Read a decompdiff corpus from an @list file

Handing the corpus over as `$(cat list)` is a bourne shell construct, so the
one invocation the tools print and the README documents did not work on
Windows. nugetfuzz already reads its package list from an @file for the same
reason; decompdiff now takes its corpus entries the same way, leaving the
shell out of it entirely.

Assisted-by: Claude:claude-opus-5[1m]:Claude Code

TestTools/README.md

@@ -72,10 +72,11 @@ download itself is `nugetfuzz --download-only`, so package selection, TFM matchi
 dependency walk behave exactly as they do in a sweep - only the decompiling is skipped.
 
 The corpus is written as a list of directories rather than one root, because a package already
-restored on this machine is used from the machine-wide NuGet cache instead of being copied:
+restored on this machine is used from the machine-wide NuGet cache instead of being copied. Pass the
+list with `@`, which both tools understand and which needs no help from the shell:
 
 ```pwsh
-dotnet run decompdiff.cs -- --old master --new my-branch -o report $(cat crawl/top-200.corpus.txt)
+dotnet run decompdiff.cs -- --old master --new my-branch -o report @crawl/top-200.corpus.txt
 ```
 
 ## decompdiff
@@ -92,6 +93,9 @@ dotnet run decompdiff.cs -- --old ../../ILSpy-master --new . -o report ~/.cache/
 dotnet run decompdiff.cs -- --old v9.1.dll --new v11.dll --refs <dir> corpus.dll
 ```
 
+A corpus argument is a dll, a directory scanned recursively for dlls, or `@file` listing either one
+per line (`#` comments allowed).
+
 An `--old`/`--new` argument is a path to `ICSharpCode.Decompiler.dll`, an ILSpy checkout, or a
 commit-ish. A checkout is restored and built in Release on demand. **Watch the timestamp in the
 header line**: an existing Release build is reused as-is; pass `--build` to force a rebuild.

TestTools/decompdiff.cs

@@ -25,7 +25,7 @@
 // round-trip tests, which verify correctness but not output quality.
 //
 // usage: dotnet run decompdiff.cs -- --old <commit-ish|ILSpy-checkout|Decompiler.dll> --new <...>
-//                                    [-o <report-dir>] [--build] [--refs <dir>]... <dll|dir>...
+//                                    [-o <report-dir>] [--build] [--refs <dir>]... <dll|dir|@list>...
 //
 // - checkout args are built on demand (Release; restore keeps packages.lock.json
 //   whole via -p:RestoreEnablePackagePruning=false); pass --build to force rebuild.
@@ -33,7 +33,8 @@
 //   the tool is run from and checked out into a worktree under
 //   ~/.cache/decompdiff/<repo>/<commit>, kept and reused so a rerun keeps the
 //   Release build it already contains.
-// - corpus dirs are scanned recursively for *.dll (e.g. ~/.cache/nugetfuzz).
+// - corpus dirs are scanned recursively for *.dll (e.g. ~/.cache/nugetfuzz); @list reads
+//   the entries from a file, one per line, as nugetfuzz does with its package list.
 // - changed/errored types are written to <report-dir>/{old,new}/...; inspect with
 //   `git diff --no-index <report-dir>/old <report-dir>/new`, or open the generated
 //   <report-dir>/index.html, which carries the same data with inline diffs.
@@ -97,13 +98,24 @@ for (int i = 0; i < args.Length; i++)
 			refDirs.Add(args[++i]);
 			break;
 		default:
-			corpus.Add(args[i]);
+			// @file lists corpus entries one per line, the same spelling nugetfuzz uses. Shells
+			// differ on how (or whether) a file expands into arguments, so the tool reads it.
+			if (args[i].StartsWith('@'))
+			{
+				corpus.AddRange(File.ReadAllLines(args[i][1..])
+					.Select(l => l.Trim())
+					.Where(l => l.Length > 0 && !l.StartsWith('#')));
+			}
+			else
+			{
+				corpus.Add(args[i]);
+			}
 			break;
 	}
 }
 if (oldSpec == null || newSpec == null || corpus.Count == 0)
 {
-	Console.Error.WriteLine("usage: decompdiff --old <commit-ish|ILSpy-checkout|Decompiler.dll> --new <...> [-o report-dir] [--build] [--refs <dir>]... <dll|dir>...");
+	Console.Error.WriteLine("usage: decompdiff --old <commit-ish|ILSpy-checkout|Decompiler.dll> --new <...> [-o report-dir] [--build] [--refs <dir>]... <dll|dir|@list>...");
 	return 1;
 }
 reportDir ??= "decompdiff-report";

TestTools/nuget-top.ps1

@@ -70,4 +70,4 @@ $dirs = $log | ForEach-Object { if ($_ -match '^\s*cached:\s*(.+)$') { $Matches[
 Set-Content -Path $corpusFile -Value $dirs
 Write-Host ""
 Write-Host "$($dirs.Count) lib directories -> $corpusFile"
-Write-Host "decompdiff --old <ref> --new <ref> -o report `$(cat $corpusFile)"
+Write-Host "dotnet run decompdiff.cs -- --old <ref> --new <ref> -o report `@$corpusFile"