[Concurrency] Diagnose Sendable violations in captures of local functions.

Author: hborla

include/swift/AST/DiagnosticsSema.def

@@ -5236,8 +5236,9 @@ ERROR(concurrent_access_of_inout_param,none,
       "concurrently-executing code",
       (DeclName))
 ERROR(non_sendable_capture,none,
-      "capture of %1 with non-sendable type %0 in a `@Sendable` closure",
-      (Type, DeclName))
+      "capture of %1 with non-sendable type %0 in a `@Sendable` "
+      "%select{local function|closure}2",
+      (Type, DeclName, bool))
 ERROR(implicit_async_let_non_sendable_capture,none,
       "capture of %1 with non-sendable type %0 in 'async let' binding",
       (Type, DeclName))

lib/Sema/TypeCheckConcurrency.cpp

@@ -2118,9 +2118,9 @@ namespace {
     }
 
     /// Check closure captures for Sendable violations.
-    void checkClosureCaptures(AbstractClosureExpr *closure) {
+    void checkLocalCaptures(AnyFunctionRef localFunc) {
       SmallVector<CapturedValue, 2> captures;
-      closure->getCaptureInfo().getLocalCaptures(captures);
+      localFunc.getCaptureInfo().getLocalCaptures(captures);
       for (const auto &capture : captures) {
         if (capture.isDynamicSelfMetadata())
           continue;
@@ -2130,14 +2130,19 @@ namespace {
         // If the closure won't execute concurrently with the context in
         // which the declaration occurred, it's okay.
         auto decl = capture.getDecl();
-        if (!mayExecuteConcurrentlyWith(closure, decl->getDeclContext()))
+        auto *context = localFunc.getAsDeclContext();
+        if (!mayExecuteConcurrentlyWith(context, decl->getDeclContext()))
           continue;
 
         Type type = getDeclContext()
             ->mapTypeIntoContext(decl->getInterfaceType())
             ->getReferenceStorageReferent();
 
-        if (closure->isImplicit()) {
+        if (type->hasError())
+          continue;
+
+        auto *closure = localFunc.getAbstractClosureExpr();
+        if (closure && closure->isImplicit()) {
           auto *patternBindingDecl = getTopPatternBindingDecl();
           if (patternBindingDecl && patternBindingDecl->isAsyncLet()) {
             diagnoseNonSendableTypes(
@@ -2152,7 +2157,8 @@ namespace {
           }
         } else {
           diagnoseNonSendableTypes(type, getDeclContext(), capture.getLoc(),
-                                   diag::non_sendable_capture, decl->getName());
+                                   diag::non_sendable_capture, decl->getName(),
+                                   /*closure=*/closure != nullptr);
         }
       }
     }
@@ -2220,6 +2226,10 @@ namespace {
 
     PreWalkAction walkToDeclPre(Decl *decl) override {
       if (auto func = dyn_cast<AbstractFunctionDecl>(decl)) {
+        if (func->isLocalContext()) {
+          checkLocalCaptures(func);
+        }
+
         contextStack.push_back(func);
       }
 
@@ -2254,7 +2264,7 @@ namespace {
 
       if (auto *closure = dyn_cast<AbstractClosureExpr>(expr)) {
         closure->setActorIsolation(determineClosureIsolation(closure));
-        checkClosureCaptures(closure);
+        checkLocalCaptures(closure);
         contextStack.push_back(closure);
         return Action::Continue(expr);
       }

test/Concurrency/sendable_checking.swift

@@ -250,6 +250,7 @@ final class NonSendable {
   // expected-note @-1 3 {{class 'NonSendable' does not conform to the 'Sendable' protocol}}
   // SendNonSendable emits 3 fewer errors here.
   // expected-targeted-and-complete-note @-3 5 {{class 'NonSendable' does not conform to the 'Sendable' protocol}}
+  // expected-complete-and-sns-note @-4 {{class 'NonSendable' does not conform to the 'Sendable' protocol}}
   var value = ""
 
   @MainActor
@@ -305,3 +306,13 @@ func callNonisolatedAsyncClosure(
   await f(ns)
   // expected-targeted-and-complete-warning@-1 {{passing argument of non-sendable type 'NonSendable' outside of main actor-isolated context may introduce data races}}
 }
+
+@available(SwiftStdlib 5.1, *)
+func testLocalCaptures() {
+  let ns = NonSendable()
+
+  @Sendable func a2() -> NonSendable {
+    return ns
+    // expected-complete-and-sns-warning@-1 {{capture of 'ns' with non-sendable type 'NonSendable' in a `@Sendable` local function}}
+  }
+}