Check file existence

In this example, access is utilized to verify file existence; however, for it to function correctly, one must specifically check for the FileNotFound error type.

//! Test file/directory existence

const std = @import("std");

pub fn main(init: std.process.Init) !void {
    const io = init.io;
    const filename = "build.zig";
    var found = true;
    std.Io.Dir.cwd().access(io, filename, .{}) catch |e| switch (e) {
        error.FileNotFound => found = false,
        else => return e,
    };

    std.debug.assert(found);
}

However, there is a gotcha described in its documentation:

Be careful of Time-Of-Check-Time-Of-Use race conditions when using this function. For example, instead of testing if a file exists and then opening it, just open it and handle the error for file not found.