Use ArrayString instead of hand rolled data structure

Cargo.lock

@@ -671,6 +671,7 @@ dependencies = [
 name = "ra_syntax"
 version = "0.1.0"
 dependencies = [
+ "arrayvec 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "drop_bomb 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "itertools 0.7.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)",

crates/ra_syntax/Cargo.toml

@@ -8,6 +8,7 @@ description = "Comment and whitespace preserving parser for the Rust langauge"
 repository = "https://github.com/rust-analyzer/rust-analyzer"
 
 [dependencies]
+arrayvec = "0.4.7"
 unicode-xid = "0.1.0"
 itertools = "0.7.8"
 drop_bomb = "0.1.4"

crates/ra_syntax/src/lib.rs

@@ -20,6 +20,7 @@
 #![allow(missing_docs)]
 //#![warn(unreachable_pub)] // rust-lang/rust#47816
 
+extern crate arrayvec;
 extern crate drop_bomb;
 extern crate itertools;
 extern crate parking_lot;

crates/ra_syntax/src/utils.rs

@@ -1,6 +1,5 @@
 use crate::{File, SyntaxKind, SyntaxNodeRef, WalkEvent};
 use std::fmt::Write;
-use std::ops::Deref;
 use std::str;
 
 /// Parse a file and create a string representation of the resulting parse tree.
@@ -80,38 +79,3 @@ pub(crate) fn validate_block_structure(root: SyntaxNodeRef) {
         }
     }
 }
-
-#[derive(Debug)]
-pub struct MutAsciiString<'a> {
-    buf: &'a mut [u8],
-    len: usize,
-}
-
-impl<'a> MutAsciiString<'a> {
-    pub fn new(buf: &'a mut [u8]) -> MutAsciiString<'a> {
-        MutAsciiString { buf, len: 0 }
-    }
-
-    pub fn as_str(&self) -> &str {
-        str::from_utf8(&self.buf[..self.len]).unwrap()
-    }
-
-    pub fn len(&self) -> usize {
-        self.len
-    }
-
-    pub fn push(&mut self, c: char) {
-        assert!(self.len() < self.buf.len());
-        assert!(c.is_ascii());
-
-        self.buf[self.len] = c as u8;
-        self.len += 1;
-    }
-}
-
-impl<'a> Deref for MutAsciiString<'a> {
-    type Target = str;
-    fn deref(&self) -> &str {
-        self.as_str()
-    }
-}

crates/ra_syntax/src/validation.rs

@@ -1,11 +1,12 @@
 use std::u32;
 
+use arrayvec::ArrayString;
+
 use crate::{
     algo::visit::{visitor_ctx, VisitorCtx},
     ast::{self, AstNode},
     File,
     string_lexing::{self, CharComponentKind},
-    utils::MutAsciiString,
     yellow::{
         SyntaxError,
         SyntaxErrorKind::*,
@@ -76,8 +77,7 @@ fn validate_char(node: ast::Char, errors: &mut Vec<SyntaxError>) {
                     return;
                 }
 
-                let mut buf = &mut [0; 6];
-                let mut code = MutAsciiString::new(buf);
+                let mut code = ArrayString::<[_; 6]>::new();
                 let mut closed = false;
                 for c in text[3..].chars() {
                     assert!(!closed, "no characters after escape is closed");