Rust: Improve handling of occurrences of the Self type parameter

Author: paldepind

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

@@ -151,25 +151,61 @@ class NonAliasPathTypeMention extends PathTypeMention {
     result = this.getQualifier().getSegment().getGenericArgList().getTypeArg(i)
   }
 
-  private TypeMention getPositionalTypeArgument(int i) {
-    result = this.getPositionalTypeArgument0(i)
+  /**
+   * Gets the type mention that instantiates the implicit `Self` type parameter
+   * for this path, if it occurs in the position of a trait bound.
+   */
+  private TypeMention getSelfTypeParameter() {
+    exists(ImplItemNode impl | this = impl.getTraitPath() and result = impl.(Impl).getSelfTy())
+    or
+    exists(Trait subTrait |
+      this = subTrait.getATypeBound().getTypeRepr().(PathTypeRepr).getPath() and
+      result.(SelfTypeParameterMention).getTrait() = subTrait
+    )
+    or
+    exists(TypeParamItemNode tp | this = tp.getABoundPath() and result = tp)
+  }
+
+  private Type getPositionalTypeArgument(int i, TypePath path) {
+    result = this.getPositionalTypeArgument0(i).resolveTypeAt(path)
     or
+    result = this.getDefaultPositionalTypeArgument(i, path)
+  }
+
+  private Type getDefaultPositionalTypeArgument(int i, TypePath path) {
     // If a type argument is not given in the path, then we use the default for
     // the type parameter if one exists for the type.
     not exists(this.getPositionalTypeArgument0(i)) and
-    result = this.resolveRootType().getTypeParameterDefault(i) and
     // Defaults only apply to type mentions in type annotations
-    this = any(PathTypeRepr ptp).getPath().getQualifier*()
+    this = any(PathTypeRepr ptp).getPath().getQualifier*() and
+    exists(Type ty, TypePath prefix |
+      ty = this.resolveRootType().getTypeParameterDefault(i).resolveTypeAt(prefix) and
+      if not ty = TSelfTypeParameter(resolved)
+      then result = ty and path = prefix
+      else
+        // When a default contains an implicit `Self` type parameter, it should
+        // be substituted for the type that implements the trait.
+        exists(TypePath suffix |
+          path = prefix.append(suffix) and
+          result = this.getSelfTypeParameter().resolveTypeAt(suffix)
+        )
+    )
   }
 
-  /** Gets the type mention in this path for the type parameter `tp`, if any. */
-  pragma[nomagic]
-  private TypeMention getTypeMentionForTypeParameter(TypeParameter tp) {
+  /**
+   * Gets the type for this path for the type parameter `tp` at `path`, when the
+   * type parameter does not correspond directly to a type mention.
+   */
+  private Type getTypeForTypeParameterAt(TypeParameter tp, TypePath path) {
     exists(int i |
-      result = this.getPositionalTypeArgument(pragma[only_bind_into](i)) and
+      result = this.getPositionalTypeArgument(pragma[only_bind_into](i), path) and
       tp = this.resolveRootType().getPositionalTypeParameter(pragma[only_bind_into](i))
     )
-    or
+  }
+
+  /** Gets the type mention in this path for the type parameter `tp`, if any. */
+  pragma[nomagic]
+  private TypeMention getTypeMentionForTypeParameter(TypeParameter tp) {
     exists(TypeAlias alias |
       result = this.getAnAssocTypeArgument(alias) and
       tp = TAssociatedTypeTypeParameter(alias)
@@ -237,9 +273,17 @@ class NonAliasPathTypeMention extends PathTypeMention {
     typePath.isEmpty() and
     result = this.resolveRootType()
     or
-    exists(TypeParameter tp, TypePath suffix |
-      result = this.getTypeMentionForTypeParameter(tp).resolveTypeAt(suffix) and
-      typePath = TypePath::cons(tp, suffix)
+    exists(TypeParameter tp, TypePath suffix | typePath = TypePath::cons(tp, suffix) |
+      result = this.getTypeForTypeParameterAt(tp, suffix)
+      or
+      result = this.getTypeMentionForTypeParameter(tp).resolveTypeAt(suffix)
+    )
+    or
+    // When the path refers to a trait, then the implicit `Self` type parameter
+    // should be instantiated from the context.
+    exists(TypePath suffix |
+      result = this.getSelfTypeParameter().resolveTypeAt(suffix) and
+      typePath = TypePath::cons(TSelfTypeParameter(resolved), suffix)
     )
   }
 }
@@ -296,6 +340,11 @@ class TraitMention extends TypeMention instanceof TraitItemNode {
     typePath.isEmpty() and
     result = TTrait(this)
     or
+    // The implicit `Self` type parameter occurs at the `Self` type parameter
+    // position.
+    typePath = TypePath::singleton(TSelfTypeParameter(this)) and
+    result = TSelfTypeParameter(this)
+    or
     exists(TypeAlias alias |
       alias = super.getAnAssocItem() and
       typePath = TypePath::singleton(result) and

rust/ql/test/library-tests/type-inference/main.rs

@@ -666,7 +666,7 @@ mod trait_default_self_type_parameter {
 
     // The trait bound on `T` uses the default for `A` which contains `Self`
     fn tp_uses_default<S: TraitWithSelfTp>(thing: S) -> i64 {
-        let _ms = thing.get_a(); // $ target=TraitWithSelfTp::get_a MISSING: type=_ms:T.S
+        let _ms = thing.get_a(); // $ target=TraitWithSelfTp::get_a type=_ms:T.S
         0
     }
 
@@ -675,7 +675,7 @@ mod trait_default_self_type_parameter {
 
     fn get_a_through_tp<S: SubTraitOfTraitWithSelfTp>(thing: &S) {
         // `thing` is a `TraitWithSelfTp` through the trait hierarchy
-        let _ms = get_a(thing); // $ target=get_a MISSING: type=_ms:T.S
+        let _ms = get_a(thing); // $ target=get_a type=_ms:T.S
     }
 
     struct MyStruct {
@@ -693,7 +693,7 @@ mod trait_default_self_type_parameter {
 
     pub fn test() {
         let s = MyStruct { value: 0 };
-        let _ms = get_a(&s); // $ target=get_a MISSING: type=_ms:T.MyStruct
+        let _ms = get_a(&s); // $ target=get_a type=_ms:T.MyStruct
     }
 }
 

rust/ql/test/library-tests/type-inference/type-inference.expected

@@ -2013,18 +2013,18 @@ inferType
 | main.rs:668:44:668:48 | thing |  | main.rs:668:24:668:41 | S |
 | main.rs:668:61:671:5 | { ... } |  | {EXTERNAL LOCATION} | i64 |
 | main.rs:669:13:669:15 | _ms |  | {EXTERNAL LOCATION} | Option |
-| main.rs:669:13:669:15 | _ms | T | main.rs:656:5:661:5 | Self [trait TraitWithSelfTp] |
+| main.rs:669:13:669:15 | _ms | T | main.rs:668:24:668:41 | S |
 | main.rs:669:19:669:23 | thing |  | main.rs:668:24:668:41 | S |
 | main.rs:669:19:669:31 | thing.get_a() |  | {EXTERNAL LOCATION} | Option |
-| main.rs:669:19:669:31 | thing.get_a() | T | main.rs:656:5:661:5 | Self [trait TraitWithSelfTp] |
+| main.rs:669:19:669:31 | thing.get_a() | T | main.rs:668:24:668:41 | S |
 | main.rs:670:9:670:9 | 0 |  | {EXTERNAL LOCATION} | i32 |
 | main.rs:670:9:670:9 | 0 |  | {EXTERNAL LOCATION} | i64 |
 | main.rs:676:55:676:59 | thing |  | file://:0:0:0:0 | & |
 | main.rs:676:55:676:59 | thing | &T | main.rs:676:25:676:52 | S |
 | main.rs:678:13:678:15 | _ms |  | {EXTERNAL LOCATION} | Option |
-| main.rs:678:13:678:15 | _ms | T | main.rs:656:5:661:5 | Self [trait TraitWithSelfTp] |
+| main.rs:678:13:678:15 | _ms | T | main.rs:676:25:676:52 | S |
 | main.rs:678:19:678:30 | get_a(...) |  | {EXTERNAL LOCATION} | Option |
-| main.rs:678:19:678:30 | get_a(...) | T | main.rs:656:5:661:5 | Self [trait TraitWithSelfTp] |
+| main.rs:678:19:678:30 | get_a(...) | T | main.rs:676:25:676:52 | S |
 | main.rs:678:25:678:29 | thing |  | file://:0:0:0:0 | & |
 | main.rs:678:25:678:29 | thing | &T | main.rs:676:25:676:52 | S |
 | main.rs:687:18:687:22 | SelfParam |  | file://:0:0:0:0 | & |
@@ -2041,9 +2041,9 @@ inferType
 | main.rs:695:17:695:37 | MyStruct {...} |  | main.rs:681:5:683:5 | MyStruct |
 | main.rs:695:35:695:35 | 0 |  | {EXTERNAL LOCATION} | i32 |
 | main.rs:696:13:696:15 | _ms |  | {EXTERNAL LOCATION} | Option |
-| main.rs:696:13:696:15 | _ms | T | main.rs:656:5:661:5 | Self [trait TraitWithSelfTp] |
+| main.rs:696:13:696:15 | _ms | T | main.rs:681:5:683:5 | MyStruct |
 | main.rs:696:19:696:27 | get_a(...) |  | {EXTERNAL LOCATION} | Option |
-| main.rs:696:19:696:27 | get_a(...) | T | main.rs:656:5:661:5 | Self [trait TraitWithSelfTp] |
+| main.rs:696:19:696:27 | get_a(...) | T | main.rs:681:5:683:5 | MyStruct |
 | main.rs:696:25:696:26 | &s |  | file://:0:0:0:0 | & |
 | main.rs:696:25:696:26 | &s | &T | main.rs:681:5:683:5 | MyStruct |
 | main.rs:696:26:696:26 | s |  | main.rs:681:5:683:5 | MyStruct |
@@ -4776,7 +4776,6 @@ inferType
 | main.rs:2312:16:2312:21 | self.0 |  | main.rs:2307:10:2307:17 | T |
 | main.rs:2312:31:2312:35 | other |  | main.rs:2305:5:2305:19 | S |
 | main.rs:2312:31:2312:35 | other | T | main.rs:2307:10:2307:17 | T |
-| main.rs:2312:31:2312:37 | other.0 |  | main.rs:2267:5:2272:5 | Self [trait MyAdd] |
 | main.rs:2312:31:2312:37 | other.0 |  | main.rs:2307:10:2307:17 | T |
 | main.rs:2320:19:2320:22 | SelfParam |  | main.rs:2305:5:2305:19 | S |
 | main.rs:2320:19:2320:22 | SelfParam | T | main.rs:2316:10:2316:17 | T |