Prefer the portable ILCompiler when publishing for the portable RID on a source-built SDK. (#41754)

Author: tmds

src/Tasks/Microsoft.NET.Build.Tasks/ProcessFrameworkReferences.cs

@@ -112,6 +112,8 @@ public class ProcessFrameworkReferences : TaskBase
         [Required]
         public string NETCoreSdkRuntimeIdentifier { get; set; }
 
+        public string NETCoreSdkPortableRuntimeIdentifier { get; set; }
+
         [Required]
         public string NetCoreRoot { get; set; }
 
@@ -778,9 +780,17 @@ private ToolPackSupport AddToolPack(
                 var packNamePattern = knownPack.GetMetadata(packName + "PackNamePattern");
                 var packSupportedRuntimeIdentifiers = knownPack.GetMetadata(packName + "RuntimeIdentifiers").Split(';');
 
+                // When publishing for the non-portable RID that matches NETCoreSdkRuntimeIdentifier, prefer NETCoreSdkRuntimeIdentifier for the host.
+                // Otherwise prefer the NETCoreSdkPortableRuntimeIdentifier.
+                // This makes non-portable SDKs behave the same as portable SDKs except for the specific case of targetting the non-portable RID.
+                // It also enables the non-portable ILCompiler to be packaged separately from the SDK and
+                // only required when publishing for the non-portable SDK RID.
+                string portableSdkRid = !string.IsNullOrEmpty(NETCoreSdkPortableRuntimeIdentifier) ? NETCoreSdkPortableRuntimeIdentifier : NETCoreSdkRuntimeIdentifier;
+                bool targetsNonPortableSdkRid = RuntimeIdentifier == NETCoreSdkRuntimeIdentifier && NETCoreSdkRuntimeIdentifier != portableSdkRid;
+                string hostRuntimeIdentifier = targetsNonPortableSdkRid ? NETCoreSdkRuntimeIdentifier : portableSdkRid;
                 // Get the best RID for the host machine, which will be used to validate that we can run crossgen for the target platform and architecture
                 var runtimeGraph = new RuntimeGraphCache(this).GetRuntimeGraph(RuntimeGraphPath);
-                var hostRuntimeIdentifier = NuGetUtils.GetBestMatchingRid(runtimeGraph, NETCoreSdkRuntimeIdentifier, packSupportedRuntimeIdentifiers, out bool wasInGraph);
+                hostRuntimeIdentifier = NuGetUtils.GetBestMatchingRid(runtimeGraph, hostRuntimeIdentifier, packSupportedRuntimeIdentifiers, out bool wasInGraph);
                 if (hostRuntimeIdentifier == null)
                 {
                     return ToolPackSupport.UnsupportedForHostRuntimeIdentifier;

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.FrameworkReferenceResolution.targets

@@ -132,6 +132,7 @@ Copyright (c) .NET Foundation. All rights reserved.
                                 KnownWebAssemblySdkPacks="@(KnownWebAssemblySdkPack)"
                                 UsingMicrosoftNETSdkWebAssembly="$(UsingMicrosoftNETSdkWebAssembly)"
                                 NETCoreSdkRuntimeIdentifier="$(NETCoreSdkRuntimeIdentifier)"
+                                NETCoreSdkPortableRuntimeIdentifier="$(NETCoreSdkPortableRuntimeIdentifier)"
                                 NetCoreRoot="$(NetCoreRoot)"
                                 NETCoreSdkVersion="$(NETCoreSdkVersion)">