Add `utf16_units`

This deprecates `.to_utf16`. `x.to_utf16()` should be replaced by either
`x.utf16_units().collect::<Vec<u16>>()` (the type annotation may be optional), or
just `x.utf16_units()` directly, if it can be used in an iterator context.

Closes #14358

[breaking-change]

2 files changed, 14 insertions, 7 deletions

diff --git a/src/libstd/dynamic_lib.rs b/src/libstd/dynamic_lib.rs
index ec2cc67a60a..728875ce260 100644
--- a/src/libstd/dynamic_lib.rs
+++ b/src/libstd/dynamic_lib.rs
@@ -281,19 +281,22 @@ pub mod dl {
 #[cfg(target_os = "win32")]
 pub mod dl {
     use c_str::ToCStr;
+    use iter::Iterator;
     use libc;
     use os;
     use ptr;
     use result::{Ok, Err, Result};
-    use str::StrAllocating;
+    use str::StrSlice;
     use str;
     use string::String;
+    use vec::Vec;
 
     pub unsafe fn open_external<T: ToCStr>(filename: T) -> *mut u8 {
         // Windows expects Unicode data
         let filename_cstr = filename.to_c_str();
         let filename_str = str::from_utf8(filename_cstr.as_bytes_no_nul()).unwrap();
-        let filename_str = filename_str.to_utf16().append_one(0);
+        let filename_str: Vec<u16> = filename_str.utf16_units().collect();
+        let filename_str = filename_str.append_one(0);
         LoadLibraryW(filename_str.as_ptr() as *const libc::c_void) as *mut u8
     }
 
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 90f4cbb2577..be3b6be57b3 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -365,7 +365,8 @@ pub fn getenv(n: &str) -> Option<String> {
     unsafe {
         with_env_lock(|| {
             use os::win32::{fill_utf16_buf_and_decode};
-            let n = n.to_utf16().append_one(0);
+            let n: Vec<u16> = n.utf16_units().collect();
+            let n = n.append_one(0);
             fill_utf16_buf_and_decode(|buf, sz| {
                 libc::GetEnvironmentVariableW(n.as_ptr(), buf, sz)
             })
@@ -411,8 +412,10 @@ pub fn setenv(n: &str, v: &str) {
 
     #[cfg(windows)]
     fn _setenv(n: &str, v: &str) {
-        let n = n.to_utf16().append_one(0);
-        let v = v.to_utf16().append_one(0);
+        let n: Vec<u16> = n.utf16_units().collect();
+        let n = n.append_one(0);
+        let v: Vec<u16> = v.utf16_units().collect();
+        let v = v.append_one(0);
         unsafe {
             with_env_lock(|| {
                 libc::SetEnvironmentVariableW(n.as_ptr(), v.as_ptr());
@@ -437,7 +440,8 @@ pub fn unsetenv(n: &str) {
 
     #[cfg(windows)]
     fn _unsetenv(n: &str) {
-        let n = n.to_utf16().append_one(0);
+        let n: Vec<u16> = n.utf16_units().collect();
+        let n = n.append_one(0);
         unsafe {
             with_env_lock(|| {
                 libc::SetEnvironmentVariableW(n.as_ptr(), ptr::null());
@@ -804,7 +808,7 @@ pub fn change_dir(p: &Path) -> bool {
     #[cfg(windows)]
     fn chdir(p: &Path) -> bool {
         let p = match p.as_str() {
-            Some(s) => s.to_utf16().append_one(0),
+            Some(s) => s.utf16_units().collect::<Vec<u16>>().append_one(0),
             None => return false,
         };
         unsafe {