IRGen: We need to emit metadata for types that are emitted with shared linkage

Otherwise one TU could only require the type descriptor without metadata
and another TU could require metadata and type descriptor. Whether the
metadata access function is available would then depend on the linking
order of the two TUs.

rdar://56929811

Author: aschwaighofer

lib/IRGen/GenDecl.cpp

@@ -1262,6 +1262,17 @@ void IRGenerator::noteUseOfTypeGlobals(NominalTypeDecl *type,
   if (!hasLazyMetadata(type))
     return;
 
+  // If the type can be generated in several TU with weak linkage we don't know
+  // which one will be picked up so we have to require the metadata. Otherwise,
+  // the situation can arise where one TU contains a type descriptor with a null
+  // metadata access function and the other TU which requires metadata has a
+  // type descriptor with a valid metadata access function but the linker picks
+  // the first one.
+  if (isAccessorLazilyGenerated(getTypeMetadataAccessStrategy(
+          type->getDeclaredType()->getCanonicalType()))) {
+    requireMetadata = RequireMetadata;
+  }
+
   // Try to create a new record of the fact that we used this type.
   auto insertResult = LazyTypeGlobals.try_emplace(type);
   auto &entry = insertResult.first->second;

test/IRGen/foreign_type_metadata.swift

@@ -0,0 +1,22 @@
+// RUN: %target-swift-frontend %s -emit-ir | %FileCheck %s
+
+// REQUIRES: objc_interop
+
+import Foundation
+
+// Make sure we emit a metadata accessor for foreign types even if the type
+// metadata is not required by this TU. Another TU could require it and the
+// linker could choose the less defined one of the two.
+
+// CHECK: @"$sSo8_NSRangeVMn" = linkonce_odr hidden constant <{ {{.*}}sSo8_NSRangeVMa{{.*}} }>, section "__TEXT,__const"
+
+func use(_ closure: @escaping (Int) -> ()) {}
+
+public func captureRange(_ r: NSRange?) {
+  var l = r
+  use {
+    if $0 == 0 {
+      l = NSRange()
+    }
+  }
+}

test/Interpreter/ForeignMetadata.swift

@@ -0,0 +1,11 @@
+// RUN: %empty-directory(%t)
+// RUN: cp %s %t/main.swift
+// RUN: %target-build-swift -o %t/main %S/Inputs/ForeignTypeMetadata1.swift  %S/Inputs/ForeignTypeMetadata2.swift %t/main.swift -swift-version 5
+// RUN: %target-codesign %t/main
+// RUN: %target-run %t/main
+
+
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+useType()

test/Interpreter/Inputs/ForeignTypeMetadata1.swift

@@ -0,0 +1,12 @@
+import Foundation
+
+func use(_ closure: @escaping (Int) -> ()) {}
+
+public func captureRange(_ r: NSRange?) {
+  var l = r
+  use {
+    if $0 == 0 {
+      l = NSRange()
+    }
+  }
+}

test/Interpreter/Inputs/ForeignTypeMetadata2.swift

@@ -0,0 +1,7 @@
+import Foundation
+
+public func useType() {
+  var x = [NSRange]()
+  x.append(NSRange())
+  print(x)
+}