SILGen: Fix crash when referencing dynamic Self from @convention(c) closure

Fixes <rdar://problem/57510056>.

Author: slavapestov

include/swift/AST/DiagnosticsSIL.def

@@ -116,7 +116,7 @@ ERROR(unsupported_c_function_pointer_conversion,none,
 ERROR(c_function_pointer_from_function_with_context,none,
       "a C function pointer cannot be formed from a "
       "%select{local function|closure}0 that captures "
-      "%select{context|generic parameters|dynamic Self type|<<error>}1",
+      "%select{context|generic parameters|dynamic Self type}1",
       (bool, unsigned))
 
 ERROR(objc_selector_malformed,none,"the type ObjectiveC.Selector is malformed",

lib/SILGen/SILGenExpr.cpp

@@ -1550,25 +1550,22 @@ ManagedValue emitCFunctionPointer(SILGenFunction &SGF,
   // C function pointers cannot capture anything from their context.
   auto captures = SGF.SGM.Types.getLoweredLocalCaptures(constant);
 
-  if (captures.hasGenericParamCaptures() ||
+  if (!captures.getCaptures().empty() ||
+      captures.hasGenericParamCaptures() ||
       captures.hasDynamicSelfCapture() ||
-      captures.hasLocalCaptures() ||
       captures.hasOpaqueValueCapture()) {
-    unsigned kind;
-    if (captures.hasLocalCaptures())
-      kind = 0;
-    else if (captures.hasGenericParamCaptures())
+    unsigned kind = 0;
+    if (captures.hasGenericParamCaptures())
       kind = 1;
-    else if (captures.hasLocalCaptures())
+    else if (captures.hasDynamicSelfCapture())
       kind = 2;
-    else
-      kind = 3;
     SGF.SGM.diagnose(expr->getLoc(),
                      diag::c_function_pointer_from_function_with_context,
                      /*closure*/ constant.hasClosureExpr(),
                      kind);
 
-    return SGF.emitUndef(constantInfo.getSILType());
+    auto loweredTy = SGF.getLoweredType(conversionExpr->getType());
+    return SGF.emitUndef(loweredTy);
   }
 
   return convertCFunctionSignature(

test/SILGen/c_function_pointers.swift

@@ -105,3 +105,10 @@ func pointers_to_nested_local_functions_in_generics<T>(x: T) -> Int{
 func capture_list_no_captures(x: Int) {
   calls({ [x] in $0 }, 0) // expected-warning {{capture 'x' was never used}}
 }
+
+class Selfless {
+  func capture_dynamic_self() {
+    calls_no_args { _ = Self.self; return 0 }
+    // expected-error@-1 {{a C function pointer cannot be formed from a closure that captures dynamic Self type}}
+  }
+}