[PrintAsObjC] Import/fwd-declare types used in @_cdecl functions.

lib/PrintAsObjC/DeclAndTypePrinter.cpp

@@ -773,7 +773,7 @@ class DeclAndTypePrinter::Implementation
 
     printAvailability(FD);
 
-    os << ';';
+    os << ";\n";
   }
 
   enum class PrintLeadingSpace : bool {

lib/PrintAsObjC/ModuleContentsWriter.cpp

@@ -235,6 +235,30 @@ class ModuleWriter {
     });
   }
 
+  void forwardDeclareType(const TypeDecl *TD) {
+    if (auto CD = dyn_cast<ClassDecl>(TD)) {
+      if (!forwardDeclare(CD)) {
+        (void)addImport(CD);
+      }
+    } else if (auto PD = dyn_cast<ProtocolDecl>(TD)) {
+      forwardDeclare(PD);
+    } else if (auto TAD = dyn_cast<TypeAliasDecl>(TD)) {
+      bool imported = false;
+      if (TAD->hasClangNode())
+        imported = addImport(TD);
+      assert((imported || !TAD->isGeneric()) &&
+             "referencing non-imported generic typealias?");
+    } else if (addImport(TD)) {
+      return;
+    } else if (auto ED = dyn_cast<EnumDecl>(TD)) {
+      forwardDeclare(ED);
+    } else if (isa<AbstractTypeParamDecl>(TD)) {
+      llvm_unreachable("should not see type params here");
+    } else {
+      assert(false && "unknown local type decl");
+    }
+  }
+
   bool forwardDeclareMemberTypes(DeclRange members, const Decl *container) {
     PrettyStackTraceDecl
         entry("printing forward declarations needed by members of", container);
@@ -312,26 +336,7 @@ class ModuleWriter {
           // FIXME: It would be nice to diagnose this.
         }
 
-        if (auto CD = dyn_cast<ClassDecl>(TD)) {
-          if (!forwardDeclare(CD)) {
-            (void)addImport(CD);
-          }
-        } else if (auto PD = dyn_cast<ProtocolDecl>(TD)) {
-          forwardDeclare(PD);
-        } else if (auto TAD = dyn_cast<TypeAliasDecl>(TD)) {
-          bool imported = false;
-          if (TAD->hasClangNode())
-            imported = addImport(TD);
-          assert((imported || !TAD->isGeneric()) && "referencing non-imported generic typealias?");
-        } else if (addImport(TD)) {
-          return;
-        } else if (auto ED = dyn_cast<EnumDecl>(TD)) {
-          forwardDeclare(ED);
-        } else if (isa<AbstractTypeParamDecl>(TD)) {
-          llvm_unreachable("should not see type params here");
-        } else {
-          assert(false && "unknown local type decl");
-        }
+        forwardDeclareType(TD);
       });
 
       if (needsToBeIndividuallyDelayed) {
@@ -374,11 +379,22 @@ class ModuleWriter {
     printer.print(CD);
     return true;
   }
-  
+
   bool writeFunc(const FuncDecl *FD) {
     if (addImport(FD))
       return true;
 
+    PrettyStackTraceDecl entry(
+        "printing forward declarations needed by function", FD);
+    ReferencedTypeFinder::walk(
+        FD->getInterfaceType(),
+        [&](ReferencedTypeFinder &finder, const TypeDecl *TD) {
+          PrettyStackTraceDecl entry("walking its interface type, currently at",
+                                     TD);
+          forwardDeclareType(TD);
+        });
+
+    os << '\n';
     printer.print(FD);
     return true;
   }

test/PrintAsObjC/cdecl-imports.swift

@@ -0,0 +1,33 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck %s -parse-as-library -emit-objc-header-path %t/swift.h
+// RUN: %FileCheck %s < %t/swift.h
+// RUN: %check-in-clang %t/swift.h
+
+// REQUIRES: objc_interop
+
+import CoreGraphics
+import Foundation
+
+// CHECK: @import CoreGraphics;
+// CHECK-NOT: @import Foundation;
+
+// CHECK: @class Bee;
+// CHECK-LABEL: Bee * _Nonnull fwd_declares_bee(void) SWIFT_WARN_UNUSED_RESULT;
+
+@_cdecl("fwd_declares_bee")
+public func fwdDeclaresBee() -> Bee { fatalError() }
+
+// CHECK: @class Hive;
+// CHECK-LABEL: void fwd_declares_hive(SWIFT_NOESCAPE Hive * _Nonnull (* _Nonnull bzzz)(Bee * _Nonnull));
+
+@_cdecl("fwd_declares_hive")
+public func fwdDeclaresHive(bzzz: @convention(c) (Bee) -> Hive) { fatalError() }
+
+// CHECK: @protocol NSWobbling;
+// CHECK-LABEL: void fwd_declares_wobble(id <NSWobbling> _Nonnull wobbler);
+
+@_cdecl("fwd_declares_wobble")
+public func fwdDeclaresWobble(wobbler: NSWobbling) { fatalError() }
+
+@_cdecl("imports_cgpoint")
+public func importsCGPoint(pt: CGPoint) { fatalError() }