Use local slice_chars

StrExt::slice_chars is deprecated and will be removed in Rust. This
lifts the implementation from Rust libstd and puts it in util::str.

This fixes a bunch of deprecation warnings in Servo.

components/layout/fragment.rs

@@ -46,7 +46,7 @@ use url::Url;
 use util::geometry::{Au, ZERO_POINT};
 use util::logical_geometry::{LogicalRect, LogicalSize, LogicalMargin, WritingMode};
 use util::range::*;
-use util::str::is_whitespace;
+use util::str::{is_whitespace, slice_chars};
 use util;
 
 /// Fragments (`struct Fragment`) are the leaves of the layout tree. They cannot position
@@ -204,8 +204,8 @@ impl fmt::Debug for SpecificFragmentInfo {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             SpecificFragmentInfo::ScannedText(ref info) => {
-                write!(f, " \"{}\"", info.run.text.slice_chars(info.range.begin().get() as usize,
-                                                               info.range.end().get() as usize))
+                write!(f, " \"{}\"", slice_chars(&*info.run.text, info.range.begin().get() as usize,
+                                                 info.range.end().get() as usize))
             }
             _ => Ok(())
         }
@@ -2094,7 +2094,8 @@ impl Fragment {
 
         let mut leading_whitespace_character_count = 0;
         {
-            let text = scanned_text_fragment_info.run.text.slice_chars(
+            let text = slice_chars(
+                &*scanned_text_fragment_info.run.text,
                 scanned_text_fragment_info.range.begin().to_usize(),
                 scanned_text_fragment_info.range.end().to_usize());
             for character in text.chars() {

components/layout/inline.rs

@@ -35,6 +35,7 @@ use unicode_bidi;
 use util::geometry::{Au, MAX_AU, ZERO_RECT};
 use util::logical_geometry::{LogicalRect, LogicalSize, WritingMode};
 use util::range::{Range, RangeIndex};
+use util::str::slice_chars;
 use util;
 
 // From gfxFontConstants.h in Firefox
@@ -1801,7 +1802,7 @@ fn strip_trailing_whitespace_if_necessary(text_run: &TextRun, range: &mut Range<
     debug!("stripping trailing whitespace: range={:?}, len={}",
            range,
            text_run.text.chars().count());
-    let text = text_run.text.slice_chars(range.begin().to_usize(), range.end().to_usize());
+    let text = slice_chars(&*text_run.text, range.begin().to_usize(), range.end().to_usize());
     let mut trailing_whitespace_character_count = 0;
     for ch in text.chars().rev() {
         if util::str::char_is_whitespace(ch) {

components/layout/lib.rs

@@ -13,7 +13,6 @@
 #![feature(mpsc_select)]
 #![feature(plugin)]
 #![feature(raw)]
-#![feature(slice_chars)]
 #![feature(step_by)]
 #![feature(str_char)]
 #![feature(unsafe_no_drop_flag)]

components/script/dom/characterdata.rs

@@ -17,7 +17,7 @@ use dom::element::Element;
 use dom::eventtarget::{EventTarget, EventTargetTypeId};
 use dom::node::{Node, NodeHelpers, NodeTypeId};
 
-use util::str::DOMString;
+use util::str::{DOMString, slice_chars};
 
 use std::borrow::ToOwned;
 use std::cell::Ref;
@@ -74,7 +74,7 @@ impl<'a> CharacterDataMethods for &'a CharacterData {
         }
         // Steps 3-4.
         let end = if length - offset < count { length } else { offset + count };
-        Ok(data.slice_chars(offset as usize, end as usize).to_owned())
+        Ok(slice_chars(&*data, offset as usize, end as usize).to_owned())
     }
 
     // https://dom.spec.whatwg.org/#dom-characterdata-appenddatadata
@@ -107,9 +107,9 @@ impl<'a> CharacterDataMethods for &'a CharacterData {
         };
         // Step 4: Mutation observers.
         // Step 5.
-        let mut data = self.data.borrow().slice_chars(0, offset as usize).to_owned();
+        let mut data = slice_chars(&*self.data.borrow(), 0, offset as usize).to_owned();
         data.push_str(&arg);
-        data.push_str(&self.data.borrow().slice_chars((offset + count) as usize, length as usize));
+        data.push_str(slice_chars(&*self.data.borrow(), (offset + count) as usize, length as usize));
         *self.data.borrow_mut() = data;
         // FIXME: Once we have `Range`, we should implement step7 to step11
         Ok(())

components/script/lib.rs

@@ -21,7 +21,6 @@
 #![feature(plugin)]
 #![feature(ref_slice)]
 #![feature(rc_unique)]
-#![feature(slice_chars)]
 #![feature(str_utf16)]
 #![feature(unicode)]
 #![feature(vec_push_all)]

components/script/textinput.rs

@@ -8,7 +8,7 @@ use clipboard_provider::ClipboardProvider;
 use dom::keyboardevent::{KeyboardEvent, KeyboardEventHelpers, key_value};
 use msg::constellation_msg::{SHIFT, CONTROL, ALT, SUPER};
 use msg::constellation_msg::{Key, KeyModifiers};
-use util::str::DOMString;
+use util::str::{DOMString, slice_chars};
 
 use std::borrow::ToOwned;
 use std::cmp::{min, max};
@@ -159,16 +159,16 @@ impl<T: ClipboardProvider> TextInput<T> {
         self.get_sorted_selection().map(|(begin, end)| {
             if begin.line != end.line {
                 let mut s = String::new();
-                s.push_str(self.lines[begin.line].slice_chars(begin.index, self.lines[begin.line].len()));
+                s.push_str(slice_chars(&self.lines[begin.line], begin.index, self.lines[begin.line].len()));
                 for (_, line) in self.lines.iter().enumerate().filter(|&(i,_)| begin.line < i && i < end.line) {
                     s.push_str("\n");
                     s.push_str(line);
                 }
                 s.push_str("\n");
-                s.push_str(self.lines[end.line].slice_chars(0, end.index));
+                s.push_str(slice_chars(&self.lines[end.line], 0, end.index));
                 s
             } else {
-                self.lines[begin.line].slice_chars(begin.index, end.index).to_owned()
+                slice_chars(&self.lines[begin.line], begin.index, end.index).to_owned()
             }
         })
     }
@@ -178,8 +178,8 @@ impl<T: ClipboardProvider> TextInput<T> {
             self.clear_selection();
 
             let new_lines = {
-                let prefix = self.lines[begin.line].slice_chars(0, begin.index);
-                let suffix = self.lines[end.line].slice_chars(end.index, self.lines[end.line].chars().count());
+                let prefix = slice_chars(&self.lines[begin.line], 0, begin.index);
+                let suffix = slice_chars(&self.lines[end.line], end.index, self.lines[end.line].chars().count());
                 let lines_prefix = &self.lines[..begin.line];
                 let lines_suffix = &self.lines[end.line + 1..];
 

components/util/str.rs

@@ -335,3 +335,27 @@ pub fn str_join<T: AsRef<str>>(strs: &[T], join: &str) -> String {
         acc
     })
 }
+
+// Lifted from Rust's StrExt implementation, which is being removed.
+pub fn slice_chars(s: &str, begin: usize, end: usize) -> &str {
+    assert!(begin <= end);
+    let mut count = 0;
+    let mut begin_byte = None;
+    let mut end_byte = None;
+
+    // This could be even more efficient by not decoding,
+    // only finding the char boundaries
+    for (idx, _) in s.char_indices() {
+        if count == begin { begin_byte = Some(idx); }
+        if count == end { end_byte = Some(idx); break; }
+        count += 1;
+    }
+    if begin_byte.is_none() && count == begin { begin_byte = Some(s.len()) }
+    if end_byte.is_none() && count == end { end_byte = Some(s.len()) }
+
+    match (begin_byte, end_byte) {
+        (None, _) => panic!("slice_chars: `begin` is beyond end of string"),
+        (_, None) => panic!("slice_chars: `end` is beyond end of string"),
+        (Some(a), Some(b)) => unsafe { s.slice_unchecked(a, b) }
+    }
+}