Only trigger write when needed

Cargo.toml

@@ -75,6 +75,8 @@ unstable_features = "forbid"
 
 [workspace.lints.clippy]
 empty_loop = "forbid"
+disallowed-types = "deny"
+disallowed-methods = "deny"
 infinite_loop = "deny"
 mem_forget = "deny"
 dbg_macro = "warn"

clippy.toml

@@ -0,0 +1,13 @@
+disallowed-types = [
+  # Inefficient. Use `.queue(…)` instead.
+  "crossterm::style::Stylize",
+  "crossterm::style::styled_content::StyledContent",
+]
+
+disallowed-methods = [
+  # We use `ahash` instead of the default hasher.
+  "std::collections::HashSet::new",
+  "std::collections::HashSet::with_capacity",
+  # Inefficient. Use `.queue(…)` instead.
+  "crossterm::style::style",
+]

src/app_state.rs

@@ -338,7 +338,7 @@ impl AppState {
     /// Mark the current exercise as done and move on to the next pending exercise if one exists.
     /// If all exercises are marked as done, run all of them to make sure that they are actually
     /// done. If an exercise which is marked as done fails, mark it as pending and continue on it.
-    pub fn done_current_exercise(&mut self, writer: &mut StdoutLock) -> Result<ExercisesProgress> {
+    pub fn done_current_exercise(&mut self, stdout: &mut StdoutLock) -> Result<ExercisesProgress> {
         let exercise = &mut self.exercises[self.current_exercise_ind];
         if !exercise.done {
             exercise.done = true;
@@ -350,7 +350,7 @@ impl AppState {
             return Ok(ExercisesProgress::NewPending);
         }
 
-        writer.write_all(RERUNNING_ALL_EXERCISES_MSG)?;
+        stdout.write_all(RERUNNING_ALL_EXERCISES_MSG)?;
 
         let n_exercises = self.exercises.len();
 
@@ -368,12 +368,12 @@ impl AppState {
                 .collect::<Vec<_>>();
 
             for (exercise_ind, handle) in handles.into_iter().enumerate() {
-                write!(writer, "\rProgress: {exercise_ind}/{n_exercises}")?;
-                writer.flush()?;
+                write!(stdout, "\rProgress: {exercise_ind}/{n_exercises}")?;
+                stdout.flush()?;
 
                 let success = handle.join().unwrap()?;
                 if !success {
-                    writer.write_all(b"\n\n")?;
+                    stdout.write_all(b"\n\n")?;
                     return Ok(Some(exercise_ind));
                 }
             }
@@ -395,13 +395,13 @@ impl AppState {
         // Write that the last exercise is done.
         self.write()?;
 
-        clear_terminal(writer)?;
-        writer.write_all(FENISH_LINE.as_bytes())?;
+        clear_terminal(stdout)?;
+        stdout.write_all(FENISH_LINE.as_bytes())?;
 
         let final_message = self.final_message.trim_ascii();
         if !final_message.is_empty() {
-            writer.write_all(final_message.as_bytes())?;
-            writer.write_all(b"\n")?;
+            stdout.write_all(final_message.as_bytes())?;
+            stdout.write_all(b"\n")?;
         }
 
         Ok(ExercisesProgress::AllDone)

src/exercise.rs

@@ -1,15 +1,27 @@
 use anyhow::Result;
-use crossterm::style::{style, StyledContent, Stylize};
-use std::{
-    fmt::{self, Display, Formatter},
-    io::Write,
+use crossterm::{
+    style::{Attribute, Color, ResetColor, SetAttribute, SetForegroundColor},
+    QueueableCommand,
 };
+use std::io::{self, StdoutLock, Write};
 
-use crate::{cmd::CmdRunner, terminal_link::TerminalFileLink};
+use crate::{
+    cmd::CmdRunner,
+    term::{terminal_file_link, write_ansi},
+};
 
 /// The initial capacity of the output buffer.
 pub const OUTPUT_CAPACITY: usize = 1 << 14;
 
+pub fn solution_link_line(stdout: &mut StdoutLock, solution_path: &str) -> io::Result<()> {
+    stdout.queue(SetAttribute(Attribute::Bold))?;
+    stdout.write_all(b"Solution")?;
+    stdout.queue(ResetColor)?;
+    stdout.write_all(b" for comparison: ")?;
+    terminal_file_link(stdout, solution_path, Color::Cyan)?;
+    stdout.write_all(b"\n")
+}
+
 // Run an exercise binary and append its output to the `output` buffer.
 // Compilation must be done before calling this method.
 fn run_bin(
@@ -18,7 +30,10 @@ fn run_bin(
     cmd_runner: &CmdRunner,
 ) -> Result<bool> {
     if let Some(output) = output.as_deref_mut() {
-        writeln!(output, "{}", "Output".underlined())?;
+        write_ansi(output, SetAttribute(Attribute::Underlined));
+        output.extend_from_slice(b"Output");
+        write_ansi(output, ResetColor);
+        output.push(b'\n');
     }
 
     let success = cmd_runner.run_debug_bin(bin_name, output.as_deref_mut())?;
@@ -28,13 +43,11 @@ fn run_bin(
             // This output is important to show the user that something went wrong.
             // Otherwise, calling something like `exit(1)` in an exercise without further output
             // leaves the user confused about why the exercise isn't done yet.
-            writeln!(
-                output,
-                "{}",
-                "The exercise didn't run successfully (nonzero exit code)"
-                    .bold()
-                    .red(),
-            )?;
+            write_ansi(output, SetAttribute(Attribute::Bold));
+            write_ansi(output, SetForegroundColor(Color::Red));
+            output.extend_from_slice(b"The exercise didn't run successfully (nonzero exit code)");
+            write_ansi(output, ResetColor);
+            output.push(b'\n');
         }
     }
 
@@ -53,18 +66,6 @@ pub struct Exercise {
     pub done: bool,
 }
 
-impl Exercise {
-    pub fn terminal_link(&self) -> StyledContent<TerminalFileLink<'_>> {
-        style(TerminalFileLink(self.path)).underlined().blue()
-    }
-}
-
-impl Display for Exercise {
-    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
-        self.path.fmt(f)
-    }
-}
-
 pub trait RunnableExercise {
     fn name(&self) -> &str;
     fn strict_clippy(&self) -> bool;

src/init.rs

@@ -1,5 +1,8 @@
 use anyhow::{bail, Context, Result};
-use crossterm::style::Stylize;
+use crossterm::{
+    style::{Attribute, Color, ResetColor, SetAttribute, SetForegroundColor},
+    QueueableCommand,
+};
 use serde::Deserialize;
 use std::{
     env::set_current_dir,
@@ -144,12 +147,14 @@ pub fn init() -> Result<()> {
             .status();
     }
 
-    writeln!(
-        stdout,
-        "{}\n\n{}",
-        "Initialization done ✓".green(),
-        POST_INIT_MSG.bold(),
-    )?;
+    stdout.queue(SetForegroundColor(Color::Green))?;
+    stdout.write_all("Initialization done ✓".as_bytes())?;
+    stdout.queue(ResetColor)?;
+    stdout.write_all(b"\n\n")?;
+
+    stdout.queue(SetAttribute(Attribute::Bold))?;
+    stdout.write_all(POST_INIT_MSG)?;
+    stdout.queue(ResetColor)?;
 
     Ok(())
 }
@@ -182,5 +187,6 @@ You probably already initialized Rustlings.
 Run `cd rustlings`
 Then run `rustlings` again";
 
-const POST_INIT_MSG: &str = "Run `cd rustlings` to go into the generated directory.
-Then run `rustlings` to get started.";
+const POST_INIT_MSG: &[u8] = b"Run `cd rustlings` to go into the generated directory.
+Then run `rustlings` to get started.
+";

src/list/state.rs

@@ -10,9 +10,14 @@ use std::{
     io::{self, StdoutLock, Write},
 };
 
-use crate::{app_state::AppState, exercise::Exercise, term::progress_bar, MAX_EXERCISE_NAME_LEN};
+use crate::{
+    app_state::AppState,
+    exercise::Exercise,
+    term::{progress_bar, terminal_file_link, CountedWrite, MaxLenWriter},
+    MAX_EXERCISE_NAME_LEN,
+};
 
-const MAX_SCROLL_PADDING: usize = 8;
+const MAX_SCROLL_PADDING: usize = 5;
 // +1 for column padding.
 const SPACE: &[u8] = &[b' '; MAX_EXERCISE_NAME_LEN + 1];
 
@@ -23,14 +28,6 @@ fn next_ln(stdout: &mut StdoutLock) -> io::Result<()> {
     Ok(())
 }
 
-// Avoids having the last written char as the last displayed one when the
-// written width is higher than the terminal width.
-// Happens on the Gnome terminal for example.
-fn next_ln_overwrite(stdout: &mut StdoutLock) -> io::Result<()> {
-    stdout.write_all(b" ")?;
-    next_ln(stdout)
-}
-
 #[derive(Copy, Clone, PartialEq, Eq)]
 pub enum Filter {
     Done,
@@ -159,40 +156,44 @@ impl<'a> ListState<'a> {
             .skip(self.row_offset)
             .take(self.max_n_rows_to_display)
         {
+            let mut writer = MaxLenWriter::new(stdout, self.term_width as usize);
+
             if self.selected_row == Some(self.row_offset + n_displayed_rows) {
-                stdout.queue(SetBackgroundColor(Color::Rgb {
-                    r: 50,
-                    g: 50,
-                    b: 50,
+                writer.stdout.queue(SetBackgroundColor(Color::Rgb {
+                    r: 40,
+                    g: 40,
+                    b: 40,
                 }))?;
-                stdout.write_all("🦀".as_bytes())?;
+                // The crab emoji has the width of two ascii chars.
+                writer.add_to_len(2);
+                writer.stdout.write_all("🦀".as_bytes())?;
             } else {
-                stdout.write_all(b"  ")?;
+                writer.write_ascii(b"  ")?;
             }
 
             if exercise_ind == current_exercise_ind {
-                stdout.queue(SetForegroundColor(Color::Red))?;
-                stdout.write_all(b">>>>>>>  ")?;
+                writer.stdout.queue(SetForegroundColor(Color::Red))?;
+                writer.write_ascii(b">>>>>>>  ")?;
             } else {
-                stdout.write_all(b"         ")?;
+                writer.write_ascii(b"         ")?;
             }
 
             if exercise.done {
-                stdout.queue(SetForegroundColor(Color::Yellow))?;
-                stdout.write_all(b"DONE     ")?;
+                writer.stdout.queue(SetForegroundColor(Color::Green))?;
+                writer.write_ascii(b"DONE     ")?;
             } else {
-                stdout.queue(SetForegroundColor(Color::Green))?;
-                stdout.write_all(b"PENDING  ")?;
+                writer.stdout.queue(SetForegroundColor(Color::Yellow))?;
+                writer.write_ascii(b"PENDING  ")?;
             }
 
-            stdout.queue(SetForegroundColor(Color::Reset))?;
+            writer.stdout.queue(SetForegroundColor(Color::Reset))?;
 
-            stdout.write_all(exercise.name.as_bytes())?;
-            stdout.write_all(&SPACE[..self.name_col_width + 2 - exercise.name.len()])?;
+            writer.write_str(exercise.name)?;
+            writer.write_ascii(&SPACE[..self.name_col_width + 2 - exercise.name.len()])?;
 
-            stdout.write_all(exercise.path.as_bytes())?;
+            terminal_file_link(&mut writer, exercise.path, Color::Blue)?;
 
-            next_ln_overwrite(stdout)?;
+            next_ln(stdout)?;
             stdout.queue(ResetColor)?;
             n_displayed_rows += 1;
         }
@@ -208,10 +209,11 @@ impl<'a> ListState<'a> {
         stdout.queue(BeginSynchronizedUpdate)?.queue(MoveTo(0, 0))?;
 
         // Header
-        stdout.write_all(b"  Current  State    Name")?;
-        stdout.write_all(&SPACE[..self.name_col_width - 2])?;
-        stdout.write_all(b"Path")?;
-        next_ln_overwrite(stdout)?;
+        let mut writer = MaxLenWriter::new(stdout, self.term_width as usize);
+        writer.write_ascii(b"  Current  State    Name")?;
+        writer.write_ascii(&SPACE[..self.name_col_width - 2])?;
+        writer.write_ascii(b"Path")?;
+        next_ln(stdout)?;
 
         // Rows
         let iter = self.app_state.exercises().iter().enumerate();
@@ -232,7 +234,7 @@ impl<'a> ListState<'a> {
             next_ln(stdout)?;
 
             progress_bar(
-                stdout,
+                &mut MaxLenWriter::new(stdout, self.term_width as usize),
                 self.app_state.n_done(),
                 self.app_state.exercises().len() as u16,
                 self.term_width,
@@ -242,59 +244,55 @@ impl<'a> ListState<'a> {
             stdout.write_all(&self.separator_line)?;
             next_ln(stdout)?;
 
+            let mut writer = MaxLenWriter::new(stdout, self.term_width as usize);
             if self.message.is_empty() {
                 // Help footer message
                 if self.selected_row.is_some() {
-                    stdout.write_all(
-                        "↓/j ↑/k home/g end/G | <c>ontinue at | <r>eset exercise".as_bytes(),
-                    )?;
+                    writer.write_str("↓/j ↑/k home/g end/G | <c>ontinue at | <r>eset exercise")?;
                     if self.narrow_term {
-                        next_ln_overwrite(stdout)?;
-                        stdout.write_all(b"filter ")?;
+                        next_ln(stdout)?;
+                        writer = MaxLenWriter::new(stdout, self.term_width as usize);
+
+                        writer.write_ascii(b"filter ")?;
                     } else {
-                        stdout.write_all(b" | filter ")?;
+                        writer.write_ascii(b" | filter ")?;
                     }
                 } else {
                     // Nothing selected (and nothing shown), so only display filter and quit.
-                    stdout.write_all(b"filter ")?;
+                    writer.write_ascii(b"filter ")?;
                 }
 
                 match self.filter {
                     Filter::Done => {
-                        stdout
+                        writer
+                            .stdout
                             .queue(SetForegroundColor(Color::Magenta))?
                             .queue(SetAttribute(Attribute::Underlined))?;
-                        stdout.write_all(b"<d>one")?;
-                        stdout.queue(ResetColor)?;
-                        stdout.write_all(b"/<p>ending")?;
+                        writer.write_ascii(b"<d>one")?;
+                        writer.stdout.queue(ResetColor)?;
+                        writer.write_ascii(b"/<p>ending")?;
                     }
                     Filter::Pending => {
-                        stdout.write_all(b"<d>one/")?;
-                        stdout
+                        writer.write_ascii(b"<d>one/")?;
+                        writer
+                            .stdout
                             .queue(SetForegroundColor(Color::Magenta))?
                             .queue(SetAttribute(Attribute::Underlined))?;
-                        stdout.write_all(b"<p>ending")?;
-                        stdout.queue(ResetColor)?;
+                        writer.write_ascii(b"<p>ending")?;
+                        writer.stdout.queue(ResetColor)?;
                     }
-                    Filter::None => stdout.write_all(b"<d>one/<p>ending")?,
+                    Filter::None => writer.write_ascii(b"<d>one/<p>ending")?,
                 }
 
-                stdout.write_all(b" | <q>uit list")?;
-
-                if self.narrow_term {
-                    next_ln_overwrite(stdout)?;
-                } else {
-                    next_ln(stdout)?;
-                }
+                writer.write_ascii(b" | <q>uit list")?;
             } else {
-                stdout.queue(SetForegroundColor(Color::Magenta))?;
-                stdout.write_all(self.message.as_bytes())?;
+                writer.stdout.queue(SetForegroundColor(Color::Magenta))?;
+                writer.write_str(&self.message)?;
                 stdout.queue(ResetColor)?;
-                next_ln_overwrite(stdout)?;
-                if self.narrow_term {
-                    next_ln(stdout)?;
-                }
+                next_ln(stdout)?;
             }
+
+            next_ln(stdout)?;
         }
 
         stdout.queue(EndSynchronizedUpdate)?.flush()

src/main.rs

@@ -22,7 +22,6 @@ mod init;
 mod list;
 mod run;
 mod term;
-mod terminal_link;
 mod watch;
 
 const CURRENT_FORMAT_VERSION: u8 = 1;

src/run.rs

@@ -1,11 +1,17 @@
-use anyhow::{bail, Result};
-use crossterm::style::{style, Stylize};
-use std::io::{self, Write};
+use anyhow::Result;
+use crossterm::{
+    style::{Color, ResetColor, SetForegroundColor},
+    QueueableCommand,
+};
+use std::{
+    io::{self, Write},
+    process::exit,
+};
 
 use crate::{
     app_state::{AppState, ExercisesProgress},
-    exercise::{RunnableExercise, OUTPUT_CAPACITY},
-    terminal_link::TerminalFileLink,
+    exercise::{solution_link_line, RunnableExercise, OUTPUT_CAPACITY},
+    term::terminal_file_link,
 };
 
 pub fn run(app_state: &mut AppState) -> Result<()> {
@@ -19,35 +25,31 @@ pub fn run(app_state: &mut AppState) -> Result<()> {
     if !success {
         app_state.set_pending(app_state.current_exercise_ind())?;
 
-        bail!(
-            "Ran {} with errors",
-            app_state.current_exercise().terminal_link(),
-        );
+        stdout.write_all(b"Ran ")?;
+        terminal_file_link(&mut stdout, app_state.current_exercise().path, Color::Blue)?;
+        stdout.write_all(b" with errors\n")?;
+        exit(1);
     }
 
-    writeln!(
-        stdout,
-        "{}{}",
-        "✓ Successfully ran ".green(),
-        exercise.path.green(),
-    )?;
+    stdout.queue(SetForegroundColor(Color::Green))?;
+    stdout.write_all("✓ Successfully ran ".as_bytes())?;
+    stdout.write_all(exercise.path.as_bytes())?;
+    stdout.queue(ResetColor)?;
+    stdout.write_all(b"\n")?;
 
     if let Some(solution_path) = app_state.current_solution_path()? {
-        writeln!(
-            stdout,
-            "\n{} for comparison: {}\n",
-            "Solution".bold(),
-            style(TerminalFileLink(&solution_path)).underlined().cyan(),
-        )?;
+        stdout.write_all(b"\n")?;
+        solution_link_line(&mut stdout, &solution_path)?;
+        stdout.write_all(b"\n")?;
     }
 
     match app_state.done_current_exercise(&mut stdout)? {
+        ExercisesProgress::CurrentPending | ExercisesProgress::NewPending => {
+            stdout.write_all(b"Next exercise: ")?;
+            terminal_file_link(&mut stdout, app_state.current_exercise().path, Color::Blue)?;
+            stdout.write_all(b"\n")?;
+        }
         ExercisesProgress::AllDone => (),
-        ExercisesProgress::CurrentPending | ExercisesProgress::NewPending => writeln!(
-            stdout,
-            "Next exercise: {}",
-            app_state.current_exercise().terminal_link(),
-        )?,
     }
 
     Ok(())

src/term.rs

@@ -1,15 +1,99 @@
-use std::io::{self, BufRead, StdoutLock, Write};
+use std::{
+    cell::Cell,
+    env, fmt, fs,
+    io::{self, BufRead, StdoutLock, Write},
+};
 
 use crossterm::{
     cursor::MoveTo,
-    style::{Color, ResetColor, SetForegroundColor},
+    style::{Attribute, Color, ResetColor, SetAttribute, SetForegroundColor},
     terminal::{Clear, ClearType},
-    QueueableCommand,
+    Command, QueueableCommand,
 };
 
+thread_local! {
+    static VS_CODE: Cell<bool> = Cell::new(env::var_os("TERM_PROGRAM").is_some_and(|v| v == "vscode"));
+}
+
+pub struct MaxLenWriter<'a, 'b> {
+    pub stdout: &'a mut StdoutLock<'b>,
+    len: usize,
+    max_len: usize,
+}
+
+impl<'a, 'b> MaxLenWriter<'a, 'b> {
+    #[inline]
+    pub fn new(stdout: &'a mut StdoutLock<'b>, max_len: usize) -> Self {
+        Self {
+            stdout,
+            len: 0,
+            max_len,
+        }
+    }
+
+    // Additional is for emojis that take more space.
+    #[inline]
+    pub fn add_to_len(&mut self, additional: usize) {
+        self.len += additional;
+    }
+}
+
+pub trait CountedWrite<'a> {
+    fn write_ascii(&mut self, ascii: &[u8]) -> io::Result<()>;
+    fn write_str(&mut self, unicode: &str) -> io::Result<()>;
+    fn stdout(&mut self) -> &mut StdoutLock<'a>;
+}
+
+impl<'a, 'b> CountedWrite<'b> for MaxLenWriter<'a, 'b> {
+    fn write_ascii(&mut self, ascii: &[u8]) -> io::Result<()> {
+        let n = ascii.len().min(self.max_len.saturating_sub(self.len));
+        if n > 0 {
+            self.stdout.write_all(&ascii[..n])?;
+            self.len += n;
+        }
+        Ok(())
+    }
+
+    fn write_str(&mut self, unicode: &str) -> io::Result<()> {
+        if let Some((ind, c)) = unicode
+            .char_indices()
+            .take(self.max_len.saturating_sub(self.len))
+            .last()
+        {
+            self.stdout
+                .write_all(&unicode.as_bytes()[..ind + c.len_utf8()])?;
+            self.len += ind + 1;
+        }
+
+        Ok(())
+    }
+
+    #[inline]
+    fn stdout(&mut self) -> &mut StdoutLock<'b> {
+        self.stdout
+    }
+}
+
+impl<'a> CountedWrite<'a> for StdoutLock<'a> {
+    #[inline]
+    fn write_ascii(&mut self, ascii: &[u8]) -> io::Result<()> {
+        self.write_all(ascii)
+    }
+
+    #[inline]
+    fn write_str(&mut self, unicode: &str) -> io::Result<()> {
+        self.write_all(unicode.as_bytes())
+    }
+
+    #[inline]
+    fn stdout(&mut self) -> &mut StdoutLock<'a> {
+        self
+    }
+}
+
 /// Terminal progress bar to be used when not using Ratataui.
-pub fn progress_bar(
-    stdout: &mut StdoutLock,
+pub fn progress_bar<'a>(
+    writer: &mut impl CountedWrite<'a>,
     progress: u16,
     total: u16,
     line_width: u16,
@@ -24,9 +108,13 @@ pub fn progress_bar(
     const MIN_LINE_WIDTH: u16 = WRAPPER_WIDTH + 4;
 
     if line_width < MIN_LINE_WIDTH {
-        return write!(stdout, "Progress: {progress}/{total} exercises");
+        writer.write_ascii(b"Progress: ")?;
+        // Integers are in ASCII.
+        writer.write_ascii(format!("{progress}/{total}").as_bytes())?;
+        return writer.write_ascii(b" exercises");
     }
 
+    let stdout = writer.stdout();
     stdout.write_all(PREFIX)?;
 
     let width = line_width - WRAPPER_WIDTH;
@@ -68,3 +156,58 @@ pub fn press_enter_prompt(stdout: &mut StdoutLock) -> io::Result<()> {
     stdout.write_all(b"\n")?;
     Ok(())
 }
+
+pub fn terminal_file_link<'a>(
+    writer: &mut impl CountedWrite<'a>,
+    path: &str,
+    color: Color,
+) -> io::Result<()> {
+    // VS Code shows its own links. This also avoids some issues, especially on Windows.
+    if VS_CODE.get() {
+        return writer.write_str(path);
+    }
+
+    let canonical_path = fs::canonicalize(path).ok();
+
+    let Some(canonical_path) = canonical_path.as_deref().and_then(|p| p.to_str()) else {
+        return writer.write_str(path);
+    };
+
+    // Windows itself can't handle its verbatim paths.
+    #[cfg(windows)]
+    let canonical_path = if canonical_path.len() > 5 && &canonical_path[0..4] == r"\\?\" {
+        &canonical_path[4..]
+    } else {
+        canonical_path
+    };
+
+    writer
+        .stdout()
+        .queue(SetForegroundColor(color))?
+        .queue(SetAttribute(Attribute::Underlined))?;
+    writer.stdout().write_all(b"\x1b]8;;file://")?;
+    writer.stdout().write_all(canonical_path.as_bytes())?;
+    writer.stdout().write_all(b"\x1b\\")?;
+    // Only this part is visible.
+    writer.write_str(path)?;
+    writer.stdout().write_all(b"\x1b]8;;\x1b\\")?;
+    writer
+        .stdout()
+        .queue(SetForegroundColor(Color::Reset))?
+        .queue(SetAttribute(Attribute::NoUnderline))?;
+
+    Ok(())
+}
+
+pub fn write_ansi(output: &mut Vec<u8>, command: impl Command) {
+    struct FmtWriter<'a>(&'a mut Vec<u8>);
+
+    impl fmt::Write for FmtWriter<'_> {
+        fn write_str(&mut self, s: &str) -> fmt::Result {
+            self.0.extend_from_slice(s.as_bytes());
+            Ok(())
+        }
+    }
+
+    let _ = command.write_ansi(&mut FmtWriter(output));
+}

src/terminal_link.rs

@@ -1,26 +0,0 @@
-use std::{
-    fmt::{self, Display, Formatter},
-    fs,
-};
-
-pub struct TerminalFileLink<'a>(pub &'a str);
-
-impl<'a> Display for TerminalFileLink<'a> {
-    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
-        let path = fs::canonicalize(self.0);
-
-        if let Some(path) = path.as_deref().ok().and_then(|path| path.to_str()) {
-            // Windows itself can't handle its verbatim paths.
-            #[cfg(windows)]
-            let path = if path.len() > 5 && &path[0..4] == r"\\?\" {
-                &path[4..]
-            } else {
-                path
-            };
-
-            write!(f, "\x1b]8;;file://{path}\x1b\\{}\x1b]8;;\x1b\\", self.0)
-        } else {
-            write!(f, "{}", self.0)
-        }
-    }
-}

src/watch.rs

@@ -72,35 +72,32 @@ pub fn watch(
 
     let mut watch_state = WatchState::new(app_state, manual_run);
 
-    watch_state.run_current_exercise()?;
+    let mut stdout = io::stdout().lock();
+    watch_state.run_current_exercise(&mut stdout)?;
 
     thread::spawn(move || terminal_event_handler(tx, manual_run));
 
     while let Ok(event) = rx.recv() {
         match event {
-            WatchEvent::Input(InputEvent::Next) => match watch_state.next_exercise()? {
+            WatchEvent::Input(InputEvent::Next) => match watch_state.next_exercise(&mut stdout)? {
                 ExercisesProgress::AllDone => break,
-                ExercisesProgress::CurrentPending => watch_state.render()?,
-                ExercisesProgress::NewPending => watch_state.run_current_exercise()?,
+                ExercisesProgress::CurrentPending => watch_state.render(&mut stdout)?,
+                ExercisesProgress::NewPending => watch_state.run_current_exercise(&mut stdout)?,
             },
-            WatchEvent::Input(InputEvent::Hint) => {
-                watch_state.show_hint()?;
-            }
+            WatchEvent::Input(InputEvent::Hint) => watch_state.show_hint(&mut stdout)?,
             WatchEvent::Input(InputEvent::List) => {
                 return Ok(WatchExit::List);
             }
             WatchEvent::Input(InputEvent::Quit) => {
-                watch_state.into_writer().write_all(QUIT_MSG)?;
+                stdout.write_all(QUIT_MSG)?;
                 break;
             }
-            WatchEvent::Input(InputEvent::Run) => watch_state.run_current_exercise()?,
-            WatchEvent::Input(InputEvent::Unrecognized) => watch_state.render()?,
+            WatchEvent::Input(InputEvent::Run) => watch_state.run_current_exercise(&mut stdout)?,
+            WatchEvent::Input(InputEvent::Unrecognized) => watch_state.render(&mut stdout)?,
             WatchEvent::FileChange { exercise_ind } => {
-                watch_state.handle_file_change(exercise_ind)?;
-            }
-            WatchEvent::TerminalResize => {
-                watch_state.render()?;
+                watch_state.handle_file_change(exercise_ind, &mut stdout)?;
             }
+            WatchEvent::TerminalResize => watch_state.render(&mut stdout)?,
             WatchEvent::NotifyErr(e) => {
                 return Err(Error::from(e).context(NOTIFY_ERR));
             }

src/watch/state.rs

@@ -1,16 +1,17 @@
 use anyhow::Result;
 use crossterm::{
-    style::{style, Stylize},
-    terminal,
+    style::{
+        Attribute, Attributes, Color, ResetColor, SetAttribute, SetAttributes, SetForegroundColor,
+    },
+    terminal, QueueableCommand,
 };
 use std::io::{self, StdoutLock, Write};
 
 use crate::{
     app_state::{AppState, ExercisesProgress},
     clear_terminal,
-    exercise::{RunnableExercise, OUTPUT_CAPACITY},
-    term::progress_bar,
-    terminal_link::TerminalFileLink,
+    exercise::{solution_link_line, RunnableExercise, OUTPUT_CAPACITY},
+    term::{progress_bar, terminal_file_link},
 };
 
 #[derive(PartialEq, Eq)]
@@ -21,7 +22,6 @@ enum DoneStatus {
 }
 
 pub struct WatchState<'a> {
-    writer: StdoutLock<'a>,
     app_state: &'a mut AppState,
     output: Vec<u8>,
     show_hint: bool,
@@ -31,10 +31,7 @@ pub struct WatchState<'a> {
 
 impl<'a> WatchState<'a> {
     pub fn new(app_state: &'a mut AppState, manual_run: bool) -> Self {
-        let writer = io::stdout().lock();
-
         Self {
-            writer,
             app_state,
             output: Vec::with_capacity(OUTPUT_CAPACITY),
             show_hint: false,
@@ -43,16 +40,11 @@ impl<'a> WatchState<'a> {
         }
     }
 
-    #[inline]
-    pub fn into_writer(self) -> StdoutLock<'a> {
-        self.writer
-    }
-
-    pub fn run_current_exercise(&mut self) -> Result<()> {
+    pub fn run_current_exercise(&mut self, stdout: &mut StdoutLock) -> Result<()> {
         self.show_hint = false;
 
         writeln!(
-            self.writer,
+            stdout,
             "\nChecking the exercise `{}`. Please wait…",
             self.app_state.current_exercise().name,
         )?;
@@ -76,11 +68,15 @@ impl<'a> WatchState<'a> {
             self.done_status = DoneStatus::Pending;
         }
 
-        self.render()?;
+        self.render(stdout)?;
         Ok(())
     }
 
-    pub fn handle_file_change(&mut self, exercise_ind: usize) -> Result<()> {
+    pub fn handle_file_change(
+        &mut self,
+        exercise_ind: usize,
+        stdout: &mut StdoutLock,
+    ) -> Result<()> {
         // Don't skip exercises on file changes to avoid confusion from missing exercises.
         // Skipping exercises must be explicit in the interactive list.
         // But going back to an earlier exercise on file change is fine.
@@ -89,92 +85,115 @@ impl<'a> WatchState<'a> {
         }
 
         self.app_state.set_current_exercise_ind(exercise_ind)?;
-        self.run_current_exercise()
+        self.run_current_exercise(stdout)
     }
 
     /// Move on to the next exercise if the current one is done.
-    pub fn next_exercise(&mut self) -> Result<ExercisesProgress> {
+    pub fn next_exercise(&mut self, stdout: &mut StdoutLock) -> Result<ExercisesProgress> {
         if self.done_status == DoneStatus::Pending {
             return Ok(ExercisesProgress::CurrentPending);
         }
 
-        self.app_state.done_current_exercise(&mut self.writer)
+        self.app_state.done_current_exercise(stdout)
     }
 
-    fn show_prompt(&mut self) -> io::Result<()> {
-        self.writer.write_all(b"\n")?;
-
+    fn show_prompt(&self, stdout: &mut StdoutLock) -> io::Result<()> {
         if self.manual_run {
-            write!(self.writer, "{}:run / ", 'r'.bold())?;
+            stdout.queue(SetAttribute(Attribute::Bold))?;
+            stdout.write_all(b"r")?;
+            stdout.queue(ResetColor)?;
+            stdout.write_all(b":run / ")?;
         }
 
         if self.done_status != DoneStatus::Pending {
-            write!(self.writer, "{}:{} / ", 'n'.bold(), "next".underlined())?;
+            stdout.queue(SetAttribute(Attribute::Bold))?;
+            stdout.write_all(b"n")?;
+            stdout.queue(ResetColor)?;
+            stdout.write_all(b":")?;
+            stdout.queue(SetAttribute(Attribute::Underlined))?;
+            stdout.write_all(b"next")?;
+            stdout.queue(ResetColor)?;
+            stdout.write_all(b" / ")?;
         }
 
         if !self.show_hint {
-            write!(self.writer, "{}:hint / ", 'h'.bold())?;
+            stdout.queue(SetAttribute(Attribute::Bold))?;
+            stdout.write_all(b"h")?;
+            stdout.queue(ResetColor)?;
+            stdout.write_all(b":hint / ")?;
         }
 
-        write!(self.writer, "{}:list / {}:quit ? ", 'l'.bold(), 'q'.bold())?;
+        stdout.queue(SetAttribute(Attribute::Bold))?;
+        stdout.write_all(b"l")?;
+        stdout.queue(ResetColor)?;
+        stdout.write_all(b":list / ")?;
 
-        self.writer.flush()
+        stdout.queue(SetAttribute(Attribute::Bold))?;
+        stdout.write_all(b"q")?;
+        stdout.queue(ResetColor)?;
+        stdout.write_all(b":quit ? ")?;
+
+        stdout.flush()
     }
 
-    pub fn render(&mut self) -> io::Result<()> {
+    pub fn render(&self, stdout: &mut StdoutLock) -> io::Result<()> {
         // Prevent having the first line shifted if clearing wasn't successful.
-        self.writer.write_all(b"\n")?;
-        clear_terminal(&mut self.writer)?;
+        stdout.write_all(b"\n")?;
+        clear_terminal(stdout)?;
 
-        self.writer.write_all(&self.output)?;
+        stdout.write_all(&self.output)?;
 
         if self.show_hint {
-            writeln!(
-                self.writer,
-                "{}\n{}\n",
-                "Hint".bold().cyan().underlined(),
-                self.app_state.current_exercise().hint,
-            )?;
+            stdout
+                .queue(SetAttributes(
+                    Attributes::from(Attribute::Bold).with(Attribute::Underlined),
+                ))?
+                .queue(SetForegroundColor(Color::Cyan))?;
+            stdout.write_all(b"Hint")?;
+            stdout.queue(ResetColor)?;
+            stdout.write_all(b"\n")?;
+
+            stdout.write_all(self.app_state.current_exercise().hint.as_bytes())?;
+            stdout.write_all(b"\n\n")?;
         }
 
         if self.done_status != DoneStatus::Pending {
-            writeln!(self.writer, "{}", "Exercise done ✓".bold().green())?;
+            stdout
+                .queue(SetAttribute(Attribute::Bold))?
+                .queue(SetForegroundColor(Color::Green))?;
+            stdout.write_all("Exercise done ✓".as_bytes())?;
+            stdout.queue(ResetColor)?;
+            stdout.write_all(b"\n")?;
 
             if let DoneStatus::DoneWithSolution(solution_path) = &self.done_status {
-                writeln!(
-                    self.writer,
-                    "{} for comparison: {}",
-                    "Solution".bold(),
-                    style(TerminalFileLink(solution_path)).underlined().cyan(),
-                )?;
+                solution_link_line(stdout, solution_path)?;
             }
 
-            writeln!(
-                self.writer,
-                "When done experimenting, enter `n` to move on to the next exercise 🦀\n",
+            stdout.write_all(
+                "When done experimenting, enter `n` to move on to the next exercise 🦀\n\n"
+                    .as_bytes(),
             )?;
         }
 
         let line_width = terminal::size()?.0;
         progress_bar(
-            &mut self.writer,
+            stdout,
             self.app_state.n_done(),
             self.app_state.exercises().len() as u16,
             line_width,
         )?;
-        writeln!(
-            self.writer,
-            "\nCurrent exercise: {}",
-            self.app_state.current_exercise().terminal_link(),
-        )?;
 
-        self.show_prompt()?;
+        stdout.write_all(b"\nCurrent exercise: ")?;
+        terminal_file_link(stdout, self.app_state.current_exercise().path, Color::Blue)?;
+        stdout.write_all(b"\n\n")?;
+
+        self.show_prompt(stdout)?;
 
         Ok(())
     }
 
-    pub fn show_hint(&mut self) -> io::Result<()> {
+    pub fn show_hint(&mut self, stdout: &mut StdoutLock) -> io::Result<()> {
         self.show_hint = true;
-        self.render()
+        self.render(stdout)
     }
 }