std.fs.cwd.makePath: integer overflow if CWD does not exist

[ehaas]

Zig Version

0.10.0-dev.1575+7f91be9c8

Steps to Reproduce

Run zig test on the following:

const std = @import("std");

test "cwd.makePath with non-existent CWD" {
    var tmp_dir = std.testing.tmpDir(.{});
    try tmp_dir.dir.setAsCwd();
    tmp_dir.cleanup();

    const cwd = std.fs.cwd();
    try cwd.makePath("sub-path");
}

Expected Behavior

The equivalent C code will set errno to ENOENT if trying to create a directory within a non-existent directory, so I would expect the test to fail with error.NotFound.

Actual Behavior

Test [1/1] test "cwd.makePath with non-existent CWD"... thread 42590880 panic: integer overflow
/Users/ehaas/source/zig/build/lib/zig/std/fs.zig:1314:35: 0x108c24ce8 in std.fs.Dir.makePath (test)
                        end_index -= 1;
                                  ^
/Users/ehaas/test.zig:9:21: 0x108c235cc in test "cwd.makePath with non-existent CWD" (test)
    try cwd.makePath("sub-path");
                    ^

[ominitay]

I don't think so?

[ominitay]

Wouldn't changing if (path.isSep(sub_path[end_index])) break; to if (path.isSep(sub_path[end_index]) or end_index == 0) break; fix this?

[ehaas]

Wouldn't changing if (path.isSep(sub_path[end_index])) break; to if (path.isSep(sub_path[end_index]) or end_index == 0) break; fix this?

That works, but it does result in an extra call to makeDir with an empty string. I think we probably want to check for end_index == 0 inside the while loop.