Improve implicit async error message

At the declaration, the implicitly async functions appear to be
synchronous, so it isn't clear why the error message is being emitted.
This patch updates the error message to indicate that the function is
implicitly asynchronous.

Author: etcwilde

include/swift/AST/DiagnosticsSema.def

@@ -4207,8 +4207,9 @@ ERROR(actor_isolated_self_independent_context,none,
         "'@actorIndependent' context",
         (DescriptiveDeclKind, DeclName))
 ERROR(actor_isolated_inout_state,none,
-      "actor-isolated %0 %1 cannot be passed 'inout' to asynchronous function",
-      (DescriptiveDeclKind, DeclName))
+      "actor-isolated %0 %1 cannot be passed 'inout' to"
+      "%select{| implicitly}2 'async' function call",
+      (DescriptiveDeclKind, DeclName, bool))
 ERROR(actor_isolated_mutating_func,none,
       "cannot call mutating async function %0 on actor-isolated %1 %2",
       (DeclName, DescriptiveDeclKind, DeclName))

lib/Sema/TypeCheckConcurrency.cpp

@@ -930,7 +930,8 @@ namespace {
           } else {
             ctx.Diags.diagnose(
                 subArg->getLoc(), diag::actor_isolated_inout_state,
-                memberDecl->getDescriptiveKind(), memberDecl->getName());
+                memberDecl->getDescriptiveKind(), memberDecl->getName(),
+                call->implicitlyAsync());
             return true;
           }
         }

test/Concurrency/actor_inout_isolation.swift

@@ -36,24 +36,24 @@ extension TestActor {
 
   // Can't pass actor-isolated primitive into a function
   func inoutAsyncFunctionCall() async {
-    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to 'async' function call}}
     await modifyAsynchronously(&value1)
   }
 
   func inoutAsyncClosureCall() async {
-    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to 'async' function call}}
     await { (_ foo: inout Int) async in foo += 1 }(&value1)
   }
 
   // Can't pass actor-isolated primitive into first-class function value
   func inoutAsyncValueCall() async {
-    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to 'async' function call}}
     await modifyAsyncValue(&value1)
   }
 
   // Can't pass property of actor-isolated state inout to async function
   func inoutPropertyStateValueCall() async {
-    // expected-error@+1{{actor-isolated property 'position' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'position' cannot be passed 'inout' to 'async' function call}}
     await modifyAsynchronously(&position.x)
   }
 }
@@ -65,7 +65,7 @@ extension TestActor {
   }
 
   func passStateIntoMethod() async {
-    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to 'async' function call}}
     await modifyByValue(&value1)
   }
 }
@@ -88,23 +88,23 @@ extension TestActor {
   func passStateIntoDifferentClassMethod() async {
     let other = NonAsyncClass()
     let otherCurry = other.modifyOtherAsync
-    // expected-error@+1{{actor-isolated property 'value2' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'value2' cannot be passed 'inout' to 'async' function call}}
     await other.modifyOtherAsync(&value2)
-    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+1{{actor-isolated property 'value1' cannot be passed 'inout' to 'async' function call}}
     await otherCurry(&value1)
     other.modifyOtherNotAsync(&value2) // This is okay since it's not async!
 
   }
 
   func callMutatingFunctionOnStruct() async {
     // expected-error@+3:20{{cannot call mutating async function 'setComponents(x:y:)' on actor-isolated property 'position'}}
-    // expected-error@+2:51{{actor-isolated property 'nextPosition' cannot be passed 'inout' to asynchronous function}}
-    // expected-error@+1:71{{actor-isolated property 'nextPosition' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+2:51{{actor-isolated property 'nextPosition' cannot be passed 'inout' to 'async' function call}}
+    // expected-error@+1:71{{actor-isolated property 'nextPosition' cannot be passed 'inout' to 'async' function call}}
     await position.setComponents(x: &nextPosition.x, y: &nextPosition.y)
 
     // expected-error@+3:20{{cannot call mutating async function 'setComponents(x:y:)' on actor-isolated property 'position'}}
-    // expected-error@+2:38{{actor-isolated property 'value1' cannot be passed 'inout' to asynchronous function}}
-    // expected-error@+1:50{{actor-isolated property 'value2' cannot be passed 'inout' to asynchronous function}}
+    // expected-error@+2:38{{actor-isolated property 'value1' cannot be passed 'inout' to 'async' function call}}
+    // expected-error@+1:50{{actor-isolated property 'value2' cannot be passed 'inout' to 'async' function call}}
     await position.setComponents(x: &value1, y: &value2)
   }
 }
@@ -120,14 +120,14 @@ extension TestActor {
   // Actor state passed inout to implicitly async function on an actor of the
   // same type
   func modifiedByOtherTestActor(_ other: TestActor) async {
-    //expected-error@+1{{actor-isolated property 'value2' cannot be passed 'inout' to asynchronous function}}
+    //expected-error@+1{{actor-isolated property 'value2' cannot be passed 'inout' to implicitly 'async' function call}}
     await other.modify(&value2)
   }
 
   // Actor state passed inout to an implicitly async function on an actor of a
   // different type
   func modifiedByOther(_ other: DifferentActor) async {
-    //expected-error@+1{{actor-isolated property 'value2' cannot be passed 'inout' to asynchronous function}}
+    //expected-error@+1{{actor-isolated property 'value2' cannot be passed 'inout' to implicitly 'async' function call}}
     await other.modify(&value2)
   }
 }