Merge branch 'main' into main

6 files changed, 321 insertions, 250 deletions

diff --git a/src/exercise.rs b/src/exercise.rs
index 664b362..19f528a 100644
--- a/src/exercise.rs
+++ b/src/exercise.rs
@@ -1,19 +1,33 @@
-use regex::Regex;
 use serde::Deserialize;
-use std::env;
 use std::fmt::{self, Display, Formatter};
 use std::fs::{self, remove_file, File};
-use std::io::Read;
+use std::io::{self, BufRead, BufReader};
 use std::path::PathBuf;
-use std::process::{self, Command};
+use std::process::{self, exit, Command, Stdio};
+use std::{array, env, mem};
+use winnow::ascii::{space0, Caseless};
+use winnow::combinator::opt;
+use winnow::Parser;
 
 const RUSTC_COLOR_ARGS: &[&str] = &["--color", "always"];
 const RUSTC_EDITION_ARGS: &[&str] = &["--edition", "2021"];
 const RUSTC_NO_DEBUG_ARGS: &[&str] = &["-C", "strip=debuginfo"];
-const I_AM_DONE_REGEX: &str = r"(?m)^\s*///?\s*I\s+AM\s+NOT\s+DONE";
 const CONTEXT: usize = 2;
 const CLIPPY_CARGO_TOML_PATH: &str = "./exercises/22_clippy/Cargo.toml";
 
+// Checks if the line contains the "I AM NOT DONE" comment.
+fn contains_not_done_comment(input: &str) -> bool {
+    (
+        space0::<_, ()>,
+        "//",
+        opt('/'),
+        space0,
+        Caseless("I AM NOT DONE"),
+    )
+        .parse_next(&mut &*input)
+        .is_ok()
+}
+
 // Get a temporary file name that is hopefully unique
 #[inline]
 fn temp_file() -> String {
@@ -58,7 +72,7 @@ pub struct Exercise {
 
 // An enum to track of the state of an Exercise.
 // An Exercise can be either Done or Pending
-#[derive(PartialEq, Debug)]
+#[derive(PartialEq, Eq, Debug)]
 pub enum State {
     // The state of the exercise once it's been completed
     Done,
@@ -67,7 +81,7 @@ pub enum State {
 }
 
 // The context information of a pending exercise
-#[derive(PartialEq, Debug)]
+#[derive(PartialEq, Eq, Debug)]
 pub struct ContextLine {
     // The source code that is still pending completion
     pub line: String,
@@ -148,7 +162,10 @@ path = "{}.rs""#,
                     .args(RUSTC_COLOR_ARGS)
                     .args(RUSTC_EDITION_ARGS)
                     .args(RUSTC_NO_DEBUG_ARGS)
-                    .output()
+                    .stdin(Stdio::null())
+                    .stdout(Stdio::null())
+                    .stderr(Stdio::null())
+                    .status()
                     .expect("Failed to compile!");
                 // Due to an issue with Clippy, a cargo clean is required to catch all lints.
                 // See https://github.com/rust-lang/rust-clippy/issues/2604
@@ -157,7 +174,10 @@ path = "{}.rs""#,
                 Command::new("cargo")
                     .args(["clean", "--manifest-path", CLIPPY_CARGO_TOML_PATH])
                     .args(RUSTC_COLOR_ARGS)
-                    .output()
+                    .stdin(Stdio::null())
+                    .stdout(Stdio::null())
+                    .stderr(Stdio::null())
+                    .status()
                     .expect("Failed to run 'cargo clean'");
                 Command::new("cargo")
                     .args(["clippy", "--manifest-path", CLIPPY_CARGO_TOML_PATH])
@@ -205,51 +225,101 @@ path = "{}.rs""#,
     }
 
     pub fn state(&self) -> State {
-        let mut source_file = File::open(&self.path).unwrap_or_else(|e| {
-            panic!(
-                "We were unable to open the exercise file {}! {e}",
-                self.path.display()
-            )
+        let source_file = File::open(&self.path).unwrap_or_else(|e| {
+            println!(
+                "Failed to open the exercise file {}: {e}",
+                self.path.display(),
+            );
+            exit(1);
         });
-
-        let source = {
-            let mut s = String::new();
-            source_file.read_to_string(&mut s).unwrap_or_else(|e| {
-                panic!(
-                    "We were unable to read the exercise file {}! {e}",
-                    self.path.display()
-                )
-            });
-            s
+        let mut source_reader = BufReader::new(source_file);
+
+        // Read the next line into `buf` without the newline at the end.
+        let mut read_line = |buf: &mut String| -> io::Result<_> {
+            let n = source_reader.read_line(buf)?;
+            if buf.ends_with('\n') {
+                buf.pop();
+                if buf.ends_with('\r') {
+                    buf.pop();
+                }
+            }
+            Ok(n)
         };
 
-        let re = Regex::new(I_AM_DONE_REGEX).unwrap();
+        let mut current_line_number: usize = 1;
+        // Keep the last `CONTEXT` lines while iterating over the file lines.
+        let mut prev_lines: [_; CONTEXT] = array::from_fn(|_| String::with_capacity(256));
+        let mut line = String::with_capacity(256);
 
-        if !re.is_match(&source) {
-            return State::Done;
-        }
+        loop {
+            let n = read_line(&mut line).unwrap_or_else(|e| {
+                println!(
+                    "Failed to read the exercise file {}: {e}",
+                    self.path.display(),
+                );
+                exit(1);
+            });
 
-        let matched_line_index = source
-            .lines()
-            .enumerate()
-            .find_map(|(i, line)| if re.is_match(line) { Some(i) } else { None })
-            .expect("This should not happen at all");
-
-        let min_line = ((matched_line_index as i32) - (CONTEXT as i32)).max(0) as usize;
-        let max_line = matched_line_index + CONTEXT;
-
-        let context = source
-            .lines()
-            .enumerate()
-            .filter(|&(i, _)| i >= min_line && i <= max_line)
-            .map(|(i, line)| ContextLine {
-                line: line.to_string(),
-                number: i + 1,
-                important: i == matched_line_index,
-            })
-            .collect();
+            // Reached the end of the file and didn't find the comment.
+            if n == 0 {
+                return State::Done;
+            }
 
-        State::Pending(context)
+            if contains_not_done_comment(&line) {
+                let mut context = Vec::with_capacity(2 * CONTEXT + 1);
+                // Previous lines.
+                for (ind, prev_line) in prev_lines
+                    .into_iter()
+                    .take(current_line_number - 1)
+                    .enumerate()
+                    .rev()
+                {
+                    context.push(ContextLine {
+                        line: prev_line,
+                        number: current_line_number - 1 - ind,
+                        important: false,
+                    });
+                }
+
+                // Current line.
+                context.push(ContextLine {
+                    line,
+                    number: current_line_number,
+                    important: true,
+                });
+
+                // Next lines.
+                for ind in 0..CONTEXT {
+                    let mut next_line = String::with_capacity(256);
+                    let Ok(n) = read_line(&mut next_line) else {
+                        // If an error occurs, just ignore the next lines.
+                        break;
+                    };
+
+                    // Reached the end of the file.
+                    if n == 0 {
+                        break;
+                    }
+
+                    context.push(ContextLine {
+                        line: next_line,
+                        number: current_line_number + 1 + ind,
+                        important: false,
+                    });
+                }
+
+                return State::Pending(context);
+            }
+
+            current_line_number += 1;
+            // Add the current line as a previous line and shift the older lines by one.
+            for prev_line in &mut prev_lines {
+                mem::swap(&mut line, prev_line);
+            }
+            // The current line now contains the oldest previous line.
+            // Recycle it for reading the next line.
+            line.clear();
+        }
     }
 
     // Check that the exercise looks to be solved using self.state()
@@ -375,4 +445,20 @@ mod test {
         let out = exercise.compile().unwrap().run().unwrap();
         assert!(out.stdout.contains("THIS TEST TOO SHALL PASS"));
     }
+
+    #[test]
+    fn test_not_done() {
+        assert!(contains_not_done_comment("// I AM NOT DONE"));
+        assert!(contains_not_done_comment("/// I AM NOT DONE"));
+        assert!(contains_not_done_comment("//  I AM NOT DONE"));
+        assert!(contains_not_done_comment("///  I AM NOT DONE"));
+        assert!(contains_not_done_comment("// I AM NOT DONE "));
+        assert!(contains_not_done_comment("// I AM NOT DONE!"));
+        assert!(contains_not_done_comment("// I am not done"));
+        assert!(contains_not_done_comment("// i am NOT done"));
+
+        assert!(!contains_not_done_comment("I AM NOT DONE"));
+        assert!(!contains_not_done_comment("// NOT DONE"));
+        assert!(!contains_not_done_comment("DONE"));
+    }
 }
diff --git a/src/main.rs b/src/main.rs
index a06f0c5..8f73dbb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,16 +1,18 @@
 use crate::exercise::{Exercise, ExerciseList};
-use crate::project::RustAnalyzerProject;
+use crate::project::write_project_json;
 use crate::run::{reset, run};
 use crate::verify::verify;
+use anyhow::Result;
 use clap::{Parser, Subcommand};
 use console::Emoji;
 use notify_debouncer_mini::notify::{self, RecursiveMode};
 use notify_debouncer_mini::{new_debouncer, DebouncedEventKind};
+use shlex::Shlex;
 use std::ffi::OsStr;
 use std::fs;
 use std::io::{self, prelude::*};
 use std::path::Path;
-use std::process::{Command, Stdio};
+use std::process::Command;
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::mpsc::{channel, RecvTimeoutError};
 use std::sync::{Arc, Mutex};
@@ -84,31 +86,32 @@ enum Subcommands {
     Lsp,
 }
 
-fn main() {
+fn main() -> Result<()> {
     let args = Args::parse();
 
     if args.command.is_none() {
         println!("\n{WELCOME}\n");
     }
 
-    if !Path::new("info.toml").exists() {
-        println!(
-            "{} must be run from the rustlings directory",
-            std::env::current_exe().unwrap().to_str().unwrap()
-        );
-        println!("Try `cd rustlings/`!");
-        std::process::exit(1);
-    }
-
-    if !rustc_exists() {
+    if which::which("rustc").is_err() {
         println!("We cannot find `rustc`.");
         println!("Try running `rustc --version` to diagnose your problem.");
         println!("For instructions on how to install Rust, check the README.");
         std::process::exit(1);
     }
 
-    let toml_str = &fs::read_to_string("info.toml").unwrap();
-    let exercises = toml::from_str::<ExerciseList>(toml_str).unwrap().exercises;
+    let info_file = fs::read_to_string("info.toml").unwrap_or_else(|e| {
+        match e.kind() {
+            io::ErrorKind::NotFound => println!(
+                "The program must be run from the rustlings directory\nTry `cd rustlings/`!",
+            ),
+            _ => println!("Failed to read the info.toml file: {e}"),
+        }
+        std::process::exit(1);
+    });
+    let exercises = toml_edit::de::from_str::<ExerciseList>(&info_file)
+        .unwrap()
+        .exercises;
     let verbose = args.nocapture;
 
     let command = args.command.unwrap_or_else(|| {
@@ -128,31 +131,43 @@ fn main() {
                 println!("{:<17}\t{:<46}\t{:<7}", "Name", "Path", "Status");
             }
             let mut exercises_done: u16 = 0;
-            let filters = filter.clone().unwrap_or_default().to_lowercase();
-            exercises.iter().for_each(|e| {
-                let fname = format!("{}", e.path.display());
+            let lowercase_filter = filter
+                .as_ref()
+                .map(|s| s.to_lowercase())
+                .unwrap_or_default();
+            let filters = lowercase_filter
+                .split(',')
+                .filter_map(|f| {
+                    let f = f.trim();
+                    if f.is_empty() {
+                        None
+                    } else {
+                        Some(f)
+                    }
+                })
+                .collect::<Vec<_>>();
+
+            for exercise in &exercises {
+                let fname = exercise.path.to_string_lossy();
                 let filter_cond = filters
-                    .split(',')
-                    .filter(|f| !f.trim().is_empty())
-                    .any(|f| e.name.contains(f) || fname.contains(f));
-                let status = if e.looks_done() {
+                    .iter()
+                    .any(|f| exercise.name.contains(f) || fname.contains(f));
+                let looks_done = exercise.looks_done();
+                let status = if looks_done {
                     exercises_done += 1;
                     "Done"
                 } else {
                     "Pending"
                 };
-                let solve_cond = {
-                    (e.looks_done() && solved)
-                        || (!e.looks_done() && unsolved)
-                        || (!solved && !unsolved)
-                };
+                let solve_cond =
+                    (looks_done && solved) || (!looks_done && unsolved) || (!solved && !unsolved);
                 if solve_cond && (filter_cond || filter.is_none()) {
                     let line = if paths {
                         format!("{fname}\n")
                     } else if names {
-                        format!("{}\n", e.name)
+                        format!("{}\n", exercise.name)
                     } else {
-                        format!("{:<17}\t{fname:<46}\t{status:<7}\n", e.name)
+                        format!("{:<17}\t{fname:<46}\t{status:<7}\n", exercise.name)
                     };
                     // Somehow using println! leads to the binary panicking
                     // when its output is piped.
@@ -168,7 +183,8 @@ fn main() {
                         });
                     }
                 }
-            });
+            }
+
             let percentage_progress = exercises_done as f32 / exercises.len() as f32 * 100.0;
             println!(
                 "Progress: You completed {} / {} exercises ({:.1} %).",
@@ -203,30 +219,17 @@ fn main() {
         }
 
         Subcommands::Lsp => {
-            let mut project = RustAnalyzerProject::new();
-            project
-                .get_sysroot_src()
-                .expect("Couldn't find toolchain path, do you have `rustc` installed?");
-            project
-                .exercises_to_json()
-                .expect("Couldn't parse rustlings exercises files");
-
-            if project.crates.is_empty() {
-                println!("Failed find any exercises, make sure you're in the `rustlings` folder");
-            } else if project.write_to_disk().is_err() {
-                println!("Failed to write rust-project.json to disk for rust-analyzer");
+            if let Err(e) = write_project_json(exercises) {
+                println!("Failed to write rust-project.json to disk for rust-analyzer: {e}");
             } else {
                 println!("Successfully generated rust-project.json");
-                println!("rust-analyzer will now parse exercises, restart your language server or editor")
+                println!("rust-analyzer will now parse exercises, restart your language server or editor");
             }
         }
 
         Subcommands::Watch { success_hints } => match watch(&exercises, verbose, success_hints) {
             Err(e) => {
-                println!(
-                    "Error: Could not watch your progress. Error message was {:?}.",
-                    e
-                );
+                println!("Error: Could not watch your progress. Error message was {e:?}.");
                 println!("Most likely you've run out of disk space or your 'inotify limit' has been reached.");
                 std::process::exit(1);
             }
@@ -243,56 +246,60 @@ fn main() {
             }
         },
     }
+
+    Ok(())
 }
 
 fn spawn_watch_shell(
-    failed_exercise_hint: &Arc<Mutex<Option<String>>>,
+    failed_exercise_hint: Arc<Mutex<Option<String>>>,
     should_quit: Arc<AtomicBool>,
 ) {
-    let failed_exercise_hint = Arc::clone(failed_exercise_hint);
     println!("Welcome to watch mode! You can type 'help' to get an overview of the commands you can use here.");
-    thread::spawn(move || loop {
-        let mut input = String::new();
-        match io::stdin().read_line(&mut input) {
-            Ok(_) => {
-                let input = input.trim();
-                if input == "hint" {
-                    if let Some(hint) = &*failed_exercise_hint.lock().unwrap() {
-                        println!("{hint}");
-                    }
-                } else if input == "clear" {
-                    println!("\x1B[2J\x1B[1;1H");
-                } else if input.eq("quit") {
-                    should_quit.store(true, Ordering::SeqCst);
-                    println!("Bye!");
-                } else if input.eq("help") {
-                    println!("Commands available to you in watch mode:");
-                    println!("  hint   - prints the current exercise's hint");
-                    println!("  clear  - clears the screen");
-                    println!("  quit   - quits watch mode");
-                    println!("  !<cmd> - executes a command, like `!rustc --explain E0381`");
-                    println!("  help   - displays this help message");
-                    println!();
-                    println!("Watch mode automatically re-evaluates the current exercise");
-                    println!("when you edit a file's contents.")
-                } else if let Some(cmd) = input.strip_prefix('!') {
-                    let parts: Vec<&str> = cmd.split_whitespace().collect();
-                    if parts.is_empty() {
-                        println!("no command provided");
-                    } else if let Err(e) = Command::new(parts[0]).args(&parts[1..]).status() {
-                        println!("failed to execute command `{}`: {}", cmd, e);
-                    }
-                } else {
-                    println!("unknown command: {input}");
+
+    thread::spawn(move || {
+        let mut input = String::with_capacity(32);
+        let mut stdin = io::stdin().lock();
+
+        loop {
+            // Recycle input buffer.
+            input.clear();
+
+            if let Err(e) = stdin.read_line(&mut input) {
+                println!("error reading command: {e}");
+            }
+
+            let input = input.trim();
+            if input == "hint" {
+                if let Some(hint) = &*failed_exercise_hint.lock().unwrap() {
+                    println!("{hint}");
                 }
+            } else if input == "clear" {
+                println!("\x1B[2J\x1B[1;1H");
+            } else if input == "quit" {
+                should_quit.store(true, Ordering::SeqCst);
+                println!("Bye!");
+            } else if input == "help" {
+                println!("{WATCH_MODE_HELP_MESSAGE}");
+            } else if let Some(cmd) = input.strip_prefix('!') {
+                let mut parts = Shlex::new(cmd);
+
+                let Some(program) = parts.next() else {
+                    println!("no command provided");
+                    continue;
+                };
+
+                if let Err(e) = Command::new(program).args(parts).status() {
+                    println!("failed to execute command `{cmd}`: {e}");
+                }
+            } else {
+                println!("unknown command: {input}\n{WATCH_MODE_HELP_MESSAGE}");
             }
-            Err(error) => println!("error reading command: {error}"),
         }
     });
 }
 
 fn find_exercise<'a>(name: &str, exercises: &'a [Exercise]) -> &'a Exercise {
-    if name.eq("next") {
+    if name == "next" {
         exercises
             .iter()
             .find(|e| !e.looks_done())
@@ -338,7 +345,6 @@ fn watch(
 
     clear_screen();
 
-    let to_owned_hint = |t: &Exercise| t.hint.to_owned();
     let failed_exercise_hint = match verify(
         exercises.iter(),
         (0, exercises.len()),
@@ -346,9 +352,9 @@ fn watch(
         success_hints,
     ) {
         Ok(_) => return Ok(WatchStatus::Finished),
-        Err(exercise) => Arc::new(Mutex::new(Some(to_owned_hint(exercise)))),
+        Err(exercise) => Arc::new(Mutex::new(Some(exercise.hint.clone()))),
     };
-    spawn_watch_shell(&failed_exercise_hint, Arc::clone(&should_quit));
+    spawn_watch_shell(Arc::clone(&failed_exercise_hint), Arc::clone(&should_quit));
     loop {
         match rx.recv_timeout(Duration::from_secs(1)) {
             Ok(event) => match event {
@@ -383,7 +389,7 @@ fn watch(
                                 Err(exercise) => {
                                     let mut failed_exercise_hint =
                                         failed_exercise_hint.lock().unwrap();
-                                    *failed_exercise_hint = Some(to_owned_hint(exercise));
+                                    *failed_exercise_hint = Some(exercise.hint.clone());
                                 }
                             }
                         }
@@ -403,19 +409,7 @@ fn watch(
     }
 }
 
-fn rustc_exists() -> bool {
-    Command::new("rustc")
-        .args(["--version"])
-        .stdout(Stdio::null())
-        .stderr(Stdio::null())
-        .stdin(Stdio::null())
-        .spawn()
-        .and_then(|mut child| child.wait())
-        .map(|status| status.success())
-        .unwrap_or(false)
-}
-
-const DEFAULT_OUT: &str = r#"Thanks for installing Rustlings!
+const DEFAULT_OUT: &str = "Thanks for installing Rustlings!
 
 Is this your first time? Don't worry, Rustlings was made for beginners! We are
 going to teach you a lot of things about Rust, but before we can get
@@ -441,7 +435,7 @@ started, here's a couple of notes about how Rustlings operates:
    autocompletion, run the command `rustlings lsp`.
 
 Got all that? Great! To get started, run `rustlings watch` in order to get the first
-exercise. Make sure to have your editor open!"#;
+exercise. Make sure to have your editor open!";
 
 const FENISH_LINE: &str = "+----------------------------------------------------+
 |          You made it to the Fe-nish line!          |
@@ -477,3 +471,13 @@ const WELCOME: &str = r"       welcome to...
  | |  | |_| \__ \ |_| | | | | | (_| \__ \
  |_|   \__,_|___/\__|_|_|_| |_|\__, |___/
                                |___/";
+
+const WATCH_MODE_HELP_MESSAGE: &str = "Commands available to you in watch mode:
+  hint   - prints the current exercise's hint
+  clear  - clears the screen
+  quit   - quits watch mode
+  !<cmd> - executes a command, like `!rustc --explain E0381`
+  help   - displays this help message
+
+Watch mode automatically re-evaluates the current exercise
+when you edit a file's contents.";
diff --git a/src/project.rs b/src/project.rs
index 00fc304..0f56de9 100644
--- a/src/project.rs
+++ b/src/project.rs
@@ -1,102 +1,83 @@
-use glob::glob;
-use serde::{Deserialize, Serialize};
+use anyhow::{Context, Result};
+use serde::Serialize;
 use std::env;
-use std::error::Error;
-use std::path::{Path, PathBuf};
-use std::process::Command;
+use std::path::PathBuf;
+use std::process::{Command, Stdio};
+
+use crate::exercise::Exercise;
 
 /// Contains the structure of resulting rust-project.json file
 /// and functions to build the data required to create the file
-#[derive(Serialize, Deserialize)]
-pub struct RustAnalyzerProject {
-    sysroot_src: String,
-    pub crates: Vec<Crate>,
+#[derive(Serialize)]
+struct RustAnalyzerProject {
+    sysroot_src: PathBuf,
+    crates: Vec<Crate>,
 }
 
-#[derive(Serialize, Deserialize)]
-pub struct Crate {
-    root_module: String,
-    edition: String,
-    deps: Vec<String>,
-    cfg: Vec<String>,
+#[derive(Serialize)]
+struct Crate {
+    root_module: PathBuf,
+    edition: &'static str,
+    // Not used, but required in the JSON file.
+    deps: Vec<()>,
+    // Only `test` is used for all crates.
+    // Therefore, an array is used instead of a `Vec`.
+    cfg: [&'static str; 1],
 }
 
 impl RustAnalyzerProject {
-    pub fn new() -> RustAnalyzerProject {
-        RustAnalyzerProject {
-            sysroot_src: String::new(),
-            crates: Vec::new(),
-        }
-    }
-
-    /// Write rust-project.json to disk
-    pub fn write_to_disk(&self) -> Result<(), std::io::Error> {
-        std::fs::write(
-            "./rust-project.json",
-            serde_json::to_vec(&self).expect("Failed to serialize to JSON"),
-        )?;
-        Ok(())
-    }
+    fn build(exercises: Vec<Exercise>) -> Result<Self> {
+        let crates = exercises
+            .into_iter()
+            .map(|exercise| Crate {
+                root_module: exercise.path,
+                edition: "2021",
+                deps: Vec::new(),
+                // This allows rust_analyzer to work inside `#[test]` blocks
+                cfg: ["test"],
+            })
+            .collect();
 
-    /// If path contains .rs extension, add a crate to `rust-project.json`
-    fn path_to_json(&mut self, path: PathBuf) -> Result<(), Box<dyn Error>> {
-        if let Some(ext) = path.extension() {
-            if ext == "rs" {
-                self.crates.push(Crate {
-                    root_module: path.display().to_string(),
-                    edition: "2021".to_string(),
-                    deps: Vec::new(),
-                    // This allows rust_analyzer to work inside #[test] blocks
-                    cfg: vec!["test".to_string()],
-                })
-            }
-        }
-
-        Ok(())
-    }
-
-    /// Parse the exercises folder for .rs files, any matches will create
-    /// a new `crate` in rust-project.json which allows rust-analyzer to
-    /// treat it like a normal binary
-    pub fn exercises_to_json(&mut self) -> Result<(), Box<dyn Error>> {
-        for path in glob("./exercises/**/*")? {
-            self.path_to_json(path?)?;
-        }
-        Ok(())
-    }
-
-    /// Use `rustc` to determine the default toolchain
-    pub fn get_sysroot_src(&mut self) -> Result<(), Box<dyn Error>> {
-        // check if RUST_SRC_PATH is set
-        if let Ok(path) = env::var("RUST_SRC_PATH") {
-            self.sysroot_src = path;
-            return Ok(());
+        if let Some(path) = env::var_os("RUST_SRC_PATH") {
+            return Ok(Self {
+                sysroot_src: PathBuf::from(path),
+                crates,
+            });
         }
 
         let toolchain = Command::new("rustc")
             .arg("--print")
             .arg("sysroot")
-            .output()?
+            .stderr(Stdio::inherit())
+            .output()
+            .context("Failed to get the sysroot from `rustc`. Do you have `rustc` installed?")?
             .stdout;
 
-        let toolchain = String::from_utf8(toolchain)?;
+        let toolchain =
+            String::from_utf8(toolchain).context("The toolchain path is invalid UTF8")?;
         let toolchain = toolchain.trim_end();
-
         println!("Determined toolchain: {toolchain}\n");
 
-        let Ok(path) = Path::new(toolchain)
-            .join("lib")
-            .join("rustlib")
-            .join("src")
-            .join("rust")
-            .join("library")
-            .into_os_string()
-            .into_string()
-        else {
-            return Err("The sysroot path is invalid UTF8".into());
-        };
-        self.sysroot_src = path;
+        let mut sysroot_src = PathBuf::with_capacity(256);
+        sysroot_src.extend([toolchain, "lib", "rustlib", "src", "rust", "library"]);
 
-        Ok(())
+        Ok(Self {
+            sysroot_src,
+            crates,
+        })
     }
 }
+
+/// Write `rust-project.json` to disk.
+pub fn write_project_json(exercises: Vec<Exercise>) -> Result<()> {
+    let content = RustAnalyzerProject::build(exercises)?;
+
+    // Using the capacity 2^14 since the file length in bytes is higher than 2^13.
+    // The final length is not known exactly because it depends on the user's sysroot path,
+    // the current number of exercises etc.
+    let mut buf = Vec::with_capacity(1 << 14);
+    serde_json::to_writer(&mut buf, &content)?;
+    std::fs::write("rust-project.json", buf)?;
+
+    Ok(())
+}
diff --git a/src/run.rs b/src/run.rs
index e0ada4c..6dd0388 100644
--- a/src/run.rs
+++ b/src/run.rs
@@ -21,7 +21,8 @@ pub fn run(exercise: &Exercise, verbose: bool) -> Result<(), ()> {
 // Resets the exercise by stashing the changes.
 pub fn reset(exercise: &Exercise) -> Result<(), ()> {
     let command = Command::new("git")
-        .args(["stash", "--"])
+        .arg("stash")
+        .arg("--")
         .arg(&exercise.path)
         .spawn();
 
diff --git a/src/ui.rs b/src/ui.rs
index 74835e1..d8177b9 100644
--- a/src/ui.rs
+++ b/src/ui.rs
@@ -1,5 +1,5 @@
 macro_rules! print_emoji {
-    ($emoji:expr, $sign:expr, $color: ident ,$fmt:literal, $ex:expr) => {{
+    ($emoji:expr, $sign:expr, $color: ident, $fmt:literal, $ex:expr) => {{
         use console::{style, Emoji};
         use std::env;
         let formatstr = format!($fmt, $ex);
diff --git a/src/verify.rs b/src/verify.rs
index cafecab..dac2562 100644
--- a/src/verify.rs
+++ b/src/verify.rs
@@ -24,7 +24,7 @@ pub fn verify<'a>(
             .progress_chars("#>-"),
     );
     bar.set_position(num_done as u64);
-    bar.set_message(format!("({:.1} %)", percentage));
+    bar.set_message(format!("({percentage:.1} %)"));
 
     for exercise in exercises {
         let compile_result = match exercise.mode {
@@ -37,7 +37,7 @@ pub fn verify<'a>(
         }
         percentage += 100.0 / total as f32;
         bar.inc(1);
-        bar.set_message(format!("({:.1} %)", percentage));
+        bar.set_message(format!("({percentage:.1} %)"));
         if bar.position() == total as u64 {
             println!(
                 "Progress: You completed {} / {} exercises ({:.1} %).",
@@ -51,6 +51,7 @@ pub fn verify<'a>(
     Ok(())
 }
 
+#[derive(PartialEq, Eq)]
 enum RunMode {
     Interactive,
     NonInteractive,
@@ -124,7 +125,7 @@ fn compile_and_test(
             if verbose {
                 println!("{}", output.stdout);
             }
-            if let RunMode::Interactive = run_mode {
+            if run_mode == RunMode::Interactive {
                 Ok(prompt_for_completion(exercise, None, success_hints))
             } else {
                 Ok(true)
@@ -191,27 +192,25 @@ fn prompt_for_completion(
         Mode::Test => "The code is compiling, and the tests pass!",
         Mode::Clippy => clippy_success_msg,
     };
-    println!();
+
     if no_emoji {
-        println!("~*~ {success_msg} ~*~")
+        println!("\n~*~ {success_msg} ~*~\n");
     } else {
-        println!("🎉 🎉 {success_msg} 🎉 🎉")
+        println!("\n🎉 🎉 {success_msg} 🎉 🎉\n");
     }
-    println!();
 
     if let Some(output) = prompt_output {
-        println!("Output:");
-        println!("{}", separator());
-        println!("{output}");
-        println!("{}", separator());
-        println!();
+        println!(
+            "Output:\n{separator}\n{output}\n{separator}\n",
+            separator = separator(),
+        );
     }
     if success_hints {
-        println!("Hints:");
-        println!("{}", separator());
-        println!("{}", exercise.hint);
-        println!("{}", separator());
-        println!();
+        println!(
+            "Hints:\n{separator}\n{}\n{separator}\n",
+            exercise.hint,
+            separator = separator(),
+        );
     }
 
     println!("You can keep working on this exercise,");
@@ -224,14 +223,14 @@ fn prompt_for_completion(
         let formatted_line = if context_line.important {
             format!("{}", style(context_line.line).bold())
         } else {
-            context_line.line.to_string()
+            context_line.line
         };
 
         println!(
             "{:>2} {}  {}",
             style(context_line.number).blue().bold(),
             style("|").blue(),
-            formatted_line
+            formatted_line,
         );
     }