Respect the target-dir config and show tests' output

src/main.rs

@@ -5,16 +5,18 @@ use crossterm::{
     terminal::{Clear, ClearType},
     ExecutableCommand,
 };
+use serde::Deserialize;
 use std::{
     io::{self, BufRead, Write},
-    path::Path,
-    process::exit,
+    path::{Path, PathBuf},
+    process::{exit, Command, Stdio},
 };
 
 use self::{app_state::AppState, dev::DevCommands, info_file::InfoFile, watch::WatchExit};
 
 mod app_state;
 mod cargo_toml;
+mod cmd;
 mod dev;
 mod embedded;
 mod exercise;
@@ -75,6 +77,11 @@ enum Subcommands {
     Dev(DevCommands),
 }
 
+#[derive(Deserialize)]
+struct CargoMetadata {
+    target_directory: PathBuf,
+}
+
 fn in_official_repo() -> bool {
     Path::new("dev/rustlings-repo.txt").exists()
 }
@@ -86,7 +93,20 @@ fn main() -> Result<()> {
         bail!("{OLD_METHOD_ERR}");
     }
 
-    which::which("cargo").context(CARGO_NOT_FOUND_ERR)?;
+    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")?
+        .target_directory;
 
     match args.command {
         Some(Subcommands::Init) => {
@@ -122,6 +142,7 @@ fn main() -> Result<()> {
     let (mut app_state, state_file_status) = AppState::new(
         info_file.exercises,
         info_file.final_message.unwrap_or_default(),
+        target_dir,
     );
 
     if let Some(welcome_message) = info_file.welcome_message {
@@ -198,7 +219,7 @@ The new method doesn't include cloning the Rustlings' repository.
 Please follow the instructions in the README:
 https://github.com/rust-lang/rustlings#getting-started";
 
-const CARGO_NOT_FOUND_ERR: &str = "Failed to find `cargo`.
+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.";