Fix prompt on windows (#2986)

* Fix typo

* Refactor prompt highlighting into RLHelper

By moving the prompt coloring to be done in
Highlighter::highlight_prompt, we sidestep the issue on Windows where
the prompt width is calculated post-coloring AND without ignoring escape
codes.

By including it in the implementation of Highlighter, Editor::readline
now operates on a plain-text prompt, so width calculation is correct.

This commit also re-arranges the trait impl order to match the
definition.

boa_cli/src/helper.rs

@@ -7,7 +7,7 @@ use rustyline::{
     validate::{MatchingBracketValidator, ValidationContext, ValidationResult, Validator},
     Completer, Helper, Hinter,
 };
-use std::borrow::Cow;
+use std::borrow::Cow::{self, Borrowed};
 
 const STRING_COLOR: Color = Color::Green;
 const KEYWORD_COLOR: Color = Color::Yellow;
@@ -33,18 +33,22 @@ const IDENTIFIER_COLOR: Color = Color::TrueColor {
     b: 214,
 };
 
+const READLINE_COLOR: Color = Color::Cyan;
+
 #[allow(clippy::upper_case_acronyms)]
 #[derive(Completer, Helper, Hinter)]
 pub(crate) struct RLHelper {
     highlighter: LineHighlighter,
     validator: MatchingBracketValidator,
+    colored_prompt: String,
 }
 
 impl RLHelper {
-    pub(crate) fn new() -> Self {
+    pub(crate) fn new(prompt: &str) -> Self {
         Self {
             highlighter: LineHighlighter,
             validator: MatchingBracketValidator::new(),
+            colored_prompt: prompt.color(READLINE_COLOR).bold().to_string(),
         }
     }
 }
@@ -63,14 +67,28 @@ impl Validator for RLHelper {
 }
 
 impl Highlighter for RLHelper {
-    fn highlight_hint<'h>(&self, hint: &'h str) -> Cow<'h, str> {
-        hint.into()
-    }
-
     fn highlight<'l>(&self, line: &'l str, pos: usize) -> Cow<'l, str> {
         self.highlighter.highlight(line, pos)
     }
 
+    // Must match signature of Highlighter::highlight_prompt, can't elide lifetimes.
+    #[allow(single_use_lifetimes)]
+    fn highlight_prompt<'b, 's: 'b, 'p: 'b>(
+        &'s self,
+        prompt: &'p str,
+        default: bool,
+    ) -> Cow<'b, str> {
+        if default {
+            Borrowed(&self.colored_prompt)
+        } else {
+            Borrowed(prompt)
+        }
+    }
+
+    fn highlight_hint<'h>(&self, hint: &'h str) -> Cow<'h, str> {
+        hint.into()
+    }
+
     fn highlight_candidate<'c>(
         &self,
         candidate: &'c str,

boa_cli/src/main.rs

@@ -77,7 +77,7 @@ use boa_engine::{
 };
 use boa_runtime::Console;
 use clap::{Parser, ValueEnum, ValueHint};
-use colored::{Color, Colorize};
+use colored::Colorize;
 use debug::init_boa_debug_object;
 use rustyline::{config::Config, error::ReadlineError, EditMode, Editor};
 use std::{
@@ -95,8 +95,6 @@ static ALLOC: jemallocator::Jemalloc = jemallocator::Jemalloc;
 /// CLI configuration for Boa.
 static CLI_HISTORY: &str = ".boa_history";
 
-const READLINE_COLOR: Color = Color::Cyan;
-
 // Added #[allow(clippy::option_option)] because to StructOpt an Option<Option<T>>
 // is an optional argument that optionally takes a value ([--opt=[val]]).
 // https://docs.rs/structopt/0.3.11/structopt/#type-magic
@@ -419,12 +417,11 @@ fn main() -> Result<(), io::Error> {
             ReadlineError::Io(e) => e,
             e => io::Error::new(io::ErrorKind::Other, e),
         })?;
-        editor.set_helper(Some(helper::RLHelper::new()));
-
-        let readline = ">> ".color(READLINE_COLOR).bold().to_string();
+        let readline = ">> ";
+        editor.set_helper(Some(helper::RLHelper::new(readline)));
 
         loop {
-            match editor.readline(&readline) {
+            match editor.readline(readline) {
                 Ok(line) if line == ".exit" => break,
                 Err(ReadlineError::Interrupted | ReadlineError::Eof) => break,
 

boa_engine/src/optimizer/mod.rs

@@ -16,7 +16,7 @@ bitflags! {
         /// Print statistics to `stdout`.
         const STATISTICS = 0b0000_0001;
 
-        /// Apply contant folding optimization.
+        /// Apply constant folding optimization.
         const CONSTANT_FOLDING = 0b0000_0010;
 
         /// Apply all optimizations.