syntax: Copy unstable str::char_at into libsyntax

Author: erickt

src/libsyntax/lib.rs

@@ -92,6 +92,7 @@ pub mod parse;
 pub mod ptr;
 pub mod show_span;
 pub mod std_inject;
+pub mod str;
 pub mod test;
 pub mod visit;
 

src/libsyntax/parse/lexer/comments.rs

@@ -13,11 +13,12 @@ pub use self::CommentStyle::*;
 use ast;
 use codemap::{BytePos, CharPos, CodeMap, Pos};
 use diagnostic;
-use parse::lexer::{is_whitespace, Reader};
-use parse::lexer::{StringReader, TokenAndSpan};
 use parse::lexer::is_block_doc_comment;
+use parse::lexer::{StringReader, TokenAndSpan};
+use parse::lexer::{is_whitespace, Reader};
 use parse::lexer;
 use print::pprust;
+use str::char_at;
 
 use std::io::Read;
 use std::usize;
@@ -209,7 +210,7 @@ fn all_whitespace(s: &str, col: CharPos) -> Option<usize> {
     let mut col = col.to_usize();
     let mut cursor: usize = 0;
     while col > 0 && cursor < len {
-        let ch = s.char_at(cursor);
+        let ch = char_at(s, cursor);
         if !ch.is_whitespace() {
             return None;
         }

src/libsyntax/parse/lexer/mod.rs

@@ -13,8 +13,9 @@ use codemap::{BytePos, CharPos, CodeMap, Pos, Span};
 use codemap;
 use diagnostic::SpanHandler;
 use ext::tt::transcribe::tt_next_token;
-use parse::token;
 use parse::token::str_to_ident;
+use parse::token;
+use str::char_at;
 
 use std::borrow::Cow;
 use std::char;
@@ -289,10 +290,10 @@ impl<'a> StringReader<'a> {
                           s: &'b str, errmsg: &'b str) -> Cow<'b, str> {
         let mut i = 0;
         while i < s.len() {
-            let ch = s.char_at(i);
+            let ch = char_at(s, i);
             let next = i + ch.len_utf8();
             if ch == '\r' {
-                if next < s.len() && s.char_at(next) == '\n' {
+                if next < s.len() && char_at(s, next) == '\n' {
                     return translate_crlf_(self, start, s, errmsg, i).into();
                 }
                 let pos = start + BytePos(i as u32);
@@ -308,12 +309,12 @@ impl<'a> StringReader<'a> {
             let mut buf = String::with_capacity(s.len());
             let mut j = 0;
             while i < s.len() {
-                let ch = s.char_at(i);
+                let ch = char_at(s, i);
                 let next = i + ch.len_utf8();
                 if ch == '\r' {
                     if j < i { buf.push_str(&s[j..i]); }
                     j = next;
-                    if next >= s.len() || s.char_at(next) != '\n' {
+                    if next >= s.len() || char_at(s, next) != '\n' {
                         let pos = start + BytePos(i as u32);
                         let end_pos = start + BytePos(next as u32);
                         rdr.err_span_(pos, end_pos, errmsg);
@@ -335,7 +336,7 @@ impl<'a> StringReader<'a> {
         if current_byte_offset < self.source_text.len() {
             assert!(self.curr.is_some());
             let last_char = self.curr.unwrap();
-            let ch = self.source_text.char_at(current_byte_offset);
+            let ch = char_at(&self.source_text, current_byte_offset);
             let next = current_byte_offset + ch.len_utf8();
             let byte_offset_diff = next - current_byte_offset;
             self.pos = self.pos + Pos::from_usize(byte_offset_diff);
@@ -357,7 +358,7 @@ impl<'a> StringReader<'a> {
     pub fn nextch(&self) -> Option<char> {
         let offset = self.byte_offset(self.pos).to_usize();
         if offset < self.source_text.len() {
-            Some(self.source_text.char_at(offset))
+            Some(char_at(&self.source_text, offset))
         } else {
             None
         }
@@ -371,9 +372,9 @@ impl<'a> StringReader<'a> {
         let offset = self.byte_offset(self.pos).to_usize();
         let s = &self.source_text[..];
         if offset >= s.len() { return None }
-        let next = offset + s.char_at(offset).len_utf8();
+        let next = offset + char_at(s, offset).len_utf8();
         if next < s.len() {
-            Some(s.char_at(next))
+            Some(char_at(s, next))
         } else {
             None
         }

src/libsyntax/parse/mod.rs

@@ -16,7 +16,7 @@ use diagnostic::{SpanHandler, mk_span_handler, default_handler, Auto, FatalError
 use parse::attr::ParserAttr;
 use parse::parser::Parser;
 use ptr::P;
-
+use str::char_at;
 
 use std::cell::{Cell, RefCell};
 use std::fs::File;
@@ -536,7 +536,7 @@ pub fn raw_str_lit(lit: &str) -> String {
 // check if `s` looks like i32 or u1234 etc.
 fn looks_like_width_suffix(first_chars: &[char], s: &str) -> bool {
     s.len() > 1 &&
-        first_chars.contains(&s.char_at(0)) &&
+        first_chars.contains(&char_at(s, 0)) &&
         s[1..].chars().all(|c| '0' <= c && c <= '9')
 }
 
@@ -673,8 +673,8 @@ pub fn integer_lit(s: &str, suffix: Option<&str>, sd: &SpanHandler, sp: Span) ->
     let orig = s;
     let mut ty = ast::UnsuffixedIntLit(ast::Plus);
 
-    if s.char_at(0) == '0' && s.len() > 1 {
-        match s.char_at(1) {
+    if char_at(s, 0) == '0' && s.len() > 1 {
+        match char_at(s, 1) {
             'x' => base = 16,
             'o' => base = 8,
             'b' => base = 2,

src/libsyntax/str.rs

@@ -0,0 +1,13 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub fn char_at(s: &str, byte: usize) -> char {
+    s[byte..].chars().next().unwrap()
+}

src/libsyntax/util/parser_testing.rs

@@ -15,6 +15,7 @@ use parse::new_parser_from_source_str;
 use parse::parser::Parser;
 use parse::token;
 use ptr::P;
+use str::char_at;
 
 /// Map a string to tts, using a made-up filename:
 pub fn string_to_tts(source_str: String) -> Vec<ast::TokenTree> {
@@ -96,24 +97,24 @@ pub fn matches_codepattern(a : &str, b : &str) -> bool {
         else if idx_a == a.len() {return false;}
         else if idx_b == b.len() {
             // maybe the stuff left in a is all ws?
-            if is_whitespace(a.char_at(idx_a)) {
+            if is_whitespace(char_at(a, idx_a)) {
                 return scan_for_non_ws_or_end(a,idx_a) == a.len();
             } else {
                 return false;
             }
         }
         // ws in both given and pattern:
-        else if is_whitespace(a.char_at(idx_a))
-           && is_whitespace(b.char_at(idx_b)) {
+        else if is_whitespace(char_at(a, idx_a))
+           && is_whitespace(char_at(b, idx_b)) {
             idx_a = scan_for_non_ws_or_end(a,idx_a);
             idx_b = scan_for_non_ws_or_end(b,idx_b);
         }
         // ws in given only:
-        else if is_whitespace(a.char_at(idx_a)) {
+        else if is_whitespace(char_at(a, idx_a)) {
             idx_a = scan_for_non_ws_or_end(a,idx_a);
         }
         // *don't* silently eat ws in expected only.
-        else if a.char_at(idx_a) == b.char_at(idx_b) {
+        else if char_at(a, idx_a) == char_at(b, idx_b) {
             idx_a += 1;
             idx_b += 1;
         }
@@ -129,7 +130,7 @@ pub fn matches_codepattern(a : &str, b : &str) -> bool {
 fn scan_for_non_ws_or_end(a : &str, idx: usize) -> usize {
     let mut i = idx;
     let len = a.len();
-    while (i < len) && (is_whitespace(a.char_at(i))) {
+    while (i < len) && (is_whitespace(char_at(a, i))) {
         i += 1;
     }
     i