Compiler: thinks a local's type is that of another local

[KirillOsenkov]

I'm seeing a recent regression in Csc, it wasn't there in 4.12.0-3.24463.9 but it is present in 4.12.0-3.24510.2 (Preview 5)

The symptoms are:

MetadataType.cs(411,36): error CS1061: 'IList<KeyValuePair<string, ulong>>' does not contain a definition for 'Attributes' and no accessible extension method 'Attributes' accepting a first argument of type 'IList<KeyValuePair<string, ulong>>' could be found (are you missing a using directive or an assembly reference?)

I can't find a standalone repro, but it looks like it thinks that a local's type is that of another local.

I can't share the repro publicly but ping me in private.

I think this is pretty bad.

[KirillOsenkov]

Oops, I missed that there was a warning:

warning CS9258: In language version preview, the 'field' keyword binds to a synthesized backing field for the property. To avoid generating a synthesized backing field, and to refer to the existing member, use 'this.field' or '@field' instead.

In the code snippet, there was a local named field.

My apologies, this is by design.

Thanks @cston for investigating.

[KirillOsenkov]

Oh, and that explains why I couldn't find a simple repro: in the simple project I didn't set the LangVersion preview.

[miloush]

ref: dotnet/csharplang#140 #74937
https://github.com/dotnet/csharplang/blob/main/proposals/field-keyword.md

especially for breaking changes dotnet/csharplang#7964

Why do we continue to allow var field = x; syntactically?

[CyrusNajmabadi]

@miloush for language questions, please submit them at csharplang. Thanks