feat: add exercise modules in diferent files/dirs

closes: https://github.com/rust-lang/rustlings/issues/1143

dev/Cargo.toml

@@ -86,6 +86,8 @@ bin = [
   { name = "modules2_sol", path = "../solutions/09_modules/modules2.rs" },
   { name = "modules3", path = "../exercises/09_modules/modules3.rs" },
   { name = "modules3_sol", path = "../solutions/09_modules/modules3.rs" },
+  { name = "modules4", path = "../exercises/09_modules/modules4.rs" },
+  { name = "modules4_sol", path = "../solutions/09_modules/modules4.rs" },
   { name = "hashmaps1", path = "../exercises/11_hashmaps/hashmaps1.rs" },
   { name = "hashmaps1_sol", path = "../solutions/11_hashmaps/hashmaps1.rs" },
   { name = "hashmaps2", path = "../exercises/11_hashmaps/hashmaps2.rs" },

exercises/09_modules/fruit.rs

@@ -0,0 +1,3 @@
+pub fn get_fav_fruit() {
+    println("Got your favourite fruit!")
+}

exercises/09_modules/modules4.rs

@@ -0,0 +1,5 @@
+// TODO: fix the compiler error for missing modules.
+
+fn main() {
+    fruit::get_fav_fruit();
+}

rustlings-macros/info.toml

@@ -544,6 +544,18 @@ hint = """
 `use` statement for these two to bring them into scope. You can use nested
 paths to bring these two in using only one line."""
 
+[[exercises]]
+name = "modules4"
+dir = "09_modules"
+test = false
+hint = """
+The mod.rs is trying to use the modules from the file cake.rs and fruit directory.
+Complete the `mod` statements to fit the use in `main`.
+
+Learn more in The Book:
+https://doc.rust-lang.org/book/ch07-05-separating-modules-into-different-files.html
+"""
+
 # HASHMAPS
 
 [[exercises]]

solutions/09_modules/fruit.rs

@@ -0,0 +1,3 @@
+pub fn get_fav_fruit() {
+    println("Got your favourite fruit!")
+}

solutions/09_modules/modules4.rs

@@ -0,0 +1,5 @@
+mod fruit;
+
+fn main() {
+    fruit::get_fav_fruit();
+}