Why does this code crash Visual Studio 2015?

Question

For some reason, even so much as typing this into a C# file in Visual Studio is enough to cause it to instantly crash. Why?

unsafe struct node {
    node*[] child;
}

It seems to occur when the IDE would start coloring keywords and the like.

Trying it in TIO spits out csc.exe exited with code 1 which isn't very helpful.

While array declarations in C# are different than in C/C++, the above seems like it should be perfectly valid. Why isn't it, and why does it crash Visual Studio?

My Visual Studio version is 14.0.23107.

VS 2012 produces a compile error: Cannot take the address of, get the size of, or declare a pointer to a managed type — LarsTech
– LarsTech, Commented Aug 7, 2018 at 17:54
I found an existing bug: github.com/dotnet/roslyn/issues/24978 — user47589
– user47589, Commented Aug 7, 2018 at 18:22
FWIW your code is not valid, as you can't take a pointer to a struct that contains a managed object in C#. And an array is a managed object. So even if VS didn't crash, that code wouldn't compile. — Lucas Trzesniewski
– Lucas Trzesniewski, Commented Aug 8, 2018 at 10:20

score 50 · Accepted Answer · 2018-08-07 20:08:44Z

50

This is a known bug in Roslyn. This bug will affect any version of Visual Studio that uses Roslyn.

If I am interpreting VersionOf.net correctly, the first version of Visual Studio with Roslyn built-in is 2015. Before then, I think it was available only as an extension. So, Visual Studio 2013 and prior should be unaffected.

It's due to be fixed in the milestone 16 release. At this time, that release is not scheduled.

Because this is a bug in Roslyn, you can "get around" it by editing and compiling the code containing the unsafe struct in an older version of Visual Studio, one that predates Roslyn. Visual Studio 2012 should work. You can then use the resultant .DLL in your current software.

An unverified fix is available if you build Roslyn yourself from this branch. The fix was made in this commit.

edited Aug 7, 2018 at 20:08

answered Aug 7, 2018 at 19:48

user47589

Sign up to request clarification or add additional context in comments.

5 Comments

Jean-François Fabre Over a year ago

according to this, you're qualifying for step number 3 or 4: meta.stackexchange.com/a/132704/382678 between awesome and legendary.

Jean-François Fabre Over a year ago

nice move answering this properly: the question is probably in the 10k tools best questions of today. So here comes the 20k ;)

user47589 Over a year ago

@Jean-FrançoisFabre What is "10k tools best questions of today"?

Jean-François Fabre Over a year ago

stackoverflow.com/tools. This question is indeed #1. seems that I was right :)

Jeppe Stig Nielsen Over a year ago

As is evident from comments (to the question, not here) by LarsTech and Lucas Trzesniewski, the code as it stands is not valid, because if the struct contains a reference type you cannot take a pointer to that struct, and an array is a reference type. So the part of the answer about compiling with an older compiler and porting the DLL may be irrelevant. Unless somebody knows of a case that is affected by this bug but will actually compile with Visual Studio 2012 (or another non-Roslyn compiler)? By the way, I think the Mono compiler has other issues (allows too much with pointers).

Collectives™ on Stack Overflow

Why does this code crash Visual Studio 2015?

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related