fs: symLink invalid relative symbolic links created on Windows

[andrewrk]

Zig Version

0.12.0-dev.987+ba656e5c9f

Steps to Reproduce and Observed Behavior

const std = @import("std");

pub fn main() !void {
 var dir = try std.fs.cwd().openDir("tmp", .{});
 defer dir.close();

 try dir.symLink("..\\b.txt", "a.txt", .{});

 var buf: [1000]u8 = undefined;
 const link_name = try dir.readLink("a.txt", &buf);

 std.debug.print("link_name: '{s}'\n", .{link_name});
}

Create the tmp directory in the current working directory and ensure it is empty.

PS C:\Users\andy\dev\zig> .\zig-out\bin\zig.exe run build-release/test.zig
link_name: 'C:\Users\andy\dev\zig\b.txt'

Expected Behavior

PS C:\Users\andy\dev\zig> .\zig-out\bin\zig.exe run build-release/test.zig
link_name: '..\b.txt'

[squeek502]

Strange, I thought I fixed this in #16847

Will take a look when I get a chance. It might be writing the symlink correctly (as relative), but converting to absolute before returning when reading it back.

EDIT: Figured it out in Discord, something like this is the fix:

Replacing

zig/lib/std/os/windows.zig

Line 773 in e44152e

else => {},

with

 // Keep relative paths relative, but anything else needs to get NT-prefixed
 else => if (!std.fs.path.isAbsoluteWindowsWTF16(target_path)) break :target_path target_path,