dotnet/roslyn

Conversion of a stackalloc expression

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#23,995 opened on Jan 2, 2018

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Area-CompilersBugConcept-Diagnostic ClarityFeature - Readonly Referenceshelp wanted

Description

Version Used: 2.6.0.62309 (d3f6b8e7)

Steps to Reproduce:

Compile following

using System;

unsafe class X
{
	public static void Main ()
	{
		int* stackSpan = (int*) stackalloc int[100];
	}
}

Expected Behavior:

C# 7.2 allows stackallow casts (don't really know why) but it now reports an odd error message when the casts are used with pre-7.2 only supported pointer types.

Actual Behavior:

error CS8346: Conversion of a stackalloc expression of type 'int' to type 'int*' is not possible

Contributor guide

Tech stack
csharp
Domain
backendtooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
basic C# knowledgeunderstanding of pointers
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the error message for stackalloc expression conversion in the Roslyn C# compiler. Look at the semantic analysis code that handles stackalloc, likely in BoundStackalloc or similar. The error CS8346 is generated; check how the type conversion is validated and why it returns 'int' instead of 'int*'. The fix might involve updating the error message or adjusting the conversion logic in the compiler's type checking phase. Refer to the issue comments for any previous attempts or discussions.
Conversion of a stackalloc expression · dotnet/roslyn#23995 | Good First Issue