Rust: Add another exception to rust/unused-variable.

Author: geoffw0

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

@@ -7,8 +7,12 @@ class DiscardVariable extends Variable {
 
 /** Holds if variable `v` is unused. */
 predicate isUnused(Variable v) {
+  // variable is accessed or initialized
   not exists(v.getAnAccess()) and
   not exists(v.getInitializer()) and
+  // variable is intentionally unused
   not v instanceof DiscardVariable and
-  not v.getPat().isInMacroExpansion()
+  // variable is in a context where is may not have a use
+  not v.getPat().isInMacroExpansion() and
+  not exists(FnPtrType fp | fp.getParamList().getParam(_).getPat() = v.getPat())
 }

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

@@ -15,6 +15,10 @@
 | main.rs:373:9:373:9 | x | Variable $@ is assigned a value that is never used. | main.rs:373:9:373:9 | x | x |
 | main.rs:381:17:381:17 | x | Variable $@ is assigned a value that is never used. | main.rs:381:17:381:17 | x | x |
 | main.rs:482:9:482:9 | c | Variable $@ is assigned a value that is never used. | main.rs:482:9:482:9 | c | c |
+| main.rs:494:16:494:16 | x | Variable $@ is assigned a value that is never used. | main.rs:494:16:494:16 | x | x |
+| main.rs:495:16:495:16 | y | Variable $@ is assigned a value that is never used. | main.rs:495:16:495:16 | y | y |
+| main.rs:496:12:496:12 | z | Variable $@ is assigned a value that is never used. | main.rs:496:12:496:12 | z | z |
+| main.rs:499:18:499:18 | x | Variable $@ is assigned a value that is never used. | main.rs:499:18:499:18 | x | x |
 | more.rs:44:9:44:14 | a_ptr4 | Variable $@ is assigned a value that is never used. | more.rs:44:9:44:14 | a_ptr4 | a_ptr4 |
 | more.rs:59:9:59:13 | d_ptr | Variable $@ is assigned a value that is never used. | more.rs:59:9:59:13 | d_ptr | d_ptr |
 | more.rs:65:9:65:17 | f_ptr | Variable $@ is assigned a value that is never used. | more.rs:65:13:65:17 | f_ptr | f_ptr |

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

@@ -19,8 +19,4 @@
 | main.rs:427:26:427:28 | val | Variable 'val' is not used. |
 | main.rs:430:21:430:23 | acc | Variable 'acc' is not used. |
 | main.rs:451:9:451:14 | unused | Variable 'unused' is not used. |
-| main.rs:494:16:494:16 | x | Variable 'x' is not used. |
-| main.rs:495:16:495:16 | y | Variable 'y' is not used. |
-| main.rs:496:12:496:12 | z | Variable 'z' is not used. |
-| main.rs:499:18:499:18 | x | Variable 'x' is not used. |
 | more.rs:24:9:24:11 | val | Variable 'val' is not used. |

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

@@ -491,12 +491,12 @@ fn references() {
 
 pub struct my_declaration {
     field1: fn(i32) -> i32,
-    field2: fn(x: i32) -> i32, // $ SPURIOUS: Alert[rust/unused-variable]
-    field3: fn(y: // $ SPURIOUS: Alert[rust/unused-variable]
-        fn(z: i32) -> i32) -> i32, // $ SPURIOUS: Alert[rust/unused-variable]
+    field2: fn(x: i32) -> i32, // $ SPURIOUS: Alert[rust/unused-value]
+    field3: fn(y: // $ SPURIOUS: Alert[rust/unused-value]
+        fn(z: i32) -> i32) -> i32, // $ SPURIOUS: Alert[rust/unused-value]
 }
 
-type MyType = fn(x: i32) -> i32; // $ SPURIOUS: Alert[rust/unused-variable]
+type MyType = fn(x: i32) -> i32; // $ SPURIOUS: Alert[rust/unused-value]
 
 trait MyTrait {
     fn my_func2(&self, x: i32) -> i32;