funcs.zig

const mymain = @import("main.zig");
var A = mymain.dummy_allocator;

main.zig

const funcs = @import("funcs.zig");

pub var dummy_allocator: u8 = undefined;

fn buildFuncMap() void {
    const info = @typeInfo(funcs);
    const decls = info.Struct.decls;
    inline for (decls) |d| {}
}

pub fn main() !void {
    dummy_allocator = 1;
    buildFuncMap();
}

$ zig build-exe main.zig
./funcs.zig:2:15: error: cannot store runtime value in compile time variable
var A = mymain.dummy_allocator;
              ^
./funcs.zig:2:1: note: referenced here
var A = mymain.dummy_allocator;
^
./main.zig:8:12: note: referenced here
    inline for (decls) |d| {}

here's a stab at exporting a main config that can be used by another module:

funcs.zig

usingnamespace @import("root").config;

const std = @import("std");

pub fn doit() void {
    std.debug.warn("(from funcs) allocator: {*}\n", .{allocator});
}

main.zig

const funcs = @import("funcs.zig");
const std = @import("std");

fn buildFuncMap() void {
    const info = @typeInfo(funcs);
    const decls = info.Struct.decls;
    inline for (decls) |d| {}
}

pub fn main() !void {
    config.allocator = std.heap.c_allocator;
    std.debug.warn("(from main) config.allocator: {*}\n", .{config.allocator});

    buildFuncMap();
    funcs.doit();
}

pub const config = struct {
    pub var allocator: *std.mem.Allocator = undefined;
};