Use AOT version of Roslyn found in local .NET SDK

This gives a massive speedup to the startup time as the NuGet version of
Roslyn takes a while to load because of JIT.

T4.Build/SdkAssemblyLoadContext.cs

@@ -0,0 +1,58 @@
+using System;
+using System.IO;
+using System.Reflection;
+using System.Runtime.Loader;
+using Mono.TextTemplating.CodeCompilation;
+
+namespace T4.Build
+{
+ class SdkAssemblyLoadContext : AssemblyLoadContext
+ {
+ readonly string runtimeDir;
+ readonly string roslynDir;
+
+ public SdkAssemblyLoadContext()
+ {
+ runtimeDir = Path.GetDirectoryName(typeof(object).Assembly.Location);
+
+ var dotnetRoot = Path.GetDirectoryName(Path.GetDirectoryName(Path.GetDirectoryName(runtimeDir)));
+ string MakeRoslynPath(string d) => Path.Combine(d, "Roslyn", "bincore");
+ var sdkDir = FindHighestVersionedDirectory(Path.Combine(dotnetRoot, "sdk"), d => Directory.Exists(MakeRoslynPath(d)));
+ roslynDir = MakeRoslynPath(sdkDir);
+ }
+
+ static string FindHighestVersionedDirectory(string parentFolder, Func<string, bool> validate)
+ {
+ string bestMatch = null;
+ SemVersion bestVersion = SemVersion.Zero;
+ foreach (var dir in Directory.EnumerateDirectories(parentFolder))
+ {
+ var name = Path.GetFileName(dir);
+ if (SemVersion.TryParse(name, out var version) && version.Major >= 0)
+ {
+ if (version > bestVersion && (validate == null || validate(dir)))
+ {
+ bestVersion = version;
+ bestMatch = dir;
+ }
+ }
+ }
+ return bestMatch;
+ }
+
+ protected override Assembly Load(AssemblyName assemblyName)
+ {
+ switch (assemblyName.Name)
+ {
+ case "Microsoft.CodeAnalysis":
+ case "Microsoft.CodeAnalysis.CSharp":
+ return LoadFromAssemblyPath(Path.Combine(roslynDir, $"{assemblyName.Name}.dll"));
+ case "System.Collections.Immutable":
+ case "System.Reflection.Metadata":
+ return LoadFromAssemblyPath(Path.Combine(runtimeDir, $"{assemblyName.Name}.dll"));
+ }
+
+ return null;
+ }
+ }
+}

T4.Build/T4.Build.nuspec

@@ -11,7 +11,7 @@
  <licenseUrl>https://licenses.nuget.org/Apache-2.0</licenseUrl>
  </metadata>
  <files>
- <file src="bin/$configuration$/$framework$/*.dll" target="tools/" />
+ <file src="bin/$configuration$/$framework$/*.dll" exclude="**/Microsoft.CodeAnalysis*.dll;**/System.Reflection.Metadata.dll;**/System.Collections.Immutable.dll" target="tools/" />
  <file src="bin/$configuration$/$framework$/*.runtimeconfig.json" target="tools/" />
  <file src="build/common.targets" target="build/common.targets" />
  <file src="build/single.targets" target="build/T4.Build.targets" />

T4.Build/TemplatingEngineExtension.cs

@@ -0,0 +1,37 @@
+using System;
+using System.IO;
+using System.Reflection;
+using Mono.TextTemplating;
+
+namespace T4.Build
+{
+ public static class RoslynTemplatingEngineExtensions
+ {
+ private static readonly object sync = new object();
+ private static MethodInfo useInProcessCompilerMethod;
+
+ private static MethodInfo UseInProcessCompilerMethod
+ {
+ get
+ {
+ lock (sync)
+ {
+ if (useInProcessCompilerMethod == null)
+ {
+ var context = new SdkAssemblyLoadContext();
+ var assembly = context.LoadFromAssemblyPath(Path.Combine(Path.GetDirectoryName(typeof(RoslynTemplatingEngineExtensions).Assembly.Location), "Mono.TextTemplating.Roslyn.dll"));
+ var extensions = assembly.GetType("Mono.TextTemplating.RoslynTemplatingEngineExtensions");
+ useInProcessCompilerMethod = extensions.GetMethod("UseInProcessCompiler", new Type[] { typeof(TemplatingEngine) });
+ }
+ }
+
+ return useInProcessCompilerMethod;
+ }
+ }
+
+ public static void UseInProcessCompiler(this TemplatingEngine engine)
+ {
+ UseInProcessCompilerMethod.Invoke(null, new object[] { engine });
+ }
+ }
+}