Type inference: Improve base type matching

shared/typeinference/codeql/typeinference/internal/TypeInference.qll

@@ -1504,6 +1504,80 @@ module Make1<LocationSig Location, InputSig1<Location> Input1> {
             hasNotTypeArgument(a, target, tp)
           )
         }
+
+        predicate baseTypeMatchAtTypeParameter(
+          Access a, AccessEnvironment e, AccessPosition apos, Declaration target, TypeParameter tp,
+          TypePath prefix, TypePath requiredPrefix
+        ) {
+          exists(
+            TypePath pathToTypeParamInConstraint, TypePath pathToTp, TypePath pathToTypeParamInSub
+          |
+            argRootTypeSatisfiesTargetTypeCand(_, target, pragma[only_bind_into](apos), tp, pathToTp) and
+            SatisfiesParameterConstraint::satisfiesConstraintAtTypeParameter(MkRelevantAccess(a,
+                pragma[only_bind_into](apos), e),
+              MkRelevantTarget(target, pragma[only_bind_into](apos)), pathToTypeParamInConstraint,
+              pathToTypeParamInSub) and
+            hasNotTypeArgument(a, target, tp)
+          |
+            /*
+             * Example:
+             *
+             * ```swift
+             * class Base<B> {
+             *   init(_ value: B) {}
+             * }
+             *
+             * class Derived<D>: Base<[D]> {
+             *   init(_ value: D) { super.init([value]) }
+             * }
+             *
+             * func foo<T>(_ value: T, _ base: Base<T>) { }
+             *
+             * foo([2], Derived(<unknown>))
+             * ```
+             *
+             * - tp = T (bound by `foo`)
+             * - prefix = pathToTypeParamInSub = "D"
+             * - requiredPrefix = "Element"
+             * - pathToTypeParamInConstraint = "B.Element"
+             * - pathToTp = "B"
+             */
+
+            pathToTypeParamInConstraint = pathToTp.appendInverse(requiredPrefix) and
+            prefix = pathToTypeParamInSub
+            or
+            /*
+             * Example:
+             *
+             * ```swift
+             * class Base<B> {
+             *   init(_ value: B) {}
+             * }
+             *
+             * class Derived<D>: Base<D> {
+             *   override init(_ value: D) { super.init(value) }
+             * }
+             *
+             * func foo<T>(_ value: T, _ base: Base<T?>) {}
+             *
+             * foo(2, Derived2(Optional.none))
+             * ```
+             *
+             * - tp = T (bound by `foo`)
+             * - prefix = "D.Wrapped"
+             * - pathToTypeParamInSub = "D"
+             * - requiredPrefix = ""
+             * - pathToTypeParamInConstraint = "B"
+             * - pathToTp = "B.Wrapped"
+             */
+
+            exists(TypePath path0 |
+              pathToTp = pathToTypeParamInConstraint.appendInverse(path0) and
+              prefix = pathToTypeParamInSub.append(path0) and
+              requiredPrefix = TypePath::nil()
+            )
+          )
+        }
       }
 
       private module AccessConstraint {
@@ -1745,6 +1819,16 @@ module Make1<LocationSig Location, InputSig1<Location> Input1> {
           )
         )
         or
+        exists(
+          Declaration target, TypePath prefix, TypePath requiredPrefix, TypePath suffix,
+          TypeParameter tp
+        |
+          AccessBaseType::baseTypeMatchAtTypeParameter(a, e, apos, target, tp, prefix,
+            requiredPrefix) and
+          typeMatch(a, e, target, requiredPrefix.appendInverse(suffix), result, tp) and
+          path = prefix.append(suffix)
+        )
+        or
         exists(
           Declaration target, TypePath prefix, TypeMention constraint,
           TypePath pathToTypeParamInConstraint, TypePath pathToTypeParamInSub

unified/ql/lib/codeql/unified/internal/FacadeAst.qll

@@ -319,4 +319,9 @@
     /** Gets the number of parameters of this function. */
     int getNumberOfParameters() { result = count(this.getAParameter()) }
   }
+
+  class ArrayLiteral extends G::ArrayLiteral {
+    /** Gets the number of elements in this array literal. */
+    int getNumberOfElements() { result = count(this.getAnElement()) }
+  }
 }

unified/ql/lib/codeql/unified/internal/typeinference/TypeInference.qll

@@ -731,6 +731,11 @@ private module Input3 implements InputSig3 {
       not exists(n.(MemberAccessExpr).getBase().(TypeMention).getTypeAt(path))
     ) and
     result instanceof UnknownType
+    or
+    hasResultValue(n) and
+    n.(ArrayLiteral).getNumberOfElements() = 0 and
+    path = TypePath::singleton(getArrayElementTypeParameter()) and
+    result instanceof UnknownType
   }
 
   pragma[nomagic]

unified/ql/test/library-tests/type-inference/generics.swift

@@ -155,22 +155,64 @@ class Derived<T1, T2>: Base<T2, T1> {
   init(_ v1: T1, _ v2: T2) {
     super.init(v2, v1)  // $ type=v2:T2 type=v1:T1 target=Base.init
   }
+
+  convenience init(_ v1: T1) {
+    fatalError()
+  }
 }
 
-class DerivedDerived<D>: Derived<D, Bool> {
-  init(_ v: D) {
-    super.init(v, true)  // $ type=v:D target=Derived.init
+class DerivedDerived<D>: Derived<[D], Bool> {
+  init(_ v: [D]) {
+    super.init(v, true)  // $ type=v@Array<Element>:D target=Derived.init
+  }
+
+  convenience init() {
+    fatalError()
   }
 }
 
+func foo<T1, T2, T3: Base<T1, T2>>(_ value1: T1, _ value2: T2, _ base: T3) -> T3 {
+  return base
+}
+
+func foo2<T1, T2>(_ value1: T1, _ value2: T2, _ base: Base<T1, T2>) {
+
+}
+
+func bar<A, B, C: Base<A, [B]>>(_ value1: A, _ value2: B, _ base: C) -> C {
+  return base
+
+}
+
+func bar2<A, B>(_ value1: A, _ value2: B, _ base: Base<A, [B]>) {}
+
+func baz<A, B, C: Base<A, B?>>(_ value1: A, _ value2: B, _ base: C) -> C {
+  return base
+
+}
+
+func baz2<A, B>(_ value1: A, _ value2: B, _ base: Base<A, B?>) {}
+
 func testDerived() {
   let d = Derived(1, "x")  // $ type=d@Derived<T1>:Int type=d@Derived<T2>:String target=Derived.init
   let v1 = d.getValue1()  // $ type=v1:String target=Base.getValue1
   let v2 = d.getValue2()  // $ type=v2:Int target=Base.getValue2
 
-  let dd = DerivedDerived("hello")  // $ type=dd@DerivedDerived<D>:String target=DerivedDerived.init
+  let dd = DerivedDerived(["hello"])  // $ type=dd@DerivedDerived<D>:String target=DerivedDerived.init
   let vv1 = dd.getValue1()  // $ type=vv1:Bool target=Base.getValue1
-  let vv2 = dd.getValue2()  // $ type=vv2:String target=Base.getValue2
+  let vv2 = dd.getValue2()  // $ type=vv2@Array<Element>:String target=Base.getValue2
+
+  let x = foo(false, [2], DerivedDerived([]))  // $ target=foo target=DerivedDerived.init type=x@DerivedDerived<D>:Int
+
+  foo2(false, [2], DerivedDerived([]))  // $ target=foo2 target=DerivedDerived.init type=DerivedDerived(...)@DerivedDerived<D>:Int
+
+  let y = bar(false, 2, DerivedDerived([]))  // $ type=y@DerivedDerived<D>:Int target=bar target=DerivedDerived.init
+
+  bar2(false, 2, DerivedDerived([]))  // $ target=bar2 target=DerivedDerived.init type=DerivedDerived(...)@DerivedDerived<D>:Int
+
+  let w = baz(false, 2, Derived(Optional.none))  // $ type=w@Derived<T1>.Optional<Wrapped>:Int target=baz target=Derived.init field=Optional.none
+
+  baz2(false, 2, Derived(Optional.none))  // $ target=baz2 target=Derived.init field=Optional.none type=Derived(...)@Derived<T1>.Optional<Wrapped>:Int
 }
 
 // --- Generics and protocols ---