Merge pull request #22398 from hvitved/rust/unused-variable-todo

Rust: Exclude 'unused variable' results for functions containing `todo!()` or `unimplemented!()`

Author: hvitved

rust/ql/src/change-notes/2026-08-20-unused-variables-in-incomplete-functions.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* The `rust/unused-variable` query no longer reports variables in functions containing the standard `todo!()` or `unimplemented!()` macros.

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

@@ -1,4 +1,5 @@
 import rust
+private import codeql.rust.internal.PathResolution
 
 /**
  * A deliberately unused variable, for example `_` or `_x`.
@@ -23,9 +24,13 @@ predicate isUnused(Variable v) {
  */
 class IncompleteCallable extends Callable {
   IncompleteCallable() {
-    exists(MacroExpr me |
-      me.getEnclosingCallable() = this and
+    exists(MacroExpr me | me.getEnclosingCallable() = this |
       not me.getMacroCall().hasMacroCallExpansion()
+      or
+      exists(ItemNode i |
+        i.getCanonicalPath(_) = ["core::macros::unimplemented", "core::macros::todo"] and
+        me.getMacroCall().resolveMacro() = i
+      )
     )
   }
 }

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

@@ -558,6 +558,14 @@ trait MyTrait {
     fn my_func2(&self, x: i32) -> i32;
 }
 
+fn unimplemented(x : i32) {
+    unimplemented!()
+}
+
+fn todo(x : i32) {
+    todo!()
+}
+
 // --- main ---
 
 fn main() {