,8 +439,8 @@ fn folds_and_closures() {
 trait Incrementable {
     fn increment(
         &mut self,
-        times: i32, // SPURIOUS: unused variable
-        unused: i32 // SPURIOUS: unused variable
+        times: i32,
+        unused: &mut i32
     );
 }
 

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

@@ -1,11 +1,11 @@
 // --- generics ---
 
 trait MySettable<T> {
-    fn set(&mut self, val: T); // SPURIOUS: unused value
+    fn set(&mut self, val: T);
 }
 
 trait MyGettable<T> {
-    fn get(&self, val: T) -> &T; // SPURIOUS: unused value
+    fn get(&self, val: T) -> &T;
 }
 
 struct MyContainer<T> {