tr: rename iter_scripts to leaves

The name `iter_scripts` is dumb and undiscoverable. More importantly,
it's misleading -- this iterator does not yield scripts. It yields
Miniscripts, which can be converted to scripts if you have ToPublicKey
and are willing to pay a cost.

Author: apoelstra

bitcoind-tests/tests/test_desc.rs

@@ -185,7 +185,7 @@ pub fn test_desc_satisfy(
             }
             // ------------------ script spend -------------
             let x_only_keypairs_reqd: Vec<(secp256k1::Keypair, TapLeafHash)> = tr
-                .iter_scripts()
+                .leaves()
                 .flat_map(|leaf| {
                     let leaf_hash = TapLeafHash::from_script(&leaf.compute_script(), LeafVersion::TapScript);
                     leaf.miniscript().iter_pk().filter_map(move |pk| {

examples/taproot.rs

@@ -66,7 +66,7 @@ fn main() {
         assert_eq!(p.internal_key(), "Ca");
 
         // Iterate through scripts
-        let mut iter = p.iter_scripts();
+        let mut iter = p.leaves();
         let mut next = iter.next().unwrap();
         assert_eq!(
             (next.depth(), next.miniscript().as_ref()),

src/descriptor/mod.rs

@@ -252,7 +252,7 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
 
     /// For a Taproot descriptor, returns the [`TapTree`] describing the Taproot tree.
     ///
-    /// To obtain the individual leaves of the tree, call [`TapTree::iter`] on the
+    /// To obtain the individual leaves of the tree, call [`TapTree::leaves`] on the
     /// returned value.
     pub fn tap_tree(&self) -> Option<&TapTree<Pk>> {
         if let Descriptor::Tr(ref tr) = self {
@@ -269,7 +269,7 @@ impl<Pk: MiniscriptKey> Descriptor<Pk> {
     pub fn tap_tree_iter(&self) -> tr::TapTreeIter<Pk> {
         if let Descriptor::Tr(ref tr) = self {
             if let Some(ref tree) = tr.tap_tree() {
-                return tree.iter();
+                return tree.leaves();
             }
         }
         tr::TapTreeIter::empty()

src/descriptor/tr/mod.rs

@@ -119,9 +119,16 @@ impl<Pk: MiniscriptKey> Tr<Pk> {
 
     /// Iterate over all scripts in merkle tree. If there is no script path, the iterator
     /// yields [`None`]
-    pub fn iter_scripts(&self) -> TapTreeIter<Pk> {
+    #[deprecated(since = "TBD", note = "use `leaves` instead")]
+    pub fn iter_scripts(&self) -> TapTreeIter<Pk> { self.leaves() }
+
+    /// Iterates over all the leaves of the tree in depth-first preorder.
+    ///
+    /// The yielded elements include the Miniscript for each leave as well as its depth
+    /// in the tree, which is the data required by PSBT (BIP 371).
+    pub fn leaves(&self) -> TapTreeIter<Pk> {
         match self.tree {
-            Some(ref t) => t.iter(),
+            Some(ref t) => t.leaves(),
             None => TapTreeIter::empty(),
         }
     }
@@ -151,7 +158,7 @@ impl<Pk: MiniscriptKey> Tr<Pk> {
             TaprootSpendInfo::new_key_spend(&secp, self.internal_key.to_x_only_pubkey(), None)
         } else {
             let mut builder = TaprootBuilder::new();
-            for leaf in self.iter_scripts() {
+            for leaf in self.leaves() {
                 let script = leaf.miniscript().encode();
                 builder = builder
                     .add_leaf(leaf.depth(), script)
@@ -170,7 +177,7 @@ impl<Pk: MiniscriptKey> Tr<Pk> {
 
     /// Checks whether the descriptor is safe.
     pub fn sanity_check(&self) -> Result<(), Error> {
-        for leaf in self.iter_scripts() {
+        for leaf in self.leaves() {
             leaf.miniscript().sanity_check()?;
         }
         Ok(())
@@ -200,7 +207,7 @@ impl<Pk: MiniscriptKey> Tr<Pk> {
         };
 
         let wu = tree
-            .iter()
+            .leaves()
             .filter_map(|leaf| {
                 let script_size = leaf.miniscript().script_size();
                 let max_sat_elems = leaf.miniscript().max_satisfaction_witness_elements().ok()?;
@@ -250,7 +257,7 @@ impl<Pk: MiniscriptKey> Tr<Pk> {
             Some(tree) => tree,
         };
 
-        tree.iter()
+        tree.leaves()
             .filter_map(|leaf| {
                 let script_size = leaf.miniscript().script_size();
                 let max_sat_elems = leaf.miniscript().max_satisfaction_witness_elements().ok()?;
@@ -495,7 +502,7 @@ impl<Pk: MiniscriptKey> Liftable<Pk> for Tr<Pk> {
 impl<Pk: MiniscriptKey> ForEachKey<Pk> for Tr<Pk> {
     fn for_each_key<'a, F: FnMut(&'a Pk) -> bool>(&'a self, mut pred: F) -> bool {
         let script_keys_res = self
-            .iter_scripts()
+            .leaves()
             .all(|leaf| leaf.miniscript().for_each_key(&mut pred));
         script_keys_res && pred(&self.internal_key)
     }
@@ -540,7 +547,7 @@ where
             absolute_timelock: None,
         };
         let mut min_wit_len = None;
-        for leaf in desc.iter_scripts() {
+        for leaf in desc.leaves() {
             let mut satisfaction = if allow_mall {
                 match leaf.miniscript().build_template(provider) {
                     s @ Satisfaction { stack: Witness::Stack(_), .. } => s,

src/descriptor/tr/taptree.rs

@@ -46,9 +46,11 @@ impl<Pk: MiniscriptKey> TapTree<Pk> {
         }
     }
 
-    /// Iterates over all miniscripts in DFS walk order compatible with the
-    /// PSBT requirements (BIP 371).
-    pub fn iter(&self) -> TapTreeIter<Pk> { TapTreeIter::from_tree(self) }
+    /// Iterates over all the leaves of the tree in depth-first preorder.
+    ///
+    /// The yielded elements include the Miniscript for each leave as well as its depth
+    /// in the tree, which is the data required by PSBT (BIP 371).
+    pub fn leaves(&self) -> TapTreeIter<Pk> { TapTreeIter::from_tree(self) }
 
     // Helper function to translate keys
     pub(super) fn translate_helper<T>(

src/psbt/mod.rs

@@ -1112,7 +1112,7 @@ fn update_item_with_descriptor_helper<F: PsbtFields>(
 
             let mut builder = taproot::TaprootBuilder::new();
 
-            for (leaf_derived, leaf) in tr_derived.iter_scripts().zip(tr_xpk.iter_scripts()) {
+            for (leaf_derived, leaf) in tr_derived.leaves().zip(tr_xpk.leaves()) {
                 debug_assert_eq!(leaf_derived.depth(), leaf.depth());
                 let leaf_script = (leaf_derived.compute_script(), leaf_derived.leaf_version());
                 let tapleaf_hash = TapLeafHash::from_script(&leaf_script.0, leaf_script.1);