[ClangImporter] Forward generic parameters to renamed typealias

While trying to import declaration which requires renaming forward
generic parameters (if any) to newly created typealias.

(cherry picked from commit 1f3714f)

Author: xedin

lib/ClangImporter/ImportDecl.cpp

@@ -5183,18 +5183,6 @@ Decl *SwiftDeclConverter::importCompatibilityTypeAlias(
   if (!typeDecl)
     return nullptr;
 
-  // Deliberately use an UnboundGenericType to avoid having to translate over
-  // generic parameters.
-  Type underlyingType;
-  if (auto *underlyingAlias = dyn_cast<TypeAliasDecl>(typeDecl)) {
-    if (underlyingAlias->isGeneric())
-      underlyingType = underlyingAlias->getUnboundGenericType();
-    else
-      underlyingType = Impl.getSugaredTypeReference(underlyingAlias);
-  } else {
-    underlyingType = cast<NominalTypeDecl>(typeDecl)->getDeclaredType();
-  }
-
   auto dc = Impl.importDeclContextOf(decl,
                                      compatibilityName.getEffectiveContext());
   if (!dc)
@@ -5205,7 +5193,15 @@ Decl *SwiftDeclConverter::importCompatibilityTypeAlias(
       decl, AccessLevel::Public, Impl.importSourceLoc(decl->getLocStart()),
       SourceLoc(), compatibilityName.getDeclName().getBaseIdentifier(),
       Impl.importSourceLoc(decl->getLocation()), /*generic params*/nullptr, dc);
-  alias->setUnderlyingType(underlyingType);
+
+  auto *GTD = dyn_cast<GenericTypeDecl>(typeDecl);
+  if (GTD && !isa<ProtocolDecl>(GTD)) {
+    alias->setGenericEnvironment(GTD->getGenericEnvironment());
+    if (GTD->isGeneric())
+      alias->setGenericParams(GTD->getGenericParams()->clone(alias));
+  }
+
+  alias->setUnderlyingType(Impl.getSugaredTypeReference(typeDecl));
 
   // Record that this is the official version of this declaration.
   Impl.ImportedDecls[{decl->getCanonicalDecl(), getVersion()}] = alias;

test/APINotes/versioned-objc.swift

@@ -34,9 +34,9 @@ func testRenamedGeneric() {
 
   class SwiftClass {}
 
-  // CHECK-DIAGS-3:[[@LINE+1]]:{{[0-9]+}}: error: 'RenamedGeneric' requires that 'SwiftClass' inherit from 'Base'
+  // CHECK-DIAGS-3:[[@LINE+1]]:{{[0-9]+}}: error: 'OldRenamedGeneric' requires that 'SwiftClass' inherit from 'Base'
   let _: OldRenamedGeneric<SwiftClass> = RenamedGeneric<SwiftClass>()
-  // CHECK-DIAGS-4:[[@LINE-1]]:{{[0-9]+}}: error: 'RenamedGeneric' requires that 'SwiftClass' inherit from 'Base'
+  // CHECK-DIAGS-4:[[@LINE-1]]:{{[0-9]+}}: error: 'OldRenamedGeneric' requires that 'SwiftClass' inherit from 'Base'
 
   // CHECK-DIAGS-3:[[@LINE+1]]:{{[0-9]+}}: error: 'RenamedGeneric' requires that 'SwiftClass' inherit from 'Base'
   let _: RenamedGeneric<SwiftClass> = OldRenamedGeneric<SwiftClass>()