expose the root source file with @import("root")

[andrewrk]

We already rely on this behavior in bootstrap.zig but it is special magic:

zig/std/special/bootstrap.zig

Line 4 in 6cc2d39

const root = @import("@root");

This proposal would make it always available and so the above code would not be special magic anymore.

It's reasonable for userland libraries to have global configuration and use the root source file for that. For example this would be a necessary component of #1778.

This, along with #1439 would allow us to move some of the global panic function magic to userland, and potentially even the startup code. build-exe would unconditionally include the startup code, which would have a comptime block which examines the root source file for main, _start, etc, and determines what it should export.

[Rocknest]

Do i understand this correctly: a file that was specified when invoking the zig compiler is the root source file (for example zig build-exe main.zig -> main.zig)?

[emekoi]

that is correct.

[shawnl]

There is a problem. If you pub const foo = @import("root"); you end up with infinite recursion. These problems are difficult to solve, as anything from the root import would have to be resolved into a constant (including a constant function pointer) before it was imported. While I agree that there should only be one root source file, an @import("root") is much more complicated that it seems at first glance.

Anyways, this muddles with the very clean namespace semantics zig has.

[shawnl]

#1778 does not need this.

You just use a comptime global in a package's namespace (does that exist?), set from the root source file.

[emekoi]

@shawnl how would this introduce infinite recursion? due to zig's lazy nature that would be perfectly fine and is no different than:

pub const foo = @This();

for the root file. the following:

use @import("@root"); // or use @This();

would be an infinite loop but that is another issue (#2580) altogether.