Require a main function in all exercises

exercises/03_if/if1.rs

@@ -10,6 +10,10 @@ pub fn bigger(a: i32, b: i32) -> i32 {
     // - additional variables
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 // Don't mind this for now :)
 #[cfg(test)]
 mod tests {

exercises/03_if/if2.rs

@@ -13,6 +13,10 @@ pub fn foo_if_fizz(fizzish: &str) -> &str {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 // No test changes needed!
 #[cfg(test)]
 mod tests {

exercises/03_if/if3.rs

@@ -27,6 +27,10 @@ pub fn animal_habitat(animal: &str) -> &'static str {
     habitat
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 // No test changes needed.
 #[cfg(test)]
 mod tests {

exercises/04_primitive_types/primitive_types4.rs

@@ -5,6 +5,10 @@
 // Execute `rustlings hint primitive_types4` or use the `hint` watch subcommand
 // for a hint.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[test]
 fn slice_out_of_array() {
     let a = [1, 2, 3, 4, 5];

exercises/04_primitive_types/primitive_types6.rs

@@ -6,6 +6,10 @@
 // Execute `rustlings hint primitive_types6` or use the `hint` watch subcommand
 // for a hint.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[test]
 fn indexing_tuple() {
     let numbers = (1, 2, 3);

exercises/05_vecs/vecs1.rs

@@ -14,6 +14,10 @@ fn array_and_vec() -> ([i32; 4], Vec<i32>) {
     (a, v)
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/05_vecs/vecs2.rs

@@ -26,6 +26,10 @@ fn vec_map(v: &Vec<i32>) -> Vec<i32> {
     }).collect()
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/07_structs/structs1.rs

@@ -14,6 +14,10 @@ struct ColorTupleStruct(/* TODO: Something goes here */);
 #[derive(Debug)]
 struct UnitLikeStruct;
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/07_structs/structs2.rs

@@ -28,6 +28,10 @@ fn create_order_template() -> Order {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/07_structs/structs3.rs

@@ -38,6 +38,10 @@ impl Package {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/08_enums/enums3.rs

@@ -45,6 +45,10 @@ impl State {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/09_strings/strings3.rs

@@ -18,6 +18,10 @@ fn replace_me(input: &str) -> String {
     ???
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/11_hashmaps/hashmaps1.rs

@@ -24,6 +24,10 @@ fn fruit_basket() -> HashMap<String, u32> {
     basket
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/11_hashmaps/hashmaps2.rs

@@ -41,6 +41,10 @@ fn fruit_basket(basket: &mut HashMap<Fruit, u32>) {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -79,7 +83,7 @@ mod tests {
         let count = basket.values().sum::<u32>();
         assert!(count > 11);
     }
-    
+
     #[test]
     fn all_fruit_types_in_basket() {
         let mut basket = get_fruit_basket();

exercises/11_hashmaps/hashmaps3.rs

@@ -5,9 +5,9 @@
 // Example: England,France,4,2 (England scored 4 goals, France 2).
 //
 // You have to build a scores table containing the name of the team, the total
-// number of goals the team scored, and the total number of goals the team 
-// conceded. One approach to build the scores table is to use a Hashmap. 
-// The solution is partially written to use a Hashmap, 
+// number of goals the team scored, and the total number of goals the team
+// conceded. One approach to build the scores table is to use a Hashmap.
+// The solution is partially written to use a Hashmap,
 // complete it to pass the test.
 //
 // Make me pass the tests!
@@ -42,6 +42,10 @@ fn build_scores_table(results: String) -> HashMap<String, Team> {
     scores
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/12_options/options1.rs

@@ -14,6 +14,10 @@ fn maybe_icecream(time_of_day: u16) -> Option<u16> {
     ???
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/12_options/options2.rs

@@ -3,6 +3,10 @@
 // Execute `rustlings hint options2` or use the `hint` watch subcommand for a
 // hint.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     #[test]

exercises/13_error_handling/errors1.rs

@@ -9,6 +9,10 @@
 // Execute `rustlings hint errors1` or use the `hint` watch subcommand for a
 // hint.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 pub fn generate_nametag_text(name: String) -> Option<String> {
     if name.is_empty() {
         // Empty names aren't allowed.

exercises/13_error_handling/errors2.rs

@@ -29,6 +29,10 @@ pub fn total_cost(item_quantity: &str) -> Result<i32, ParseIntError> {
     Ok(qty * cost_per_item + processing_fee)
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/13_error_handling/errors4.rs

@@ -19,6 +19,10 @@ impl PositiveNonzeroInteger {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[test]
 fn test_creation() {
     assert!(PositiveNonzeroInteger::new(10).is_ok());

exercises/13_error_handling/errors6.rs

@@ -54,6 +54,10 @@ impl PositiveNonzeroInteger {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

exercises/14_generics/generics2.rs

@@ -16,6 +16,10 @@ impl Wrapper {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/15_traits/traits2.rs

@@ -14,6 +14,10 @@ trait AppendBar {
 
 // TODO: Implement trait `AppendBar` for a vector of strings.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/15_traits/traits3.rs

@@ -23,6 +23,10 @@ struct OtherSoftware {
 impl Licensed for SomeSoftware {} // Don't edit this line
 impl Licensed for OtherSoftware {} // Don't edit this line
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/15_traits/traits4.rs

@@ -25,6 +25,10 @@ fn compare_license_types(software: ??, software_two: ??) -> bool {
     software.licensing_info() == software_two.licensing_info()
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/17_tests/tests1.rs

@@ -10,6 +10,10 @@
 // Execute `rustlings hint tests1` or use the `hint` watch subcommand for a
 // hint.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     #[test]

exercises/17_tests/tests2.rs

@@ -6,6 +6,10 @@
 // Execute `rustlings hint tests2` or use the `hint` watch subcommand for a
 // hint.
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     #[test]

exercises/17_tests/tests3.rs

@@ -11,6 +11,10 @@ pub fn is_even(num: i32) -> bool {
     num % 2 == 0
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/17_tests/tests4.rs

@@ -7,7 +7,7 @@
 
 struct Rectangle {
     width: i32,
-    height: i32
+    height: i32,
 }
 
 impl Rectangle {
@@ -16,10 +16,14 @@ impl Rectangle {
         if width <= 0 || height <= 0 {
             panic!("Rectangle width and height cannot be negative!")
         }
-        Rectangle {width, height}
+        Rectangle { width, height }
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/18_iterators/iterators2.rs

@@ -33,6 +33,10 @@ pub fn capitalize_words_string(words: &[&str]) -> String {
     String::new()
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/18_iterators/iterators3.rs

@@ -43,6 +43,10 @@ fn list_of_results() -> () {
     let division_results = numbers.into_iter().map(|n| divide(n, 27));
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/18_iterators/iterators4.rs

@@ -15,6 +15,10 @@ pub fn factorial(num: u64) -> u64 {
     // Execute `rustlings hint iterators4` for hints.
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/18_iterators/iterators5.rs

@@ -55,6 +55,10 @@ fn count_collection_iterator(collection: &[HashMap<String, Progress>], value: Pr
     todo!();
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/19_smart_pointers/cow1.rs

@@ -25,6 +25,10 @@ fn abs_all<'a, 'b>(input: &'a mut Cow<'b, [i32]>) -> &'a mut Cow<'b, [i32]> {
     input
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/23_conversions/as_ref_mut.rs

@@ -26,6 +26,10 @@ fn num_sq<T>(arg: &mut T) {
     ???
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

exercises/quiz1.rs

@@ -16,6 +16,10 @@
 // Put your function here!
 // fn calculate_price_of_apples {
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 // Don't modify this function!
 #[test]
 fn verify_test() {

exercises/quiz2.rs

@@ -40,6 +40,10 @@ mod my_module {
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     // TODO: What do we need to import to have `transformer` in scope?

exercises/quiz3.rs

@@ -24,11 +24,17 @@ pub struct ReportCard {
 
 impl ReportCard {
     pub fn print(&self) -> String {
-        format!("{} ({}) - achieved a grade of {}",
-            &self.student_name, &self.student_age, &self.grade)
+        format!(
+            "{} ({}) - achieved a grade of {}",
+            &self.student_name, &self.student_age, &self.grade
+        )
     }
 }
 
+fn main() {
+    // You can optionally experiment here.
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/dev/check.rs

@@ -1,8 +1,9 @@
-use anyhow::{bail, Context, Result};
+use anyhow::{anyhow, bail, Context, Error, Result};
 use std::{
     cmp::Ordering,
-    fs::{self, read_dir},
-    path::PathBuf,
+    fs::{self, read_dir, OpenOptions},
+    io::Read,
+    path::{Path, PathBuf},
 };
 
 use crate::{
@@ -18,6 +19,7 @@ fn check_info_file_exercises(info_file: &InfoFile) -> Result<hashbrown::HashSet<
     let mut names = hashbrown::HashSet::with_capacity(info_file.exercises.len());
     let mut paths = hashbrown::HashSet::with_capacity(info_file.exercises.len());
 
+    let mut file_buf = String::with_capacity(1 << 14);
     for exercise_info in &info_file.exercises {
         if exercise_info.name.is_empty() {
             bail!("Found an empty exercise name in `info.toml`");
@@ -31,7 +33,10 @@ fn check_info_file_exercises(info_file: &InfoFile) -> Result<hashbrown::HashSet<
 
         if let Some(dir) = &exercise_info.dir {
             if dir.is_empty() {
-                bail!("Found an empty dir name in `info.toml`");
+                bail!(
+                    "The exercise `{}` has an empty dir name in `info.toml`",
+                    exercise_info.name,
+                );
             }
             if let Some(c) = forbidden_char(dir) {
                 bail!("Char `{c}` in the exercise dir `{dir}` is not allowed");
@@ -44,23 +49,37 @@ fn check_info_file_exercises(info_file: &InfoFile) -> Result<hashbrown::HashSet<
 
         if !names.insert(exercise_info.name.as_str()) {
             bail!(
-                "The exercise name {} is duplicated. Exercise names must all be unique",
+                "The exercise name `{}` is duplicated. Exercise names must all be unique",
                 exercise_info.name,
             );
         }
 
-        paths.insert(PathBuf::from(exercise_info.path()));
+        let path = exercise_info.path();
+
+        OpenOptions::new()
+            .read(true)
+            .open(&path)
+            .with_context(|| format!("Failed to open the file {path}"))?
+            .read_to_string(&mut file_buf)
+            .with_context(|| format!("Failed to read the file {path}"))?;
+
+        if !file_buf.contains("fn main()") {
+            bail!("The `main` function is missing in the file `{path}`.\nCreate at least an empty `main` function to avoid language server errors");
+        }
+
+        file_buf.clear();
+
+        paths.insert(PathBuf::from(path));
     }
 
     Ok(paths)
 }
 
-fn check_exercise_dir_files(
-    info_file: &InfoFile,
-    info_file_paths: hashbrown::HashSet<PathBuf>,
-) -> Result<hashbrown::HashSet<String>> {
-    let mut names = hashbrown::HashSet::with_capacity(info_file.exercises.len());
+fn unexpected_file(path: &Path) -> Error {
+    anyhow!("Found the file `{}`. Only `README.md` and Rust files related to an exercise in `info.toml` are allowed in the `exercises` directory", path.display())
+}
 
+fn check_exercise_dir_files(info_file_paths: hashbrown::HashSet<PathBuf>) -> Result<()> {
     for entry in read_dir("exercises").context("Failed to open the `exercises` directory")? {
         let entry = entry.context("Failed to read the `exercises` directory")?;
 
@@ -72,11 +91,9 @@ fn check_exercise_dir_files(
             }
 
             if !info_file_paths.contains(&path) {
-                bail!("`{}` is expected to be an exercise file corresponding to some exercise in `info.toml`", path.display());
+                return Err(unexpected_file(&path));
             }
 
-            let file_name = file_name.to_string_lossy();
-            names.insert(file_name[..file_name.len() - 3].to_string());
             continue;
         }
 
@@ -89,7 +106,7 @@ fn check_exercise_dir_files(
             let path = entry.path();
 
             if !entry.file_type().unwrap().is_file() {
-                bail!("Found {} but expected only files", path.display());
+                bail!("Found `{}` but expected only files. Only one level of exercise nesting is allowed", path.display());
             }
 
             let file_name = path.file_name().unwrap();
@@ -98,21 +115,15 @@ fn check_exercise_dir_files(
             }
 
             if !info_file_paths.contains(&path) {
-                bail!("`{}` is expected to be an exercise file corresponding to some exercise in `info.toml`", path.display());
+                return Err(unexpected_file(&path));
             }
-
-            // The file name must be valid Unicode with the `.rs` extension
-            // because it is part of the info file paths.
-            let file_name = file_name.to_string_lossy();
-            let file_name_without_rs_extension = file_name[..file_name.len() - 3].to_string();
-            names.insert(file_name_without_rs_extension);
         }
     }
 
-    Ok(names)
+    Ok(())
 }
 
-fn check_info_file(info_file: &InfoFile) -> Result<()> {
+fn check_exercises(info_file: &InfoFile) -> 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"),
@@ -120,17 +131,7 @@ fn check_info_file(info_file: &InfoFile) -> Result<()> {
     }
 
     let info_file_paths = check_info_file_exercises(info_file)?;
-    let names_in_exercises_dir = check_exercise_dir_files(info_file, info_file_paths)?;
-
-    // Now, we know that every file has an exercise in `info.toml`.
-    // But we need to check that every exercise in `info.toml` has a file.
-    if names_in_exercises_dir.len() != info_file.exercises.len() {
-        for exercise_info in &info_file.exercises {
-            if !names_in_exercises_dir.contains(&exercise_info.name) {
-                bail!("The file `{}` is missing", exercise_info.path());
-            }
-        }
-    }
+    check_exercise_dir_files(info_file_paths)?;
 
     Ok(())
 }
@@ -190,7 +191,7 @@ fn check_cargo_toml(
 
 pub fn check() -> Result<()> {
     let info_file = InfoFile::parse()?;
-    check_info_file(&info_file)?;
+    check_exercises(&info_file)?;
 
     if DEVELOPING_OFFICIAL_RUSTLINGS {
         check_cargo_toml(