Implement rawtr() descriptor

lib/bitcoin/descriptor.rb

@@ -19,6 +19,7 @@ module Descriptor
     autoload :Tr,  'bitcoin/descriptor/tr'
     autoload :MultiA,  'bitcoin/descriptor/multi_a'
     autoload :SortedMultiA, 'bitcoin/descriptor/sorted_multi_a'
+    autoload :RawTr,  'bitcoin/descriptor/raw_tr'
     autoload :Checksum, 'bitcoin/descriptor/checksum'
 
     module_function
@@ -104,6 +105,13 @@ def tr(key, tree = nil)
       Tr.new(key, tree)
     end
 
+    # Generate taproot output script descriptor.
+    # @param [String] key
+    # @return [Bitcoin::Descriptor::RawTr]
+    def rawtr(key)
+      RawTr.new(key)
+    end
+
     # Generate tapscript multisig output for given keys.
     # @param [Integer] threshold the threshold of multisig.
     # @param [Array[String]] keys an array of keys.
@@ -169,6 +177,8 @@ def parse(string, top_level = true)
         else
           tr(key, parse(rest, false))
         end
+      when 'rawtr'
+        rawtr(args_str)
       else
         raise ArgumentError, "Parse failed: #{string}"
       end

lib/bitcoin/descriptor/raw_tr.rb

@@ -0,0 +1,21 @@
+module Bitcoin
+  module Descriptor
+    # rawtr() expression
+    class RawTr < KeyExpression
+      include Bitcoin::Opcodes
+
+      def type
+        :rawtr
+      end
+
+      def top_level?
+        true
+      end
+
+      def to_script
+        k = extract_pubkey(key)
+        Bitcoin::Script.new << OP_1 << k.xonly_pubkey
+      end
+    end
+  end
+end

spec/bitcoin/descriptor_spec.rb

@@ -405,4 +405,17 @@
         .to raise_error(ArgumentError, "Multisig threshold cannot be larger than the number of keys.")
     end
   end
+
+  describe 'rawtr()' do
+    it do
+      expect(rawtr("xprv9vHkqa6EV4sPZHYqZznhT2NPtPCjKuDKGY38FBWLvgaDx45zo9WQRUT3dKYnjwih2yJD9mkrocEZXo1ex8G81dwSM1fwqWpWkeS3v86pgKt/86'/1'/0'/1/0").to_hex).
+        to eq('51205172af752f057d543ce8e4a6f8dcf15548ec6be44041bfa93b72e191cfc8c1ee')
+      desc_rawtr = "rawtr(xprv9vHkqa6EV4sPZHYqZznhT2NPtPCjKuDKGY38FBWLvgaDx45zo9WQRUT3dKYnjwih2yJD9mkrocEZXo1ex8G81dwSM1fwqWpWkeS3v86pgKt/86'/1'/0'/1/0)#q8dqvgc8"
+      rawtr = described_class.parse(desc_rawtr)
+      expect(rawtr.to_s(checksum: true)).to eq(desc_rawtr)
+      expect(rawtr('L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1').to_hex).to eq('5120a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd')
+      desc_rawtr = "rawtr(xpub68FQ9imX6mCWacw6eNRjaa8q8ynnHmUd5i7MVR51ZMPP5JycyfVHSLQVFPHMYiTybWJnSBL2tCBpy6aJTR2DYrshWYfwAxs8SosGXd66d8/*, xpub69Mvq3QMipdvnd9hAyeTnT5jrkcBuLErV212nsGf3qr7JPWysc9HnNhCsazdzj1etSx28hPSE8D7DnceFbNdw4Kg8SyRfjE2HFLv1P8TSGc/*)"
+      expect{described_class.parse(desc_rawtr)}.to raise_error(ArgumentError)
+    end
+  end
 end