erroneous dependency loop with root import

[marler8997]

Reproduce the issue with these 2 files:

main.zig:

pub const foo = true;

usingnamespace if (@import("lib.zig").root_foo) struct {} else struct {};
usingnamespace if (@import("lib.zig").root_foo) struct {} else struct {};

pub fn main() void { }

lib.zig:

pub const root_foo = @import("root").foo;

./main.zig:4:38: error: dependency loop detected
usingnamespace if (@import("lib.zig").root_foo) struct {} else struct {};
                                     ^
./lib.zig:1:37: note: referenced here
pub const root_foo = @import("root").foo;
                                    ^
./main.zig:3:38: note: referenced here
usingnamespace if (@import("lib.zig").root_foo) struct {} else struct {};
                                     ^
/home/marler8997/zig/0.8.0-dev.1120+300ebbd56/files/lib/std/builtin.zig:669:73: note: referenced here
pub const panic: PanicFn = if (@hasDecl(root, "panic")) root.panic else default_panic;

What makes the dependency loop go away?

1. the error goes away if you comment out one of the usingnamespace lines in main.zig

usingnamespace if (@import("lib.zig").root_foo) struct {} else struct {};
//usingnamespace if (@import("lib.zig").root_foo) struct {} else struct {};

2. the error goes away if @import("lib.zig") is aliased and reused:

const lib = @import("lib.zig");
usingnamespace if (lib.root_foo) struct {} else struct {};
usingnamespace if (lib.root_foo) struct {} else struct {};

3. the error goes away if lib.zig is removed and replaced with a struct:

const lib = struct { pub const root_foo = @import("root").foo; };
usingnamespace if (lib.root_foo) struct {} else struct {};
usingnamespace if (lib.root_foo) struct {} else struct {};

Use Case

This error was found when trying to use a root variable UNICODE to select different win32 symbol aliases, like CreateFile is set to CreateFileA or CreateFileW based on @import("root").UNICODE. The affected project is https://github.com/marlersoft/zigwin32

[mikdusan]

no more compiler errors

$ zig version
0.11.0-dev.1095+8bd734d60

$ zig build-obj main.zig
# no stdout/stderr (good)