Error in `ImmutableArray` initialization using C#12 collection literals

[eduherminio]

Description

ImmutableArrays are throwing an exception when being initialized at runtime in some circumstances:

• When debugging the project from Visual Studio
• When publishing the project (self-contained, trimmed, single-file in my case).

However, they work from CLI

This can be especially painful because tests pass CI but then everything collapses at runtime initialization. Real life CI example:

• This CI passes: https://github.com/lynx-chess/Lynx/actions/runs/6165990734
• The windows executable can be downloaded from there fails.
• Checking out the branch (immutable-arrays-cleaned) and running it locally has the same behavior: works OK from command line, fails from VS

Simplified example below:

Reproduction Steps

dotnet new console -n immutable

Program.cs

using System.Collections.Immutable;

Console.WriteLine($"Hello, World from {Constants.Coordinates[0]}");


public static class Constants
{
    public static readonly ImmutableArray<string> Coordinates =
    [
        "a8", "b8", "c8", "d8", "e8", "f8", "g8", "h8",
        "a7", "b7", "c7", "d7", "e7", "f7", "g7", "h7",
        "a6", "b6", "c6", "d6", "e6", "f6", "g6", "h6",
        "a5", "b5", "c5", "d5", "e5", "f5", "g5", "h5",
        "a4", "b4", "c4", "d4", "e4", "f4", "g4", "h4",
        "a3", "b3", "c3", "d3", "e3", "f3", "g3", "h3",
        "a2", "b2", "c2", "d2", "e2", "f2", "g2", "h2",
        "a1", "b1", "c1", "d1", "e1", "f1", "g1", "h1"
    ];
}

immutable.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <LangVersion>preview</LangVersion>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

Expected behavior

Runs normally, prints this in all the cases

Hello, World from a8

Actual behavior

Failes from Visual Studio or when the project is published:

$> dotnet run -c Release
Hello, World from a8
$> dotnet run -c Debug
Hello, World from a8
$> dotnet publish -c Release --self-contained /p:PublishSingleFile=true /p:PublishTrimmed=true --runtime win-x64 -o ./output && output/immutable.exe
Unhandled exception. System.TypeInitializationException: The type initializer for 'Constants' threw an exception.
 ---> System.TypeLoadException
   at Constants..cctor()
   --- End of inner exception stack trace ---
   at Program.<Main>$(String[]) in C:\dev\tmp\immutable\Program.cs:line 3
C:\dev\tmp\immutable>

From Visual Studio, while debugging:

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=System.Collections.Immutable
  StackTrace:
   at System.Collections.Immutable.ImmutableArray`1.Add(T item)
   at Constants..cctor() in C:\dev\tmp\immutable\Program.cs:line 8

Regression?

No response

Known Workarounds

No response

Configuration

.NET SDK:
 Version:   8.0.100-rc.1.23455.8
 Commit:    e14caf947f

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19045
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.100-rc.1.23455.8\

.NET workloads installed:
There are no installed workloads to display.

Host:
  Version:      8.0.0-rc.1.23419.4
  Architecture: x64
  Commit:       92959931a3
  RID:          win-x64

Microsoft Visual Studio Enterprise 2022 (64-bit) - Version 17.7.0

Other information

No response

[agocke]

Looks like a bug in the linker.

The compiler-synthesized InlineArray type has the following IL in the untrimmed code:

.class private auto ansi sealed beforefieldinit '<>y__InlineArray64'<T>
	extends [System.Runtime]System.ValueType
{
	.custom instance void [System.Runtime]System.Runtime.CompilerServices.InlineArrayAttribute::.ctor(int32) = (
		01 00 40 00 00 00 00 00
	)
	// Fields
	.field private !T _element0
	.custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor() = (
		01 00 00 00
	)

} // end of class <>y__InlineArray64

while it has this IL in the trimmed code:

.class private auto ansi sealed beforefieldinit '<>y__InlineArray64'<T>
	extends [System.Private.CoreLib]System.ValueType
{
	.custom instance void [System.Private.CoreLib]System.Runtime.CompilerServices.InlineArrayAttribute::.ctor(int32) = (
		01 00 40 00 00 00 00 00
	)
} // end of class <>y__InlineArray64

[agocke]

Note the following from the draft C# language spec, which presumably indicates a runtime requirement:

Since there is a guarantee that the first element in an inline array type is aligned at the beginning of the type (no gap), compiler will use the following code to get a Span value:

That implies that types with InlineArray need to have their fields preserved.

[agocke]

@sbomer @vitek-karas

Tagging subscribers to this area: @agocke, @sbomer, @vitek-karas
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

ImmutableArrays are throwing an exception when being initialized at runtime in some circumstances:

• When debugging the project from Visual Studio
• When publishing the project (self-contained, trimmed, single-file in my case).

However, they work from CLI

This can be especially painful because tests pass CI but then everything collapses at runtime initialization. Real life CI example:

• This CI passes: https://github.com/lynx-chess/Lynx/actions/runs/6165990734
• The windows executable can be downloaded from there fails.
• Checking out the branch (immutable-arrays-cleaned) and running it locally has the same behavior: works OK from command line, fails from VS

Simplified example below:

Reproduction Steps

dotnet new console -n immutable

Program.cs

using System.Collections.Immutable;

Console.WriteLine($"Hello, World from {Constants.Coordinates[0]}");


public static class Constants
{
    public static readonly ImmutableArray<string> Coordinates =
    [
        "a8", "b8", "c8", "d8", "e8", "f8", "g8", "h8",
        "a7", "b7", "c7", "d7", "e7", "f7", "g7", "h7",
        "a6", "b6", "c6", "d6", "e6", "f6", "g6", "h6",
        "a5", "b5", "c5", "d5", "e5", "f5", "g5", "h5",
        "a4", "b4", "c4", "d4", "e4", "f4", "g4", "h4",
        "a3", "b3", "c3", "d3", "e3", "f3", "g3", "h3",
        "a2", "b2", "c2", "d2", "e2", "f2", "g2", "h2",
        "a1", "b1", "c1", "d1", "e1", "f1", "g1", "h1"
    ];
}

immutable.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <LangVersion>preview</LangVersion>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

Expected behavior

Runs normally, prints this in all the cases

Hello, World from a8

Actual behavior

Failes from Visual Studio or when the project is published:

$> dotnet run -c Release
Hello, World from a8
$> dotnet run -c Debug
Hello, World from a8
$> dotnet publish -c Release --self-contained /p:PublishSingleFile=true /p:PublishTrimmed=true --runtime win-x64 -o ./output && output/immutable.exe
Unhandled exception. System.TypeInitializationException: The type initializer for 'Constants' threw an exception.
 ---> System.TypeLoadException
   at Constants..cctor()
   --- End of inner exception stack trace ---
   at Program.<Main>$(String[]) in C:\dev\tmp\immutable\Program.cs:line 3
C:\dev\tmp\immutable>

From Visual Studio, while debugging:

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=System.Collections.Immutable
  StackTrace:
   at System.Collections.Immutable.ImmutableArray`1.Add(T item)
   at Constants..cctor() in C:\dev\tmp\immutable\Program.cs:line 8

Regression?

No response

Known Workarounds

No response

Configuration

.NET SDK:
 Version:   8.0.100-rc.1.23455.8
 Commit:    e14caf947f

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19045
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.100-rc.1.23455.8\

.NET workloads installed:
There are no installed workloads to display.

Host:
  Version:      8.0.0-rc.1.23419.4
  Architecture: x64
  Commit:       92959931a3
  RID:          win-x64

Microsoft Visual Studio Enterprise 2022 (64-bit) - Version 17.7.0

Other information

No response

Author:	eduherminio
Assignees:	-
Labels:	area-Tools-ILLink, needs-area-label
Milestone:	8.0.0