Improve integration with CLI restore in SDK mode

In SDK mode we can just always read the package references from the startup file and therefore Restore will Just Work.

In non-SDK mode we'll depend on an initial run and it's mostly for IDE usage where this problem doesn't exist because VS will detect the generated targets changed and will automatically invoke a restore while you're editing.

Author: kzu

src/SmallSharp/EmitTargets.cs

@@ -29,6 +29,11 @@ public class EmitTargets : Task
     [Required]
     public required string TargetsFile { get; set; }
 
+    [Required]
+    public required bool UsingSDK { get; set; }
+
+    public ITaskItem[] PackageReferences { get; set; } = [];
+
     [Output]
     public ITaskItem[] Packages { get; set; } = [];
 
@@ -38,6 +43,9 @@ public class EmitTargets : Task
     [Output]
     public ITaskItem[] Properties { get; set; } = [];
 
+    [Output]
+    public bool RestoreNeeded { get; set; } = false;
+
     public override bool Execute()
     {
         if (StartupFile is null)
@@ -103,7 +111,8 @@ public override bool Execute()
 
         WriteXml(TargetsFile, new XElement("Project",
             new XElement("PropertyGroup", properties),
-            new XElement("ItemGroup", items)
+            // don't emit package references in SDK mode, since we'll add them from the SDK targets.
+            UsingSDK ? new XElement("ItemGroup") : new XElement("ItemGroup", items)
         ));
 
         WriteXml(Path.Combine(BaseIntermediateOutputPath, "SmallSharp.sdk.props"), new XElement("Project",
@@ -116,6 +125,23 @@ public override bool Execute()
             new XElement("PropertyGroup",
                 [new XElement("SmallSharpProjectExtensionPropsImported", "true")])));
 
+        // Determine if a restore is needed: if any discovered #:package (id+version) is not already
+        // present in the incoming PackageReferences list.
+        foreach (var pkg in packages)
+        {
+            var id = pkg.ItemSpec;
+            var version = pkg.GetMetadata("Version");
+            var exists = PackageReferences?.Any(r =>
+                string.Equals(r.ItemSpec, id, StringComparison.OrdinalIgnoreCase) &&
+                string.Equals(r.GetMetadata("Version"), version, StringComparison.OrdinalIgnoreCase)) == true;
+
+            if (!exists)
+            {
+                RestoreNeeded = true;
+                break;
+            }
+        }
+
         return true;
     }
 

src/SmallSharp/Sdk.targets

@@ -8,9 +8,10 @@
 
   <Import Project="..\build\SmallSharp.targets" />
 
-  <Target Name="ImplicitPackageReferenceFromStartupFile" BeforeTargets="_GenerateProjectRestoreGraphPerFramework;ResolvePackageAssets"
+  <Target Name="ImplicitPackageReferenceFromStartupFile" 
+          BeforeTargets="_GenerateProjectRestoreGraphPerFramework;ResolvePackageAssets;CompileDesignTime;CollectUpToDateCheckInputDesignTime"
           DependsOnTargets="StartupFile"
-          Condition="'$(StartupFile)' != '' and Exists('$(StartupFile)') and '$(SmallSharpProjectExtensionPropsImported)' != 'true'">
+          Condition="'$(StartupFile)' != '' and Exists('$(StartupFile)')">
 
     <!-- Optimize for restore success on first run without previously running our targets -->
     <ReadLinesFromFile File="$(StartupFile)">

src/SmallSharp/SmallSharp.targets

@@ -168,13 +168,16 @@
   <Target Name="EmitTargets" DependsOnTargets="CollectStartupFile;SelectTopLevelCompile;SelectStartupFile" 
           Inputs="@(Compile);$(ActiveDebugProfile);$(ActiveFile);Properties\launchSettings.json" 
           Outputs="$(SmallSharpPackagesProps);$(SmallSharpPackagesTargets)">
-    <EmitTargets StartupFile="$(StartupFile)"
+    <EmitTargets StartupFile="$(StartupFile)" 
+                 UsingSDK="$(UsingSmallSharpSDK)"
+                 PackageReferences="@(PackageReferences)"
                  PropsFile="$(SmallSharpPackagesProps)"
                  TargetsFile="$(SmallSharpPackagesTargets)"
                  BaseIntermediateOutputPath="$(BaseIntermediateOutputPath)">
       <Output TaskParameter="Packages" ItemName="FileBasedPackage" />
       <Output TaskParameter="Properties" PropertyName="FileBasedProperty" />
       <Output TaskParameter="Sdks" PropertyName="FileBasedSdk" />
+      <Output TaskParameter="RestoreNeeded" PropertyName="RestoreNeeded" />
     </EmitTargets>
     <Error Code="SCS001" Condition="'@(FileBasedSdk)' != '' and '$(UsingSmallSharpSDK)' != 'true'"
            Text="Using #:sdk directives requires using SmallSharp as an SDK instead of a package reference: &lt;Project Sdk='SmallSharp/$(SmallSharpVersion)'&gt;" />

src/demo.ps1

@@ -6,8 +6,8 @@ jq --arg version "$version" '.["msbuild-sdks"].SmallSharp = $version' global.jso
 
 # build with each top-level file as the active one
 foreach ($file in gci *.cs) {
-    rm -r -fo obj -ea 0
-    dotnet build Demo.csproj -p:ActiveFile=$($file.Name) -bl
+    # rm -r -fo obj -ea 0
+    dotnet build Demo.csproj -p:ActiveFile=$($file.Name) -bl:"$($file.BaseName).binlog"
     if ($LASTEXITCODE -ne 0) {
         Write-Error "Build failed for $($file.Name)"
         popd; popd;