Contextual return types for expression-bodied members

[SLaks]

class C {
	partial A => new partial();
	async B => new async();
}

class partial {}
class async {}

The first line compiles; the second one does not.

Why not?
Why is async different from partial?

http://tryroslyn.azurewebsites.net/#b:master/f:>ilr/MYGwhgzhAEDC0G8BQBIADmATgFwJZhGgEFoBeAPmgDsBTAd2gx3xAAoBKAblUgE8rg0AEJlKtBnwEduAXyRJQkGEzwFEcxVGiTBCGUA=

[DavidArno]

async is in scope as a keyword in this example as it could be the start of an async B F( ... method declaration.

[alrz]

@DavidArno So is partial in partial methods. Note that it will compile in other cases,

async M() => new async();
async M { get => new async(); }

[DavidArno]

Oh, I forgot about partial methods. In that case it does indeed appear to be a parser inconsistency issue.

[gafter]

partial is a contextual keyword. The context is that the following token must be class, struct, or void.

async is a contextual keyword. It is treated as a keyword when it appears in a position that could be a member modifier.

They are different because they are specified to be different.

[gafter]

The spec does say, however

contextual keywords can conflict with declared names. In such cases, the declared name takes precedence over the use of the identifier as a contextual keyword.

[jcouv]

Fix is in for 15.7 preview 4.

[jcouv]

Thanks @alrz for the fix!