std: add predicate pattern support to OsStr

Due to technical limitations adding support for predicate as patterns
on OsStr slices must be done via core::pattern::Predicate wrapper type.
This isn’t ideal but for the time being it’s the best option I’ve came
up with.

The core of the issue (as I understand it) is that FnMut is a foreign
type in std crate where OsStr is defined.

Using predicate as a pattern on OsStr is the final piece which now
allows parsing command line arguments.

library/std/src/ffi/os_str.rs

@@ -1731,6 +1731,104 @@ unsafe impl<'hs> ReverseSearcher<&'hs OsStr> for CharSearcher<'hs> {
 #[unstable(feature = "pattern", issue = "27721")]
 impl<'hs> DoubleEndedSearcher<&'hs OsStr> for CharSearcher<'hs> {}
 
+#[unstable(feature = "pattern", issue = "27721")]
+// FIXME: Using Predicate because of:
+//     error[E0210]: type parameter `F` must be covered by another type when it
+//                   appears before the first local type (`OsStr`)
+//         --> library/std/src/ffi/os_str.rs:1697:11
+//          |
+//     1697 | impl<'hs, F: FnMut(char) -> bool> core::pattern::Pattern<&'hs OsStr> for F {
+//          |           ^ type parameter `F` must be covered by another type
+//                        when it appears before the first local type (`OsStr`)
+impl<'hs, F: FnMut(char) -> bool> core::pattern::Pattern<&'hs OsStr>
+    for core::pattern::Predicate<F>
+{
+    type Searcher = PredicateSearcher<'hs, F>;
+
+    fn into_searcher(self, haystack: &'hs OsStr) -> Self::Searcher {
+        Self::Searcher::new(haystack, self.into_fn())
+    }
+
+    fn is_contained_in(self, haystack: &'hs OsStr) -> bool {
+        self.into_fn().is_contained_in(core::str_bytes::Bytes::from(haystack))
+    }
+
+    fn is_prefix_of(self, haystack: &'hs OsStr) -> bool {
+        self.into_fn().is_prefix_of(core::str_bytes::Bytes::from(haystack))
+    }
+
+    fn is_suffix_of(self, haystack: &'hs OsStr) -> bool {
+        self.into_fn().is_suffix_of(core::str_bytes::Bytes::from(haystack))
+    }
+
+    /// Removes the pattern from the front of haystack, if it matches.
+    fn strip_prefix_of(self, haystack: &'hs OsStr) -> Option<&'hs OsStr> {
+        self.into_fn()
+            .strip_prefix_of(core::str_bytes::Bytes::from(haystack))
+            .map(|bytes| bytes.into())
+    }
+
+    /// Removes the pattern from the back of haystack, if it matches.
+    fn strip_suffix_of(self, haystack: &'hs OsStr) -> Option<&'hs OsStr>
+    where
+        Self::Searcher: ReverseSearcher<&'hs OsStr>,
+    {
+        self.into_fn()
+            .strip_suffix_of(core::str_bytes::Bytes::from(haystack))
+            .map(|bytes| bytes.into())
+    }
+}
+
+#[derive(Clone, Debug)]
+#[unstable(feature = "pattern", issue = "27721")]
+pub struct PredicateSearcher<'hs, P>(core::str_bytes::PredicateSearcher<'hs, BytesFlavour, P>);
+
+impl<'hs, P> PredicateSearcher<'hs, P> {
+    fn new(haystack: &'hs OsStr, pred: P) -> PredicateSearcher<'hs, P> {
+        Self(core::str_bytes::PredicateSearcher::new(haystack.into(), pred))
+    }
+}
+
+#[unstable(feature = "pattern", issue = "27721")]
+unsafe impl<'hs, P: FnMut(char) -> bool> Searcher<&'hs OsStr> for PredicateSearcher<'hs, P> {
+    #[inline(always)]
+    fn haystack(&self) -> &'hs OsStr {
+        self.0.haystack().into()
+    }
+
+    #[inline(always)]
+    fn next(&mut self) -> SearchStep {
+        self.0.next()
+    }
+    #[inline(always)]
+    fn next_match(&mut self) -> Option<(usize, usize)> {
+        self.0.next_match()
+    }
+    #[inline(always)]
+    fn next_reject(&mut self) -> Option<(usize, usize)> {
+        self.0.next_reject()
+    }
+}
+
+#[unstable(feature = "pattern", issue = "27721")]
+unsafe impl<'hs, P: FnMut(char) -> bool> ReverseSearcher<&'hs OsStr> for PredicateSearcher<'hs, P> {
+    #[inline(always)]
+    fn next_back(&mut self) -> SearchStep {
+        self.0.next_back()
+    }
+    #[inline(always)]
+    fn next_match_back(&mut self) -> Option<(usize, usize)> {
+        self.0.next_match_back()
+    }
+    #[inline(always)]
+    fn next_reject_back(&mut self) -> Option<(usize, usize)> {
+        self.0.next_reject_back()
+    }
+}
+
+#[unstable(feature = "pattern", issue = "27721")]
+impl<'hs, P: FnMut(char) -> bool> DoubleEndedSearcher<&'hs OsStr> for PredicateSearcher<'hs, P> {}
+
 #[unstable(feature = "pattern", issue = "27721")]
 impl<'hs, 'p> core::pattern::Pattern<&'hs OsStr> for &'p str {
     type Searcher = StrSearcher<'hs, 'p>;

library/std/tests/os_str.rs

@@ -1,6 +1,6 @@
 #![feature(associated_type_bounds, pattern)]
 
-use core::pattern::{Pattern, Searcher, ReverseSearcher};
+use core::pattern::{Pattern, Searcher, ReverseSearcher, predicate};
 use std::borrow::Cow;
 use std::ffi::{OsStr, OsString};
 
@@ -111,6 +111,23 @@ fn do_test_short_flag(valid: bool) {
     assert_eq!(Some(&*os("shórt")), arg.strip_prefix('-'));
     assert_eq!(Some(&*os("shórt")), arg.strip_prefix("-"));
     assert_eq!(None, arg.strip_prefix("--"));
+
+    // A bit awkward but closure can be used to test short options character
+    // by character.
+    let mut switch = '\0';
+    let mut check_switch = |chr| {
+        switch = chr;
+        chr == 's' || chr == 'h'
+    };
+    assert_eq!(
+        Some(&*os("hórt")),
+        os("shórt").strip_prefix(predicate(&mut check_switch))
+    );
+    assert_eq!(
+        Some(&*os("órt")),
+        os("hórt").strip_prefix(predicate(&mut check_switch))
+    );
+    assert_eq!(None, os("órt").strip_prefix(predicate(&mut check_switch)));
 }
 
 #[test]
@@ -157,15 +174,21 @@ fn test_le() {
 #[test]
 fn test_find() {
     assert_eq!(find("hello", 'l'), Some(2));
+    assert_eq!(find("hello", predicate(|c: char| c == 'o')), Some(4));
     assert!(find("hello", 'x').is_none());
+    assert!(find("hello", predicate(|c: char| c == 'x')).is_none());
     assert_eq!(find("ประเทศไทย中华Việt Nam", '华'), Some(30));
+    assert_eq!(find("ประเทศไทย中华Việt Nam", predicate(|c: char| c == '华')), Some(30));
 }
 
 #[test]
 fn test_rfind() {
     assert_eq!(rfind("hello", 'l'), Some(3));
+    assert_eq!(rfind("hello", predicate(|c: char| c == 'o')), Some(4));
     assert!(rfind("hello", 'x').is_none());
+    assert!(rfind("hello", predicate(|c: char| c == 'x')).is_none());
     assert_eq!(rfind("ประเทศไทย中华Việt Nam", '华'), Some(30));
+    assert_eq!(rfind("ประเทศไทย中华Việt Nam", predicate(|c: char| c == '华')), Some(30));
 }
 
 /*
@@ -1832,13 +1855,27 @@ fn test_split_char_iterator() {
     rsplit.reverse();
     assert_eq!(rsplit, ["\nMäry", "häd", "ä", "little", "lämb\nLittle", "lämb\n"]);
 
+    let split: Vec<&OsStr> = os(data).split(predicate(|c: char| c == ' ')).collect();
+    assert_eq!(split, ["\nMäry", "häd", "ä", "little", "lämb\nLittle", "lämb\n"]);
+
+    let mut rsplit: Vec<&OsStr> = os(data).split(predicate(|c: char| c == ' ')).rev().collect();
+    rsplit.reverse();
+    assert_eq!(rsplit, ["\nMäry", "häd", "ä", "little", "lämb\nLittle", "lämb\n"]);
+
     // Unicode
     let split: Vec<&OsStr> = os(data).split('ä').collect();
     assert_eq!(split, ["\nM", "ry h", "d ", " little l", "mb\nLittle l", "mb\n"]);
 
     let mut rsplit: Vec<&OsStr> = os(data).split('ä').rev().collect();
     rsplit.reverse();
     assert_eq!(rsplit, ["\nM", "ry h", "d ", " little l", "mb\nLittle l", "mb\n"]);
+
+    let split: Vec<&OsStr> = os(data).split(predicate(|c: char| c == 'ä')).collect();
+    assert_eq!(split, ["\nM", "ry h", "d ", " little l", "mb\nLittle l", "mb\n"]);
+
+    let mut rsplit: Vec<&OsStr> = os(data).split(predicate(|c: char| c == 'ä')).rev().collect();
+    rsplit.reverse();
+    assert_eq!(rsplit, ["\nM", "ry h", "d ", " little l", "mb\nLittle l", "mb\n"]);
 }
 
 #[test]