devlooped · kzu · Sep 1, 2025 · Sep 1, 2025
diff --git a/readme.md b/readme.md
@@ -28,12 +28,13 @@ To pay the Maintenance Fee, [become a Sponsor](https://github.com/sponsors/devlo
 
 C# [top-level programs](https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/program-structure/top-level-statements) 
 allow a very intuitive, simple and streamlined experience for quickly spiking or learning C#. 
-The addition of [dotnet run app.cs](https://devblogs.microsoft.com/dotnet/announcing-dotnet-run-app/) in 
-.NET 10 takes this further by allowing package references and even MSBuild properties to be 
+The addition of [file-based apps](https://devblogs.microsoft.com/dotnet/announcing-dotnet-run-app/) in 
+.NET 10 [takes this further](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives#file-based-apps) by allowing package references and even MSBuild properties to be 
 specified per file:
 
 ```csharp
 #:package Humanizer@2.14.1
+#:property LangVersion=preview
 
 using Humanizer;
 
@@ -70,42 +71,57 @@ files in subdirectories and those will behave like normal compile items.
 ## Usage
 
 SmallSharp works by just installing the 
-[SmallSharp](https://nuget.org/packages/SmallSharp) nuget package in a C# console project.
-
-Recommended installation as an SDK:
+[SmallSharp](https://nuget.org/packages/SmallSharp) nuget package in a C# console project 
+and adding a couple extra properties to the project file:
 
 ```xml
 <Project Sdk="Microsoft.NET.Sdk">
 
-  <Sdk Name="SmallSharp" Version="2.0.0" />
-
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>net10.0</TargetFramework>
+
+    <!-- 👇 additional properties required in package mode -->
+    <ImportProjectExtensionProps>true</ImportProjectExtensionProps>
+    <ImportProjectExtensionTargets>true</ImportProjectExtensionTargets>   
   </PropertyGroup>
 
+  <ItemGroup>
+    <PackageReference Include="SmallSharp" Version="*" PrivateAssets="all" />
+  </ItemGroup>
+
 </Project>
 ```
 
-Or as a regular package reference:
+If your file-based apps use the `#:sdk` [directive](https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/preprocessor-directives#file-based-apps), 
+you need to add SmallSharp as an SDK reference instead so the SDK is picked up by the 
+generated targets/props instead of the project file. You also don't need the additional 
+properties since the SDK mode sets them automatically for you: 
+
 ```xml
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="SmallSharp/2.1.0">
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>net10.0</TargetFramework>
   </PropertyGroup>
 
-  <ItemGroup>
-    <PackageReference Include="SmallSharp" Version="*" />
-  </ItemGroup>
-
 </Project>
 ```
 
+> [!IMPORTANT]
+> If no `#:sdk` directive is provided by a specific C# file-based app, the `Microsoft.NET.SDK` will be 
+> used by default in this SDK mode.
+
 Keep adding as many top-level programs as you need, and switch between them easily by simply 
 selecting the desired file from the Start button dropdown.
 
+When running from the command-line, you can select the file to run by passing it as an argument to `dotnet run`:
+
+```bash
+dotnet run -p:ActiveFile program1.cs
+```
+
 ## How It Works
 
 This nuget package leverages in concert the following standalone and otherwise 
@@ -116,6 +132,7 @@ unrelated features of the compiler, nuget and MSBuild:
 3. Whenever changed, the dropdown selection is persisted as the `$(ActiveDebugProfile)` MSBuild property in a file 
    named after the project with the `.user` extension
 4. This file is imported before NuGet-provided MSBuild targets
+5. VS ignores `#:` directives when adding the flag `FileBasedProgram` to the `$(Features)` project property.
 
 Using the above features in concert, **SmallSharp** essentially does the following:
 
@@ -138,7 +155,7 @@ since the "Main" file selection is performed exclusively via MSBuild item manipu
 > [!TIP]
 > It is recommended to keep the project file to its bare minimum, usually having just the SmallSharp 
 > SDK reference, and do all project/package references in the top-level files using the `#:package` and 
-> `#:property` directives for improved isolation between the top-level programs.
+> `#:property` directives for improved isolation between the different file-based apps.
 
 ```xml
 <Project Sdk="Microsoft.NET.Sdk">

diff --git a/src/SmallSharp/EmitTargets.cs b/src/SmallSharp/EmitTargets.cs
@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.IO;
+using System.Linq;
 using System.Text.RegularExpressions;
 using System.Xml;
 using System.Xml.Linq;
@@ -10,29 +11,52 @@ namespace SmallSharp;
 
 public class EmitTargets : Task
 {
+    static readonly Regex sdkExpr = new(@"^#:sdk\s+([^@]+?)(@(.+))?$");
     static readonly Regex packageExpr = new(@"^#:package\s+([^@]+)@(.+)$");
     static readonly Regex propertyExpr = new(@"^#:property\s+([^\s]+)\s+(.+)$");
 
     [Required]
-    public ITaskItem? StartupFile { get; set; }
+    public required ITaskItem StartupFile { get; set; }
 
     [Required]
-    public string TargetsFile { get; set; } = "SmallSharp.targets";
+    public required string BaseIntermediateOutputPath { get; set; }
+
+    [Required]
+    public required string PropsFile { get; set; }
+
+    [Required]
+    public required string TargetsFile { get; set; }
+
+    [Required]
+    public bool UsingSmallSharpSDK { get; set; } = false;
 
     [Output]
     public ITaskItem[] Packages { get; set; } = [];
 
+    [Output]
+    public ITaskItem[] Sdks { get; set; } = [];
+
+    [Output]
+    public ITaskItem[] Properties { get; set; } = [];
+
+    [Output]
+    public bool Success { get; set; } = false;
+
     public override bool Execute()
     {
         if (StartupFile is null)
             return false;
 
         var packages = new List<ITaskItem>();
+        var sdkItems = new List<ITaskItem>();
+        var propItems = new List<ITaskItem>();
+
         var filePath = StartupFile.GetMetadata("FullPath");
         var contents = File.ReadAllLines(filePath);
 
         var items = new List<XElement>();
         var properties = new List<XElement>();
+        var sdks = new List<XAttribute[]>();
 
         foreach (var line in contents)
         {
@@ -50,27 +74,72 @@ public override bool Execute()
                     new XAttribute("Include", id),
                     new XAttribute("Version", version)));
             }
+            else if (sdkExpr.Match(line) is { Success: true } sdkMatch)
+            {
+                var name = sdkMatch.Groups[1].Value.Trim();
+                var version = sdkMatch.Groups[2].Value.Trim();
+                if (!string.IsNullOrEmpty(version))
+                {
+                    sdkItems.Add(new TaskItem(name, new Dictionary<string, string>
+                    {
+                        { "Version", version }
+                    }));
+                    sdks.Add([new XAttribute("Sdk", name), new XAttribute("Version", version)]);
+                }
+                else
+                {
+                    sdkItems.Add(new TaskItem(name));
+                    sdks.Add([new XAttribute("Sdk", name)]);
+                }
+            }
             else if (propertyExpr.Match(line) is { Success: true } propMatch)
             {
                 var name = propMatch.Groups[1].Value.Trim();
                 var value = propMatch.Groups[2].Value.Trim();
 
+                propItems.Add(new TaskItem(name, new Dictionary<string, string>
+                {
+                    { "Value", value }
+                }));
                 properties.Add(new XElement(name, value));
             }
         }
 
         Packages = [.. packages];
+        Sdks = [.. sdkItems];
+        Properties = [.. propItems];
+
+        if (sdks.Count > 0 && !UsingSmallSharpSDK)
+        {
+            Log.LogError($"When using #:sdk directive(s), you must use SmallSharp as an SDK: <Project Sdk=\"SmallSharp/{ThisAssembly.Project.Version}\">.");
+            return false;
+        }
+
+        // We only emit the default SDK if the SmallSharpSDK is in use, since otherwise the 
+        // project file is expected to define its own SDK and we'd be duplicating it.
+        if (sdks.Count == 0)
+            sdks.Add([new XAttribute("Sdk", "Microsoft.NET.Sdk")]);
+
+        WriteXml(TargetsFile, new XElement("Project",
+            new XElement("PropertyGroup", properties),
+            new XElement("ItemGroup", items)
+        ));
+
+        WriteXml(Path.Combine(BaseIntermediateOutputPath, "SmallSharp.sdk.props"), new XElement("Project",
+            sdks.Select(x => new XElement("Import", [new XAttribute("Project", "Sdk.props"), .. x]))));
 
-        var doc = new XDocument(
-            new XElement("Project",
-                new XElement("PropertyGroup", properties),
-                new XElement("ItemGroup", items)
-            )
-        );
+        WriteXml(Path.Combine(BaseIntermediateOutputPath, "SmallSharp.sdk.targets"), new XElement("Project",
+            sdks.Select(x => new XElement("Import", [new XAttribute("Project", "Sdk.targets"), .. x]))));
 
-        using var writer = XmlWriter.Create(TargetsFile, new XmlWriterSettings { Indent = true });
-        doc.Save(writer);
+        WriteXml(PropsFile, new XElement("Project"));
 
+        Success = true;
         return true;
     }
+
+    void WriteXml(string path, XElement root)
+    {
+        using var writer = XmlWriter.Create(path, new XmlWriterSettings { Indent = true });
+        root.Save(writer);
+    }
 }
diff --git a/src/SmallSharp/Sdk.Empty.props b/src/SmallSharp/Sdk.Empty.props
@@ -0,0 +1,3 @@
+<Project>
+  <!-- This is needed since the Microsoft.NET.SDK Sdk.props imports the Microsoft.Common.props unconditionally -->
+</Project>
diff --git a/src/SmallSharp/Sdk.props b/src/SmallSharp/Sdk.props
@@ -1,14 +1,25 @@
 <Project>
 
-  <Import Project="..\build\SmallSharp.props" />
-
   <PropertyGroup>
     <ImportProjectExtensionProps>true</ImportProjectExtensionProps>
     <ImportProjectExtensionTargets>true</ImportProjectExtensionTargets>
+
+    <!-- Since we use this to build StartupFile list and as an SDK, we might not have .NET SDK imported yet (i.e. no C# files at all) -->
+    <UsingSmallSharpSDK>true</UsingSmallSharpSDK>
+
+    <!-- Workaround https://github.com/dotnet/sdk/issues/50573 -->
+    <AlternateCommonProps>$(MSBuildThisFileDirectory)\Sdk.Empty.props</AlternateCommonProps>
   </PropertyGroup>
 
-  <ItemGroup>
-    <PackageReference Include="JsonPoke" Version="1.2.0" PrivateAssets="all" />
-  </ItemGroup>
+  <!-- Import Common.props explicitly we're too early here to use MSBuildProjectExtensionsPath -->
+  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="'$(MicrosoftCommonPropsHasBeenImported)' != 'true' and Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
+
+  <Import Project="Sdk.props" Sdk="Microsoft.NET.SDK"
+       Condition="!Exists('$(MSBuildProjectExtensionsPath)SmallSharp.sdks.props')" />
+
+  <Import Project="$(MSBuildProjectExtensionsPath)SmallSharp.sdks.props" 
+       Condition="Exists('$(MSBuildProjectExtensionsPath)SmallSharp.sdks.props')" />
+
+  <Import Project="..\build\SmallSharp.props" />
 
 </Project>
diff --git a/src/SmallSharp/Sdk.targets b/src/SmallSharp/Sdk.targets
@@ -1,5 +1,33 @@
 <Project>
 
+  <Import Project="Sdk.targets" Sdk="Microsoft.NET.SDK"
+       Condition="!Exists('$(MSBuildProjectExtensionsPath)SmallSharp.sdks.targets')" />
+
+  <Import Project="$(MSBuildProjectExtensionsPath)SmallSharp.sdks.targets"
+       Condition="Exists('$(MSBuildProjectExtensionsPath)SmallSharp.sdks.targets')" />
+
   <Import Project="..\build\SmallSharp.targets" />
 
+  <Target Name="ImplicitPackageReferenceFromStartupFile" BeforeTargets="_GenerateProjectRestoreGraphPerFramework"
+          DependsOnTargets="StartupFile"
+          Condition="'$(StartupFile)' != '' and Exists('$(StartupFile)') and '$(RestoreNeeded)' == 'true'" >
+
+    <!-- Optimize for restore success on first run without previously running our targets -->
+    <ReadLinesFromFile File="$(StartupFile)">
+      <Output TaskParameter="Lines" ItemName="_StartupFileLines" />
+    </ReadLinesFromFile>
+
+    <ItemGroup>
+      <_PkgLines Include="@(_StartupFileLines)"
+                 Condition="$([MSBuild]::ValueOrDefault('%(Identity)', '').StartsWith('#:package '))" />
+
+      <_PkgReference Include="$([MSBuild]::ValueOrDefault('%(_PkgLines.Identity)', '').Substring(10))" />
+
+      <PackageReference Condition="'@(_PkgReference)' != ''" Include="$([MSBuild]::ValueOrDefault('%(_PkgReference.Identity)', '').Split('@')[0])">
+        <Version>$([MSBuild]::ValueOrDefault('%(_PkgReference.Identity)', '').Split('@')[1])</Version>
+      </PackageReference>
+    </ItemGroup>
+
+  </Target>
+
 </Project>
diff --git a/src/SmallSharp/SmallSharp.csproj b/src/SmallSharp/SmallSharp.csproj
@@ -24,20 +24,26 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="NuGetizer" Version="1.3.0" />
-    <PackageReference Include="JsonPoke" Version="1.2.0" />
     <PackageReference Include="Microsoft.Build.Tasks.Core" Version="17.13.26" Pack="false" />
+    <PackageReference Include="NuGetizer" Version="1.3.0" />
+    <PackageReference Include="JsonPoke" Version="1.2.0" Pack="false" GeneratePathProperty="true" />
+    <PackageReference Include="NuGet.Versioning" Version="6.14.0" PrivateAssets="all" />
+    <PackageReference Include="PolySharp" Version="1.15.0" PrivateAssets="all" />
+    <PackageReference Include="ThisAssembly.Project" Version="2.0.14" PrivateAssets="all" />
   </ItemGroup>
 
   <ItemGroup>
     <None Include="..\_._" PackFolder="lib\netstandard2.0" Visible="false" />
     <None Update="SmallSharp.targets" PackFolder="$(PackFolder)" CopyToOutputDirectory="PreserveNewest" />
     <None Update="SmallSharp.Before.targets" PackFolder="$(PackFolder)" CopyToOutputDirectory="PreserveNewest" />
-    <None Update="Sdk.props;Sdk.targets" PackFolder="Sdk" CopyToOutputDirectory="PreserveNewest" />
+    <None Update="Sdk.*" PackFolder="Sdk" CopyToOutputDirectory="PreserveNewest" />
+    <None Include="$(PkgJsonPoke)\build\JsonPoke.dll" PackFolder="$(PackFolder)" CopyToOutputDirectory="PreserveNewest" Visible="false" />
+    <None Include="$(PkgJsonPoke)\build\Newtonsoft.Json.dll" PackFolder="$(PackFolder)" CopyToOutputDirectory="PreserveNewest" Visible="false" />
   </ItemGroup>
 
   <ItemGroup>
-    <UpToDateCheckInput Include="SmallSharp.targets;SmallSharp.Before.targets;Sdk.props;Sdk.targets" />
+    <UpToDateCheckInput Include="SmallSharp.targets;SmallSharp.Before.targets;Sdk.props;Sdk.Empty.props;Sdk.targets" />
+    <ProjectProperty Include="PackageVersion" />
   </ItemGroup>
 
 </Project>
diff --git a/src/SmallSharp/SmallSharp.props b/src/SmallSharp/SmallSharp.props
@@ -6,6 +6,8 @@
 
     <!-- Capture project-level properties before they are defaulted by Microsoft.Common.targets -->
     <CustomBeforeMicrosoftCSharpTargets>$(MSBuildThisFileDirectory)\SmallSharp.Before.props</CustomBeforeMicrosoftCSharpTargets>
-</PropertyGroup>
+
+    <UsingSmallSharpSDK Condition="'$(UsingSmallSharpSDK)' == ''">false</UsingSmallSharpSDK>
+  </PropertyGroup>
 
 </Project>