Add a blueprint policy command

Computes the policy ID of a minting policy; added guards for blueprint address to check that it's not a minting policy; Wasn't 100% sure where the errors should live, so I'm happy to move them if there's objections

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

@@ -49,6 +49,26 @@ pub enum Error {
     ))]
     ParameterizedValidator { n: usize },
 
+    #[error(
+        "I couldn't compute the address of the given validator because it's actually a minting policy!",
+    )]
+    #[diagnostic(code("aiken::blueprint::address::minting_validator"))]
+    #[diagnostic(help(
+        "I can only compute addresses for spending validators. Did you mean to call {blueprint_policy_command} instead?",
+        blueprint_policy_command = "blueprint policy".if_supports_color(Stdout, |s| s.purple()),
+    ))]
+    UnexpectedMintingValidator,
+
+    #[error(
+        "I couldn't compute the policyId of the given validator because it's actually a spending policy!",
+    )]
+    #[diagnostic(code("aiken::blueprint::address::spending_validator"))]
+    #[diagnostic(help(
+        "I can only compute policyIds for minting validators. Did you mean to call {blueprint_address_command} instead?",
+        blueprint_address_command = "blueprint address".if_supports_color(Stdout, |s| s.purple()),
+    ))]
+    UnexpectedSpendingValidator,
+
     #[error("I stumble upon something else than a constant when I expected one.")]
     #[diagnostic(code("aiken:blueprint::apply::malformed::argument"))]
     #[diagnostic(help(

crates/aiken-project/src/lib.rs

@@ -27,9 +27,10 @@ use indexmap::IndexMap;
 use miette::NamedSource;
 use options::{CodeGenMode, Options};
 use package_name::PackageName;
-use pallas::ledger::addresses::{
+use pallas::ledger::{addresses::{
     Address, Network, ShelleyAddress, ShelleyDelegationPart, StakePayload,
-};
+}, primitives::babbage::{self as cardano, PolicyId}};
+use pallas_traverse::ComputeHash;
 use script::{EvalHint, EvalInfo, Script};
 use std::{
     collections::HashMap,
@@ -369,6 +370,11 @@ where
         let when_missing = |known_validators| Error::NoValidatorNotFound { known_validators };
 
         blueprint.with_validator(title, when_too_many, when_missing, |validator| {
+            // Make sure we're not calculating the address for a minting validator
+            if validator.datum.is_none() {
+                return Err(blueprint::error::Error::UnexpectedMintingValidator.into());
+            }
+
             let n = validator.parameters.len();
             if n > 0 {
                 Err(blueprint::error::Error::ParameterizedValidator { n }.into())
@@ -380,6 +386,37 @@ where
         })
     }
 
+    pub fn policy(
+        &self,
+        title: Option<&String>
+    ) -> Result<PolicyId, Error> {
+        // Read blueprint
+        let blueprint = File::open(self.blueprint_path())
+            .map_err(|_| blueprint::error::Error::InvalidOrMissingFile)?;
+        let blueprint: Blueprint = serde_json::from_reader(BufReader::new(blueprint))?;
+
+        // Error handlers for ambiguous / missing validators
+        let when_too_many =
+            |known_validators| Error::MoreThanOneValidatorFound { known_validators };
+        let when_missing = |known_validators| Error::NoValidatorNotFound { known_validators };
+
+        blueprint.with_validator(title, when_too_many, when_missing, |validator| {
+            // Make sure we're not calculating the policy for a spending validator
+            if validator.datum.is_some() {
+                return Err(blueprint::error::Error::UnexpectedSpendingValidator.into());
+            }
+
+            let n = validator.parameters.len();
+            if n > 0 {
+                Err(blueprint::error::Error::ParameterizedValidator { n }.into())
+            } else {
+                let cbor = validator.program.to_cbor().unwrap();
+                let validator_hash = cardano::PlutusV2Script(cbor.into()).compute_hash();
+                Ok(validator_hash)
+            }
+        })
+    }
+
     pub fn apply_parameter(
         &self,
         title: Option<&String>,