ILSpy/ILSpy.Tests/FixtureAssembly.cs

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using System;
using System.Collections.Immutable;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;
using System.Reflection.Metadata;
using System.Reflection.Metadata.Ecma335;
using System.Threading.Tasks;

using ICSharpCode.ILSpyX;

using ICSharpCode.ILSpy.ViewModels;

namespace ICSharpCode.ILSpy.Tests;

/// <summary>
/// Emits a tiny throwaway assembly to a temp file so the project-export / save-code / compare
/// tests can exercise the full pipeline without decompiling a multi-hundred-type framework
/// assembly. The default assembly list loads System.Linq, CoreLib and the Uri assembly; targeting
/// those made each of these tests run for ~10s purely on the type count. A handful of public
/// members is enough to produce a non-empty .cs, a real namespace subtree and a resolvable
/// .csproj, while keeping each test well under a second.
/// </summary>
public static class FixtureAssembly
{
	/// <summary>Short name of the single public type a caller can assert on / navigate to.</summary>
	public const string TypeName = "Greeter";

	/// <summary>Name of a member of <see cref="TypeName"/> a caller can assert is decompiled.</summary>
	public const string MemberName = "Hello";

	/// <summary>
	/// Emits a fresh fixture assembly named <paramref name="name"/> to a temp file and returns its
	/// path. Each call produces a distinct file so callers can build solutions / comparisons out of
	/// several fixtures.
	/// </summary>
	public static string Emit(string name)
	{
		var ab = new PersistedAssemblyBuilder(new AssemblyName(name), typeof(object).Assembly);
		var module = ab.DefineDynamicModule(name);

		var greeter = module.DefineType($"{name}.{TypeName}", TypeAttributes.Public | TypeAttributes.Class);
		var hello = greeter.DefineMethod(
			MemberName, MethodAttributes.Public | MethodAttributes.Static, typeof(string), Type.EmptyTypes);
		var il = hello.GetILGenerator();
		il.Emit(OpCodes.Ldstr, $"hello from {name}");
		il.Emit(OpCodes.Ret);
		greeter.CreateType();

		// A second type in a nested namespace so the namespace subtree and the project layout are
		// not entirely trivial.
		var widget = module.DefineType($"{name}.Widgets.Widget", TypeAttributes.Public | TypeAttributes.Class);
		var add = widget.DefineMethod(
			"Add", MethodAttributes.Public | MethodAttributes.Static, typeof(int), [typeof(int), typeof(int)]);
		var il2 = add.GetILGenerator();
		il2.Emit(OpCodes.Ldarg_0);
		il2.Emit(OpCodes.Ldarg_1);
		il2.Emit(OpCodes.Add);
		il2.Emit(OpCodes.Ret);
		widget.CreateType();

		// Unique directory (not filename) so the file is "<name>.dll": the assembly's ShortName then
		// equals <name> and matches the "<name>" namespace prefix the types use, keeping FindNode
		// paths simple.
		var dir = Path.Combine(Path.GetTempPath(), $"ILSpyFixture_{Guid.NewGuid():N}");
		Directory.CreateDirectory(dir);
		var path = Path.Combine(dir, $"{name}.dll");
		ab.Save(path);
		return path;
	}

	/// <summary>
	/// Emits a fixture assembly and opens it through the production Open command, returning the
	/// loaded assembly once its load result is available.
	/// </summary>
	public static Task<LoadedAssembly> OpenFixtureAsync(this MainWindowViewModel vm, string name = "Fixture")
	{
		ArgumentNullException.ThrowIfNull(vm);
		return vm.OpenAssemblyAsync(Emit(name));
	}

	/// <summary>
	/// Writes a standalone portable PDB to a temp file and returns its path. It carries a metadata
	/// root but no PE image, so it loads as a metadata-only file -- the "(Debug Metadata)" entry
	/// ILSpy shows for a .pdb opened on its own. Callers use it for the selection member that loads
	/// successfully yet holds nothing to decompile.
	/// </summary>
	public static string EmitStandalonePdb(string name)
	{
		// An all-zero row count set describes an empty type system, which is all this needs: the file
		// only has to be readable as metadata, not to match any particular assembly.
		var pdbBuilder = new PortablePdbBuilder(
			new MetadataBuilder(), ImmutableArray.CreateRange(new int[MetadataTokens.TableCount]), default);
		var blob = new BlobBuilder();
		pdbBuilder.Serialize(blob);

		var dir = Path.Combine(Path.GetTempPath(), $"ILSpyPdbFixture_{Guid.NewGuid():N}");
		Directory.CreateDirectory(dir);
		var path = Path.Combine(dir, $"{name}.pdb");
		File.WriteAllBytes(path, blob.ToArray());
		return path;
	}

	/// <summary>
	/// Opens a standalone portable PDB, returning it once it has loaded. It loads successfully but is
	/// metadata-only, so the export paths have to tell it apart from both a real assembly and a file
	/// that failed to load.
	/// </summary>
	public static async Task<LoadedAssembly> OpenMetadataOnlyFixtureAsync(this MainWindowViewModel vm, string name = "MetadataOnly")
	{
		ArgumentNullException.ThrowIfNull(vm);

		var path = EmitStandalonePdb(name);
		vm.AssemblyTreeModel.OpenFiles([path]);
		await Waiters.WaitForAsync(
			() => vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
				.Any(a => string.Equals(a.FileName, path, StringComparison.OrdinalIgnoreCase)),
			description: $"metadata-only file '{path}' to appear in the active list");

		var loaded = vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
			.First(a => string.Equals(a.FileName, path, StringComparison.OrdinalIgnoreCase));
		await loaded.GetLoadResultAsync();
		return loaded;
	}

	/// <summary>
	/// Opens a file that is not a PE image at all, returning it once the load has failed. Callers use
	/// it to build the mixed selections the export paths have to cope with. Unlike
	/// <see cref="TestHarness.OpenAssemblyAsync"/> this waits on <see cref="LoadedAssembly.HasLoadError"/>
	/// rather than the load result, which for such a file rethrows the load failure.
	/// </summary>
	public static async Task<LoadedAssembly> OpenBrokenFixtureAsync(this MainWindowViewModel vm, string name = "Broken")
	{
		ArgumentNullException.ThrowIfNull(vm);

		var dir = Path.Combine(Path.GetTempPath(), $"ILSpyBrokenFixture_{Guid.NewGuid():N}");
		Directory.CreateDirectory(dir);
		var path = Path.Combine(dir, $"{name}.dll");
		await File.WriteAllTextAsync(path, "not a real PE file");

		vm.AssemblyTreeModel.OpenFiles([path]);
		await Waiters.WaitForAsync(
			() => vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
				.Any(a => string.Equals(a.FileName, path, StringComparison.OrdinalIgnoreCase)),
			description: $"broken assembly '{path}' to appear in the active list");

		var loaded = vm.AssemblyTreeModel.AssemblyList!.GetAssemblies()
			.First(a => string.Equals(a.FileName, path, StringComparison.OrdinalIgnoreCase));
		await Waiters.WaitForAsync(() => loaded.HasLoadError, description: $"'{path}' to fail loading");
		return loaded;
	}
}