Diagnose multiple @Lifetime attributes with same target

Author: meg-gupta

include/swift/AST/DiagnosticsSema.def

@@ -8005,6 +8005,8 @@ ERROR(lifetime_dependence_invalid_inherit_escapable_type, none,
 ERROR(lifetime_dependence_cannot_use_parsed_borrow_consuming, none,
       "invalid use of borrow dependence with consuming ownership",
       ())
+ERROR(lifetime_dependence_duplicate_target, none,
+      "invalid duplicate target lifetime dependencies on function", ())
 
 //===----------------------------------------------------------------------===//
 //                             MARK: Sending

lib/AST/LifetimeDependence.cpp

@@ -376,14 +376,26 @@ populateLifetimeDependence(AbstractFunctionDecl *afd, LifetimeEntry *entry) {
 
 std::optional<ArrayRef<LifetimeDependenceInfo>>
 LifetimeDependenceInfo::fromLifetimeAttribute(AbstractFunctionDecl *afd) {
+  auto *dc = afd->getDeclContext();
+  auto &ctx = dc->getASTContext();
+  auto &diags = ctx.Diags;
+  
   SmallVector<LifetimeDependenceInfo, 1> lifetimeDependencies;
+  llvm::SmallSet<unsigned, 1> lifetimeDependentTargets;
   auto lifetimeAttrs = afd->getAttrs().getAttributes<LifetimeAttr>();
   for (auto attr : lifetimeAttrs) {
     auto lifetimeDependenceInfo =
         populateLifetimeDependence(afd, attr->getLifetimeEntry());
     if (!lifetimeDependenceInfo.has_value()) {
       return std::nullopt;
     }
+    auto targetIndex = lifetimeDependenceInfo->getTargetIndex();
+    if (lifetimeDependentTargets.contains(targetIndex)) {
+      // TODO: Diagnose at the source location of the @lifetime attribute with
+      // duplicate target.
+      diags.diagnose(afd->getLoc(), diag::lifetime_dependence_duplicate_target);
+    }
+    lifetimeDependentTargets.insert(targetIndex);
     lifetimeDependencies.push_back(*lifetimeDependenceInfo);
   }
 

test/Sema/lifetime_attr.swift

@@ -34,3 +34,8 @@ func invalidDependence(_ x: consuming Klass) -> NE {
   NE()
 }
 
+@lifetime(result: source) 
+@lifetime(result: source) // TODO: display error here
+func invalidTarget(_ result: inout NE, _ source: consuming NE) { // expected-error{{invalid duplicate target lifetime dependencies on function}}
+  result = source
+}