Add type-safe SignalWithStart (#193)

README.md

@@ -519,6 +519,8 @@ Some things to note about the above code:
   `StartWorkflowAsync` would be a compile-time failure.
 * The `handle` is also typed with the workflow result, so `GetResultAsync()` returns a `string` as expected.
 * A shortcut extension `ExecuteWorkflowAsync` is available that is just `StartWorkflowAsync` + `GetResultAsync`.
+* `SignalWithStart` method is present on the workflow options to make the workflow call a signal-with-start call which
+  means it will only start the workflow if it's not running, but send a signal to it regardless.
 
 #### Invoking Activities
 

src/Temporalio/Client/WorkflowOptions.cs

@@ -1,5 +1,7 @@
 using System;
 using System.Collections.Generic;
+using System.Linq.Expressions;
+using System.Threading.Tasks;
 using Temporalio.Api.Enums.V1;
 using Temporalio.Common;
 
@@ -105,6 +107,32 @@ public WorkflowOptions(string id, string taskQueue)
         /// </summary>
         public RpcOptions? Rpc { get; set; }
 
+        /// <summary>
+        /// Perform a signal-with-start which will only start the workflow if it's not already
+        /// running, but send a signal to it regardless. This is just sugar for manually setting
+        /// <see cref="StartSignal" /> and <see cref="StartSignalArgs" /> directly.
+        /// </summary>
+        /// <typeparam name="TWorkflow">Workflow class type.</typeparam>
+        /// <param name="signalCall">Invocation or a workflow signal method.</param>
+        public void SignalWithStart<TWorkflow>(Expression<Func<TWorkflow, Task>> signalCall)
+        {
+            var (method, args) = ExpressionUtil.ExtractCall(signalCall);
+            SignalWithStart(Workflows.WorkflowSignalDefinition.NameFromMethodForCall(method), args);
+        }
+
+        /// <summary>
+        /// Perform a signal-with-start which will only start the workflow if it's not already
+        /// running, but send a signal to it regardless. This is just sugar for manually setting
+        /// <see cref="StartSignal" /> and <see cref="StartSignalArgs" /> directly.
+        /// </summary>
+        /// <param name="signal">Signal name.</param>
+        /// <param name="args">Signal args.</param>
+        public void SignalWithStart(string signal, IReadOnlyCollection<object?> args)
+        {
+            StartSignal = signal;
+            StartSignalArgs = args;
+        }
+
         /// <summary>
         /// Create a shallow copy of these options.
         /// </summary>

tests/Temporalio.Tests/Worker/WorkflowWorkerTests.cs

@@ -956,6 +956,43 @@ await handle.SignalAsync(
         });
     }
 
+    [Fact]
+    public async Task ExecuteWorkflowAsync_Signals_SignalWithStart()
+    {
+        await ExecuteWorkerAsync<SignalWorkflow>(async worker =>
+        {
+            // Start the workflow with a signal
+            var options = new WorkflowOptions(
+                id: $"workflow-{Guid.NewGuid()}",
+                taskQueue: worker.Options.TaskQueue!);
+            options.SignalWithStart((SignalWorkflow wf) => wf.Signal1Async("signalval1"));
+            var handle = await Env.Client.StartWorkflowAsync(
+                (SignalWorkflow wf) => wf.RunAsync(),
+                options);
+            // Confirm signal received
+            Assert.Equal(
+                new List<string>
+                {
+                    "Signal1: signalval1",
+                },
+                await handle.QueryAsync(wf => wf.Events()));
+            // Do it again, confirm signal received on same workflow
+            options.SignalWithStart((SignalWorkflow wf) => wf.Signal1Async("signalval2"));
+            var newHandle = await Env.Client.StartWorkflowAsync(
+                (SignalWorkflow wf) => wf.RunAsync(),
+                options);
+            Assert.Equal(handle.ResultRunId, newHandle.ResultRunId);
+            // Confirm signal received
+            Assert.Equal(
+                new List<string>
+                {
+                    "Signal1: signalval1",
+                    "Signal1: signalval2",
+                },
+                await handle.QueryAsync(wf => wf.Events()));
+        });
+    }
+
     [Workflow]
     public class BadSignalArgsDroppedWorkflow
     {
@@ -3939,8 +3976,12 @@ private async Task ExecuteWorkerAsync<TWf>(
         TemporalWorkerOptions? options = null,
         IWorkerClient? client = null)
     {
-        await ExecuteWorkerAsyncReturning<TWf, bool>(
-            (w) => action(w).ContinueWith(t => true),
+        await ExecuteWorkerAsyncReturning<TWf, ValueTuple>(
+            async (w) =>
+            {
+                await action(w);
+                return ValueTuple.Create();
+            },
             options,
             client);
     }