Compiler crash

[igor-muratov]

Any version below apr 17:

using System;

namespace ConsoleApp3
{
    class BC { }
    class DC1 : BC { }
    class DC2 : BC { }
    class Program
    {
        static void Main(string[] args)
        {
        }

        private string Q(BC bclass, int n = 0)
        {
            switch (bclass)
            {
                case DC1 mc:

                    string A(BC map)
                    {
                        return "";
                    }

                    string B(BC map) 
                    {
                        switch (map)
                        {
                            case DC1 ne:
                                Action<int> a = _ => B(new DC2());
                                return "";
                            case DC2 b: 
                                return C(b);
                            default:
                                return A(map);
                        }
                    }

                    string C(BC map)
                    {
                        switch (map)
                        {
                            case DC1 me:
                                return n.ToString();
                            default:
                                return "";
                        }
                    }
                    break;

                default:
                    break;
            }

            return "";
        }
    }
}

"csc.exe" exited with code -2146232797

[binki]

The repro can be made more minimal:

using System;

class Program
{
    void Q(int n = 0)
    {
        {
            object mc;

            string B(object map)
            {
                Action<int> a = _ => B(new object());
                return n.ToString();
            }
        }
    }
}

I think this is the same as #19182 as the pared down repro exhibits the same features: lambda accessing inner scope of a block (B is in inner scope of the {}), local method referencing variables outside of the enclosing block (n) and variables inside the block (B via lambda?).

[jcouv]

This seems the same stacktrace as #15322
Ping @agocke to confirm and verify.

System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at Microsoft.CodeAnalysis.CodeGen.LocalSlotManager.GetLocal(ILocalSymbol symbol) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\Core\Portable\CodeGen\LocalSlotManager.cs:line 148
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.GetLocal(LocalSymbol symbol) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 1422
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.GetLocal(BoundLocal localExpression) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitStatement.cs:line 1417
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitLocalLoad(BoundLocal local, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 1129
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCore(BoundExpression expression, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 116
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpression(BoundExpression expression, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 56
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitDelegateCreation(BoundExpression node, BoundExpression receiver, Boolean isExtensionMethod, MethodSymbol method, TypeSymbol delegateType, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitConversion.cs:line 263
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitDelegateCreationExpression(BoundDelegateCreationExpression expression, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 640
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCore(BoundExpression expression, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 100
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpression(BoundExpression expression, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 56
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitAssignmentValue(BoundAssignmentOperator assignmentOperator) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 2227
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitAssignmentExpression(BoundAssignmentOperator assignmentOperator, UseKind useKind) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 1871
   at Microsoft.CodeAnalysis.CSharp.CodeGen.CodeGenerator.EmitExpressionCore(BoundExpression expression, Boolean used) in D:\#TeamCity\buildAgent\work\596e688e8f7f38c8\!roslyn\sources\dotnet\src\Compilers\CSharp\Portable\CodeGen\EmitExpression.cs:line 88

[agocke]

This looks very similar, but I think it's a different bug. When I looked into it, the problem was that here we were erasing the fact that the lambda captured B and incorrectly placed the frame higher up in the method. This causes us to have a missing frame pointer, but because our proxies system doesn't know what scope the proxies are actually valid in we don't notice until CodeGen, where we ask for a local that doesn't exist.

The reason we were erasing B in analysis is due to an overaggressive optimization for closures calling local functions assuming we don't need an explicit frame pointer, we only need this (which is technically a frame pointer, but is usually ambient).

[agocke]

I think https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=403646 contains another repro of this bug:

using System;
class C
{
    static void F(Action a)
    {
        object x = null;
        {
            object y = null;
            void G(object z)
            {
                F(() => G(x));
            }
        }
    }
}