Compilation of raw backslash is failing in C# backend

[MikaelMayer]

Dafny version

Since 4.4.0 at least

Code to produce this issue

method Main() {
  print @"\";
}

Command to run and resulting output

dafny build -t:cs file.dfy

What happened?

We get this exception:

Unhandled exception: System.IndexOutOfRangeException: Index was outside the bounds of the array.
   at System.String.get_Chars(Int32 index)
   at Microsoft.Dafny.Util.TokensWithEscapes(String p, Boolean isVerbatimString)+MoveNext() in C:\Users
\mimayere\Documents\dafny\Source\DafnyCore\Generic\Util.cs:line 406
   at System.Linq.Enumerable.SelectEnumerableIterator`2.MoveNext()
   at System.String.Join(String separator, IEnumerable`1 values)
   at Microsoft.Dafny.Util.ReplaceTokensWithEscapes(String s, Regex pattern, MatchEvaluator evaluator)
in dafny\Source\DafnyCore\Generic\Util.cs:line 293
   at Microsoft.Dafny.Util.ExpandUnicodeEscapes(String s, Boolean lowerCaseU) in C:\Users\mimayere\Docu
ments\dafny\Source\DafnyCore\Generic\Util.cs:line 299
   at Microsoft.Dafny.Compilers.CsharpCodeGenerator.EmitStringLiteral(String str, Boolean isVerbatim, C
oncreteSyntaxTree wr) in dafny\Source\DafnyCore\Backends\CSharp\CsharpCodeG
enerator.cs:line 2300
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.TrStringLiteral(StringLiteralExpr str, Concrete
SyntaxTree wr) in dafny\Source\DafnyCore\Backends\SinglePassCodeGenerator\S
inglePassCodeGenerator.cs:line 5206
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.StringLiteral(StringLiteralExpr str) in C:\User
s\mimayere\Documents\dafny\Source\DafnyCore\Backends\SinglePassCodeGenerator\SinglePassCodeGenerator.cs
:line 5199
   at Microsoft.Dafny.Compilers.CsharpCodeGenerator.EmitLiteralExpr(ConcreteSyntaxTree wr, LiteralExpr
e) in dafny\Source\DafnyCore\Backends\CSharp\CsharpCodeGenerator.cs:line 22
52
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.EmitExpr(Expression expr, Boolean inLetExprBody
, ConcreteSyntaxTree wr, ConcreteSyntaxTree wStmts) in dafny\Source\DafnyCo
re\Backends\SinglePassCodeGenerator\SinglePassCodeGenerator.Expression.cs:line 31
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.Expr(Expression expr, Boolean inLetExprBody, Co
ncreteSyntaxTree wStmts) in dafny\Source\DafnyCore\Backends\SinglePassCodeG
enerator\SinglePassCodeGenerator.cs:line 4829
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.EmitBinaryExpr(Boolean inLetExprBody, ConcreteS
yntaxTree wr, ConcreteSyntaxTree wStmts, BinaryExpr binary) in dafny\Source
\DafnyCore\Backends\SinglePassCodeGenerator\SinglePassCodeGenerator.Expression.cs:line 646
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.EmitExpr(Expression expr, Boolean inLetExprBody
, ConcreteSyntaxTree wr, ConcreteSyntaxTree wStmts) in dafny\Source\DafnyCo
re\Backends\SinglePassCodeGenerator\SinglePassCodeGenerator.Expression.cs:line 317
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.TrExprOpt(Expression expr, Type resultType, Con
creteSyntaxTree wr, ConcreteSyntaxTree wStmts, Boolean inLetExprBody, IVariable accumulatorVar, Optimiz
edExpressionContinuation continuation) in dafny\Source\DafnyCore\Backends\S
inglePassCodeGenerator\SinglePassCodeGenerator.cs:line 3042
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.TrExprOpt(Expression expr, Type resultType, Con
creteSyntaxTree wr, ConcreteSyntaxTree wStmts, Boolean inLetExprBody, IVariable accumulatorVar, Optimiz
edExpressionContinuation continuation) in dafny\Source\DafnyCore\Backends\S
inglePassCodeGenerator\SinglePassCodeGenerator.cs:line 3050
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.TrExprOpt(Expression expr, Type resultType, Con
creteSyntaxTree wr, ConcreteSyntaxTree wStmts, Boolean inLetExprBody, IVariable accumulatorVar, Optimiz
edExpressionContinuation continuation) in dafny\Source\DafnyCore\Backends\S
inglePassCodeGenerator\SinglePassCodeGenerator.cs:line 3050
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.CompileReturnBody(Expression body, Type resultT
ype, ConcreteSyntaxTree wr, IVariable accumulatorVar) in dafny\Source\Dafny
Core\Backends\SinglePassCodeGenerator\SinglePassCodeGenerator.cs:line 3179
   at Microsoft.Dafny.Compilers.SinglePassCodeGenerator.CompileFunction(Function f, IClassWriter cw, Bo
olean lookasideBody) in dafny\Source\DafnyCore\Backends\SinglePassCodeGener
ator\SinglePassCodeGenerator.cs:line 2814

What type of operating system are you experiencing the problem on?

Windows