Decompiling foreach over an inline array emits invalid '<PrivateImplementationDetails>.InlineArrayElementRef'

[siegfriedpammer]

Summary

Decompiling a foreach over an inline array value produces code that does not compile: it references the compiler-internal <PrivateImplementationDetails>.InlineArrayElementRef helper, whose type name contains angle brackets and cannot be written in C#.

Steps to reproduce

Compile this with an optimizing compiler:

using System.Runtime.CompilerServices;

[InlineArray(4)]
public struct Buf4 { private int _element0; }

public static class C
{
    public static int Sum(Buf4 b)
    {
        int s = 0;
        foreach (int x in b) s += x;
        return s;
    }
}

Decompile type C.

Actual output

public static int Sum(Buf4 b)
{
    int num = 0;
    for (int i = 0; i < 4; i++)
    {
        int num2 = global::<PrivateImplementationDetails>.InlineArrayElementRef<Buf4, int>(ref b, i);
        num += num2;
    }
    return num;
}

This does not compile (error CS1001: Identifier expected at global::<PrivateImplementationDetails>). <PrivateImplementationDetails> is a compiler-generated type and InlineArrayElementRef<TBuffer, TElement> is a helper the compiler emits there to lower foreach over an inline-array value; the decompiler does not recognize the pattern and emits the raw call.

Expected output

Valid C# equivalent to the source, e.g. reconstructing the loop via the inline-array indexer:

public static int Sum(Buf4 b)
{
    int num = 0;
    for (int i = 0; i < 4; i++)
    {
        num += b[i];
    }
    return num;
}

(or the original foreach).

Scope

• Specific to foreach over an inline array. Other inline-array patterns decompile correctly: direct indexing (b[0]), for with the indexer, index-from-end (b[^1]), range/slice (b[1..4]), implicit Span<T> conversion, ref-to-element, passing as a span, and inline-array fields.
• Not currently covered by InlineArrayTests.

Version

ICSharpCode.Decompiler: 11.0.0 (current master).

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This issue was filed by an AI agent (Claude, claude-opus-4-8, via Claude Code) on behalf of the repo owner.