[stackalloc-init] Improve error tolerance when parsing invalid implicit stackalloc arrays

[alrz]

No description provided.

[alrz]

The error message should probably be changed. I'll wait for review feedback before changing it.

[CyrusNajmabadi]

The error message should probably be changed. I'll wait for review feedback before changing it.

Agreed.

[sharwell]

@jinujoseph Shouldn't this be assigned to the compiler team instead of me?

[jcouv]

LGTM Thanks

[jcouv]

Tagging @VSadov @gafter for review. Thanks

[VSadov]

LGTM, but we need a better error. Any good ideas?

Example of where the current error might sound strange:
(there is no type here)

                // (4,28): error CS1575: A stackalloc expression requires [] after type
                //         var x = stackalloc[3,] { 1, 2, 3 };

[jcouv]

I think the error message we use elsewhere is something like "expected ]". Maybe that's better?

[VSadov]

@jcouv - just to clarify, are you suggesting simply putting an error on the first unexpected token and produce some standard " expected ']' " ?

Considering that the stackalloc is a fairly advanced feature, this would seem sufficient.

[jcouv]

Yes, that's what I was suggesting.

For context, here's the error we just added for implicit array creation (https://github.com/dotnet/roslyn/pull/24706/files#diff-0d8acdaeed6fd4e02198f6e3745d6d2dR286): "Invalid rank specifier: expected ',' or ']'".

For stackalloc (var x = stackalloc[3,] { 1, 2, 3 };), we could use "Invalid rank specificier: expected ']'".

[alrz]

Invalid rank specificier: expected ']'".

to be clear, should this be a new error or we should update the existing one?

[jcouv]

@alrz It seems that error CS1575: A stackalloc expression requires [] after type is still useful.
Also, we can't use error CS0178: Invalid rank specifier: expected ',' or ']' since comma doesn't make sense in the context of stackalloc.
So this would be a new error code and message.

[gafter]

[gafter]

@VSadov There are two reviews of this PR now.

[alrz]

I should add the new error. will push it asap.

[gafter]

specificier [](start = 25, length = 11)

"specificier"??? I think this is a typo.

[alrz]

oops.

[jcouv]

Still LGTM
Thanks!