路径里的反斜杠在 Linux 上换成斜杠

- 教材写 AppDomain.CurrentDomain.BaseDirectory + "Camera\\"，Linux 上反斜杠会成为文件名的一部分
- 编译时把传给 System.IO（File、Directory、Path、各种 Stream）和 Image / Bitmap 读写文件方法的
  路径参数包上 Sim.Host.WindowsPaths.Fix；只包语义上确实是这些方法里名字带 path / file / dir 的
  字符串参数，不换行，编辑器里看到的仍是原代码

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

runtime/Sim.Runner/PathRewriter.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Operations;
+using Microsoft.CodeAnalysis.Text;
+
+namespace Sim.Runner;
+
+/// <summary>
+/// 编译前把传给 System.IO（File、Directory、Path、FileStream、StreamWriter 等）和 Image / Bitmap 读写文件方法的路径参数
+/// 包上 Sim.Host.WindowsPaths.Fix(...)：教材按 Windows 写 AppDomain.CurrentDomain.BaseDirectory + "Camera\\"，
+/// 在 Linux 上反斜杠要换成斜杠。只包语义上确实是这些方法里名字带 path / file / dir 的字符串参数；
+/// 改写不换行，报错和异常里的行号不变。学生在编辑器里看到的仍是原来的代码。
+/// </summary>
+internal static class PathRewriter
+{
+    private const string Fix = "global::Sim.Host.WindowsPaths.Fix";
+
+    public static CSharpCompilation Rewrite(CSharpCompilation compilation)
+    {
+        var result = compilation;
+        foreach (var tree in compilation.SyntaxTrees)
+        {
+            var model = compilation.GetSemanticModel(tree);
+            var root = tree.GetRoot();
+            var targets = root.DescendantNodes()
+                .Where(n => n is InvocationExpressionSyntax or BaseObjectCreationExpressionSyntax)
+                .SelectMany(n => PathArguments(model.GetOperation(n)))
+                .ToHashSet();
+            if (targets.Count == 0) continue;
+            var rewritten = root.ReplaceNodes(targets, (_, node) =>
+                SyntaxFactory.ParseExpression($"{Fix}({node.WithoutTrivia().ToFullString()})").WithTriviaFrom(node));
+            result = result.ReplaceSyntaxTree(tree,
+                CSharpSyntaxTree.ParseText(SourceText.From(rewritten.ToFullString(), Encoding.UTF8), (CSharpParseOptions)tree.Options, tree.FilePath));
+        }
+        return result;
+    }
+
+    /// <summary>调用里要包起来的路径参数（只取学生直接写的表达式；不含反斜杠的字符串常量不用包）</summary>
+    private static IEnumerable<ExpressionSyntax> PathArguments(IOperation? operation)
+    {
+        var (method, arguments) = operation switch
+        {
+            IInvocationOperation invocation => (invocation.TargetMethod, invocation.Arguments),
+            IObjectCreationOperation creation when creation.Constructor != null => (creation.Constructor, creation.Arguments),
+            _ => (null, default),
+        };
+        if (method == null || !HandlesFiles(method.ContainingType)) yield break;
+        foreach (var argument in arguments)
+        {
+            if (argument.Parameter is not { } parameter || !IsPathName(parameter.Name)) continue;
+            var values = argument.ArgumentKind == ArgumentKind.ParamArray && argument.Value is IArrayCreationOperation { Initializer: { } init }
+                ? init.ElementValues
+                : [argument.Value];
+            foreach (var value in values)
+            {
+                if (value.IsImplicit || value.Type?.SpecialType != SpecialType.System_String) continue;
+                if (value.ConstantValue is { HasValue: true, Value: string constant } && !constant.Contains('\\')) continue;
+                if (value.Syntax is ExpressionSyntax expression) yield return expression;
+            }
+        }
+    }
+
+    private static bool HandlesFiles(INamedTypeSymbol type)
+    {
+        var ns = type.ContainingNamespace?.ToDisplayString();
+        return ns == "System.IO" || (ns == "System.Drawing" && type.Name is "Image" or "Bitmap");
+    }
+
+    private static bool IsPathName(string name) =>
+        name.Contains("path", StringComparison.OrdinalIgnoreCase)
+        || name.Contains("file", StringComparison.OrdinalIgnoreCase)
+        || name.Contains("dir", StringComparison.OrdinalIgnoreCase);
+}

runtime/Sim.Runner/StudentCompiler.cs

@@ -57,7 +57,7 @@ internal static class StudentCompiler
         using var peStream = new MemoryStream();
         using var pdbStream = new MemoryStream();
         // 编译改写后的代码（旧版线程 API 换成平台实现，DateTime.Now 换成虚拟时钟），API 检查仍针对学生写的原始代码
-        var emit = ClockRewriter.Rewrite(LegacyThreadRewriter.Rewrite(compilation)).Emit(peStream, pdbStream,
+        var emit = PathRewriter.Rewrite(ClockRewriter.Rewrite(LegacyThreadRewriter.Rewrite(compilation))).Emit(peStream, pdbStream,
             options: new EmitOptions(debugInformationFormat: DebugInformationFormat.PortablePdb),
             manifestResources: EmptyControlResources(compilation));
         var denied = ApiPolicy.Check(compilation).ToList();