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fix(lang): only capture a policy's ref where its script runs #333

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Merged
scarmuega merged 1 commit into from
Jun 7, 2026
Merged

fix(lang): only capture a policy's ref where its script runs #333

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72 changes: 25 additions & 47 deletions crates/tx3-lang/src/lowering.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -91,12 +91,8 @@ fn coerce_identifier_into_asset_def(identifier: &ast::Identifier) -> Result<ast:
}
}

/// Reference-script UTxOs discovered while lowering a single transaction.
///
/// When a ref-backed policy is used in a script-requiring position (e.g. the
/// `from` of an input), its `ref` UTxO must be added to the transaction's
/// reference inputs so the script becomes available on chain. We collect those
/// refs here and drain them into `Tx.references` once the body is lowered.
/// Reference-script UTxOs collected during lowering, drained into
/// `Tx.references`.
#[derive(Debug, Default)]
struct RefAccumulator {
refs: Vec<ir::Expression>,
Expand All @@ -115,13 +111,10 @@ pub(crate) struct Context {
is_asset_expr: bool,
is_datum_expr: bool,
is_address_expr: bool,
// Sticky: a policy referenced anywhere in this subtree stands in for a
// script that must run (e.g. a mint/burn policy), so its ref UTxO should be
// captured even though the policy lowers to a plain hash here. Carried
// through the `enter_*` transitions like `script_refs`.
// Within this subtree, a ref-backed policy's script runs, so its ref UTxO
// is captured. Sticky across `enter_*`.
capture_policy_ref: bool,
// Shared across all `enter_*`-derived contexts within one tx lowering so
// refs captured deep in an expression reach the top-level `Tx` assembly.
// Shared across `enter_*` clones so captures from any depth reach `Tx`.
script_refs: Rc<RefCell<RefAccumulator>>,
}

Expand Down Expand Up @@ -156,9 +149,8 @@ impl Context {
}
}

/// Enter a subtree (e.g. a mint/burn amount) where any referenced policy's
/// script must run, so its ref UTxO should be captured as a reference
/// input. Sticky across nested `enter_*` transitions.
/// Mark this subtree as one where a referenced policy's script runs, so its
/// ref UTxO is captured. Sticky across nested `enter_*`.
pub fn capturing_policy_refs(&self) -> Self {
Self {
capture_policy_ref: true,
Expand All @@ -182,9 +174,7 @@ impl Context {
self.capture_policy_ref
}

/// Record a reference-script UTxO discovered during lowering. Dedups so the
/// same ref used by several inputs (or an explicit `reference` block) lands
/// once.
/// Record a reference-script UTxO, deduplicating.
pub fn record_script_ref(&self, r#ref: ir::Expression) {
self.script_refs.borrow_mut().record(r#ref);
}
Expand Down Expand Up @@ -263,11 +253,10 @@ impl IntoLower for ast::Identifier {
ast::Symbol::PolicyDef(x) => {
let policy = x.into_lower(ctx)?;

// The policy stands in for a script that must run — as a script
// credential in an address (`from`), or as a mint/burn policy.
// For a ref-backed policy, capture its `ref` UTxO so it lands in
// the tx's reference inputs. Hash-only policies yield `None`.
if ctx.is_address_expr() || ctx.captures_policy_refs() {
// Capture the ref UTxO only where the script runs, not in every
// address position (an output `to` receives funds without
// running the script). Hash-only policies yield `None`.
if ctx.captures_policy_refs() {
if let Some(r#ref) = policy.script.as_utxo_ref() {
ctx.record_script_ref(r#ref);
}
Expand Down Expand Up @@ -670,7 +659,8 @@ impl IntoLower for ast::InputBlockField {
fn into_lower(&self, ctx: &Context) -> Result<Self::Output, Error> {
match self {
ast::InputBlockField::From(x) => {
let ctx = ctx.enter_address_expr();
// Spending from a script address runs its script.
let ctx = ctx.enter_address_expr().capturing_policy_refs();
x.into_lower(&ctx)
}
ast::InputBlockField::DatumIs(_) => todo!(),
Expand Down Expand Up @@ -793,9 +783,7 @@ impl IntoLower for ast::MintBlockField {

fn into_lower(&self, ctx: &Context) -> Result<Self::Output, Error> {
match self {
// A policy referenced in the minted/burned amount is the policy
// whose script must run, so capture its ref UTxO as a reference
// input (analogous to a script credential in an input's `from`).
// Minting/burning runs the asset's policy script.
ast::MintBlockField::Amount(x) => x.into_lower(&ctx.capturing_policy_refs()),
ast::MintBlockField::Redeemer(x) => x.into_lower(ctx),
}
Expand Down Expand Up @@ -936,16 +924,13 @@ impl IntoLower for ast::TxDef {
type Output = ir::Tx;

fn into_lower(&self, ctx: &Context) -> Result<Self::Output, Error> {
// Seed the ref accumulator with explicit `reference` blocks first, so a
// ref that is also implied by a policy used as `from` dedups to one
// entry (and explicit refs keep their leading position).
// Seed with explicit `reference` blocks first so they dedup against,
// and precede, refs that the body derives from ref-backed policies.
for reference in self.references.iter() {
let r#ref = reference.r#ref.into_lower(ctx)?;
ctx.record_script_ref(r#ref);
}

// Lowering the body populates the accumulator with the `ref` UTxOs of
// any ref-backed policies used in script-requiring positions.
let inputs = self
.inputs
.iter()
Expand Down Expand Up @@ -1137,27 +1122,20 @@ mod tests {
test_lowering!(reference_script);

test_lowering!(policy_reference_script, |txs| {
// A ref-backed policy used as `from` contributes its `ref` UTxO as a
// reference input.
// ref-backed policy as `from`
assert_eq!(txs["spend"].references.len(), 1);

// The same ref-backed policy across two inputs is deduped to one
// reference input.
// same ref across two inputs is deduped
assert_eq!(txs["spend_two"].references.len(), 1);

// A hash-only policy contributes no reference input.
// hash-only policy: nothing to reference
assert!(txs["spend_hash_only"].references.is_empty());

// A ref-backed policy used to mint contributes its `ref` UTxO as a
// reference input.
// ref-backed mint
assert_eq!(txs["mint_token"].references.len(), 1);

// A ref-backed policy used to burn contributes its `ref` UTxO as a
// reference input.
// ref-backed burn
assert_eq!(txs["burn_token"].references.len(), 1);

// A hash-only policy used to mint contributes no reference input.
// hash-only mint: nothing to reference
assert!(txs["mint_hash_only"].references.is_empty());
// output recipient only: script does not run, no reference input
assert!(txs["send_to_policy"].references.is_empty());
});

test_lowering!(withdrawal);
Expand Down
90 changes: 90 additions & 0 deletions examples/policy_reference_script.send_to_policy.tir
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Original file line number Diff line number Diff line change
@@ -0,0 +1,90 @@
{
"fees": {
"EvalParam": "ExpectFees"
},
"references": [],
"inputs": [
{
"name": "funding",
"utxos": {
"EvalParam": {
"ExpectInput": [
"funding",
{
"address": {
"EvalParam": {
"ExpectValue": [
"receiver",
"Address"
]
}
},
"min_amount": {
"Assets": [
{
"policy": "None",
"asset_name": "None",
"amount": {
"EvalParam": {
"ExpectValue": [
"quantity",
"Int"
]
}
}
}
]
},
"ref": "None",
"many": false,
"collateral": false
}
]
}
},
"redeemer": "None"
}
],
"outputs": [
{
"address": {
"EvalCompiler": {
"BuildScriptAddress": {
"Bytes": [
171,
205,
239,
18,
52
]
}
}
},
"datum": "None",
"amount": {
"Assets": [
{
"policy": "None",
"asset_name": "None",
"amount": {
"EvalParam": {
"ExpectValue": [
"quantity",
"Int"
]
}
}
}
]
},
"optional": false
}
],
"validity": null,
"mints": [],
"burns": [],
"adhoc": [],
"collateral": [],
"signers": null,
"metadata": []
}
29 changes: 21 additions & 8 deletions examples/policy_reference_script.tx3
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Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,7 @@ policy Validator {

policy HashOnly = 0xABCDEF1234;

// A ref-backed policy used as `from` contributes its `ref` UTxO as a
// reference input.
// ref-backed policy as `from`: ref UTxO becomes a reference input
tx spend(
quantity: Int
) {
Expand Down Expand Up @@ -43,7 +42,7 @@ tx spend_two() {
}
}

// A hash-only policy used as `from` contributes no reference input.
// hash-only policy as `from`: no reference input
tx spend_hash_only() {
input locked {
from: HashOnly,
Expand All @@ -56,8 +55,7 @@ tx spend_hash_only() {
}
}

// Minting under a ref-backed policy contributes its `ref` UTxO as a reference
// input.
// ref-backed mint policy: ref UTxO becomes a reference input
tx mint_token() {
mint {
amount: AnyAsset(Validator, "TOKEN", 1),
Expand All @@ -70,8 +68,7 @@ tx mint_token() {
}
}

// Burning under a ref-backed policy contributes its `ref` UTxO as a reference
// input.
// ref-backed burn policy: ref UTxO becomes a reference input
tx burn_token() {
input funding {
from: Receiver,
Expand All @@ -89,7 +86,7 @@ tx burn_token() {
}
}

// Minting under a hash-only policy contributes no reference input.
// hash-only mint policy: no reference input
tx mint_hash_only() {
mint {
amount: AnyAsset(HashOnly, "TOKEN", 1),
Expand All @@ -101,3 +98,19 @@ tx mint_hash_only() {
amount: AnyAsset(HashOnly, "TOKEN", 1),
}
}

// ref-backed policy as output recipient only: script does not run, no
// reference input
tx send_to_policy(
quantity: Int
) {
input funding {
from: Receiver,
min_amount: Ada(quantity),
}

output {
to: Validator,
amount: Ada(quantity),
}
}
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