Rust: Fix unused value FPs due to unexpanded macro calls as well.

Author: geoffw0

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

@@ -21,5 +21,6 @@ where
   // avoid overlap with the unused variable query
   not isUnused(v) and
   not v instanceof DiscardVariable and
-  not write.isInMacroExpansion()
+  not write.isInMacroExpansion() and
+  not isAllowableUnused(v)
 select write, "Variable $@ is assigned a value that is never used.", v, v.getText()

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

@@ -11,24 +11,9 @@
 import rust
 import UnusedVariable
 
-/**
- * A callable for which we have incomplete information, for example because an unexpanded
- * macro call is present. These callables are prone to false positive results from unused
- * entities queries, unless they are excluded from results.
- */
-class IncompleteCallable extends Callable {
-  IncompleteCallable() {
-    exists(MacroExpr me |
-      me.getEnclosingCallable() = this and
-      not me.getMacroCall().hasExpanded()
-    )
-  }
-}
-
 from Variable v
 where
   isUnused(v) and
   not isAllowableUnused(v) and
-  not v instanceof DiscardVariable and
-  not v.getEnclosingCfgScope() instanceof IncompleteCallable
+  not v instanceof DiscardVariable
 select v, "Variable '" + v + "' is not used."

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

@@ -16,6 +16,20 @@ predicate isUnused(Variable v) {
   not exists(v.getInitializer())
 }
 
+/**
+ * A callable for which we have incomplete information, for example because an unexpanded
+ * macro call is present. These callables are prone to false positive results from unused
+ * entities queries, unless they are excluded from results.
+ */
+class IncompleteCallable extends Callable {
+  IncompleteCallable() {
+    exists(MacroExpr me |
+      me.getEnclosingCallable() = this and
+      not me.getMacroCall().hasExpanded()
+    )
+  }
+}
+
 /**
  * Holds if variable `v` is in a context where we may not find a use for it,
  * but that's expected and should not be considered a problem.
@@ -24,6 +38,9 @@ predicate isAllowableUnused(Variable v) {
   // in a macro expansion
   v.getPat().isInMacroExpansion()
   or
+  // declared in an incomplete callable
+  v.getEnclosingCfgScope() instanceof IncompleteCallable
+  or
   // a 'self' variable
   v.getText() = "self"
 }

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

@@ -14,7 +14,6 @@
 | main.rs:284:13:284:17 | total | Variable $@ is assigned a value that is never used. | main.rs:252:13:252:17 | total | total |
 | main.rs:377:9:377:9 | x | Variable $@ is assigned a value that is never used. | main.rs:377:9:377:9 | x | x |
 | main.rs:385:17:385:17 | x | Variable $@ is assigned a value that is never used. | main.rs:385:17:385:17 | x | x |
-| main.rs:510:9:510:9 | d | Variable $@ is assigned a value that is never used. | main.rs:510:9:510:9 | d | d |
 | main.rs:550:9:550:20 | var_in_macro | Variable $@ is assigned a value that is never used. | main.rs:550:9:550:20 | var_in_macro | var_in_macro |
 | main.rs:559:9:559:9 | c | Variable $@ is assigned a value that is never used. | main.rs:559:9:559:9 | c | c |
 | 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 |

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

@@ -507,7 +507,7 @@ fn macros2() {
 }
 
 fn macros3() {
-    let d: u16 = 4; // $ SPURIOUS: Alert[rust/unused-value]
+    let d: u16 = 4;
 
     undefined_macro_call!(d);
 }