Merge #911: Return error from at_derivation_index when descriptor has no wildcard

1062144 feat(descriptor): deprecate at_derivation_index, add derive_at_index and TryFrom (Yeji Han)

Pull request description:

  Closes #829. 
  
  - Previously, calling `at_derivation_index()` on a descriptor without wildcards would silently ignore the index and return the descriptor unchanged. This was error-prone because callers would expect different indices to produce different addresses.
  - Callers that need to convert a non-wildcard descriptor to a definite one should use `DefiniteDescriptorKey::new()` on individual keys, or check `has_wildcard()` before calling `at_derivation_index()`.
  - Add edge case tests for `at_derivation_index` wildcard check


ACKs for top commit:
  apoelstra:
    ACK 1062144; successfully ran local tests


Tree-SHA512: 820b8bc543b6884997839374aba3de0d78511c603763650816fe676936795b345e0bec96e19c6a334261b0b0eb252f9f7ae72dee9537830b69d21c485181a0fb

Author: apoelstra

bitcoind-tests/tests/test_cpp.rs

@@ -30,7 +30,7 @@ pub(crate) fn parse_miniscripts(pubdata: &PubData) -> Vec<Descriptor<DefiniteDes
     for line in read_lines("tests/data/random_ms.txt") {
         let ms = test_util::parse_insane_ms(&line.unwrap(), pubdata);
         let wsh = Descriptor::new_wsh(ms).unwrap();
-        desc_vec.push(wsh.at_derivation_index(0).unwrap());
+        desc_vec.push(wsh.into_definite().unwrap());
     }
     desc_vec
 }

bitcoind-tests/tests/test_desc.rs

@@ -85,10 +85,13 @@ pub fn test_desc_satisfy(
         .unwrap();
     assert_eq!(blocks.0.len(), 1);
 
-    let definite_desc = test_util::parse_test_desc(descriptor, &testdata.pubdata)
-        .map_err(|_| DescError::DescParseError)?
-        .at_derivation_index(0)
-        .unwrap();
+    let desc = test_util::parse_test_desc(descriptor, &testdata.pubdata)
+        .map_err(|_| DescError::DescParseError)?;
+    let definite_desc = if desc.has_wildcard() {
+        desc.derive_at_index(0).unwrap()
+    } else {
+        desc.into_definite().unwrap()
+    };
 
     let derived_desc = definite_desc.derived_descriptor(&secp);
     let desc_address = derived_desc.address(bitcoin::Network::Regtest);
@@ -449,10 +452,13 @@ fn test_plan_satisfy(
         .unwrap();
     assert_eq!(blocks.0.len(), 1);
 
-    let definite_desc = test_util::parse_test_desc(descriptor, &testdata.pubdata)
-        .map_err(|_| DescError::DescParseError)?
-        .at_derivation_index(0)
-        .unwrap();
+    let desc = test_util::parse_test_desc(descriptor, &testdata.pubdata)
+        .map_err(|_| DescError::DescParseError)?;
+    let definite_desc = if desc.has_wildcard() {
+        desc.derive_at_index(0).unwrap()
+    } else {
+        desc.into_definite().unwrap()
+    };
 
     let derived_desc = definite_desc.derived_descriptor(&secp);
     let desc_address = derived_desc

examples/big.rs

@@ -33,7 +33,7 @@ fn main() {
     use_descriptor(Descriptor::<String>::from_str(&i).unwrap());
 
     let a = d
-        .at_derivation_index(0)
+        .derive_at_index(0)
         .unwrap()
         .address(bitcoin::Network::Bitcoin)
         .unwrap();

examples/taptree_of_horror/taptree_of_horror.rs

@@ -186,7 +186,7 @@ fn main() {
     let policy_desc: Descriptor<DescriptorPublicKey> = pol.compile_tr(None).unwrap();
 
     // Now, using this public descriptor create the script address
-    let derived_descriptor = policy_desc.at_derivation_index(0).unwrap();
+    let derived_descriptor = policy_desc.derive_at_index(0).unwrap();
     let _script_address = derived_descriptor.address(Network::Regtest).unwrap();
     println!("the receiving address of this script is: {}", _script_address);
     println!("\ndescriptor is: {}\n", policy_desc);

src/descriptor/key.rs

@@ -358,6 +358,7 @@ pub enum NonDefiniteKeyError {
     Wildcard,
     Multipath,
     HardenedStep,
+    NoWildcard,
 }
 
 impl fmt::Display for NonDefiniteKeyError {
@@ -368,6 +369,9 @@ impl fmt::Display for NonDefiniteKeyError {
             Self::HardenedStep => {
                 f.write_str("key with hardened derivation steps cannot be a DerivedDescriptorKey")
             }
+            Self::NoWildcard => {
+                f.write_str("descriptor does not have a wildcard; cannot derive at index")
+            }
         }
     }
 }