Sema: Diagnose init calls as uses of generic params.

We currently emit the allocating initializer of an @objc initializer of a generic ObjC class as a true generic function rather than pseudogeneric (rdar://problem/27796375). This would be a breaking change and has nonobvious tradeoffs if we "fix" it, so for the time being, just diagnose attempts to invoke an initializer from inside an @objc generic extension method. It's easy to work around by as!-casting the result of constructing the upper bound type. Fixes rdar://problem/26867815.

Author: jckarter

lib/Sema/TypeCheckCaptures.cpp

@@ -199,6 +199,13 @@ class FindCapturedVars : public ASTWalker {
   std::pair<bool, Expr *> walkToDeclRefExpr(DeclRefExpr *DRE) {
     auto *D = DRE->getDecl();
 
+    // Capture the generic parameters of the decl.
+    if (!AFR.isObjC() || !D->isObjC() || isa<ConstructorDecl>(D)) {
+      for (auto sub : DRE->getDeclRef().getSubstitutions()) {
+        checkType(sub.getReplacement(), DRE->getLoc());
+      }
+    }
+
     // DC is the DeclContext where D was defined
     // CurDC is the DeclContext where D was referenced
     auto DC = D->getDeclContext();
@@ -430,17 +437,22 @@ class FindCapturedVars : public ASTWalker {
               && !E->getType()->is<AnyMetatypeType>());
 
     // Accessing @objc members doesn't require type metadata.
+    // rdar://problem/27796375 -- allocating init entry points for ObjC
+    // initializers are generated as true Swift generics, so reify type
+    // parameters.
     if (auto memberRef = dyn_cast<MemberRefExpr>(E))
       return !memberRef->getMember().getDecl()->hasClangNode();
 
     if (auto applyExpr = dyn_cast<ApplyExpr>(E)) {
       if (auto methodApply = dyn_cast<ApplyExpr>(applyExpr->getFn())) {
         if (auto callee = dyn_cast<DeclRefExpr>(methodApply->getFn())) {
-          return !callee->getDecl()->isObjC();
+          return !callee->getDecl()->isObjC()
+            || isa<ConstructorDecl>(callee->getDecl());
         }
       }
       if (auto callee = dyn_cast<DeclRefExpr>(applyExpr->getFn())) {
-        return !callee->getDecl()->isObjC();
+        return !callee->getDecl()->isObjC()
+          || isa<ConstructorDecl>(callee->getDecl());
       }
     }
 

test/ClangModules/objc_bridging_generics.swift

@@ -265,6 +265,14 @@ extension AnimalContainer {
     T.apexPredator = x // expected-note{{used here}}
   }
 
+  // rdar://problem/27796375 -- allocating init entry points for ObjC
+  // initializers are generated as true Swift generics, so reify type
+  // parameters.
+  // expected-error@+1{{extension of a generic Objective-C class cannot access the class's generic parameters}}
+  func usesGenericParamE(_ x: T) {
+    _ = GenericClass(thing: x) // expected-note{{used here}}
+  }
+
   func checkThatMethodsAreObjC() {
     _ = #selector(AnimalContainer.doesntUseGenericParam1)
     _ = #selector(AnimalContainer.doesntUseGenericParam2)
@@ -283,9 +291,11 @@ extension AnimalContainer {
 
 extension PettableContainer {
   func doesntUseGenericParam(_ x: T, _ y: T.Type) {
-    _ = type(of: x).init(fur: x).other()
+    // TODO: rdar://problem/27796375--allocating entry points are emitted as
+    // true generics.
+    // _ = type(of: x).init(fur: x).other()
     _ = type(of: x).adopt().other()
-    _ = y.init(fur: x).other()
+    // _ = y.init(fur: x).other()
     _ = y.adopt().other()
     x.pet()
     x.pet(with: x)