Ensure dotnet build works too

Both `ImportProjectExtensionProps` and `ImportProjectExtensionTargets` must be set to true, and we now use `MSBuildProjectExtensionsPath` to leverage the standard way of importing these targets.

See dotnet/msbuild#9512

Fixes #139

Author: kzu

src/Demo/global.json

@@ -1,5 +1,5 @@
 {
   "msbuild-sdks": {
-    "SmallSharp": "42.42.516-main"
+    "SmallSharp": "2.0.0"
   }
 }

src/SmallSharp/Sdk.props

@@ -2,6 +2,11 @@
 
   <Import Project="..\build\SmallSharp.props" />
 
+  <PropertyGroup>
+    <ImportProjectExtensionProps>true</ImportProjectExtensionProps>
+    <ImportProjectExtensionTargets>true</ImportProjectExtensionTargets>
+  </PropertyGroup>
+
   <ItemGroup>
     <PackageReference Include="JsonPoke" Version="1.2.0" PrivateAssets="all" />
   </ItemGroup>

src/SmallSharp/SmallSharp.Before.props

@@ -0,0 +1,8 @@
+<Project>
+
+  <PropertyGroup>
+    <_ImportProjectExtensionProps>$(ImportProjectExtensionProps)</_ImportProjectExtensionProps>
+    <_ImportProjectExtensionTargets>$(ImportProjectExtensionTargets)</_ImportProjectExtensionTargets>
+  </PropertyGroup>
+
+</Project>

src/SmallSharp/SmallSharp.csproj

@@ -32,11 +32,12 @@
   <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" />
   </ItemGroup>
 
   <ItemGroup>
-    <UpToDateCheckInput Include="SmallSharp.targets;Sdk.props;Sdk.targets" />
+    <UpToDateCheckInput Include="SmallSharp.targets;SmallSharp.Before.targets;Sdk.props;Sdk.targets" />
   </ItemGroup>
 
 </Project>

src/SmallSharp/SmallSharp.props

@@ -1,11 +1,11 @@
 <Project>
 
   <PropertyGroup>
-    <!-- We emit Directory.Packages.props for #:package references -->
-    <!--<CentralPackageFloatingVersionsEnabled>true</CentralPackageFloatingVersionsEnabled>
-    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>-->
     <!-- This disables compilation error in VS for #: prefix -->
     <Features Condition="'$(MSBuildIsRestoring)' != 'true'">$(Features);FileBasedProgram</Features>
-  </PropertyGroup>
+
+    <!-- Capture project-level properties before they are defaulted by Microsoft.Common.targets -->
+    <CustomBeforeMicrosoftCSharpTargets>$(MSBuildThisFileDirectory)\SmallSharp.Before.props</CustomBeforeMicrosoftCSharpTargets>
+</PropertyGroup>
 
 </Project>

src/SmallSharp/SmallSharp.targets

@@ -8,9 +8,10 @@
     </UserProjectNamespace>
     <StartupFile>$(ActiveDebugProfile)</StartupFile>
     <StartupFile Condition="'$(ActiveDebugProfile)' == '' or !Exists('$(ActiveDebugProfile)')">$(ActiveCompile)</StartupFile>
-    <StartupFileDependsOn>CollectStartupFile;SelectStartupFile;SelectTopLevelCompile;UpdateLaunchSettings;EmitTargets</StartupFileDependsOn>
-  
-    <SmallSharpPackagesTargets>$(MSBuildProjectDirectory)\$(BaseIntermediateOutputPath)SmallSharp.targets</SmallSharpPackagesTargets>
+    <StartupFileDependsOn>EnsureImportProjectExtensions;CollectStartupFile;SelectStartupFile;SelectTopLevelCompile;UpdateLaunchSettings;EmitTargets</StartupFileDependsOn>
+    
+    <!-- For CLI dotnet run, users should set ImportProjectExtensionTargets=true -->
+    <SmallSharpPackagesTargets>$(MSBuildProjectExtensionsPath)$(MSBuildProjectFile).smallsharp.targets</SmallSharpPackagesTargets>
   </PropertyGroup>
 
   <ItemGroup>
@@ -30,6 +31,10 @@
 
   <Target Name="StartupFile" BeforeTargets="BeforeCompile;CoreCompile;CompileDesignTime;CollectUpToDateCheckInputDesignTime" DependsOnTargets="$(StartupFileDependsOn)" />
 
+  <Target Name="EnsureImportProjectExtensions" Condition="'$(_ImportProjectExtensionProps)' != 'true' or '$(_ImportProjectExtensionTargets)' != 'true'">
+    <Error Code="SCS01" Text="Setting ImportProjectExtensionProps and ImportProjectExtensionTargets project properties to 'true' is required by SmallSharp to support C# package and project directives." />
+  </Target>
+
   <Target Name="CollectStartupFile">
     <ItemGroup>
       <StartupFile Include="*$(DefaultLanguageSourceExtension)" />
@@ -162,8 +167,6 @@
     </EmitTargets>
   </Target>
 
-  <Import Project="$(SmallSharpPackagesTargets)" Condition="Exists('$(SmallSharpPackagesTargets)')" />
-
   <UsingTask TaskName="SortItems" TaskFactory="RoslynCodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
     <ParameterGroup>
       <!-- ITaskItem[] input and sorted output -->