[release/3.1] Fix use of ilasm during test builds when using a 3.0 SDK (#27818)

* Add fix for restore of ilasm

The restore logic in buildtools tried to use a netcoreapp2.1 TFM for Linux-musl.
This ended up restoring Linux-x64 binaries which then broke the test build.
This change works around this by saving a copy of the depproj that BuildTools used into
the tree and restore it as a 3.0 app manually in init-tools on our side of the build.

* Change to a 3.0 SDK for servicing

Author: hoyosjs

global.json

@@ -1,6 +1,6 @@
 {
   "tools": {
-    "dotnet": "3.0.100-preview6-012264"
+    "dotnet": "3.0.100"
   },
   "native-tools": {
     "cmake": "3.11.1",

init-tools.cmd

@@ -105,9 +105,6 @@ if NOT exist "%BUILD_TOOLS_PATH%\init-tools.cmd" (
 
 :afterbuildtoolsrestore
 
-:: Ask init-tools to also restore ILAsm
-set /p ILASMCOMPILER_VERSION=< "%~dp0ILAsmVersion.txt"
-
 echo Initializing BuildTools...
 echo Running: "%BUILD_TOOLS_PATH%\init-tools.cmd" "%~dp0" "%DOTNET_CMD%" "%TOOLRUNTIME_DIR%" >> "%INIT_TOOLS_LOG%"
 call "%BUILD_TOOLS_PATH%\init-tools.cmd" "%~dp0" "%DOTNET_CMD%" "%TOOLRUNTIME_DIR%" "%PACKAGES_DIR%" >> "%INIT_TOOLS_LOG%"
@@ -117,6 +114,12 @@ if not [%INIT_TOOLS_ERRORLEVEL%]==[0] (
   goto :error
 )
 
+REM ILasm/ILDasm used to be restored by buildtools. The reference there was a netocreapp2.0, which was prior to our support of linux-musl. We initialize it locally as a 3.0 with the new SDK.
+set /p ILASM_VERSION=< "%~dp0ILAsmVersion.txt"
+if [%NATIVE_TOOLS_RID%] == [] set NATIVE_TOOLS_RID=win-x64
+echo Running: call "%DOTNET_CMD%" build "%~dp0tests\ilasm-restore\ilasm.depproj" --no-cache --packages "%PACKAGES_DIR%" -r "%NATIVE_TOOLS_RID%" /p:ILAsmPackageVersion="%ILASM_VERSION%" /p:ExpectedILAsmPath="%TOOLRUNTIME_DIR%\ilasm" >> "%INIT_TOOLS_LOG%"
+call "%DOTNET_CMD%" build "%~dp0tests\ilasm-restore\ilasm.depproj" --no-cache --packages "%PACKAGES_DIR%" -r "%NATIVE_TOOLS_RID%" /p:ILAsmPackageVersion="%ILASM_VERSION%" /p:ExpectedILAsmPath="%TOOLRUNTIME_DIR%\ilasm"
+
 :: Create semaphore file
 echo Done initializing tools.
 if NOT exist "%BUILD_TOOLS_SEMAPHORE_DIR%" mkdir "%BUILD_TOOLS_SEMAPHORE_DIR%"

init-tools.sh

@@ -153,15 +153,8 @@ if [ -z "${__ILASM_RID-}" ]; then
 fi
 
 echo "Using RID $__ILASM_RID for BuildTools native tools"
-
-export ILASMCOMPILER_VERSION=$__ILASM_VERSION
 export NATIVE_TOOLS_RID=$__ILASM_RID
 
-if [ -n "${DotNetBootstrapCliTarPath-}" ]; then
-    # Assume ilasm is not in nuget yet when bootstrapping...
-    unset ILASMCOMPILER_VERSION
-fi
-
 # Build tools only supported on x64
 if [ "${__PKG_ARCH}" != "x64" ] &&  [ "${__PKG_ARCH}" != "arm" ]; then
     echo "Skipped installing build tools."
@@ -178,6 +171,14 @@ else
         exit 1
     fi
 
+
+    if [ ! -n "${DotNetBootstrapCliTarPath-}" ]; then
+        # Assume ilasm is not in nuget yet when bootstrapping...
+        # ILasm/ILDasm used to be restored by buildtools. The reference there was a netocreapp2.0, which was prior to our support of linux-musl. We initialize it locally as a 3.0 with the new SDK.
+        echo "Running: eval $__DOTNET_CMD build ${__scriptpath}/tests/ilasm-restore/ilasm.depproj --no-cache --packages $__PACKAGES_DIR -r $NATIVE_TOOLS_RID -p:ILAsmPackageVersion=$__ILASM_VERSION  -p:ExpectedILAsmPath=$__TOOLRUNTIME_DIR/ilasm" >> "$__init_tools_log"
+        eval "$__DOTNET_CMD" build "${__scriptpath}/tests/ilasm-restore/ilasm.depproj" --no-cache --packages "$__PACKAGES_DIR" -r "$NATIVE_TOOLS_RID" -p:ILAsmPackageVersion="$__ILASM_VERSION" -p:ExpectedILAsmPath="$__TOOLRUNTIME_DIR/ilasm"
+    fi
+
     echo "Making all .sh files executable under Tools."
     # Executables restored with .NET Core 2.0 do not have executable permission flags. https://github.com/NuGet/Home/issues/4424
     ls "$__scriptpath/Tools/"*.sh | xargs chmod +x

tests/ilasm-restore/Directory.Build.props

@@ -0,0 +1,6 @@
+<Project>
+  <!-- 
+    This project works around a restore issue in buildtools for musl distros. It shouldn't use any
+    other properties in the test tree. This file prevents any imports.
+  -->
+</Project>

tests/ilasm-restore/Directory.Build.targets

@@ -0,0 +1,6 @@
+<Project>
+  <!-- 
+    This project works around a restore issue in buildtools for musl distros. It shouldn't use any
+    other properties in the test tree. This file prevents any imports.
+  -->
+</Project>

tests/ilasm-restore/ilasm.depproj

@@ -0,0 +1,30 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <!-- This file is largely a copy of the BuildTools equivalent -->
+  <PropertyGroup>
+    <!-- suppress the attempt to copy build output. -->
+    <CopyBuildOutputToOutputDirectory>false</CopyBuildOutputToOutputDirectory>
+    <DisableImplicitFrameworkReferences>true</DisableImplicitFrameworkReferences>
+  </PropertyGroup>
+
+  <Target Name="CoreCompile">
+    <Copy SourceFiles="@(NativeCopyLocalItems)" DestinationFolder="$(ExpectedILAsmPath)" />
+  </Target>
+
+  <!-- Required by Common.Targets -->
+  <Target Name="CreateManifestResourceNames" />
+
+  <PropertyGroup>
+    <NuGetTargetMoniker>.NETCoreApp,Version=v3.0</NuGetTargetMoniker>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+    <RidSpecificAssets>true</RidSpecificAssets>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NETCore.ILAsm" Version="$(ILAsmPackageVersion)" />
+    <PackageReference Include="Microsoft.NETCore.ILDAsm" Version="$(ILAsmPackageVersion)" />
+
+    <!-- ILAsm has a very unfortunate runtime dependency on CoreCLR, so we need to grab that too -->
+    <!-- https://github.com/dotnet/coreclr/issues/15059 -->
+    <PackageReference Include="Microsoft.NETCore.Runtime.CoreCLR" Version="$(ILAsmPackageVersion)" />
+  </ItemGroup>
+</Project>