Add generic conversion traits

This commit:

* Introduces `std::convert`, providing an implementation of
RFC 529.

* Deprecates the `AsPath`, `AsOsStr`, and `IntoBytes` traits, all
in favor of the corresponding generic conversion traits.

  Consequently, various IO APIs now take `AsRef<Path>` rather than
`AsPath`, and so on. Since the types provided by `std` implement both
traits, this should cause relatively little breakage.

* Deprecates many `from_foo` constructors in favor of `from`.

* Changes `PathBuf::new` to take no argument (creating an empty buffer,
  as per convention). The previous behavior is now available as
  `PathBuf::from`.

* De-stabilizes `IntoCow`. It's not clear whether we need this separate trait.

Closes #22751
Closes #14433

[breaking-change]

src/compiletest/compiletest.rs

@@ -20,6 +20,8 @@
 #![feature(std_misc)]
 #![feature(test)]
 #![feature(path_ext)]
+#![feature(convert)]
+#![feature(str_char)]
 
 #![deny(warnings)]
 
@@ -115,7 +117,7 @@ pub fn parse_config(args: Vec<String> ) -> Config {
 
     fn opt_path(m: &getopts::Matches, nm: &str) -> PathBuf {
         match m.opt_str(nm) {
-            Some(s) => PathBuf::new(&s),
+            Some(s) => PathBuf::from(&s),
             None => panic!("no option (=path) found for {}", nm),
         }
     }
@@ -130,18 +132,18 @@ pub fn parse_config(args: Vec<String> ) -> Config {
         compile_lib_path: matches.opt_str("compile-lib-path").unwrap(),
         run_lib_path: matches.opt_str("run-lib-path").unwrap(),
         rustc_path: opt_path(matches, "rustc-path"),
-        clang_path: matches.opt_str("clang-path").map(|s| PathBuf::new(&s)),
+        clang_path: matches.opt_str("clang-path").map(|s| PathBuf::from(&s)),
         valgrind_path: matches.opt_str("valgrind-path"),
         force_valgrind: matches.opt_present("force-valgrind"),
-        llvm_bin_path: matches.opt_str("llvm-bin-path").map(|s| PathBuf::new(&s)),
+        llvm_bin_path: matches.opt_str("llvm-bin-path").map(|s| PathBuf::from(&s)),
         src_base: opt_path(matches, "src-base"),
         build_base: opt_path(matches, "build-base"),
         aux_base: opt_path(matches, "aux-base"),
         stage_id: matches.opt_str("stage-id").unwrap(),
         mode: matches.opt_str("mode").unwrap().parse().ok().expect("invalid mode"),
         run_ignored: matches.opt_present("ignored"),
         filter: filter,
-        logfile: matches.opt_str("logfile").map(|s| PathBuf::new(&s)),
+        logfile: matches.opt_str("logfile").map(|s| PathBuf::from(&s)),
         runtool: matches.opt_str("runtool"),
         host_rustcflags: matches.opt_str("host-rustcflags"),
         target_rustcflags: matches.opt_str("target-rustcflags"),

src/compiletest/header.rs

@@ -328,10 +328,10 @@ fn parse_exec_env(line: &str) -> Option<(String, String)> {
 
 fn parse_pp_exact(line: &str, testfile: &Path) -> Option<PathBuf> {
     match parse_name_value_directive(line, "pp-exact") {
-      Some(s) => Some(PathBuf::new(&s)),
+      Some(s) => Some(PathBuf::from(&s)),
       None => {
         if parse_name_directive(line, "pp-exact") {
-            testfile.file_name().map(|s| PathBuf::new(s))
+            testfile.file_name().map(|s| PathBuf::from(s))
         } else {
             None
         }

src/compiletest/runtest.rs

@@ -1440,7 +1440,7 @@ fn aux_output_dir_name(config: &Config, testfile: &Path) -> PathBuf {
 }
 
 fn output_testname(testfile: &Path) -> PathBuf {
-    PathBuf::new(testfile.file_stem().unwrap())
+    PathBuf::from(testfile.file_stem().unwrap())
 }
 
 fn output_base_name(config: &Config, testfile: &Path) -> PathBuf {

src/libcollections/borrow.rs

@@ -14,6 +14,7 @@
 
 use core::clone::Clone;
 use core::cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd};
+use core::convert::AsRef;
 use core::hash::{Hash, Hasher};
 use core::marker::Sized;
 use core::ops::Deref;
@@ -291,10 +292,9 @@ impl<'a, B: ?Sized> Hash for Cow<'a, B> where B: Hash + ToOwned
 }
 
 /// Trait for moving into a `Cow`
-#[stable(feature = "rust1", since = "1.0.0")]
+#[unstable(feature = "into_cow", reason = "may be replaced by `convert::Into`")]
 pub trait IntoCow<'a, B: ?Sized> where B: ToOwned {
     /// Moves `self` into `Cow`
-    #[stable(feature = "rust1", since = "1.0.0")]
     fn into_cow(self) -> Cow<'a, B>;
 }
 
@@ -304,3 +304,10 @@ impl<'a,  B: ?Sized> IntoCow<'a, B> for Cow<'a, B> where B: ToOwned {
         self
     }
 }
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T: Clone> AsRef<T> for Cow<'a, T> {
+    fn as_ref(&self) -> &T {
+        self
+    }
+}

src/libcollections/lib.rs

@@ -36,6 +36,7 @@
 #![feature(unsafe_no_drop_flag)]
 #![feature(step_by)]
 #![feature(str_char)]
+#![feature(convert)]
 #![cfg_attr(test, feature(rand, rustc_private, test))]
 #![cfg_attr(test, allow(deprecated))] // rand
 

src/libcollections/slice.rs

@@ -88,6 +88,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use alloc::boxed::Box;
+use core::convert::AsRef;
 use core::clone::Clone;
 use core::cmp::Ordering::{self, Greater, Less};
 use core::cmp::{self, Ord, PartialEq};
@@ -1088,23 +1089,23 @@ pub trait SliceConcatExt<T: ?Sized, U> {
     fn connect(&self, sep: &T) -> U;
 }
 
-impl<T: Clone, V: AsSlice<T>> SliceConcatExt<T, Vec<T>> for [V] {
+impl<T: Clone, V: AsRef<[T]>> SliceConcatExt<T, Vec<T>> for [V] {
     fn concat(&self) -> Vec<T> {
-        let size = self.iter().fold(0, |acc, v| acc + v.as_slice().len());
+        let size = self.iter().fold(0, |acc, v| acc + v.as_ref().len());
         let mut result = Vec::with_capacity(size);
         for v in self {
-            result.push_all(v.as_slice())
+            result.push_all(v.as_ref())
         }
         result
     }
 
     fn connect(&self, sep: &T) -> Vec<T> {
-        let size = self.iter().fold(0, |acc, v| acc + v.as_slice().len());
+        let size = self.iter().fold(0, |acc, v| acc + v.as_ref().len());
         let mut result = Vec::with_capacity(size + self.len());
         let mut first = true;
         for v in self {
             if first { first = false } else { result.push(sep.clone()) }
-            result.push_all(v.as_slice())
+            result.push_all(v.as_ref())
         }
         result
     }

src/libcollections/str.rs

@@ -61,10 +61,10 @@ use core::iter::AdditiveIterator;
 use core::iter::{Iterator, IteratorExt, Extend};
 use core::option::Option::{self, Some, None};
 use core::result::Result;
-use core::slice::AsSlice;
 use core::str as core_str;
 use unicode::str::{UnicodeStr, Utf16Encoder};
 
+use core::convert::AsRef;
 use vec_deque::VecDeque;
 use borrow::{Borrow, ToOwned};
 use string::String;
@@ -86,51 +86,47 @@ pub use core::str::{Searcher, ReverseSearcher, DoubleEndedSearcher, SearchStep};
 Section: Creating a string
 */
 
-impl<S: Str> SliceConcatExt<str, String> for [S] {
+impl<S: AsRef<str>> SliceConcatExt<str, String> for [S] {
     fn concat(&self) -> String {
-        let s = self.as_slice();
-
-        if s.is_empty() {
+        if self.is_empty() {
             return String::new();
         }
 
         // `len` calculation may overflow but push_str will check boundaries
-        let len = s.iter().map(|s| s.as_slice().len()).sum();
+        let len = self.iter().map(|s| s.as_ref().len()).sum();
         let mut result = String::with_capacity(len);
 
-        for s in s {
-            result.push_str(s.as_slice())
+        for s in self {
+            result.push_str(s.as_ref())
         }
 
         result
     }
 
     fn connect(&self, sep: &str) -> String {
-        let s = self.as_slice();
-
-        if s.is_empty() {
+        if self.is_empty() {
             return String::new();
         }
 
         // concat is faster
         if sep.is_empty() {
-            return s.concat();
+            return self.concat();
         }
 
         // this is wrong without the guarantee that `self` is non-empty
         // `len` calculation may overflow but push_str but will check boundaries
-        let len = sep.len() * (s.len() - 1)
-            + s.iter().map(|s| s.as_slice().len()).sum();
+        let len = sep.len() * (self.len() - 1)
+            + self.iter().map(|s| s.as_ref().len()).sum();
         let mut result = String::with_capacity(len);
         let mut first = true;
 
-        for s in s {
+        for s in self {
             if first {
                 first = false;
             } else {
                 result.push_str(sep);
             }
-            result.push_str(s.as_slice());
+            result.push_str(s.as_ref());
         }
         result
     }

src/libcollections/string.rs

@@ -814,6 +814,7 @@ impl<'a, 'b> PartialEq<Cow<'a, str>> for &'b str {
 }
 
 #[unstable(feature = "collections", reason = "waiting on Str stabilization")]
+#[allow(deprecated)]
 impl Str for String {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -973,6 +974,27 @@ impl<T: fmt::Display + ?Sized> ToString for T {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl AsRef<str> for String {
+    fn as_ref(&self) -> &str {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a> From<&'a str> for String {
+    fn from(s: &'a str) -> String {
+        s.to_string()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Into<Vec<u8>> for String {
+    fn into(self) -> Vec<u8> {
+        self.into_bytes()
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl IntoCow<'static, str> for String {
     #[inline]
@@ -989,6 +1011,7 @@ impl<'a> IntoCow<'a, str> for &'a str {
     }
 }
 
+#[allow(deprecated)]
 impl<'a> Str for Cow<'a, str> {
     #[inline]
     fn as_slice<'b>(&'b self) -> &'b str {

src/libcollections/vec.rs

@@ -1369,7 +1369,7 @@ impl<T> ops::Index<ops::RangeFull> for Vec<T> {
     type Output = [T];
     #[inline]
     fn index(&self, _index: &ops::RangeFull) -> &[T] {
-        self.as_slice()
+        self
     }
 }
 
@@ -1406,7 +1406,13 @@ impl<T> ops::IndexMut<ops::RangeFull> for Vec<T> {
 impl<T> ops::Deref for Vec<T> {
     type Target = [T];
 
-    fn deref(&self) -> &[T] { self.as_slice() }
+    fn deref(&self) -> &[T] {
+        unsafe {
+            let p = *self.ptr;
+            assume(p != 0 as *mut T);
+            slice::from_raw_parts(p, self.len)
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1548,6 +1554,7 @@ impl<T: Ord> Ord for Vec<T> {
     }
 }
 
+#[allow(deprecated)]
 impl<T> AsSlice<T> for Vec<T> {
     /// Returns a slice into `self`.
     ///
@@ -1562,11 +1569,7 @@ impl<T> AsSlice<T> for Vec<T> {
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     fn as_slice(&self) -> &[T] {
-        unsafe {
-            let p = *self.ptr;
-            assume(p != 0 as *mut T);
-            slice::from_raw_parts(p, self.len)
-        }
+        self
     }
 }
 
@@ -1614,6 +1617,41 @@ impl<T: fmt::Debug> fmt::Debug for Vec<T> {
     }
 }
 
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsRef<Vec<T>> for Vec<T> {
+    fn as_ref(&self) -> &Vec<T> {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> Into<Vec<T>> for Vec<T> {
+    fn into(self) -> Vec<T> {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<T> AsRef<[T]> for Vec<T> {
+    fn as_ref(&self) -> &[T] {
+        self
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a, T: Clone> From<&'a [T]> for Vec<T> {
+    fn from(s: &'a [T]) -> Vec<T> {
+        s.to_vec()
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl<'a> From<&'a str> for Vec<u8> {
+    fn from(s: &'a str) -> Vec<u8> {
+        s.as_bytes().to_vec()
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // Clone-on-write
 ////////////////////////////////////////////////////////////////////////////////