'fopen64 cannot be interpreted at compile time' for __gshared File

[NotSpooky via Digitalmars-d-learn]

On Saturday, 25 March 2017 at 15:52:15 UTC, crimaniak wrote:
> Simple File test:
>
>     void main()
>     {
>         import std.stdio;
>
>         File f = File("test.txt", "w");
>
>         f.writeln("hello");
>     }
>
> All works as expected.
>
> Now let's add __gshared:
>
>     void main()
>     {
>         import std.stdio;
>
>         __gshared File f = File("test.txt", "w");
>
>         f.writeln("hello");
>     }
>
> Now we have:
>
> /usr/include/dmd/phobos/std/stdio.d(3797): Error: fopen64 
> cannot be interpreted at compile time, because it has no 
> available source code
> /usr/include/dmd/phobos/std/stdio.d(3804):        called from 
> here: fopenImpl(namez.ptr(), modez.ptr())
> /usr/include/dmd/phobos/std/stdio.d(404):        called from 
> here: fopen(name, stdioOpenmode)
> /usr/include/dmd/phobos/std/stdio.d(404):        called from 
> here: errnoEnforce(fopen(name, stdioOpenmode), delegate 
> string() => text("Cannot open file `", name, "' in mode `", 
> stdioOpenmode, "'"))
> /usr/include/dmd/phobos/std/stdio.d(404):        called from 
> here: this.this(errnoEnforce(fopen(name, stdioOpenmode), 
> delegate string() => text("Cannot open file `", name, "' in 
> mode `", stdioOpenmode, "'")), name, 1u, false)
> file.d(5):        called from here: ((File __slFile648 = 
> File(null, null);) , __slFile648).this("test.txt", "w")
>
> Oooops! Who can explain this error message to me?
>
> DMD64 D Compiler v2.073.0

__gshared implies static, that is, known at compile time (ct), 
that means the File constructor should be done at ct and thus 
open the file. Compile time function execution doesn't allow IO 
operations, however you can use 
https://dlang.org/spec/expression.html#ImportExpression if you 
want to read a file at compile time.