Give ~Escapable _read accessors with borrow scope borrowed ownership

This applies to all _read accessors whose result depends on a borrow
of self. In this case, the coroutine defines the borrow scope, and the
~Escapable property value can only be used within that scope. This
makes it impossible to synthesize a getter. Returning the ~Escpable
value from the getter would always escape the coroutine.

Author: atrick

lib/Sema/TypeCheckStorage.cpp

@@ -869,6 +869,18 @@ OpaqueReadOwnershipRequest::evaluate(Evaluator &evaluator,
     return OpaqueReadOwnership::Borrowed;
   };
 
+  if (auto *accessorDecl = storage->getAccessor(AccessorKind::Read)) {
+    auto lifetimeDependencies = accessorDecl->getLifetimeDependencies();
+    if (lifetimeDependencies.has_value() && !lifetimeDependencies->empty()) {
+      for (auto &lifetimeDependenceInfo : *lifetimeDependencies) {
+        if (lifetimeDependenceInfo.hasScopeLifetimeParamIndices()) {
+          // A scoped lifetime dependence borrows its source.
+          return OpaqueReadOwnership::Borrowed;
+        }
+      }
+    }
+  }
+
   if (storage->getAccessor(AccessorKind::Read2))
     return OpaqueReadOwnership::Borrowed;
 

test/SILGen/accessor_borrow.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-emit-silgen -module-name accessor_borrow -Xllvm -sil-full-demangle %s | %FileCheck %s
+
+struct NE: ~Escapable {}
+
+struct NEContainer: ~Copyable {
+  // This accessor borrows self. Do not synthesize a getter.
+  var ne_coroutine: NE {
+    _read {
+      NE()
+    }
+  }
+}