kennytm
commented
6 years ago I would think that there would be an opaque Prefix struct, and something like
.into_os_prefix()would provide you with an os-specific enum to match against.
The Prefix variant of the Component enum contains the opaque struct PrefixComponent, not the enum Prefix.
This means a backward-compatible option 5 is available:
impl<'a> PrefixComponent<'a> {
/// On Windows, returns the parsed prefix data.
///
/// On other platforms, the returned value is unspecified.
#[cfg_attr(
target_os = "redox",
rustc_deprecated(
since = "1.29.0",
reason = "The prefix component is meaningless on Redox. Use `.scheme()` instead",
),
)]
pub fn kind(&self) -> Prefix<'a> { ... }
}
mod redox {
pub trait PrefixComponentExt<'a> {
// Obtains the scheme of the Redox path (URL).
fn scheme(&self) -> &'a OsStr;
}
impl<'a> PrefixComponentExt<'a> for PrefixComponent<'a> {
fn scheme(&self) -> &'a OsStr { self.as_os_str() }
}
}
jackpot51
4lDO2
ian-h-chamberlain
joshtriplett
rfcbot
rustbot
Ayush1325
m-ou-se
retep998
Path::componentsis incorrect on Redox. I would like to develop the solution here: https://github.com/rust-lang/rust/pull/51537.The following is a description of the problem.
Suppose you have the following path:
file:/home/user/foo/bar.txtYou split the path into components using
Path::componentsIn Linux, this would be equivalent to the following:
Joining the components with the current directory would give you a path such as this:
./file:/home/user/foo/bar.txtIn Redox, we want to be able to get from the original path to components back to the original path without any modifications. Here are examples of this usage of
Path::components:https://github.com/uutils/coreutils/search?q=components
In Redox, we have the following options for the
file:component:Component::Normal("file:")Component::Normal("file:")followed byComponent::RootDirComponent::Prefix(Prefix::Verbatim("file:"))Component::Prefix(Prefix::Scheme("file:"))Option 1
Component::Normal("file:")The path mentioned above would end up being the following after being rebuilt from its components:
./file:/home/user/foo/bar.txtThis is the old way of doing things. It not only makes
Path::componentsuseless on Redox. Canonicalizing a path will always add a scheme likefile:to the beginning, so it is likely that path handling will be incorrect. Absolute paths would always be interpreted as relative.:x: This option is unusable for Redox.
Option 2
Component::Normal("file:")followed byComponent::RootDirThis would preserve the original meaning of the path, such that it could be rebuilt from its components as follows:
file:/home/user/foo/bar.txtHowever, this may require a large amount of work to handle, as it seems likely that code exists that only checks the first component for being
Component::RootDirorComponent::Prefixin order to identify an absolute path.The documentation for
Prefixprovides one such example, which has likely inspired similar usage:https://doc.rust-lang.org/std/path/enum.Prefix.html#examples
:x: This option would likely break the expectations of many consumers of the
Prefixenum.Option 3
Component::Prefix(Prefix::Verbatim("file:"))This option preserves the original meaning of the path, a rebuilt path would be this:
file:/home/user/foo/bar.txtThis, however, is overloading a variant meant to be used on Windows, for a path looking like this:
\\?\home\user\foo\bar.txtThis means different code will be needed when running on Redox to correctly parse paths to components and turn components into paths.
:heavy_check_mark: This does leave the enum untouched, while allowing for the correct parsing of paths on Redox. The only downside is a possible lack of clarity due to overloading the meaning of the
Prefix::Verbatimvariant.Option 4
Component::Prefix(Prefix::Scheme("file:"))This option also preserves the original meaning of the path, a rebuilt path would be this:
file:/home/user/foo/bar.txtThis is the most clear option, having separate code to handle specifically the Redox scheme abstraction.
This has the downside of changing a stable enum,
Prefix. There is, however, the possibility of having the extra enum variant be#[cfg(target_os = "redox")], so as to preserve thePrefixenum on other platforms.:heavy_check_mark: This option could be used to have correct path parsing without affecting the stability of the
Prefixenum on non-Redox platforms, if acfgattribute is used.Conclusion
Potentially the
Prefixenum would be done different after a major version bump, perhaps using extension traits that are platform specific. I would think that there would be an opaquePrefixstruct, and something like.into_os_prefix()would provide you with an os-specific enum to match against.For the time being, options 3 and 4 seem to be possible, with some caveats, and would allow code using stable Rust to quickly do-the-right-thing on Redox.