Unreachable code reached when using UNC paths on Windows

[JerwuQu]

Using absolute paths related to network shares (starting with \\...) will result in stdlib reaching unreachable, meaning it's impossible to recover from. Preferred would be if it spat an error such as error.UnsupportedDrive so it can be handled gracefully, or if support for them was added.

Note that getting the working dir handle from std.fs.cwd() whilst on a network share works, and you can use openDir, openFile, and all other relative methods from there. Meaning if you've somehow gotten a handle, you can access and read/write files. Afaik it only breaks when you try to use absolute paths.

Getting working dir from std.fs.cwd() whilst on a network share and then running realpath on the handle also breaks with unreachable.

I've only experienced this because I've done development in WSL2, which Windows has mounted as a network share.

Example:

const std = @import("std");

pub fn main() !void {
    const path = "\\\\wsl$\\Arch\\home\\jerwuqu";
    std.debug.print("Is absolute: {}\n", .{std.fs.path.isAbsolute(path)});

    _ = try std.fs.openDirAbsolute(path, .{});
    std.debug.print("OK!\n", .{});
}

Output:

Is absolute: true
thread 19092 panic: reached unreachable code
Panicked during a panic. Aborting.

[star-tek-mb]

std.c.fopen can open files on WSL, but std.fs.openFileAbsolute can't with \\wsl.localhost\Debian like path

[star-tek-mb]

For files on network share we must use UNC:

var content = try std.fs.cwd().readFileAlloc(allocator, "\\??\\UNC\\wsl.localhost\\Debian\\home\\noobtek\\main.c", std.math.maxInt(usize));

For local files UNC also can be used:

var content = try std.fs.cwd().readFileAlloc(allocator, "\\??\\UNC\\localhost\\D$\\main.c", std.math.maxInt(usize));

\\??\\UNC\\localhost\\D:\\main.c - doesn't work.

So, I think we need to handle these edge cases, at least on std.debug on stack traces.

[andrewrk]

Fix reverted in b5fad3a due to master branch CI failures

[squeek502]

This can be re-closed since the fix was reinstated in #15905