Rust: Resolve Self paths in type definitions

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

@@ -119,6 +119,15 @@ private ItemNode getAChildSuccessor(ItemNode item, string name, SuccessorKind ki
     if result.isPublic()
     then kind.isBoth()
     else kind.isInternal()
+  or
+  // `Self` has scoping rules similar to type parameters and can be considered
+  // an implicit type parameter child of the introducing item.
+  // - https://doc.rust-lang.org/stable/reference/paths.html#r-paths.qualifiers.type-self
+  // - https://doc.rust-lang.org/stable/reference/names/scopes.html#r-names.scopes.self
+  (item instanceof TypeItemTypeItemNode or item instanceof ImplOrTraitItemNode) and
+  name = "Self" and
+  kind.isInternal() and
+  result = item
 }
 
 private module UseOption = Option<Use>;
@@ -405,9 +414,6 @@ abstract class ItemNode extends Locatable {
       this instanceof SourceFile and
       builtin(name, result)
       or
-      name = "Self" and
-      this = result.(ImplOrTraitItemNode).getAnItemInSelfScope()
-      or
       name = "crate" and
       this = result.(CrateItemNode).getASourceFile()
     )
@@ -718,26 +724,12 @@ class FunctionItemNode extends AssocItemNode, ParameterizableItemNode instanceof
 }
 
 abstract class ImplOrTraitItemNode extends ItemNode {
-  /** Gets an item that may refer to this node using `Self`. */
-  pragma[nomagic]
-  ItemNode getAnItemInSelfScope() {
-    result = this
-    or
-    result.getImmediateParent() = this
-    or
-    exists(ItemNode mid |
-      mid = this.getAnItemInSelfScope() and
-      result.getImmediateParent() = mid and
-      not mid instanceof ImplOrTraitItemNode
-    )
-  }
-
   /** Gets a `Self` path that refers to this item. */
   cached
   Path getASelfPath() {
     Stages::PathResolutionStage::ref() and
     isUnqualifiedSelfPath(result) and
-    result = this.getAnItemInSelfScope().getADescendant()
+    this = unqualifiedPathLookup(result, _, _)
   }
 
   /** Gets an associated item belonging to this trait or `impl` block. */
@@ -1610,11 +1602,7 @@ private predicate unqualifiedPathLookup(ItemNode ancestor, string name, Namespac
   // lookup in an outer scope, but only if the item is not declared in inner scope
   exists(ItemNode mid |
     unqualifiedPathLookup(mid, name, ns, encl) and
-    not declares(mid, ns, name) and
-    not (
-      name = "Self" and
-      mid = any(ImplOrTraitItemNode i).getAnItemInSelfScope()
-    )
+    not declares(mid, ns, name)
   |
     ancestor = getOuterScope(mid)
     or

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

@@ -1060,12 +1060,12 @@ mod self_constructors {
 mod self_types {
     struct NonEmptyListStruct<T> {
         head: T,                 // $ item=T
-        tail: Option<Box<Self>>, // $ item=Option item=Box MISSING: item=NonEmptyListStruct
+        tail: Option<Box<Self>>, // $ item=Option item=Box item=NonEmptyListStruct
     }
 
     enum NonEmptyListEnum<T> {
         Single(T),          // $ item=T
-        Cons(T, Box<Self>), // $ item=T item=Box MISSING: item=NonEmptyListEnum
+        Cons(T, Box<Self>), // $ item=T item=Box item=NonEmptyListEnum
     }
 
     #[rustfmt::skip]
@@ -1075,7 +1075,7 @@ mod self_types {
           : Copy // $ item=Copy
     > {
         single: T,           // $ item=T
-        cons: (T, &'a Self), // $ item=T MISSING: item=NonEmptyListUnion
+        cons: (T, &'a Self), // $ item=T item=NonEmptyListUnion
     }
 }
 

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

@@ -536,12 +536,15 @@ resolvePath
 | main.rs:1062:15:1062:15 | T | main.rs:1061:31:1061:31 | T |
 | main.rs:1063:15:1063:31 | Option::<...> | {EXTERNAL LOCATION} | enum Option |
 | main.rs:1063:22:1063:30 | Box::<...> | {EXTERNAL LOCATION} | struct Box |
+| main.rs:1063:26:1063:29 | Self | main.rs:1061:5:1064:5 | struct NonEmptyListStruct |
 | main.rs:1067:16:1067:16 | T | main.rs:1066:27:1066:27 | T |
 | main.rs:1068:14:1068:14 | T | main.rs:1066:27:1066:27 | T |
 | main.rs:1068:17:1068:25 | Box::<...> | {EXTERNAL LOCATION} | struct Box |
+| main.rs:1068:21:1068:24 | Self | main.rs:1066:5:1069:5 | enum NonEmptyListEnum |
 | main.rs:1075:13:1075:16 | Copy | {EXTERNAL LOCATION} | trait Copy |
 | main.rs:1077:17:1077:17 | T | main.rs:1074:9:1074:9 | T |
 | main.rs:1078:16:1078:16 | T | main.rs:1074:9:1074:9 | T |
+| main.rs:1078:23:1078:26 | Self | main.rs:1071:5:1079:5 | union NonEmptyListUnion |
 | main.rs:1083:5:1083:6 | my | main.rs:1:1:1:7 | mod my |
 | main.rs:1083:5:1083:14 | ...::nested | my.rs:1:1:1:15 | mod nested |
 | main.rs:1083:5:1083:23 | ...::nested1 | my/nested.rs:1:1:17:1 | mod nested1 |