Step.Run does not account for child cwd and cache path being on different drives

[albertxavier100]

Zig Version

0.15.2 and 0.15.1

Steps to Reproduce and Observed Behavior

Hey guys, I'm new to zig, and tried to build a repo from source. But I got the below errors are from ziglang. I tried both 0.15.1 and 0.15.2, but both of them failed. Thank you for helping in advance!

1. git clone https://github.com/rockorager/libvaxis
2. zig build
3. Got the below errors

PS D:\Download_D\Repos\libvaxis> zig version
0.15.2
PS D:\Download_D\Repos\libvaxis> zig build
thread 62000 panic: reached unreachable code
C:\Users\alber\.zvm\0.15.2\lib\std\debug.zig:559:14: 0x7ff6080192ad in assert (build_zcu.obj)
    if (!ok) unreachable; // assertion failure
             ^
C:\Users\alber\.zvm\0.15.2\lib\std\Build\Step\Run.zig:662:11: 0x7ff60817bd6e in convertPathArg (build_zcu.obj)
    assert(!std.fs.path.isAbsolute(child_cwd_rel));
          ^
C:\Users\alber\.zvm\0.15.2\lib\std\Build\Step\Run.zig:746:39: 0x7ff6081091d4 in make (build_zcu.obj)
                    run.convertPathArg(.{ .root_dir = .cwd(), .sub_path = file_path }),
                                      ^
C:\Users\alber\.zvm\0.15.2\lib\std\Build\Step.zig:255:33: 0x7ff6080d1015 in make (build_zcu.obj)
    const make_result = s.makeFn(s, options);
                                ^
C:\Users\alber\.zvm\0.15.2\lib\compiler\build_runner.zig:1169:31: 0x7ff6080bbe0a in workerMakeOneStep (build_zcu.obj)
    const make_result = s.make(.{
                              ^
C:\Users\alber\.zvm\0.15.2\lib\std\Thread\Pool.zig:118:39: 0x7ff6080bc669 in runFn (build_zcu.obj)
            @call(.auto, func, closure.arguments);
                                      ^
C:\Users\alber\.zvm\0.15.2\lib\std\Thread\Pool.zig:293:27: 0x7ff6080eda63 in worker (build_zcu.obj)
            runnable.runFn(runnable, id);
                          ^
C:\Users\alber\.zvm\0.15.2\lib\std\Thread.zig:509:13: 0x7ff6080cf13c in callFn__anon_79381 (build_zcu.obj)
            @call(.auto, f, args);
            ^
C:\Users\alber\.zvm\0.15.2\lib\std\Thread.zig:622:30: 0x7ff6080ba872 in entryFn (build_zcu.obj)
                return callFn(f, self.fn_args);
                             ^
???:?:?: 0x7ffee28ae8d6 in ??? (KERNEL32.DLL)
???:?:?: 0x7ffee47ec53b in ??? (ntdll.dll)
error: unable to read results of configure phase from '.zig-cache\tmp\f649d05f91dd5bb7': FileNotFound
PS D:\Download_D\Repos\libvaxis> ables.zig)

Expected Behavior

zig build without errors

[albertxavier100]

I printed the paths in Run.zig:

fn convertPathArg(run: *Run, path: Build.Cache.Path) []const u8 {
    const b = run.step.owner;
    const path_str = path.toString(b.graph.arena) catch @panic("OOM");
    if (std.fs.path.isAbsolute(path_str)) {
        // Absolute paths don't need changing.
        return path_str;
    }
    const child_cwd_rel: []const u8 = rel: {
        const child_lazy_cwd = run.cwd orelse break :rel path_str;
        const child_cwd = child_lazy_cwd.getPath3(b, &run.step).toString(b.graph.arena) catch @panic("OOM");
        // Convert it from relative to *our* cwd, to relative to the *child's* cwd.
        std.debug.print("@@@@@@@@@@@@@@@@@ child_cwd: {s}\n", .{child_cwd});
        std.debug.print("@@@@@@@@@@@@@@@@@ path_str: {s}\n", .{path_str});
        break :rel std.fs.path.relative(b.graph.arena, child_cwd, path_str) catch @panic("OOM");
    };
    std.debug.print("@@@@@@@@@@@@@@@@@ child_cwd_rel: {s}\n", .{child_cwd_rel});
    assert(!std.fs.path.isAbsolute(child_cwd_rel));
    // We're not done yet. In some cases this path must be prefixed with './':
    // * On POSIX, the executable name cannot be a single component like 'foo'
    // * Some executables might treat a leading '-' like a flag, which we must avoid
    // There's no harm in it, so just *always* apply this prefix.
    return std.fs.path.join(b.graph.arena, &.{ ".", child_cwd_rel }) catch @panic("OOM");
}

@@@@@@@@@@@@@@@@@ child_cwd: C:\Users\alber\AppData\Local\zig\p\uucode-0.1.0-ZZjBPj96QADXyt5sqwBJUnhaDYs_qBeeKijZvlRa0eqM
@@@@@@@@@@@@@@@@@ path_str: .zig-cache\o\51f77dc82cebe03aadd130e8bd333554\uucode_build_tables.exe
@@@@@@@@@@@@@@@@@ child_cwd_rel: D:\Download_D\Repos\libvaxis\.zig-cache\o\51f77dc82cebe03aadd130e8bd333554\uucode_build_tables.exe

Moved my project to C:\xxx as a workaround

[squeek502]

This is a regression introduced in #24218