Switch CsWin32RunAsBuildTask to EmitSingleFile by default (for VS incremental scenario) (#1565)

Author: jevansaks

src/CsWin32Generator/Program.cs

@@ -264,6 +264,12 @@ private Task<bool> GenerateCode(
             options.ComInterop.UseComSourceGenerators = true;
         }
 
+        // Set EmitSingleFile to true by default if unspecified.
+        // We put everything in a single file to avoid needing to kick design-time-build to re-run to pick up the newly generated files.
+        // We _could_ make this happen using the AdditionalDesignTimeBuildInput item group but that makes design time build re-run each time
+        // NativeMethods.txt changes and we want to avoid triggering DTBs if possible.
+        options.EmitSingleFile ??= true;
+
         this.VerboseWriteLine($"Loaded generator options. AllowMarshaling: {options.AllowMarshaling}, ClassName: {options.ClassName}");
 
         // Validate metadata files exist

src/Microsoft.Windows.CsWin32/Generator.cs

@@ -775,7 +775,7 @@ nsContents.Key is object
                         : nsContents.ToArray());
         }
 
-        if (this.options.EmitSingleFile)
+        if (this.options.EmitSingleFile == true)
         {
             CompilationUnitSyntax file = CompilationUnit()
                 .AddMembers(starterNamespace.AddMembers(GroupMembersByNamespace(this.NamespaceMembers).ToArray()))
@@ -862,7 +862,7 @@ nsContents.Key is object
 
         if (this.compilation?.GetTypeByMetadataName("System.Reflection.AssemblyMetadataAttribute") is not null)
         {
-            if (this.options.EmitSingleFile)
+            if (this.options.EmitSingleFile == true)
             {
                 KeyValuePair<string, CompilationUnitSyntax> originalEntry = normalizedResults.Single();
                 normalizedResults[originalEntry.Key] = originalEntry.Value.WithLeadingTrivia().AddAttributeLists(CsWin32StampAttribute).WithLeadingTrivia(originalEntry.Value.GetLeadingTrivia());

src/Microsoft.Windows.CsWin32/GeneratorOptions.cs

@@ -20,10 +20,10 @@ public record GeneratorOptions
     public string ClassName { get; set; } = "PInvoke";
 
     /// <summary>
-    /// Gets or sets a value indicating whether to emit a single source file as opposed to types spread across many files.
+    /// Gets or sets a value indicating whether to emit a single source file as opposed to types spread across many files, 'null' indicates to use the recommended default for the environment.
     /// </summary>
-    /// <value>The default value is <see langword="false" />.</value>
-    public bool EmitSingleFile { get; set; }
+    /// <value>The default value is <see langword="null" />.</value>
+    public bool? EmitSingleFile { get; set; }
 
     /// <summary>
     /// Gets or sets a value indicating whether to expose the generated APIs publicly (as opposed to internally).

src/Microsoft.Windows.CsWin32/build/Microsoft.Windows.CsWin32.targets

@@ -95,12 +95,4 @@
     </ItemGroup>
 
   </Target>
-
-  <!-- Add the items to AdditionalDesignTimeBuildInput as well so that DesignTimeBuilds re-run when NativeMethods.txt contents change.
-       VS seems to evaluate this directly (not looking at the DesignTimeBuild outputs) and so we can't do it in a Target.
-       And VS doesn't support conditions on FileName or things like that in a top-level ItemGroup so just include all AdditionalFiles 
-       as ContentSensitive. Worst case the DesignTimeBuild runs on files other than NativeMethods.txt. -->
-  <ItemGroup Condition="'$(CsWin32RunAsBuildTask)'=='true'">
-    <AdditionalDesignTimeBuildInput Include="@(AdditionalFiles)" ContentSensitive="true" />
-  </ItemGroup>
 </Project>

test/GenerationSandbox.BuildTask.Tests/NativeMethods.json

@@ -1,6 +1,5 @@
 {
   "$schema": "..\\..\\src\\Microsoft.Windows.CsWin32\\settings.schema.json",
-  "emitSingleFile": true,
   "allowMarshaling": true,
   "public": false,
   "comInterop": {