Add the format version

info.toml

@@ -1,3 +1,5 @@
+format_version = 1
+
 welcome_message = """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
 started, here's a couple of notes about how Rustlings operates:

src/info_file.rs

@@ -39,6 +39,7 @@ impl ExerciseInfo {
 
 #[derive(Deserialize)]
 pub struct InfoFile {
+    pub format_version: u8,
     pub welcome_message: Option<String>,
     pub final_message: Option<String>,
     pub exercises: Vec<ExerciseInfo>,

src/main.rs

@@ -1,4 +1,4 @@
-use anyhow::{Context, Result};
+use anyhow::{bail, Context, Result};
 use app_state::StateFileStatus;
 use clap::{Parser, Subcommand};
 use crossterm::{
@@ -24,6 +24,8 @@ mod watch;
 
 use self::{app_state::AppState, dev::DevCommands, info_file::InfoFile, watch::WatchExit};
 
+const CURRENT_FORMAT_VERSION: u8 = 1;
+
 /// Rustlings is a collection of small exercises to get you used to writing and reading Rust code
 #[derive(Parser)]
 #[command(version)]
@@ -66,6 +68,10 @@ fn main() -> Result<()> {
 
     let info_file = InfoFile::parse()?;
 
+    if info_file.format_version > CURRENT_FORMAT_VERSION {
+        bail!(FORMAT_VERSION_HIGHER_ERR);
+    }
+
     if matches!(args.command, Some(Subcommands::Init)) {
         init::init(&info_file.exercises).context("Initialization failed")?;
         println!("{POST_INIT_MSG}");
@@ -156,6 +162,11 @@ const CARGO_NOT_FOUND_ERR: &str = "Failed to find `cargo`.
 Did you already install Rust?
 Try running `cargo --version` to diagnose the problem.";
 
+const FORMAT_VERSION_HIGHER_ERR: &str =
+    "The format version specified in the `info.toml` file is higher than the last one supported.
+It is possible that you have an outdated version of Rustlings.
+Try to install the latest Rustlings version first.";
+
 const POST_INIT_MSG: &str = "Done initialization!
 
 Run `cd rustlings` to go into the generated directory.