[Issue 12821] Missed redundant storage class / protection errors.

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12821

--- Comment #2 from Kenji Hara <k.hara.pg at gmail.com> ---
(In reply to Iain Buclaw from comment #0)
> Penultimately, the following throw an error unless you specify void.  All of
> which seems redundant as there's no return type.
> 
> immutable foo() { }       // Without 'this' cannot be immutable
> immutable void foo() { }  // OK

'immutable' does not modify return type. But in module scope, 'this' qualifier
for non-member function is meaningless and "Without 'this' cannot be immutable"
error occurs in first case. But second case does not raise same error, and it's
inconsistent behavior.

> const foo() { }           // Without 'this' cannot be const
> const void foo() { }      // OK
> inout foo() { }           // Without 'this' cannot be inout
> inout void foo() { }      // OK
> shared foo() { }          // Without 'this' cannot be shared
> shared void foo() { }     // OK

As well, same "Without 'this' cannot be xxx" error should occur in all cases.

To improve compiler behavior, I opened issue 12967.

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