Stabilize std::path

This commit stabilizes essentially all of the new `std::path` API. The
API itself is changed in a couple of ways (which brings it in closer
alignment with the RFC):

* `.` components are now normalized away, unless they appear at the
  start of a path. This in turn effects the semantics of e.g. asking for
  the file name of `foo/` or `foo/.`, both of which yield `Some("foo")`
  now. This semantics is what the original RFC specified, and is also
  desirable given early experience rolling out the new API.

* The `parent` function now succeeds if, and only if, the path has at
  least one non-root/prefix component. This change affects `pop` as
  well.

* The `Prefix` component now involves a separate `PrefixComponent`
  struct, to better allow for keeping both parsed and unparsed prefix data.

In addition, the `old_path` module is now deprecated.

Closes #23264

[breaking-change]

4 files changed, 4 insertions, 13 deletions

diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index 62d98be8b85..eb0daac3ab8 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -195,11 +195,7 @@ fn res_rel_file(cx: &mut ExtCtxt, sp: codemap::Span, arg: &Path) -> PathBuf {
     // NB: relative paths are resolved relative to the compilation unit
     if !arg.is_absolute() {
         let mut cu = PathBuf::new(&cx.codemap().span_to_filename(sp));
-        if cu.parent().is_some() {
-            cu.pop();
-        } else {
-            cu = PathBuf::new("");
-        }
+        cu.pop();
         cu.push(arg);
         cu
     } else {
diff --git a/src/libsyntax/lib.rs b/src/libsyntax/lib.rs
index ba3f495cdac..90f0dc30c75 100644
--- a/src/libsyntax/lib.rs
+++ b/src/libsyntax/lib.rs
@@ -38,7 +38,6 @@
 #![feature(staged_api)]
 #![feature(std_misc)]
 #![feature(unicode)]
-#![feature(path)]
 #![feature(io)]
 #![feature(path_ext)]
 
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 28d757e9be9..495c619c273 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -5254,13 +5254,7 @@ impl<'a> Parser<'a> {
                     -> (ast::Item_, Vec<ast::Attribute> ) {
         let mut prefix = PathBuf::new(&self.sess.span_diagnostic.cm
                                            .span_to_filename(self.span));
-        // FIXME(acrichto): right now "a".pop() == "a", but need to confirm with
-        //                  aturon whether this is expected or not.
-        if prefix.parent().is_some() {
-            prefix.pop();
-        } else {
-            prefix = PathBuf::new("");
-        }
+        prefix.pop();
         let mut dir_path = prefix;
         for part in &self.mod_path_stack {
             dir_path.push(&**part);
diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 61a3a5ca82a..17b42e4e05c 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -25,6 +25,7 @@ use serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::fmt;
 use std::mem;
 use std::ops::Deref;
+#[allow(deprecated)]
 use std::old_path::BytesContainer;
 use std::rc::Rc;
 
@@ -638,6 +639,7 @@ impl Deref for InternedString {
     fn deref(&self) -> &str { &*self.string }
 }
 
+#[allow(deprecated)]
 impl BytesContainer for InternedString {
     fn container_as_bytes<'a>(&'a self) -> &'a [u8] {
         // FIXME #12938: This is a workaround for the incorrect signature