Display more descriptive error on missing manifest

Before:

  ```
  ❯ aiken check
  Error:
    × No such file or directory (os error 2)
  ```

  After:

  ```
  ❯ aiken check
  Error:
    × Missing 'aiken.toml' manifest in /Users/ktorz/Documents/Projects/aiken-lang/aiken
    help: Try running `aiken new <REPOSITORY/PROJECT>` to initialise a project with an example manifest.
  ```

  Co-authored-by: KtorZ <matthias.benkort@gmail.com>

crates/cli/src/lib.rs

@@ -1,9 +1,7 @@
-use std::collections::BTreeMap;
-use std::{env, path::PathBuf, process};
-
 use aiken_project::{pretty, script::EvalInfo, telemetry, Project};
 use miette::IntoDiagnostic;
 use owo_colors::OwoColorize;
+use std::{collections::BTreeMap, env, path::PathBuf, process};
 use uplc::machine::cost_model::ExBudget;
 
 pub mod cmd;

crates/project/src/config.rs

@@ -1,10 +1,8 @@
-use std::{fmt::Display, fs, path::PathBuf};
-
+use crate::error::Error;
 use aiken_lang::ast::Span;
 use miette::NamedSource;
 use serde::{de::Visitor, Deserialize, Serialize};
-
-use crate::error::Error;
+use std::{fmt::Display, fs, path::PathBuf};
 
 #[derive(Deserialize)]
 pub struct Config {
@@ -112,7 +110,8 @@ impl Display for Platform {
 impl Config {
     pub fn load(dir: PathBuf) -> Result<Config, Error> {
         let config_path = dir.join("aiken.toml");
-        let raw_config = fs::read_to_string(&config_path)?;
+        let raw_config = fs::read_to_string(&config_path)
+            .map_err(|_| Error::MissingManifest { path: dir.clone() })?;
 
         let result: Self = toml::from_str(&raw_config).map_err(|e| Error::TomlLoading {
             path: config_path.clone(),

crates/project/src/error.rs

@@ -52,6 +52,9 @@ pub enum Error {
         help: String,
     },
 
+    #[error("Missing 'aiken.toml' manifest in {path}")]
+    MissingManifest { path: PathBuf },
+
     #[error("Cyclical module imports")]
     ImportCycle { modules: Vec<String> },
 
@@ -175,6 +178,7 @@ impl Error {
             Error::FileIo { .. } => None,
             Error::Format { .. } => None,
             Error::StandardIo(_) => None,
+            Error::MissingManifest { path } => Some(path.to_path_buf()),
             Error::TomlLoading { path, .. } => Some(path.to_path_buf()),
             Error::ImportCycle { .. } => None,
             Error::List(_) => None,
@@ -195,6 +199,7 @@ impl Error {
             Error::FileIo { .. } => None,
             Error::Format { .. } => None,
             Error::StandardIo(_) => None,
+            Error::MissingManifest { .. } => None,
             Error::TomlLoading { src, .. } => Some(src.to_string()),
             Error::ImportCycle { .. } => None,
             Error::List(_) => None,
@@ -243,6 +248,7 @@ impl Diagnostic for Error {
             Error::Parse { .. } => Some(Box::new("aiken::parser")),
             Error::Type { .. } => Some(Box::new("aiken::check")),
             Error::StandardIo(_) => None,
+            Error::MissingManifest { .. } => None,
             Error::TomlLoading { .. } => Some(Box::new("aiken::loading::toml")),
             Error::Format { .. } => None,
             Error::ValidatorMustReturnBool { .. } => Some(Box::new("aiken::scripts")),
@@ -270,6 +276,7 @@ impl Diagnostic for Error {
             Error::Parse { error, .. } => error.kind.help(),
             Error::Type { error, .. } => error.help(),
             Error::StandardIo(_) => None,
+            Error::MissingManifest { .. } => Some(Box::new("Try running `aiken new <REPOSITORY/PROJECT>` to initialise a project with an example manifest.")),
             Error::TomlLoading { .. } => None,
             Error::Format { .. } => None,
             Error::ValidatorMustReturnBool { .. } => Some(Box::new("Try annotating the validator's return type with Bool")),
@@ -315,6 +322,7 @@ impl Diagnostic for Error {
             Error::ImportCycle { .. } => None,
             Error::List(_) => None,
             Error::Parse { error, .. } => error.labels(),
+            Error::MissingManifest { .. } => None,
             Error::Type { error, .. } => error.labels(),
             Error::StandardIo(_) => None,
             Error::TomlLoading { location, .. } => {
@@ -349,6 +357,7 @@ impl Diagnostic for Error {
             Error::Parse { named, .. } => Some(named),
             Error::Type { named, .. } => Some(named),
             Error::StandardIo(_) => None,
+            Error::MissingManifest { .. } => None,
             Error::TomlLoading { named, .. } => Some(named),
             Error::Format { .. } => None,
             Error::ValidatorMustReturnBool { named, .. } => Some(named),