[Issue 19763] New: Cannot construct immutable struct from pure mutable struct

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=19763

          Issue ID: 19763
           Summary: Cannot construct immutable struct from pure mutable
                    struct
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: doob at me.com

The following example fails to compile:

struct Foo
{
    const(char)* filename;
    this(const(char)*) pure { }
}

void main()
{
    immutable a = Foo(null);
}

Error:

cannot implicitly convert expression `Foo(null).this(null)` of type `Foo` to
`immutable(Foo)`

But this code compiles:

struct Foo
{
    const(char)* filename;
    this(const(char)*) pure { }
}

Foo newFoo() pure
{
    return Foo(null);
}

void main()
{
    immutable a = newFoo();
}

Also if "const(char)* filename" is changed to "char* filename" the first
example compiles.

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