Compiler crashes when emitting EnC delta for assembly with synthesized inline array types

[tmat]

Repro:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;

[CollectionBuilder(typeof(MyCollectionBuilder), nameof(MyCollectionBuilder.Create))]
public struct MyCollection<T> : IEnumerable<T>
{
    private readonly List<T> _list;
    public MyCollection(List<T> list) { _list = list; }
    public IEnumerator<T> GetEnumerator() => _list.GetEnumerator();
    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}
public class MyCollectionBuilder
{
    public static MyCollection<T> Create<T>(ReadOnlySpan<T> items)
    {
        return new MyCollection<T>(new List<T>(items.ToArray()));
    }
}

class Program
{
    static void Main()
    {
        MyCollection<int> y = F1();
    }

    static MyCollection<int> F1()
    {
        MyCollection<int> x = [0, 1, 2];
        Console.WriteLine(1);
        return x;
    }
}

Breakpoint to F1, F5, change Console.WriteLine(1); and step.

System.NullReferenceException: 'Object reference not set to an instance of an object.'

>	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.Emit.PEModuleBuilder.EnsureInlineArrayTypeExists(Microsoft.CodeAnalysis.SyntaxNode syntaxNode, Microsoft.CodeAnalysis.CSharp.SyntheticBoundNodeFactory factory, int arrayLength, Microsoft.CodeAnalysis.DiagnosticBag diagnostics) Line 1980	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.CreateAndPopulateInlineArray(Microsoft.CodeAnalysis.SyntaxNode syntax, Microsoft.CodeAnalysis.CSharp.Symbols.TypeWithAnnotations elementType, System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.CSharp.BoundExpression> elements, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CSharp.Symbols.LocalSymbol> locals, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CSharp.BoundExpression> sideEffects) Line 234	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitCollectionBuilderCollectionExpression(Microsoft.CodeAnalysis.CSharp.BoundCollectionExpression node) Line 191	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitCollectionExpression(Microsoft.CodeAnalysis.CSharp.BoundCollectionExpression node) Line 36	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundCollectionExpression.Accept(Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor visitor) Line 6336	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeRewriterWithStackGuard.VisitExpressionWithoutStackGuard(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 97	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor.VisitExpressionWithStackGuard(ref int recursionDepth, Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 212	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeRewriterWithStackGuard.VisitExpressionWithStackGuard(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 92	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitExpressionImpl(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 245	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitExpression(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 209	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitConversion(Microsoft.CodeAnalysis.CSharp.BoundConversion node) Line 64	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundConversion.Accept(Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor visitor) Line 2874	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeRewriterWithStackGuard.VisitExpressionWithoutStackGuard(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 97	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor.VisitExpressionWithStackGuard(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 242	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor.VisitExpressionWithStackGuard(ref int recursionDepth, Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 216	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundTreeRewriterWithStackGuard.VisitExpressionWithStackGuard(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 92	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitExpressionImpl(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 245	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitExpression(Microsoft.CodeAnalysis.CSharp.BoundExpression node) Line 209	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitLocalDeclaration(Microsoft.CodeAnalysis.CSharp.BoundLocalDeclaration node) Line 16	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundLocalDeclaration.Accept(Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor visitor) Line 3315	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitStatement(Microsoft.CodeAnalysis.CSharp.BoundStatement node) Line 220	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitPossibleUsingDeclaration(Microsoft.CodeAnalysis.CSharp.BoundStatement node, System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.CSharp.BoundStatement> statements, int statementIndex, out bool replacedLocalDeclarations) Line 98	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitStatementSubList(Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CSharp.BoundStatement> builder, System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.CSharp.BoundStatement> statements, int startIndex) Line 56	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitBlock(Microsoft.CodeAnalysis.CSharp.BoundBlock node) Line 23	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.BoundBlock.Accept(Microsoft.CodeAnalysis.CSharp.BoundTreeVisitor visitor) Line 3219	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.VisitStatement(Microsoft.CodeAnalysis.CSharp.BoundStatement node) Line 220	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.LocalRewriter.Rewrite(Microsoft.CodeAnalysis.CSharp.CSharpCompilation compilation, Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol method, int methodOrdinal, Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol containingType, Microsoft.CodeAnalysis.CSharp.BoundStatement statement, Microsoft.CodeAnalysis.CSharp.TypeCompilationState compilationState, Microsoft.CodeAnalysis.CSharp.SynthesizedSubmissionFields previousSubmissionFields, bool allowOmissionOfConditionalCalls, Microsoft.CodeAnalysis.Emit.MethodInstrumentation instrumentation, Microsoft.CodeAnalysis.CodeGen.DebugDocumentProvider debugDocumentProvider, Microsoft.CodeAnalysis.CSharp.BindingDiagnosticBag diagnostics, out System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.CodeGen.SourceSpan> codeCoverageSpans, out bool sawLambdas, out bool sawLocalFunctions, out bool sawAwaitInExceptionHandler) Line 125	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.LowerBodyOrInitializer(Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol method, int methodOrdinal, Microsoft.CodeAnalysis.CSharp.BoundStatement body, Microsoft.CodeAnalysis.CSharp.SynthesizedSubmissionFields previousSubmissionFields, Microsoft.CodeAnalysis.CSharp.TypeCompilationState compilationState, Microsoft.CodeAnalysis.Emit.MethodInstrumentation instrumentation, Microsoft.CodeAnalysis.CodeGen.DebugDocumentProvider debugDocumentProvider, out System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.CodeGen.SourceSpan> codeCoverageSpans, Microsoft.CodeAnalysis.CSharp.BindingDiagnosticBag diagnostics, ref Microsoft.CodeAnalysis.CodeGen.VariableSlotAllocator lazyVariableSlotAllocator, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CodeGen.LambdaDebugInfo> lambdaDebugInfoBuilder, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CodeGen.ClosureDebugInfo> closureDebugInfoBuilder, Microsoft.CodeAnalysis.PooledObjects.ArrayBuilder<Microsoft.CodeAnalysis.CodeGen.StateMachineStateDebugInfo> stateMachineStateDebugInfoBuilder, out Microsoft.CodeAnalysis.CSharp.StateMachineTypeSymbol stateMachineTypeOpt) Line 1433	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethod(Microsoft.CodeAnalysis.CSharp.Symbols.MethodSymbol methodSymbol, int methodOrdinal, ref Microsoft.CodeAnalysis.CSharp.Binder.ProcessedFieldInitializers processedInitializers, Microsoft.CodeAnalysis.CSharp.SynthesizedSubmissionFields previousSubmissionFields, Microsoft.CodeAnalysis.CSharp.TypeCompilationState compilationState) Line 1226	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileNamedType(Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol containingType) Line 527	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.VisitNamedType(Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol symbol, Microsoft.CodeAnalysis.CSharp.TypeCompilationState arg) Line 417	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.Symbols.NamedTypeSymbol.Accept<Microsoft.CodeAnalysis.CSharp.TypeCompilationState, object>(Microsoft.CodeAnalysis.CSharp.CSharpSymbolVisitor<Microsoft.CodeAnalysis.CSharp.TypeCompilationState, object> visitor, Microsoft.CodeAnalysis.CSharp.TypeCompilationState argument) Line 727	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileNamespace(Microsoft.CodeAnalysis.CSharp.Symbols.NamespaceSymbol symbol) Line 396	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.MethodCompiler.CompileMethodBodies(Microsoft.CodeAnalysis.CSharp.CSharpCompilation compilation, Microsoft.CodeAnalysis.CSharp.Emit.PEModuleBuilder moduleBeingBuiltOpt, bool emittingPdb, bool hasDeclarationErrors, bool emitMethodBodies, Microsoft.CodeAnalysis.CSharp.BindingDiagnosticBag diagnostics, System.Predicate<Microsoft.CodeAnalysis.CSharp.Symbol> filterOpt, System.Threading.CancellationToken cancellationToken) Line 159	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.CSharpCompilation.CompileMethods(Microsoft.CodeAnalysis.Emit.CommonPEModuleBuilder moduleBuilder, bool emittingPdb, Microsoft.CodeAnalysis.DiagnosticBag diagnostics, System.Predicate<Microsoft.CodeAnalysis.Symbols.ISymbolInternal> filterOpt, System.Threading.CancellationToken cancellationToken) Line 3402	C#
 	Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.Compilation.Compile(Microsoft.CodeAnalysis.Emit.CommonPEModuleBuilder moduleBuilder, bool emittingPdb, Microsoft.CodeAnalysis.DiagnosticBag diagnostics, System.Predicate<Microsoft.CodeAnalysis.Symbols.ISymbolInternal> filterOpt, System.Threading.CancellationToken cancellationToken) Line 2590	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.Emit.EmitHelpers.EmitDifference(Microsoft.CodeAnalysis.CSharp.CSharpCompilation compilation, Microsoft.CodeAnalysis.Emit.EmitBaseline baseline, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.Emit.SemanticEdit> edits, System.Func<Microsoft.CodeAnalysis.ISymbol, bool> isAddedSymbol, System.IO.Stream metadataStream, System.IO.Stream ilStream, System.IO.Stream pdbStream, Microsoft.CodeAnalysis.CodeGen.CompilationTestData testData, System.Threading.CancellationToken cancellationToken) Line 78	C#
 	Microsoft.CodeAnalysis.CSharp.dll!Microsoft.CodeAnalysis.CSharp.CSharpCompilation.EmitDifference(Microsoft.CodeAnalysis.Emit.EmitBaseline baseline, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.Emit.SemanticEdit> edits, System.Func<Microsoft.CodeAnalysis.ISymbol, bool> isAddedSymbol, System.IO.Stream metadataStream, System.IO.Stream ilStream, System.IO.Stream pdbStream, Microsoft.CodeAnalysis.CodeGen.CompilationTestData testData, System.Threading.CancellationToken cancellationToken) Line 3635	C#
 	Microsoft.CodeAnalysis.dll!Microsoft.CodeAnalysis.Compilation.EmitDifference(Microsoft.CodeAnalysis.Emit.EmitBaseline baseline, System.Collections.Generic.IEnumerable<Microsoft.CodeAnalysis.Emit.SemanticEdit> edits, System.Func<Microsoft.CodeAnalysis.ISymbol, bool> isAddedSymbol, System.IO.Stream metadataStream, System.IO.Stream ilStream, System.IO.Stream pdbStream, System.Threading.CancellationToken cancellationToken) Line 3101	C#
 	Microsoft.CodeAnalysis.Features.dll!Microsoft.CodeAnalysis.EditAndContinue.EditSession.EmitSolutionUpdateAsync(Microsoft.CodeAnalysis.Solution solution, Microsoft.CodeAnalysis.EditAndContinue.ActiveStatementSpanProvider solutionActiveStatementSpanProvider, Microsoft.CodeAnalysis.EditAndContinue.UpdateId updateId, System.Threading.CancellationToken cancellationToken) Line 1013	C#

Relates to test plan #67826

[tmat]

@cston

[tmat]

Simpler repro:

Just accessing inline array elements causes the same crash:

using System.Collections.Generic;
using System.Runtime.CompilerServices;

[InlineArray(2)]
public struct Buffer
{
    private int _element0;
}

class Program
{
    static void Main()
    {
        var b1 = new Buffer();

        b1[0] = 1;
        b1[1] = 2;

        Console.WriteLine(1);
    }
}

[jcouv]

@tmat If you had bandwidth to help on that one, that'd be great. Otherwise, it will likely have to wait until Aleksey is back and 17.9.

[AlekseyTs]

@jcouv, @cston Judging by the call stack, it looks like the crash is primarily related to Collection Expressions (VisitCollectionBuilderCollectionExpression, EnsureInlineArrayTypeExists). Even if there is an issue with a simpler scenario mentioned at #69398 (comment), I doubt the call stack is the same. If the call stack, however, mentions the same methods, it is also related to changes made for Collection Expressions. Bottom line, I think the issue is either specific to Collection Expressions, or we have two separate and unrelated issues, which should be tracked and triaged separately.

[tmat]

I'm working on a fix.