Merge pull request #15781 from jckarter/demangle-symbolic-reference-nested-type

Runtime: Properly handle demangling nested generic typerefs with symbolic manglings.

Author: jckarter

stdlib/public/runtime/MetadataLookup.cpp

@@ -747,8 +747,20 @@ class DecodedMetadataBuilder {
     // Figure out the various levels of generic parameters we have in
     // this type.
     std::vector<unsigned> genericParamCounts;
-    bool innermostIsGeneric =
-      _gatherGenericParameterCounts(typeDecl, genericParamCounts);
+    bool innermostIsGeneric;
+
+    // If we have no parent given, try to form the whole type in one go.
+    if (!parent) {
+      innermostIsGeneric = !genericArgs.empty();
+      if (innermostIsGeneric) {
+        genericParamCounts.push_back(genericArgs.size());
+      }
+    // Otherwise, we'll need to steal the generic arguments from the parent
+    // type to build a nested type.
+    } else {
+      innermostIsGeneric = _gatherGenericParameterCounts(typeDecl,
+                                                         genericParamCounts);
+    }
     bool isGeneric = !genericParamCounts.empty();
 
     // Gather the generic arguments.

test/stdlib/Mirror.swift

@@ -782,4 +782,20 @@ mirrors.test("String.init") {
   expectEqual("42", String(reflecting: 42))
   expectEqual("\"42\"", String(reflecting: "42"))
 }
+
+struct a<b>  {
+    enum c{}
+}
+class d  {}
+struct e<f> {
+    var constraints: [Int: a<f>.c] = [:]
+}
+
+mirrors.test("field with generic nested type") {
+  let x = e<d>()
+  
+  expectTrue(type(of: Mirror(reflecting: x).children.first!.value)
+              == [Int: a<d>.c].self)
+}
+
 runAllTests()