Refactor build steps to generate blueprints instead

The blueprint is generated at the root of the repository and is
  intended to be versioned with the rest. It acts as a business card
  that contains many practical information. There's a variety of tools
  we can then build on top of open-source contracts. And, quite
  importantly, the blueprint is language-agnostic; it isn't specific to
  Aiken. So it is really meant as an interop format within the
  ecosystem.

crates/aiken-project/src/blueprint/error.rs

@@ -0,0 +1,59 @@
+use super::schema;
+use crate::module::CheckedModule;
+use aiken_lang::ast::{Span, TypedFunction};
+use miette::{Diagnostic, NamedSource};
+use std::{fmt::Debug, path::PathBuf};
+
+#[derive(Debug, thiserror::Error, Diagnostic)]
+pub enum Error {
+    #[error("Validator functions must return Bool")]
+    ValidatorMustReturnBool {
+        path: PathBuf,
+        src: String,
+        named: NamedSource,
+        location: Span,
+    },
+    #[error("Validator\n\n{name}\n\nrequires at least {at_least} arguments")]
+    WrongValidatorArity {
+        name: String,
+        at_least: u8,
+        location: Span,
+        path: PathBuf,
+        src: String,
+        named: NamedSource,
+    },
+    #[error(transparent)]
+    Schema(schema::Error),
+}
+
+pub fn assert_return_bool(module: &CheckedModule, def: &TypedFunction) -> Result<(), Error> {
+    if !def.return_type.is_bool() {
+        Err(Error::ValidatorMustReturnBool {
+            location: def.location,
+            src: module.code.clone(),
+            path: module.input_path.clone(),
+            named: NamedSource::new(module.input_path.display().to_string(), module.code.clone()),
+        })
+    } else {
+        Ok(())
+    }
+}
+
+pub fn assert_min_arity(
+    module: &CheckedModule,
+    def: &TypedFunction,
+    at_least: u8,
+) -> Result<(), Error> {
+    if def.arguments.len() < at_least as usize {
+        Err(Error::WrongValidatorArity {
+            location: def.location,
+            src: module.code.clone(),
+            path: module.input_path.clone(),
+            named: NamedSource::new(module.input_path.display().to_string(), module.code.clone()),
+            name: def.name.clone(),
+            at_least,
+        })
+    } else {
+        Ok(())
+    }
+}