If a package func has a default arg, its symbol is not generated

in TBD, causing a linker error. This is because the default arg
is not generated during silgen. This PR adds a check to make sure
it's represented by SILDeclRef and its linkage emitted.

Resolves rdar://116184295

Author: elsh

lib/SIL/IR/SILSymbolVisitor.cpp

@@ -420,9 +420,14 @@ class SILSymbolVisitorImpl : public ASTVisitor<SILSymbolVisitorImpl> {
 
   void visitDefaultArguments(ValueDecl *VD, ParameterList *PL) {
     auto moduleDecl = VD->getModuleContext();
-    auto publicDefaultArgGenerators = moduleDecl->isTestingEnabled() ||
-                                      moduleDecl->arePrivateImportsEnabled();
-    if (Ctx.getOpts().PublicSymbolsOnly && !publicDefaultArgGenerators)
+    // Check if symbols should be more visible than their declared access level.
+    // In case of `package` access level, the symbol should be visible by an
+    // external module in the same package, thus the default argument should be
+    // generated and its linkage emitted.
+    auto shouldGenerateDefaultArgs = moduleDecl->isTestingEnabled() ||
+                                     moduleDecl->arePrivateImportsEnabled() ||
+                                     VD->getFormalAccess() == AccessLevel::Package;
+    if (Ctx.getOpts().PublicSymbolsOnly && !shouldGenerateDefaultArgs)
       return;
 
     // In Swift 3 (or under -enable-testing), default arguments (of public

test/Sema/package_symbol_with_default_arg.swift

@@ -0,0 +1,63 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-build-swift-dylib(%t/%target-library-name(Utils)) %t/Utils.swift \
+// RUN:  -module-name Utils -package-name mypkg \
+// RUN:  -emit-module -emit-module-path %t/Utils.swiftmodule \
+// RUN:  -emit-tbd -emit-tbd-path %t/libUtils.tbd -Xfrontend -tbd-install_name=%t/libUtils.dylib
+
+// RUN: %FileCheck %s --check-prefix CHECK-TBD < %t/libUtils.tbd
+// CHECK-TBD-NOT: _$s5Utils6pubBar3argS2i_tFfA_
+// CHECK-TBD-NOT: _$s5Utils11internalBar3argS2i_tF
+// CHECK-TBD-NOT: _$s5Utils11internalBar3argS2i_tFfA_
+// CHECK-TBD-NOT: _$s5Utils11internalFoo3argS2i_tF
+// CHECK-TBD: _$s5Utils6pkgBar3argS2i_tF
+// CHECK-TBD: _$s5Utils6pkgBar3argS2i_tFfA_
+// CHECK-TBD: _$s5Utils6pkgFoo3argS2i_tF
+// CHECK-TBD: _$s5Utils6pubBar3argS2i_tF
+// CHECK-TBD: _$s5Utils6pubFoo3argS2i_tF
+
+// RUN: %target-build-swift-dylib(%t/%target-library-name(UtilsForTesting)) %t/Utils.swift \
+// RUN:  -module-name UtilsForTesting -package-name testpkg \
+// RUN:  -emit-module -emit-module-path %t/UtilsForTesting.swiftmodule \
+// RUN:  -emit-tbd -emit-tbd-path %t/libUtilsForTesting.tbd -Xfrontend -tbd-install_name=%t/libUtilsForTesting.dylib \
+// RUN:  -enable-testing
+
+
+// RUN: %FileCheck %s --check-prefix CHECK-TEST < %t/libUtilsForTesting.tbd
+// CHECK-TEST-NOT: _$s15UtilsForTesting6pubBar3argS2i_tFfA_
+// CHECK-TEST: _$s15UtilsForTesting11internalBar3argS2i_tF
+// CHECK-TEST: _$s15UtilsForTesting11internalBar3argS2i_tFfA_
+// CHECK-TEST: _$s15UtilsForTesting11internalFoo3argS2i_tF
+// CHECK-TEST: _$s15UtilsForTesting6pkgBar3argS2i_tF
+// CHECK-TEST: _$s15UtilsForTesting6pkgBar3argS2i_tFfA_
+// CHECK-TEST: _$s15UtilsForTesting6pkgFoo3argS2i_tF
+// CHECK-TEST: _$s15UtilsForTesting6pubBar3argS2i_tF
+// CHECK-TEST: _$s15UtilsForTesting6pubFoo3argS2i_tF
+
+// RUN: %target-build-swift -I %t -L %t -lUtils %t/main.swift -o %t/main %target-rpath(%t) -package-name mypkg
+
+// RUN: %target-codesign %t/main
+// RUN: %target-run %t/main %t/%target-library-name(Utils) > %t/run-result.output
+// RUN: %FileCheck %s < %t/run-result.output
+
+
+//--- Utils.swift
+public func pubBar(arg: Int = 1) -> Int { return arg + 11 }
+package func pkgBar(arg: Int = 1) -> Int { return arg + 12 }
+func internalBar(arg: Int = 1) -> Int { return arg + 13 }
+
+public func pubFoo(arg: Int) -> Int { return arg + 1 }
+package func pkgFoo(arg: Int) -> Int { return arg + 2 }
+func internalFoo(arg: Int) -> Int { return arg + 3 }
+
+//--- main.swift
+import Utils
+
+let a = pubBar()
+let b = pkgBar()
+
+let c = pubFoo(arg: 3)
+let d = pkgFoo(arg: 5)
+
+print(a, b, c, d) // CHECK: 12 13 4 7