The purpose is as follows:
- Stop using `mrb_locale_from_utf8()`.
- Because there is no corresponding `mrb_utf8_from_locale()`.
- Because on Windows, for example, if the code page is 932 (CP932, likely ShiftJIS), it cannot be distinguished from the second byte 0x5c (\), and returns wrong results.
- Stop using `dirname(3)`.
- Because leading consecutive slashes are not truncated.
For example, if `/////a/b` is given, CRuby returns `/a`, but mruby so far returns `/////a`.
- Because the `path` argument cannot be passed in an immutable form.
- Stop using `_splitpath()` in the Windows implementation.
- Because there is no support for UNC paths with up to 32767 characters.
ref. https://learn.microsoft.com/ja-jp/dotnet/standard/io/file-path-formats#unc-paths
- Because modifying the result of paths terminated by a directory separator.
Previously, for example, `C:/` would return `C:.` instead of `C:/`, and `a/b/` would return `a/b` instead of `a`.
- The inner method `File._gethome` could be read as intending to use the `USERPROFILE` environment variable instead on Windows when the `HOME` environment variable is not available.
In reality, however, this was not the case.
- The result of `File.expand_path` should unify path separators with `/`, but it did not.
Since `mruby-io` does not depend on `mruby-env` even for test builds, it is impossible that `ENV` constants are defined.
Therefore, define `MRubyIOTestUtil::ENV_HOME` for alternative use.
dearblue