[Concurrency] Teach Type::stripConcurrency to handle generic arguments

Author: xedin

lib/AST/Type.cpp

@@ -1109,6 +1109,25 @@ Type TypeBase::stripConcurrency(bool recurse, bool dropGlobalActor) {
     return Type(this);
   }
 
+  if (auto *BGT = getAs<BoundGenericType>()) {
+    if (!recurse)
+      return Type(this);
+
+    bool anyChanged = false;
+    SmallVector<Type, 2> genericArgs;
+    llvm::transform(BGT->getGenericArgs(), std::back_inserter(genericArgs),
+                    [&](Type argTy) {
+                      auto newArgTy =
+                          argTy->stripConcurrency(recurse, dropGlobalActor);
+                      anyChanged |= !newArgTy->isEqual(argTy);
+                      return newArgTy;
+                    });
+
+    return anyChanged ? BoundGenericType::get(BGT->getDecl(), BGT->getParent(),
+                                              genericArgs)
+                      : Type(this);
+  }
+
   return Type(this);
 }
 

test/Concurrency/sendable_preconcurrency_erasure.swift

@@ -0,0 +1,14 @@
+// RUN: %target-swift-emit-silgen %s -verify -swift-version 5 | %FileCheck %s
+
+// REQUIRES: concurrency
+
+// Test erasure in generic arguments
+do {
+  struct S<T> {
+  }
+
+  @preconcurrency func test(_: S<any Sendable>) {}
+  // CHECK-LABEL: sil private [ossa] @$s31sendable_preconcurrency_erasure4testL_yyAA1SL_VyypGF
+  @preconcurrency func test(_: S<Array<@Sendable () -> Void>>) {}
+  // CHECK-LABEL: sil private [ossa] @$s31sendable_preconcurrency_erasure4testL0_yyAA1SL_VySayyycGGF
+}