Merge #399: Use KeySource instead of tuple

f8945d0 Use KeySource instead of tuple (Tobin C. Harding)

Pull request description:

  Clippy emits:

   warning: very complex type used. Consider factoring parts into `type` definitions

  The type we return is more complex than needed because we do not use the `bip32::KeySource` alias but instead write the full tuple `(byp32::Fingerprint, bip32::DerivationPath)`.

  To fix the clippy warning we have at least 3 options

  1. Add an alias for the complex return type
  2. Add a compiler directive to quieten clippy
  3. Use `bip32::KeySource` instead of tuple

  (1) seems like an overkill
  (2) means we loose lint coverage for the whole function

  Elect to do (3), the best of 3 imperfect solutions.

ACKs for top commit:
  apoelstra:
    ACK f8945d0
  sanket1729:
    ACK f8945d0

Tree-SHA512: a3f8112d29cdb81d09492277958cad895bdcc4cb933d68b4d25c02cf0ca079922a0d903c3e48ec701bc51f15d8c66d05e9dc7ba56031c28d4a88bc7df1fbaa89

Author: sanket1729

src/descriptor/key.rs

@@ -539,8 +539,7 @@ impl FromStr for DescriptorSecretKey {
 impl<K: InnerXKey> DescriptorXKey<K> {
     fn parse_xkey_origin(
         s: &str,
-    ) -> Result<(&str, Option<(bip32::Fingerprint, bip32::DerivationPath)>), DescriptorKeyParseError>
-    {
+    ) -> Result<(&str, Option<bip32::KeySource>), DescriptorKeyParseError> {
         for ch in s.as_bytes() {
             if *ch < 20 || *ch > 127 {
                 return Err(DescriptorKeyParseError(