Merge 59e8f70e55 into 8df66f7991

update struct name in hashmap3

.github/workflows/rust.yml

@@ -24,8 +24,6 @@ jobs:
           globs: "exercises/**/*.md"
       - name: Run cargo fmt
         run: cargo fmt --all --check
-      - name: Run rustfmt on solutions
-        run: rustfmt --check --edition 2021 --color always solutions/**/*.rs
   test:
     runs-on: ${{ matrix.os }}
     strategy:

CHANGELOG.md

@@ -1,3 +1,14 @@
+<a name="6.2.0"></a>
+
+## 6.2.0 (2024-08-08)
+
+- Show a helpful error message when trying to install Rustlings with a Rust version lower than the minimum one that Rustlings supports.
+- Remove the state file and the solutions directory from the generated `.gitignore` file.
+- Add a `README.md` file to the `solutions/` directory.
+- Run the final check of all exercises in parallel.
+- Small exercise improvements.
+- `dev check`: Check that all solutions are formatted with `rustfmt`.
+
 <a name="6.1.0"></a>
 
 ## 6.1.0 (2024-07-10)

Cargo.lock

@@ -116,9 +116,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "clap"
-version = "4.5.11"
+version = "4.5.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "35723e6a11662c2afb578bcf0b88bf6ea8e21282a953428f240574fcc3a2b5b3"
+checksum = "0fbb260a053428790f3de475e304ff84cdbc4face759ea7a3e64c1edd938a7fc"
 dependencies = [
  "clap_builder",
  "clap_derive",
@@ -126,9 +126,9 @@ dependencies = [
 
 [[package]]
 name = "clap_builder"
-version = "4.5.11"
+version = "4.5.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "49eb96cbfa7cfa35017b7cd548c75b14c3118c98b423041d70562665e07fb0fa"
+checksum = "64b17d7ea74e9f833c7dbf2cbe4fb12ff26783eda4782a8975b72f895c9b4d99"
 dependencies = [
  "anstream",
  "anstyle",
@@ -138,9 +138,9 @@ dependencies = [
 
 [[package]]
 name = "clap_derive"
-version = "4.5.11"
+version = "4.5.13"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5d029b67f89d30bbb547c89fd5161293c0aec155fc691d7924b64550662db93e"
+checksum = "501d359d5f3dcaf6ecdeee48833ae73ec6e42723a1e52419c79abf9507eec0a0"
 dependencies = [
  "heck",
  "proc-macro2",
@@ -264,9 +264,9 @@ checksum = "2304e00983f87ffb38b55b444b5e3b60a884b5d30c0fca7d82fe33449bbe55ea"
 
 [[package]]
 name = "indexmap"
-version = "2.2.6"
+version = "2.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "168fb715dda47215e360912c096649d23d58bf392ac62f73919e831745e40f26"
+checksum = "de3fc2e30ba82dd1b3911c8de1ffc143c74a914a14e99514d7637e3099df5ea0"
 dependencies = [
  "equivalent",
  "hashbrown",
@@ -357,9 +357,9 @@ checksum = "a7a70ba024b9dc04c27ea2f0c0548feb474ec5c54bba33a7f72f873a39d07b24"
 
 [[package]]
 name = "lru"
-version = "0.12.3"
+version = "0.12.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d3262e75e648fce39813cb56ac41f3c3e3f65217ebf3844d818d1f9398cfb0dc"
+checksum = "37ee39891760e7d94734f6f63fedc29a2e4a152f836120753a72503f09fcf904"
 dependencies = [
  "hashbrown",
 ]
@@ -419,12 +419,12 @@ checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
 
 [[package]]
 name = "os_pipe"
-version = "1.2.0"
+version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29d73ba8daf8fac13b0501d1abeddcfe21ba7401ada61a819144b6c2a4f32209"
+checksum = "5ffd2b0a5634335b135d5728d84c5e0fd726954b87111f7506a61c502280d982"
 dependencies = [
  "libc",
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -587,20 +587,21 @@ dependencies = [
 
 [[package]]
 name = "serde_json"
-version = "1.0.120"
+version = "1.0.122"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4e0d21c9a8cae1235ad58a00c11cb40d4b1e5c784f1ef2c537876ed6ffd8b7c5"
+checksum = "784b6203951c57ff748476b126ccb5e8e2959a5c19e5c617ab1956be3dbc68da"
 dependencies = [
  "itoa",
+ "memchr",
  "ryu",
  "serde",
 ]
 
 [[package]]
 name = "serde_spanned"
-version = "0.6.6"
+version = "0.6.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "79e674e01f999af37c49f70a6ede167a8a60b2503e56c5599532a65baa5969a0"
+checksum = "eb5b1b31579f3811bf615c144393417496f152e12ac8b7663bf664f4a815306d"
 dependencies = [
  "serde",
 ]
@@ -617,9 +618,9 @@ dependencies = [
 
 [[package]]
 name = "signal-hook-mio"
-version = "0.2.3"
+version = "0.2.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "29ad2e15f37ec9a6cc544097b78a1ec90001e9f71b81338ca39f430adaca99af"
+checksum = "34db1a06d485c9142248b7a054f034b349b212551f3dfd19c94d45a754a217cd"
 dependencies = [
  "libc",
  "mio",
@@ -698,18 +699,18 @@ dependencies = [
 
 [[package]]
 name = "toml_datetime"
-version = "0.6.6"
+version = "0.6.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4badfd56924ae69bcc9039335b2e017639ce3f9b001c393c1b2d1ef846ce2cbf"
+checksum = "0dd7358ecb8fc2f8d014bf86f6f638ce72ba252a2c3a2572f2a795f1d23efb41"
 dependencies = [
  "serde",
 ]
 
 [[package]]
 name = "toml_edit"
-version = "0.22.16"
+version = "0.22.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "278f3d518e152219c994ce877758516bca5e118eaed6996192a774fb9fbf0788"
+checksum = "583c44c02ad26b0c3f3066fe629275e50627026c51ac2e595cca4c230ce1ce1d"
 dependencies = [
  "indexmap",
  "serde",
@@ -755,9 +756,9 @@ checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
 
 [[package]]
 name = "version_check"
-version = "0.9.4"
+version = "0.9.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
+checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
 [[package]]
 name = "walkdir"
@@ -793,11 +794,11 @@ checksum = "ac3b87c63620426dd9b991e5ce0329eff545bccbbb34f3be09ff6fb6ab51b7b6"
 
 [[package]]
 name = "winapi-util"
-version = "0.1.8"
+version = "0.1.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4d4cc384e1e73b93bafa6fb4f1df8c41695c8a91cf9c4c64358067d15a7b6c6b"
+checksum = "cf221c93e13a30d793f7645a0e7762c55d169dbb0a49671918a2319d289b10bb"
 dependencies = [
- "windows-sys 0.52.0",
+ "windows-sys 0.59.0",
 ]
 
 [[package]]
@@ -824,6 +825,15 @@ dependencies = [
  "windows-targets 0.52.6",
 ]
 
+[[package]]
+name = "windows-sys"
+version = "0.59.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e38bc4d79ed67fd075bcc251a1c39b32a1776bbe92e5bef1f0bf1f8c531853b"
+dependencies = [
+ "windows-targets 0.52.6",
+]
+
 [[package]]
 name = "windows-targets"
 version = "0.48.5"
@@ -947,9 +957,9 @@ checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
 
 [[package]]
 name = "winnow"
-version = "0.6.15"
+version = "0.6.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "557404e450152cd6795bb558bca69e43c585055f4606e3bcae5894fc6dac9ba0"
+checksum = "68a9bda4691f099d435ad181000724da8e5899daa10713c2d432552b9ccd3a6f"
 dependencies = [
  "memchr",
 ]

Cargo.toml

@@ -8,18 +8,19 @@ exclude = [
 [workspace.package]
 version = "6.1.0"
 authors = [
-  "Liv <mokou@fastmail.com>",
-  "Mo Bitar <mo8it@proton.me>",
+  "Mo Bitar <mo8it@proton.me>", # https://github.com/mo8it
+  "Liv <mokou@fastmail.com>", # https://github.com/shadows-withal
   # Alumni
-  "Carol (Nichols || Goulding) <carol.nichols@gmail.com>",
+  "Carol (Nichols || Goulding) <carol.nichols@gmail.com>", # https://github.com/carols10cents
 ]
 repository = "https://github.com/rust-lang/rustlings"
 license = "MIT"
-edition = "2021"
+edition = "2021" # On Update: Update the edition of the `rustfmt` command that checks the solutions.
+rust-version = "1.80"
 
 [workspace.dependencies]
 serde = { version = "1.0.204", features = ["derive"] }
-toml_edit = { version = "0.22.16", default-features = false, features = ["parse", "serde"] }
+toml_edit = { version = "0.22.20", default-features = false, features = ["parse", "serde"] }
 
 [package]
 name = "rustlings"
@@ -29,6 +30,7 @@ authors.workspace = true
 repository.workspace = true
 license.workspace = true
 edition.workspace = true
+rust-version.workspace = true
 keywords = [
   "exercise",
   "learning",
@@ -45,13 +47,13 @@ include = [
 
 [dependencies]
 anyhow = "1.0.86"
-clap = { version = "4.5.11", features = ["derive"] }
+clap = { version = "4.5.13", features = ["derive"] }
 hashbrown = "0.14.5"
 notify-debouncer-mini = { version = "0.4.1", default-features = false }
-os_pipe = "1.2.0"
+os_pipe = "1.2.1"
 ratatui = { version = "0.27.0", default-features = false, features = ["crossterm"] }
 rustlings-macros = { path = "rustlings-macros", version = "=6.1.0" }
-serde_json = "1.0.120"
+serde_json = "1.0.122"
 serde.workspace = true
 toml_edit.workspace = true
 
@@ -63,3 +65,7 @@ panic = "abort"
 
 [package.metadata.release]
 pre-release-hook = ["./release-hook.sh"]
+
+# TODO: Remove after the following fix is released: https://github.com/rust-lang/rust-clippy/pull/13102
+[lints.clippy]
+needless_option_as_deref = "allow"

README.md

@@ -17,7 +17,7 @@ It contains code examples and exercises similar to Rustlings, but online.
 
 ### Installing Rust
 
-Before installing Rustlings, you need to have _Rust installed_.
+Before installing Rustlings, you need to have the **latest version of Rust** installed.
 Visit [www.rust-lang.org/tools/install](https://www.rust-lang.org/tools/install) for further instructions on installing Rust.
 This will also install _Cargo_, Rust's package/project manager.
 
@@ -88,8 +88,6 @@ While working with Rustlings, please use a modern terminal for the best user exp
 The default terminal on Linux and Mac should be sufficient.
 On Windows, we recommend the [Windows Terminal](https://aka.ms/terminal).
 
-If you use VS Code, the builtin terminal should also be fine.
-
 ## Doing exercises
 
 The exercises are sorted by topic and can be found in the subdirectory `exercises/<topic>`.

dev/Cargo.toml

@@ -116,6 +116,8 @@ bin = [
   { name = "generics1_sol", path = "../solutions/14_generics/generics1.rs" },
   { name = "generics2", path = "../exercises/14_generics/generics2.rs" },
   { name = "generics2_sol", path = "../solutions/14_generics/generics2.rs" },
+  { name = "generics3", path = "../exercises/14_generics/generics3.rs" },
+  { name = "generics3_sol", path = "../solutions/14_generics/generics3.rs" },
   { name = "traits1", path = "../exercises/15_traits/traits1.rs" },
   { name = "traits1_sol", path = "../solutions/15_traits/traits1.rs" },
   { name = "traits2", path = "../exercises/15_traits/traits2.rs" },
@@ -195,3 +197,9 @@ name = "exercises"
 edition = "2021"
 # Don't publish the exercises on crates.io!
 publish = false
+
+[profile.release]
+panic = "abort"
+
+[profile.dev]
+panic = "abort"

exercises/11_hashmaps/hashmaps3.rs

@@ -10,12 +10,12 @@ use std::collections::HashMap;
 
 // A structure to store the goal details of a team.
 #[derive(Default)]
-struct Team {
+struct TeamScores {
     goals_scored: u8,
     goals_conceded: u8,
 }
 
-fn build_scores_table(results: &str) -> HashMap<&str, Team> {
+fn build_scores_table(results: &str) -> HashMap<&str, TeamScores> {
     // The name of the team is the key and its associated struct is the value.
     let mut scores = HashMap::new();
 

exercises/13_error_handling/errors6.rs

@@ -25,7 +25,7 @@ impl ParsePosNonzeroError {
     }
 
     // TODO: Add another error conversion function here.
-    // fn from_parseint(???) -> Self { ??? }
+    // fn from_parse_int(???) -> Self { ??? }
 }
 
 #[derive(PartialEq, Debug)]

exercises/14_generics/generics3.rs

@@ -0,0 +1,54 @@
+// generics3.rs
+// Execute `rustlings hint generics3` or use the `hint` watch subcommand for a hint.
+
+// This function should take an array of `Option` elements and returns array of not None elements
+// TODO fix this function signature
+fn into_dispose_nulls(list: Vec<Option<&str>>) -> Vec<&str> {
+    list.into_iter().flatten().collect()
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn store_str_on_list() {
+        let names_list = vec![Some("maria"), Some("jacob"), None, Some("kacper"), None];
+        let only_values = into_dispose_nulls(names_list);
+        assert_eq!(only_values.len(), 3);
+    }
+
+    #[test]
+    fn store_numbers_on_list() {
+        let numbers_list = vec![Some(1), Some(2), None, Some(3)];
+        let only_values = into_dispose_nulls(numbers_list);
+        assert_eq!(only_values.len(), 3);
+    }
+
+    #[test]
+    fn store_custom_type_on_list() {
+        #[allow(dead_code)]
+        struct Rectangle {
+            width: i32,
+            height: i32,
+        }
+        impl Rectangle {
+            fn new(width: i32, height: i32) -> Self {
+                Self { width, height }
+            }
+        }
+
+        let custom_list = vec![
+            Some(Rectangle::new(1, 2)),
+            None,
+            None,
+            Some(Rectangle::new(3, 4)),
+        ];
+        let only_values = into_dispose_nulls(custom_list);
+        assert_eq!(only_values.len(), 2);
+    }
+}

release-hook.sh

@@ -9,6 +9,5 @@ cargo upgrades
 # Similar to CI
 cargo clippy -- --deny warnings
 cargo fmt --all --check
-rustfmt --check --edition 2021 solutions/**/*.rs
 cargo test --workspace --all-targets
 cargo run -- dev check --require-solutions

rustlings-macros/Cargo.toml

@@ -6,6 +6,7 @@ authors.workspace = true
 repository.workspace = true
 license.workspace = true
 edition.workspace = true
+rust-version.workspace = true
 include = [
   "/src/",
   "/info.toml",

rustlings-macros/info.toml

@@ -571,7 +571,7 @@ name = "hashmaps3"
 dir = "11_hashmaps"
 hint = """
 Hint 1: Use the `entry()` and `or_insert()` (or `or_insert_with()`) methods of
-        `HashMap` to insert the default value of `Team` if a team doesn't
+        `HashMap` to insert the default value of `TeamScores` if a team doesn't
         exist in the table yet.
 
 Learn more in The Book:
@@ -744,6 +744,17 @@ hint = """
 Related section in The Book:
 https://doc.rust-lang.org/book/ch10-01-syntax.html#in-method-definitions"""
 
+[[exercises]]
+name = "generics3"
+dir = "14_generics"
+hint = """
+Vectors in Rust use generics to create dynamically-sized arrays of any type.
+The `into_dispose_nulls` function takes a vector as an argument, but only accepts vectors that store the &str type.
+To allow the function to accept vectors that store any type, you can leverage your knowledge about generics.
+If you're unsure how to proceed, please refer to the Rust Book at:
+https://doc.rust-lang.org/book/ch10-01-syntax.html#in-function-definitions.
+"""
+
 # TRAITS
 
 [[exercises]]

solutions/11_hashmaps/hashmaps3.rs

@@ -10,12 +10,12 @@ use std::collections::HashMap;
 
 // A structure to store the goal details of a team.
 #[derive(Default)]
-struct Team {
+struct TeamScores {
     goals_scored: u8,
     goals_conceded: u8,
 }
 
-fn build_scores_table(results: &str) -> HashMap<&str, Team> {
+fn build_scores_table(results: &str) -> HashMap<&str, TeamScores> {
     // The name of the team is the key and its associated struct is the value.
     let mut scores = HashMap::new();
 
@@ -28,13 +28,17 @@ fn build_scores_table(results: &str) -> HashMap<&str, Team> {
         let team_2_score: u8 = split_iterator.next().unwrap().parse().unwrap();
 
         // Insert the default with zeros if a team doesn't exist yet.
-        let team_1 = scores.entry(team_1_name).or_insert_with(Team::default);
+        let team_1 = scores
+            .entry(team_1_name)
+            .or_insert_with(TeamScores::default);
         // Update the values.
         team_1.goals_scored += team_1_score;
         team_1.goals_conceded += team_2_score;
 
         // Similarely for the second team.
-        let team_2 = scores.entry(team_2_name).or_insert_with(Team::default);
+        let team_2 = scores
+            .entry(team_2_name)
+            .or_insert_with(TeamScores::default);
         team_2.goals_scored += team_2_score;
         team_2.goals_conceded += team_1_score;
     }

solutions/13_error_handling/errors6.rs

@@ -24,7 +24,7 @@ impl ParsePosNonzeroError {
         Self::Creation(err)
     }
 
-    fn from_parseint(err: ParseIntError) -> Self {
+    fn from_parse_int(err: ParseIntError) -> Self {
         Self::ParseInt(err)
     }
 }
@@ -44,7 +44,7 @@ impl PositiveNonzeroInteger {
     fn parse(s: &str) -> Result<Self, ParsePosNonzeroError> {
         // Return an appropriate error instead of panicking when `parse()`
         // returns an error.
-        let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parseint)?;
+        let x: i64 = s.parse().map_err(ParsePosNonzeroError::from_parse_int)?;
         //                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
         Self::new(x).map_err(ParsePosNonzeroError::from_creation)
     }

solutions/14_generics/generics3.rs

@@ -0,0 +1,53 @@
+// generics3.rs
+// Execute `rustlings hint generics3` or use the `hint` watch subcommand for a hint.
+
+// Here we added generic type `T` to function signature
+// Now this function can be used with vector of any
+fn into_dispose_nulls<T>(list: Vec<Option<T>>) -> Vec<T> {
+    list.into_iter().flatten().collect()
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn store_str_on_list() {
+        let names_list = vec![Some("maria"), Some("jacob"), None, Some("kacper"), None];
+        let only_values = into_dispose_nulls(names_list);
+        assert_eq!(only_values.len(), 3);
+    }
+
+    #[test]
+    fn store_numbers_on_list() {
+        let numbers_list = vec![Some(1), Some(2), None, Some(3)];
+        let only_values = into_dispose_nulls(numbers_list);
+        assert_eq!(only_values.len(), 3);
+    }
+
+    #[test]
+    fn store_custom_type_on_list() {
+        struct Rectangle {
+            width: i32,
+            height: i32,
+        }
+        impl Rectangle {
+            fn new(width: i32, height: i32) -> Self {
+                Self { width, height }
+            }
+        }
+
+        let custom_list = vec![
+            Some(Rectangle::new(1, 2)),
+            None,
+            None,
+            Some(Rectangle::new(3, 4)),
+        ];
+        let only_values = into_dispose_nulls(custom_list);
+        assert_eq!(only_values.len(), 2);
+    }
+}

solutions/README.md

@@ -0,0 +1,6 @@
+# Official Rustlings solutions
+
+Before you finish an exercise, its solution file will only contain an empty `main` function.
+The content of this file will be automatically replaced by the actual solution once you finish the exercise.
+
+Note that these solution are often only _one possibility_ to solve an exercise.

src/app_state.rs

@@ -1,19 +1,18 @@
-use anyhow::{bail, Context, Result};
-use ratatui::crossterm::style::Stylize;
-use serde::Deserialize;
+use anyhow::{bail, Context, Error, Result};
 use std::{
     fs::{self, File},
     io::{Read, StdoutLock, Write},
-    path::{Path, PathBuf},
+    path::Path,
     process::{Command, Stdio},
+    thread,
 };
 
 use crate::{
     clear_terminal,
+    cmd::CmdRunner,
     embedded::EMBEDDED_FILES,
-    exercise::{Exercise, RunnableExercise, OUTPUT_CAPACITY},
+    exercise::{Exercise, RunnableExercise},
     info_file::ExerciseInfo,
-    DEBUG_PROFILE,
 };
 
 const STATE_FILE_NAME: &str = ".rustlings-state.txt";
@@ -34,31 +33,6 @@ pub enum StateFileStatus {
     NotRead,
 }
 
-// Parses parts of the output of `cargo metadata`.
-#[derive(Deserialize)]
-struct CargoMetadata {
-    target_directory: PathBuf,
-}
-
-pub fn parse_target_dir() -> Result<PathBuf> {
-    // Get the target directory from Cargo.
-    let metadata_output = Command::new("cargo")
-        .arg("metadata")
-        .arg("-q")
-        .arg("--format-version")
-        .arg("1")
-        .arg("--no-deps")
-        .stdin(Stdio::null())
-        .stderr(Stdio::inherit())
-        .output()
-        .context(CARGO_METADATA_ERR)?
-        .stdout;
-
-    serde_json::de::from_slice::<CargoMetadata>(&metadata_output)
-        .context("Failed to read the field `target_directory` from the `cargo metadata` output")
-        .map(|metadata| metadata.target_directory)
-}
-
 pub struct AppState {
     current_exercise_ind: usize,
     exercises: Vec<Exercise>,
@@ -68,8 +42,7 @@ pub struct AppState {
     // Preallocated buffer for reading and writing the state file.
     file_buf: Vec<u8>,
     official_exercises: bool,
-    // Cargo's target directory.
-    target_dir: PathBuf,
+    cmd_runner: CmdRunner,
 }
 
 impl AppState {
@@ -123,7 +96,7 @@ impl AppState {
         exercise_infos: Vec<ExerciseInfo>,
         final_message: String,
     ) -> Result<(Self, StateFileStatus)> {
-        let target_dir = parse_target_dir()?;
+        let cmd_runner = CmdRunner::build()?;
 
         let exercises = exercise_infos
             .into_iter()
@@ -134,8 +107,7 @@ impl AppState {
                 let path = exercise_info.path().leak();
                 let name = exercise_info.name.leak();
                 let dir = exercise_info.dir.map(|dir| &*dir.leak());
-
-                let hint = exercise_info.hint.trim().to_owned();
+                let hint = exercise_info.hint.leak().trim_ascii();
 
                 Exercise {
                     dir,
@@ -157,7 +129,7 @@ impl AppState {
             final_message,
             file_buf: Vec::with_capacity(2048),
             official_exercises: !Path::new("info.toml").exists(),
-            target_dir,
+            cmd_runner,
         };
 
         let state_file_status = slf.update_from_file();
@@ -186,8 +158,8 @@ impl AppState {
     }
 
     #[inline]
-    pub fn target_dir(&self) -> &Path {
-        &self.target_dir
+    pub fn cmd_runner(&self) -> &CmdRunner {
+        &self.cmd_runner
     }
 
     // Write the state file.
@@ -336,7 +308,7 @@ impl AppState {
     /// Official exercises: Dump the solution file form the binary and return its path.
     /// Third-party exercises: Check if a solution file exists and return its path in that case.
     pub fn current_solution_path(&self) -> Result<Option<String>> {
-        if DEBUG_PROFILE {
+        if cfg!(debug_assertions) {
             return Ok(None);
         }
 
@@ -373,34 +345,49 @@ impl AppState {
 
         if let Some(ind) = self.next_pending_exercise_ind() {
             self.set_current_exercise_ind(ind)?;
-
             return Ok(ExercisesProgress::NewPending);
         }
 
         writer.write_all(RERUNNING_ALL_EXERCISES_MSG)?;
 
-        let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
-        for (exercise_ind, exercise) in self.exercises().iter().enumerate() {
-            write!(writer, "Running {exercise} ... ")?;
-            writer.flush()?;
+        let n_exercises = self.exercises.len();
 
-            let success = exercise.run_exercise(&mut output, &self.target_dir)?;
-            if !success {
-                writeln!(writer, "{}\n", "FAILED".red())?;
+        let pending_exercise_ind = thread::scope(|s| {
+            let handles = self
+                .exercises
+                .iter_mut()
+                .map(|exercise| {
+                    s.spawn(|| {
+                        let success = exercise.run_exercise(None, &self.cmd_runner)?;
+                        exercise.done = success;
+                        Ok::<_, Error>(success)
+                    })
+                })
+                .collect::<Vec<_>>();
 
-                self.current_exercise_ind = exercise_ind;
+            for (exercise_ind, handle) in handles.into_iter().enumerate() {
+                write!(writer, "\rProgress: {exercise_ind}/{n_exercises}")?;
+                writer.flush()?;
 
-                // No check if the exercise is done before setting it to pending
-                // because no pending exercise was found.
-                self.exercises[exercise_ind].done = false;
-                self.n_done -= 1;
-
-                self.write()?;
-
-                return Ok(ExercisesProgress::NewPending);
+                let success = handle.join().unwrap()?;
+                if !success {
+                    writer.write_all(b"\n\n")?;
+                    return Ok(Some(exercise_ind));
+                }
             }
 
-            writeln!(writer, "{}", "ok".green())?;
+            Ok::<_, Error>(None)
+        })?;
+
+        if let Some(pending_exercise_ind) = pending_exercise_ind {
+            self.current_exercise_ind = pending_exercise_ind;
+            self.n_done = self
+                .exercises
+                .iter()
+                .filter(|exercise| exercise.done)
+                .count() as u16;
+            self.write()?;
+            return Ok(ExercisesProgress::NewPending);
         }
 
         // Write that the last exercise is done.
@@ -409,7 +396,7 @@ impl AppState {
         clear_terminal(writer)?;
         writer.write_all(FENISH_LINE.as_bytes())?;
 
-        let final_message = self.final_message.trim();
+        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")?;
@@ -419,14 +406,9 @@ impl AppState {
     }
 }
 
-const CARGO_METADATA_ERR: &str = "Failed to run the command `cargo metadata …`
-Did you already install Rust?
-Try running `cargo --version` to diagnose the problem.";
-
 const RERUNNING_ALL_EXERCISES_MSG: &[u8] = b"
 All exercises seem to be done.
 Recompiling and running all exercises to make sure that all of them are actually done.
-
 ";
 
 const FENISH_LINE: &str = "+----------------------------------------------------+
@@ -462,7 +444,7 @@ mod tests {
             path: "exercises/0.rs",
             test: false,
             strict_clippy: false,
-            hint: String::new(),
+            hint: "",
             done: false,
         }
     }
@@ -476,7 +458,7 @@ mod tests {
             final_message: String::new(),
             file_buf: Vec::new(),
             official_exercises: true,
-            target_dir: PathBuf::new(),
+            cmd_runner: CmdRunner::build().unwrap(),
         };
 
         let mut assert = |done: [bool; 3], expected: [Option<usize>; 3]| {

src/cmd.rs

@@ -1,30 +1,44 @@
 use anyhow::{Context, Result};
-use std::{io::Read, path::Path, process::Command};
+use serde::Deserialize;
+use std::{
+    io::Read,
+    path::PathBuf,
+    process::{Command, Stdio},
+};
 
 /// Run a command with a description for a possible error and append the merged stdout and stderr.
 /// The boolean in the returned `Result` is true if the command's exit status is success.
-pub fn run_cmd(mut cmd: Command, description: &str, output: &mut Vec<u8>) -> Result<bool> {
-    let (mut reader, writer) = os_pipe::pipe()
-        .with_context(|| format!("Failed to create a pipe to run the command `{description}``"))?;
+fn run_cmd(mut cmd: Command, description: &str, output: Option<&mut Vec<u8>>) -> Result<bool> {
+    let spawn = |mut cmd: Command| {
+        // NOTE: The closure drops `cmd` which prevents a pipe deadlock.
+        cmd.stdin(Stdio::null())
+            .spawn()
+            .with_context(|| format!("Failed to run the command `{description}`"))
+    };
 
-    let writer_clone = writer.try_clone().with_context(|| {
-        format!("Failed to clone the pipe writer for the command `{description}`")
-    })?;
+    let mut handle = if let Some(output) = output {
+        let (mut reader, writer) = os_pipe::pipe().with_context(|| {
+            format!("Failed to create a pipe to run the command `{description}``")
+        })?;
 
-    let mut handle = cmd
-        .stdout(writer_clone)
-        .stderr(writer)
-        .spawn()
-        .with_context(|| format!("Failed to run the command `{description}`"))?;
+        let writer_clone = writer.try_clone().with_context(|| {
+            format!("Failed to clone the pipe writer for the command `{description}`")
+        })?;
 
-    // Prevent pipe deadlock.
-    drop(cmd);
+        cmd.stdout(writer_clone).stderr(writer);
+        let handle = spawn(cmd)?;
 
-    reader
-        .read_to_end(output)
-        .with_context(|| format!("Failed to read the output of the command `{description}`"))?;
+        reader
+            .read_to_end(output)
+            .with_context(|| format!("Failed to read the output of the command `{description}`"))?;
 
-    output.push(b'\n');
+        output.push(b'\n');
+
+        handle
+    } else {
+        cmd.stdout(Stdio::null()).stderr(Stdio::null());
+        spawn(cmd)?
+    };
 
     handle
         .wait()
@@ -32,50 +46,100 @@ pub fn run_cmd(mut cmd: Command, description: &str, output: &mut Vec<u8>) -> Res
         .map(|status| status.success())
 }
 
-pub struct CargoCmd<'a> {
-    pub subcommand: &'a str,
-    pub args: &'a [&'a str],
-    pub bin_name: &'a str,
-    pub description: &'a str,
-    /// RUSTFLAGS="-A warnings"
-    pub hide_warnings: bool,
-    /// Added as `--target-dir` if `Self::dev` is true.
-    pub target_dir: &'a Path,
-    /// The output buffer to append the merged stdout and stderr.
-    pub output: &'a mut Vec<u8>,
-    /// true while developing Rustlings.
-    pub dev: bool,
+// Parses parts of the output of `cargo metadata`.
+#[derive(Deserialize)]
+struct CargoMetadata {
+    target_directory: PathBuf,
 }
 
-impl<'a> CargoCmd<'a> {
-    /// Run `cargo SUBCOMMAND --bin EXERCISE_NAME … ARGS`.
-    pub fn run(&mut self) -> Result<bool> {
+pub struct CmdRunner {
+    target_dir: PathBuf,
+}
+
+impl CmdRunner {
+    pub fn build() -> Result<Self> {
+        // Get the target directory from Cargo.
+        let metadata_output = Command::new("cargo")
+            .arg("metadata")
+            .arg("-q")
+            .arg("--format-version")
+            .arg("1")
+            .arg("--no-deps")
+            .stdin(Stdio::null())
+            .stderr(Stdio::inherit())
+            .output()
+            .context(CARGO_METADATA_ERR)?
+            .stdout;
+
+        let target_dir = serde_json::de::from_slice::<CargoMetadata>(&metadata_output)
+            .context("Failed to read the field `target_directory` from the `cargo metadata` output")
+            .map(|metadata| metadata.target_directory)?;
+
+        Ok(Self { target_dir })
+    }
+
+    pub fn cargo<'out>(
+        &self,
+        subcommand: &str,
+        bin_name: &str,
+        output: Option<&'out mut Vec<u8>>,
+    ) -> CargoSubcommand<'out> {
         let mut cmd = Command::new("cargo");
-        cmd.arg(self.subcommand);
+        cmd.arg(subcommand).arg("-q").arg("--bin").arg(bin_name);
 
         // A hack to make `cargo run` work when developing Rustlings.
-        if self.dev {
-            cmd.arg("--manifest-path")
-                .arg("dev/Cargo.toml")
-                .arg("--target-dir")
-                .arg(self.target_dir);
+        #[cfg(debug_assertions)]
+        cmd.arg("--manifest-path")
+            .arg("dev/Cargo.toml")
+            .arg("--target-dir")
+            .arg(&self.target_dir);
+
+        if output.is_some() {
+            cmd.arg("--color").arg("always");
         }
 
-        cmd.arg("--color")
-            .arg("always")
-            .arg("-q")
-            .arg("--bin")
-            .arg(self.bin_name)
-            .args(self.args);
+        CargoSubcommand { cmd, output }
+    }
 
-        if self.hide_warnings {
-            cmd.env("RUSTFLAGS", "-A warnings");
-        }
+    /// The boolean in the returned `Result` is true if the command's exit status is success.
+    pub fn run_debug_bin(&self, bin_name: &str, output: Option<&mut Vec<u8>>) -> Result<bool> {
+        // 7 = "/debug/".len()
+        let mut bin_path =
+            PathBuf::with_capacity(self.target_dir.as_os_str().len() + 7 + bin_name.len());
+        bin_path.push(&self.target_dir);
+        bin_path.push("debug");
+        bin_path.push(bin_name);
 
-        run_cmd(cmd, self.description, self.output)
+        run_cmd(Command::new(&bin_path), &bin_path.to_string_lossy(), output)
     }
 }
 
+pub struct CargoSubcommand<'out> {
+    cmd: Command,
+    output: Option<&'out mut Vec<u8>>,
+}
+
+impl<'out> CargoSubcommand<'out> {
+    #[inline]
+    pub fn args<'arg, I>(&mut self, args: I) -> &mut Self
+    where
+        I: IntoIterator<Item = &'arg str>,
+    {
+        self.cmd.args(args);
+        self
+    }
+
+    /// The boolean in the returned `Result` is true if the command's exit status is success.
+    #[inline]
+    pub fn run(self, description: &str) -> Result<bool> {
+        run_cmd(self.cmd, description, self.output)
+    }
+}
+
+const CARGO_METADATA_ERR: &str = "Failed to run the command `cargo metadata …`
+Did you already install Rust?
+Try running `cargo --version` to diagnose the problem.";
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -86,7 +150,7 @@ mod tests {
         cmd.arg("Hello");
 
         let mut output = Vec::with_capacity(8);
-        run_cmd(cmd, "echo …", &mut output).unwrap();
+        run_cmd(cmd, "echo …", Some(&mut output)).unwrap();
 
         assert_eq!(output, b"Hello\n\n");
     }

src/dev.rs

@@ -2,8 +2,6 @@ use anyhow::{bail, Context, Result};
 use clap::Subcommand;
 use std::path::PathBuf;
 
-use crate::DEBUG_PROFILE;
-
 mod check;
 mod new;
 mod update;
@@ -32,7 +30,7 @@ impl DevCommands {
     pub fn run(self) -> Result<()> {
         match self {
             Self::New { path, no_git } => {
-                if DEBUG_PROFILE {
+                if cfg!(debug_assertions) {
                     bail!("Disabled in the debug build");
                 }
 

src/dev/check.rs

@@ -1,22 +1,19 @@
-use anyhow::{anyhow, bail, Context, Result};
+use anyhow::{anyhow, bail, Context, Error, Result};
 use std::{
     cmp::Ordering,
     fs::{self, read_dir, OpenOptions},
     io::{self, Read, Write},
     path::{Path, PathBuf},
-    sync::{
-        atomic::{self, AtomicBool},
-        Mutex,
-    },
+    process::{Command, Stdio},
     thread,
 };
 
 use crate::{
-    app_state::parse_target_dir,
     cargo_toml::{append_bins, bins_start_end_ind, BINS_BUFFER_CAPACITY},
+    cmd::CmdRunner,
     exercise::{RunnableExercise, OUTPUT_CAPACITY},
     info_file::{ExerciseInfo, InfoFile},
-    CURRENT_FORMAT_VERSION, DEBUG_PROFILE,
+    CURRENT_FORMAT_VERSION,
 };
 
 // Find a char that isn't allowed in the exercise's `name` or `dir`.
@@ -24,24 +21,27 @@ fn forbidden_char(input: &str) -> Option<char> {
     input.chars().find(|c| !c.is_alphanumeric() && *c != '_')
 }
 
-// Check that the Cargo.toml file is up-to-date.
+// Check that the `Cargo.toml` file is up-to-date.
 fn check_cargo_toml(
     exercise_infos: &[ExerciseInfo],
-    current_cargo_toml: &str,
+    cargo_toml_path: &str,
     exercise_path_prefix: &[u8],
 ) -> Result<()> {
-    let (bins_start_ind, bins_end_ind) = bins_start_end_ind(current_cargo_toml)?;
+    let current_cargo_toml = fs::read_to_string(cargo_toml_path)
+        .with_context(|| format!("Failed to read the file `{cargo_toml_path}`"))?;
+
+    let (bins_start_ind, bins_end_ind) = bins_start_end_ind(&current_cargo_toml)?;
 
     let old_bins = &current_cargo_toml.as_bytes()[bins_start_ind..bins_end_ind];
     let mut new_bins = Vec::with_capacity(BINS_BUFFER_CAPACITY);
     append_bins(&mut new_bins, exercise_infos, exercise_path_prefix);
 
     if old_bins != new_bins {
-        if DEBUG_PROFILE {
-            bail!("The file `dev/Cargo.toml` is outdated. Please run `cargo run -- dev update` to update it");
+        if cfg!(debug_assertions) {
+            bail!("The file `dev/Cargo.toml` is outdated. Please run `cargo run -- dev update` to update it. Then run `cargo run -- dev check` again");
         }
 
-        bail!("The file `Cargo.toml` is outdated. Please run `rustlings dev update` to update it");
+        bail!("The file `Cargo.toml` is outdated. Please run `rustlings dev update` to update it. Then run `rustlings dev check` again");
     }
 
     Ok(())
@@ -71,7 +71,7 @@ fn check_info_file_exercises(info_file: &InfoFile) -> Result<hashbrown::HashSet<
             }
         }
 
-        if exercise_info.hint.trim().is_empty() {
+        if exercise_info.hint.trim_ascii().is_empty() {
             bail!("The exercise `{name}` has an empty hint. Please provide a hint or at least tell the user why a hint isn't needed for this exercise");
         }
 
@@ -162,46 +162,45 @@ fn check_unexpected_files(
     Ok(())
 }
 
-fn check_exercises_unsolved(info_file: &InfoFile, target_dir: &Path) -> Result<()> {
-    let error_occurred = AtomicBool::new(false);
-
+fn check_exercises_unsolved(info_file: &InfoFile, cmd_runner: &CmdRunner) -> Result<()> {
     println!(
         "Running all exercises to check that they aren't already solved. This may take a while…\n",
     );
     thread::scope(|s| {
-        for exercise_info in &info_file.exercises {
-            if exercise_info.skip_check_unsolved {
-                continue;
-            }
-
-            s.spawn(|| {
-                let error = |e| {
-                    let mut stderr = io::stderr().lock();
-                    stderr.write_all(e).unwrap();
-                    stderr.write_all(b"\nProblem with the exercise ").unwrap();
-                    stderr.write_all(exercise_info.name.as_bytes()).unwrap();
-                    stderr.write_all(SEPARATOR).unwrap();
-                    error_occurred.store(true, atomic::Ordering::Relaxed);
-                };
-
-                let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
-                match exercise_info.run_exercise(&mut output, target_dir) {
-                    Ok(true) => error(b"Already solved!"),
-                    Ok(false) => (),
-                    Err(e) => error(e.to_string().as_bytes()),
+        let handles = info_file
+            .exercises
+            .iter()
+            .filter_map(|exercise_info| {
+                if exercise_info.skip_check_unsolved {
+                    return None;
                 }
-            });
+
+                Some((
+                    exercise_info.name.as_str(),
+                    s.spawn(|| exercise_info.run_exercise(None, cmd_runner)),
+                ))
+            })
+            .collect::<Vec<_>>();
+
+        for (exercise_name, handle) in handles {
+            let Ok(result) = handle.join() else {
+                bail!("Panic while trying to run the exericse {exercise_name}");
+            };
+
+            match result {
+                Ok(true) => bail!(
+                    "The exercise {exercise_name} is already solved.\n{SKIP_CHECK_UNSOLVED_HINT}",
+                ),
+                Ok(false) => (),
+                Err(e) => return Err(e),
+            }
         }
-    });
 
-    if error_occurred.load(atomic::Ordering::Relaxed) {
-        bail!(CHECK_EXERCISES_UNSOLVED_ERR);
-    }
-
-    Ok(())
+        Ok(())
+    })
 }
 
-fn check_exercises(info_file: &InfoFile, target_dir: &Path) -> Result<()> {
+fn check_exercises(info_file: &InfoFile, cmd_runner: &CmdRunner) -> Result<()> {
     match info_file.format_version.cmp(&CURRENT_FORMAT_VERSION) {
         Ordering::Less => bail!("`format_version` < {CURRENT_FORMAT_VERSION} (supported version)\nPlease migrate to the latest format version"),
         Ordering::Greater => bail!("`format_version` > {CURRENT_FORMAT_VERSION} (supported version)\nTry updating the Rustlings program"),
@@ -209,88 +208,123 @@ fn check_exercises(info_file: &InfoFile, target_dir: &Path) -> Result<()> {
     }
 
     let info_file_paths = check_info_file_exercises(info_file)?;
-    check_unexpected_files("exercises", &info_file_paths)?;
+    let handle = thread::spawn(move || check_unexpected_files("exercises", &info_file_paths));
 
-    check_exercises_unsolved(info_file, target_dir)
+    check_exercises_unsolved(info_file, cmd_runner)?;
+    handle.join().unwrap()
 }
 
-fn check_solutions(require_solutions: bool, info_file: &InfoFile, target_dir: &Path) -> Result<()> {
-    let paths = Mutex::new(hashbrown::HashSet::with_capacity(info_file.exercises.len()));
-    let error_occurred = AtomicBool::new(false);
+enum SolutionCheck {
+    Success { sol_path: String },
+    MissingRequired,
+    MissingOptional,
+    RunFailure { output: Vec<u8> },
+    Err(Error),
+}
 
+fn check_solutions(
+    require_solutions: bool,
+    info_file: &InfoFile,
+    cmd_runner: &CmdRunner,
+) -> Result<()> {
     println!("Running all solutions. This may take a while…\n");
     thread::scope(|s| {
-        for exercise_info in &info_file.exercises {
-            s.spawn(|| {
-                let error = |e| {
-                    let mut stderr = io::stderr().lock();
-                    stderr.write_all(e).unwrap();
-                    stderr
-                        .write_all(b"\nFailed to run the solution of the exercise ")
-                        .unwrap();
-                    stderr.write_all(exercise_info.name.as_bytes()).unwrap();
-                    stderr.write_all(SEPARATOR).unwrap();
-                    error_occurred.store(true, atomic::Ordering::Relaxed);
-                };
+        let handles = info_file
+            .exercises
+            .iter()
+            .map(|exercise_info| {
+                s.spawn(|| {
+                    let sol_path = exercise_info.sol_path();
+                    if !Path::new(&sol_path).exists() {
+                        if require_solutions {
+                            return SolutionCheck::MissingRequired;
+                        }
 
-                let path = exercise_info.sol_path();
-                if !Path::new(&path).exists() {
-                    if require_solutions {
-                        error(b"Solution missing");
+                        return SolutionCheck::MissingOptional;
                     }
 
-                    // No solution to check.
-                    return;
-                }
-
-                let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
-                match exercise_info.run_solution(&mut output, target_dir) {
-                    Ok(true) => {
-                        paths.lock().unwrap().insert(PathBuf::from(path));
+                    let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
+                    match exercise_info.run_solution(Some(&mut output), cmd_runner) {
+                        Ok(true) => SolutionCheck::Success { sol_path },
+                        Ok(false) => SolutionCheck::RunFailure { output },
+                        Err(e) => SolutionCheck::Err(e),
                     }
-                    Ok(false) => error(&output),
-                    Err(e) => error(e.to_string().as_bytes()),
+                })
+            })
+            .collect::<Vec<_>>();
+
+        let mut sol_paths = hashbrown::HashSet::with_capacity(info_file.exercises.len());
+        let mut fmt_cmd = Command::new("rustfmt");
+        fmt_cmd
+            .arg("--check")
+            .arg("--edition")
+            .arg("2021")
+            .arg("--color")
+            .arg("always")
+            .stdin(Stdio::null());
+
+        for (exercise_info, handle) in info_file.exercises.iter().zip(handles) {
+            let Ok(check_result) = handle.join() else {
+                bail!(
+                    "Panic while trying to run the solution of the exericse {}",
+                    exercise_info.name,
+                );
+            };
+
+            match check_result {
+                SolutionCheck::Success { sol_path } => {
+                    fmt_cmd.arg(&sol_path);
+                    sol_paths.insert(PathBuf::from(sol_path));
                 }
-            });
+                SolutionCheck::MissingRequired => {
+                    bail!(
+                        "The solution of the exercise {} is missing",
+                        exercise_info.name,
+                    );
+                }
+                SolutionCheck::MissingOptional => (),
+                SolutionCheck::RunFailure { output } => {
+                    io::stderr().lock().write_all(&output)?;
+                    bail!(
+                        "Running the solution of the exercise {} failed with the error above",
+                        exercise_info.name,
+                    );
+                }
+                SolutionCheck::Err(e) => return Err(e),
+            }
         }
-    });
 
-    if error_occurred.load(atomic::Ordering::Relaxed) {
-        bail!("At least one solution failed. See the output above.");
-    }
+        let handle = s.spawn(move || check_unexpected_files("solutions", &sol_paths));
 
-    check_unexpected_files("solutions", &paths.into_inner().unwrap())?;
+        if !fmt_cmd
+            .status()
+            .context("Failed to run `rustfmt` on all solution files")?
+            .success()
+        {
+            bail!("Some solutions aren't formatted. Run `rustfmt` on them");
+        }
 
-    Ok(())
+        handle.join().unwrap()
+    })
 }
 
 pub fn check(require_solutions: bool) -> Result<()> {
     let info_file = InfoFile::parse()?;
 
-    // A hack to make `cargo run -- dev check` work when developing Rustlings.
-    if DEBUG_PROFILE {
-        check_cargo_toml(
-            &info_file.exercises,
-            include_str!("../../dev-Cargo.toml"),
-            b"../",
-        )?;
+    if cfg!(debug_assertions) {
+        // A hack to make `cargo run -- dev check` work when developing Rustlings.
+        check_cargo_toml(&info_file.exercises, "dev/Cargo.toml", b"../")?;
     } else {
-        let current_cargo_toml =
-            fs::read_to_string("Cargo.toml").context("Failed to read the file `Cargo.toml`")?;
-        check_cargo_toml(&info_file.exercises, &current_cargo_toml, b"")?;
+        check_cargo_toml(&info_file.exercises, "Cargo.toml", b"")?;
     }
 
-    let target_dir = parse_target_dir()?;
-    check_exercises(&info_file, &target_dir)?;
-    check_solutions(require_solutions, &info_file, &target_dir)?;
+    let cmd_runner = CmdRunner::build()?;
+    check_exercises(&info_file, &cmd_runner)?;
+    check_solutions(require_solutions, &info_file, &cmd_runner)?;
 
-    println!("\nEverything looks fine!");
+    println!("Everything looks fine!");
 
     Ok(())
 }
 
-const SEPARATOR: &[u8] =
-    b"\n========================================================================================\n";
-
-const CHECK_EXERCISES_UNSOLVED_ERR: &str = "At least one exercise is already solved or failed to run. See the output above.
-If this is an intro exercise that is intended to be already solved, add `skip_check_unsolved = true` to the exercise's metadata in the `info.toml` file.";
+const SKIP_CHECK_UNSOLVED_HINT: &str = "If this is an introduction exercise that is intended to be already solved, add `skip_check_unsolved = true` to the exercise's metadata in the `info.toml` file";

src/dev/new.rs

@@ -76,8 +76,8 @@ pub fn new(path: &Path, no_git: bool) -> Result<()> {
 
 pub const GITIGNORE: &[u8] = b".rustlings-state.txt
 Cargo.lock
-target
-.vscode
+target/
+.vscode/
 !.vscode/extensions.json
 ";
 

src/dev/update.rs

@@ -4,18 +4,19 @@ use std::fs;
 use crate::{
     cargo_toml::updated_cargo_toml,
     info_file::{ExerciseInfo, InfoFile},
-    DEBUG_PROFILE,
 };
 
 // Update the `Cargo.toml` file.
 fn update_cargo_toml(
     exercise_infos: &[ExerciseInfo],
-    current_cargo_toml: &str,
-    exercise_path_prefix: &[u8],
     cargo_toml_path: &str,
+    exercise_path_prefix: &[u8],
 ) -> Result<()> {
+    let current_cargo_toml = fs::read_to_string(cargo_toml_path)
+        .with_context(|| format!("Failed to read the file `{cargo_toml_path}`"))?;
+
     let updated_cargo_toml =
-        updated_cargo_toml(exercise_infos, current_cargo_toml, exercise_path_prefix)?;
+        updated_cargo_toml(exercise_infos, &current_cargo_toml, exercise_path_prefix)?;
 
     fs::write(cargo_toml_path, updated_cargo_toml)
         .context("Failed to write the `Cargo.toml` file")?;
@@ -26,21 +27,14 @@ fn update_cargo_toml(
 pub fn update() -> Result<()> {
     let info_file = InfoFile::parse()?;
 
-    // A hack to make `cargo run -- dev update` work when developing Rustlings.
-    if DEBUG_PROFILE {
-        update_cargo_toml(
-            &info_file.exercises,
-            include_str!("../../dev-Cargo.toml"),
-            b"../",
-            "dev/Cargo.toml",
-        )
-        .context("Failed to update the file `dev/Cargo.toml`")?;
+    if cfg!(debug_assertions) {
+        // A hack to make `cargo run -- dev update` work when developing Rustlings.
+        update_cargo_toml(&info_file.exercises, "dev/Cargo.toml", b"../")
+            .context("Failed to update the file `dev/Cargo.toml`")?;
 
         println!("Updated `dev/Cargo.toml`");
     } else {
-        let current_cargo_toml =
-            fs::read_to_string("Cargo.toml").context("Failed to read the file `Cargo.toml`")?;
-        update_cargo_toml(&info_file.exercises, &current_cargo_toml, b"", "Cargo.toml")
+        update_cargo_toml(&info_file.exercises, "Cargo.toml", &[])
             .context("Failed to update the file `Cargo.toml`")?;
 
         println!("Updated `Cargo.toml`");

src/exercise.rs

@@ -3,44 +3,39 @@ use ratatui::crossterm::style::{style, StyledContent, Stylize};
 use std::{
     fmt::{self, Display, Formatter},
     io::Write,
-    path::{Path, PathBuf},
-    process::Command,
 };
 
-use crate::{
-    cmd::{run_cmd, CargoCmd},
-    in_official_repo,
-    terminal_link::TerminalFileLink,
-    DEBUG_PROFILE,
-};
+use crate::{cmd::CmdRunner, terminal_link::TerminalFileLink};
 
 /// The initial capacity of the output buffer.
 pub const OUTPUT_CAPACITY: usize = 1 << 14;
 
 // Run an exercise binary and append its output to the `output` buffer.
 // Compilation must be done before calling this method.
-fn run_bin(bin_name: &str, output: &mut Vec<u8>, target_dir: &Path) -> Result<bool> {
-    writeln!(output, "{}", "Output".underlined())?;
+fn run_bin(
+    bin_name: &str,
+    mut output: Option<&mut Vec<u8>>,
+    cmd_runner: &CmdRunner,
+) -> Result<bool> {
+    if let Some(output) = output.as_deref_mut() {
+        writeln!(output, "{}", "Output".underlined())?;
+    }
 
-    // 7 = "/debug/".len()
-    let mut bin_path = PathBuf::with_capacity(target_dir.as_os_str().len() + 7 + bin_name.len());
-    bin_path.push(target_dir);
-    bin_path.push("debug");
-    bin_path.push(bin_name);
+    let success = cmd_runner.run_debug_bin(bin_name, output.as_deref_mut())?;
 
-    let success = run_cmd(Command::new(&bin_path), &bin_path.to_string_lossy(), output)?;
-
-    if !success {
-        // 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(),
-        )?;
+    if let Some(output) = output {
+        if !success {
+            // 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(),
+            )?;
+        }
     }
 
     Ok(success)
@@ -54,7 +49,7 @@ pub struct Exercise {
     pub path: &'static str,
     pub test: bool,
     pub strict_clippy: bool,
-    pub hint: String,
+    pub hint: &'static str,
     pub done: bool,
 }
 
@@ -77,89 +72,77 @@ pub trait RunnableExercise {
 
     // Compile, check and run the exercise or its solution (depending on `bin_name´).
     // The output is written to the `output` buffer after clearing it.
-    fn run(&self, bin_name: &str, output: &mut Vec<u8>, target_dir: &Path) -> Result<bool> {
-        output.clear();
-
-        // Developing the official Rustlings.
-        let dev = DEBUG_PROFILE && in_official_repo();
-
-        let build_success = CargoCmd {
-            subcommand: "build",
-            args: &[],
-            bin_name,
-            description: "cargo build …",
-            hide_warnings: false,
-            target_dir,
-            output,
-            dev,
+    fn run(
+        &self,
+        bin_name: &str,
+        mut output: Option<&mut Vec<u8>>,
+        cmd_runner: &CmdRunner,
+    ) -> Result<bool> {
+        if let Some(output) = output.as_deref_mut() {
+            output.clear();
         }
-        .run()?;
+
+        let build_success = cmd_runner
+            .cargo("build", bin_name, output.as_deref_mut())
+            .run("cargo build …")?;
         if !build_success {
             return Ok(false);
         }
 
-        // Discard the output of `cargo build` because it will be shown again by Clippy.
-        output.clear();
+        // Discard the compiler output because it will be shown again by `cargo test` or Clippy.
+        if let Some(output) = output.as_deref_mut() {
+            output.clear();
+        }
+
+        if self.test() {
+            let output_is_some = output.is_some();
+            let mut test_cmd = cmd_runner.cargo("test", bin_name, output.as_deref_mut());
+            if output_is_some {
+                test_cmd.args(["--", "--color", "always", "--show-output"]);
+            }
+            let test_success = test_cmd.run("cargo test …")?;
+            if !test_success {
+                run_bin(bin_name, output, cmd_runner)?;
+                return Ok(false);
+            }
+
+            // Discard the compiler output because it will be shown again by Clippy.
+            if let Some(output) = output.as_deref_mut() {
+                output.clear();
+            }
+        }
+
+        let mut clippy_cmd = cmd_runner.cargo("clippy", bin_name, output.as_deref_mut());
 
         // `--profile test` is required to also check code with `[cfg(test)]`.
-        let clippy_args: &[&str] = if self.strict_clippy() {
-            &["--profile", "test", "--", "-D", "warnings"]
+        if self.strict_clippy() {
+            clippy_cmd.args(["--profile", "test", "--", "-D", "warnings"]);
         } else {
-            &["--profile", "test"]
-        };
-        let clippy_success = CargoCmd {
-            subcommand: "clippy",
-            args: clippy_args,
-            bin_name,
-            description: "cargo clippy …",
-            hide_warnings: false,
-            target_dir,
-            output,
-            dev,
-        }
-        .run()?;
-        if !clippy_success {
-            return Ok(false);
+            clippy_cmd.args(["--profile", "test"]);
         }
 
-        if !self.test() {
-            return run_bin(bin_name, output, target_dir);
-        }
+        let clippy_success = clippy_cmd.run("cargo clippy …")?;
+        let run_success = run_bin(bin_name, output, cmd_runner)?;
 
-        let test_success = CargoCmd {
-            subcommand: "test",
-            args: &["--", "--color", "always", "--show-output"],
-            bin_name,
-            description: "cargo test …",
-            // Hide warnings because they are shown by Clippy.
-            hide_warnings: true,
-            target_dir,
-            output,
-            dev,
-        }
-        .run()?;
-
-        let run_success = run_bin(bin_name, output, target_dir)?;
-
-        Ok(test_success && run_success)
+        Ok(clippy_success && run_success)
     }
 
     /// Compile, check and run the exercise.
     /// The output is written to the `output` buffer after clearing it.
     #[inline]
-    fn run_exercise(&self, output: &mut Vec<u8>, target_dir: &Path) -> Result<bool> {
-        self.run(self.name(), output, target_dir)
+    fn run_exercise(&self, output: Option<&mut Vec<u8>>, cmd_runner: &CmdRunner) -> Result<bool> {
+        self.run(self.name(), output, cmd_runner)
     }
 
     /// Compile, check and run the exercise's solution.
     /// The output is written to the `output` buffer after clearing it.
-    fn run_solution(&self, output: &mut Vec<u8>, target_dir: &Path) -> Result<bool> {
+    fn run_solution(&self, output: Option<&mut Vec<u8>>, cmd_runner: &CmdRunner) -> Result<bool> {
         let name = self.name();
-        let mut bin_name = String::with_capacity(name.len());
+        let mut bin_name = String::with_capacity(name.len() + 4);
         bin_name.push_str(name);
         bin_name.push_str("_sol");
 
-        self.run(&bin_name, output, target_dir)
+        self.run(&bin_name, output, cmd_runner)
     }
 }
 

src/init.rs

@@ -3,30 +3,40 @@ use ratatui::crossterm::style::Stylize;
 use std::{
     env::set_current_dir,
     fs::{self, create_dir},
-    io::ErrorKind,
+    io::{self, Write},
     path::Path,
     process::{Command, Stdio},
 };
 
-use crate::{cargo_toml::updated_cargo_toml, embedded::EMBEDDED_FILES, info_file::InfoFile};
+use crate::{
+    cargo_toml::updated_cargo_toml, embedded::EMBEDDED_FILES, info_file::InfoFile,
+    term::press_enter_prompt,
+};
 
 pub fn init() -> Result<()> {
-    // Prevent initialization in a directory that contains the file `Cargo.toml`.
-    // This can mean that Rustlings was already initialized in this directory.
-    // Otherwise, this can cause problems with Cargo workspaces.
+    let rustlings_dir = Path::new("rustlings");
+    if rustlings_dir.exists() {
+        bail!(RUSTLINGS_DIR_ALREADY_EXISTS_ERR);
+    }
+
+    let mut stdout = io::stdout().lock();
+    let mut init_git = true;
+
     if Path::new("Cargo.toml").exists() {
-        bail!(CARGO_TOML_EXISTS_ERR);
-    }
-
-    let rustlings_path = Path::new("rustlings");
-    if let Err(e) = create_dir(rustlings_path) {
-        if e.kind() == ErrorKind::AlreadyExists {
-            bail!(RUSTLINGS_DIR_ALREADY_EXISTS_ERR);
+        if Path::new("exercises").exists() && Path::new("solutions").exists() {
+            bail!(IN_INITIALIZED_DIR_ERR);
         }
-        return Err(e.into());
+
+        stdout.write_all(CARGO_TOML_EXISTS_PROMPT_MSG)?;
+        press_enter_prompt(&mut stdout)?;
+        init_git = false;
     }
 
-    set_current_dir("rustlings")
+    stdout.write_all(b"This command will create the directory `rustlings/` which will contain the exercises.\nPress ENTER to continue ")?;
+    press_enter_prompt(&mut stdout)?;
+
+    create_dir(rustlings_dir).context("Failed to create the `rustlings/` directory")?;
+    set_current_dir(rustlings_dir)
         .context("Failed to change the current directory to `rustlings/`")?;
 
     let info_file = InfoFile::parse()?;
@@ -35,6 +45,11 @@ pub fn init() -> Result<()> {
         .context("Failed to initialize the `rustlings/exercises` directory")?;
 
     create_dir("solutions").context("Failed to create the `solutions/` directory")?;
+    fs::write(
+        "solutions/README.md",
+        include_bytes!("../solutions/README.md"),
+    )
+    .context("Failed to create the file rustlings/solutions/README.md")?;
     for dir in EMBEDDED_FILES.exercise_dirs {
         let mut dir_path = String::with_capacity(10 + dir.name.len());
         dir_path.push_str("solutions/");
@@ -70,18 +85,21 @@ pub fn init() -> Result<()> {
     fs::write(".vscode/extensions.json", VS_CODE_EXTENSIONS_JSON)
         .context("Failed to create the file `rustlings/.vscode/extensions.json`")?;
 
-    // Ignore any Git error because Git initialization is not required.
-    let _ = Command::new("git")
-        .arg("init")
-        .stdin(Stdio::null())
-        .stderr(Stdio::null())
-        .status();
+    if init_git {
+        // Ignore any Git error because Git initialization is not required.
+        let _ = Command::new("git")
+            .arg("init")
+            .stdin(Stdio::null())
+            .stderr(Stdio::null())
+            .status();
+    }
 
-    println!(
+    writeln!(
+        stdout,
         "\n{}\n\n{}",
         "Initialization done ✓".green(),
         POST_INIT_MSG.bold(),
-    );
+    )?;
 
     Ok(())
 }
@@ -92,16 +110,14 @@ const INIT_SOLUTION_FILE: &[u8] = b"fn main() {
 }
 ";
 
-const GITIGNORE: &[u8] = b".rustlings-state.txt
-solutions
-Cargo.lock
-target
-.vscode
+const GITIGNORE: &[u8] = b"Cargo.lock
+target/
+.vscode/
 ";
 
 pub const VS_CODE_EXTENSIONS_JSON: &[u8] = br#"{"recommendations":["rust-lang.rust-analyzer"]}"#;
 
-const CARGO_TOML_EXISTS_ERR: &str = "The current directory contains the file `Cargo.toml`.
+const IN_INITIALIZED_DIR_ERR: &str = "It looks like Rustlings is already initialized in this directory.
 
 If you already initialized Rustlings, run the command `rustlings` for instructions on getting started with the exercises.
 Otherwise, please run `rustlings init` again in another directory.";
@@ -112,5 +128,19 @@ You probably already initialized Rustlings.
 Run `cd rustlings`
 Then run `rustlings` again";
 
+const CARGO_TOML_EXISTS_PROMPT_MSG: &[u8] = br#"You are about to initialize Rustlings in a directory that already contains a `Cargo.toml` file!
+
+  => It is recommended to abort with CTRL+C and initialize Rustlings in another directory <=
+
+If you know what you are doing and want to initialize Rustlings in a Cargo workspace,
+then you need to add its directory to `members` in the `workspace` section of the `Cargo.toml` file:
+
+```toml
+[workspace]
+members = ["rustlings"]
+```
+
+Press ENTER if you are sure that you want to continue after reading the warning above "#;
+
 const POST_INIT_MSG: &str = "Run `cd rustlings` to go into the generated directory.
 Then run `rustlings` to get started.";

src/main.rs

@@ -2,10 +2,11 @@ use anyhow::{bail, Context, Result};
 use app_state::StateFileStatus;
 use clap::{Parser, Subcommand};
 use std::{
-    io::{self, BufRead, IsTerminal, StdoutLock, Write},
+    io::{self, IsTerminal, Write},
     path::Path,
     process::exit,
 };
+use term::{clear_terminal, press_enter_prompt};
 
 use self::{app_state::AppState, dev::DevCommands, info_file::InfoFile, watch::WatchExit};
 
@@ -20,35 +21,11 @@ mod init;
 mod list;
 mod progress_bar;
 mod run;
+mod term;
 mod terminal_link;
 mod watch;
 
 const CURRENT_FORMAT_VERSION: u8 = 1;
-const DEBUG_PROFILE: bool = {
-    #[allow(unused_assignments, unused_mut)]
-    let mut debug_profile = false;
-
-    #[cfg(debug_assertions)]
-    {
-        debug_profile = true;
-    }
-
-    debug_profile
-};
-
-// The current directory is the official Rustligns repository.
-fn in_official_repo() -> bool {
-    Path::new("dev/rustlings-repo.txt").exists()
-}
-
-fn clear_terminal(stdout: &mut StdoutLock) -> io::Result<()> {
-    stdout.write_all(b"\x1b[H\x1b[2J\x1b[3J")
-}
-
-fn press_enter_prompt() -> io::Result<()> {
-    io::stdin().lock().read_until(b'\n', &mut Vec::new())?;
-    Ok(())
-}
 
 /// Rustlings is a collection of small exercises to get you used to writing and reading Rust code
 #[derive(Parser)]
@@ -89,20 +66,12 @@ enum Subcommands {
 fn main() -> Result<()> {
     let args = Args::parse();
 
-    if !DEBUG_PROFILE && in_official_repo() {
+    if cfg!(not(debug_assertions)) && Path::new("dev/rustlings-repo.txt").exists() {
         bail!("{OLD_METHOD_ERR}");
     }
 
     match args.command {
         Some(Subcommands::Init) => {
-            {
-                let mut stdout = io::stdout().lock();
-                stdout.write_all(b"This command will create the directory `rustlings/` which will contain the exercises.\nPress ENTER to continue ")?;
-                stdout.flush()?;
-                press_enter_prompt()?;
-                stdout.write_all(b"\n")?;
-            }
-
             return init::init().context("Initialization failed");
         }
         Some(Subcommands::Dev(dev_command)) => return dev_command.run(),
@@ -132,11 +101,12 @@ fn main() -> Result<()> {
                 let mut stdout = io::stdout().lock();
                 clear_terminal(&mut stdout)?;
 
-                let welcome_message = welcome_message.trim();
+                let welcome_message = welcome_message.trim_ascii();
                 write!(stdout, "{welcome_message}\n\nPress ENTER to continue ")?;
-                stdout.flush()?;
-                press_enter_prompt()?;
+                press_enter_prompt(&mut stdout)?;
                 clear_terminal(&mut stdout)?;
+                // Flush to be able to show errors occuring before printing a newline to stdout.
+                stdout.flush()?;
             }
             StateFileStatus::Read => (),
         }

src/run.rs

@@ -11,7 +11,7 @@ use crate::{
 pub fn run(app_state: &mut AppState) -> Result<()> {
     let exercise = app_state.current_exercise();
     let mut output = Vec::with_capacity(OUTPUT_CAPACITY);
-    let success = exercise.run_exercise(&mut output, app_state.target_dir())?;
+    let success = exercise.run_exercise(Some(&mut output), app_state.cmd_runner())?;
 
     let mut stdout = io::stdout().lock();
     stdout.write_all(&output)?;

src/term.rs

@@ -0,0 +1,12 @@
+use std::io::{self, BufRead, StdoutLock, Write};
+
+pub fn clear_terminal(stdout: &mut StdoutLock) -> io::Result<()> {
+    stdout.write_all(b"\x1b[H\x1b[2J\x1b[3J")
+}
+
+pub fn press_enter_prompt(stdout: &mut StdoutLock) -> io::Result<()> {
+    stdout.flush()?;
+    io::stdin().lock().read_until(b'\n', &mut Vec::new())?;
+    stdout.write_all(b"\n")?;
+    Ok(())
+}

src/watch/state.rs

@@ -54,7 +54,7 @@ impl<'a> WatchState<'a> {
         let success = self
             .app_state
             .current_exercise()
-            .run_exercise(&mut self.output, self.app_state.target_dir())?;
+            .run_exercise(Some(&mut self.output), self.app_state.cmd_runner())?;
         if success {
             self.done_status =
                 if let Some(solution_path) = self.app_state.current_solution_path()? {

tests/test_exercises/Cargo.toml

@@ -1,11 +0,0 @@
-bin = [
-  { name = "compilation_success", path = "exercises/compilation_success.rs" },
-  { name = "compilation_failure", path = "exercises/compilation_failure.rs" },
-  { name = "test_success", path = "exercises/test_success.rs" },
-  { name = "test_failure", path = "exercises/test_failure.rs" },
-]
-
-[package]
-name = "test_exercises"
-edition = "2021"
-publish = false

tests/test_exercises/dev/Cargo.toml

@@ -0,0 +1,11 @@
+bin = [
+  { name = "compilation_success", path = "../exercises/compilation_success.rs" },
+  { name = "compilation_failure", path = "../exercises/compilation_failure.rs" },
+  { name = "test_success", path = "../exercises/test_success.rs" },
+  { name = "test_failure", path = "../exercises/test_failure.rs" },
+]
+
+[package]
+name = "test_exercises"
+edition = "2021"
+publish = false