Rust: Fix spurious path resolution

The annotated impl block was filtered away, but it's children where not. This caused the associated type `Foo` to appear as if it was an item in the scope outside of the impl block.

Author: paldepind

rust/ql/lib/codeql/rust/internal/PathResolution.qll

@@ -78,6 +78,24 @@ private ItemNode getAChildSuccessor(ItemNode item, string name, SuccessorKind ki
   )
 }
 
+/**
+ * Holds if `n` is superceded by an attribute macro expansion. That is, `n` is
+ * an item or a transitive child of an item with an attribute macro expansion.
+ */
+predicate supercededByAttributeMacroExpansion(AstNode n) {
+  n.(Item).hasAttributeMacroExpansion()
+  or
+  exists(AstNode parent |
+    n.getParentNode() = parent and
+    supercededByAttributeMacroExpansion(parent) and
+    // Don't exclude expansions themselves as they supercede other nodes.
+    not n = parent.(Item).getAttributeMacroExpansion() and
+    // Don't consider attributes themselves to be superceded.  E.g., in `#[a] fn
+    // f() {}` the macro expansion supercedes `fn f() {}` but not `#[a]`.
+    not n instanceof Attr
+  )
+}
+
 /**
  * An item that may be referred to by a path, and which is a node in
  * the _item graph_.
@@ -158,7 +176,7 @@ private ItemNode getAChildSuccessor(ItemNode item, string name, SuccessorKind ki
 abstract class ItemNode extends Locatable {
   ItemNode() {
     // Exclude items that are superceded by the expansion of an attribute macro.
-    not this.(Item).hasAttributeMacroExpansion()
+    not supercededByAttributeMacroExpansion(this)
   }
 
   /** Gets the (original) name of this item. */

rust/ql/test/library-tests/path-resolution/main.rs

@@ -784,7 +784,7 @@ mod impl_with_attribute_macro {
 
     pub fn test() {
         // This should resolve to the struct, not the associated type.
-        let _x: Foo; // $ item=IFoo SPURIOUS: item=IATrait_i64_Foo
+        let _x: Foo; // $ item=IFoo
     } // impl_with_attribute_macro::test
 }
 

rust/ql/test/library-tests/path-resolution/path-resolution.expected

@@ -356,7 +356,6 @@ resolvePath
 | main.rs:779:21:779:23 | i64 | {EXTERNAL LOCATION} | struct i64 |
 | main.rs:781:11:781:13 | i64 | {EXTERNAL LOCATION} | struct i64 |
 | main.rs:787:17:787:19 | Foo | main.rs:772:5:772:15 | struct Foo |
-| main.rs:787:17:787:19 | Foo | main.rs:779:27:782:9 | type Foo |
 | main.rs:792:5:792:6 | my | main.rs:1:1:1:7 | mod my |
 | main.rs:792:5:792:14 | ...::nested | my.rs:1:1:1:15 | mod nested |
 | main.rs:792:5:792:23 | ...::nested1 | my/nested.rs:1:1:17:1 | mod nested1 |