Version Used:

Microsoft Visual Studio Community 2019 Preview
Version 16.8.0 Preview 3.1

C# Tools 3.8.0-3.20458.6+b446afd34759150c2ea3b86ab794104e12e64db1

Steps to Reproduce:

1. Write code:

class X
{
    partial public string Foo();
}

2. Observe CS0267 on partial modifier.
3. Be confused by error message.

Expected Behavior:

Error message communicating invalid partial placement taking new partial methods (non-void) into account. I don't have a good proposal, but maybe addition of 'or method return type' would be enough.

Actual Behavior:

CS0267 says

The partial modifier can only appear immediately before 'class', 'record', 'struct', 'interface' or 'void'

It misses the non-void return type allowed on C#9 partial methods.