Add compile_tr() policy compiler for Taptree-native descriptors

Author: kwsantiago

src/CMakeLists.txt

@@ -181,6 +181,7 @@ add_library(bitcoin_common STATIC EXCLUDE_FROM_ALL
   script/descriptor.cpp
   script/miniscript.cpp
   script/parsing.cpp
+  script/policy.cpp
   script/sign.cpp
   script/signingprovider.cpp
   script/solver.cpp

src/script/descriptor.cpp

@@ -9,6 +9,7 @@
 #include <pubkey.h>
 #include <script/miniscript.h>
 #include <script/parsing.h>
+#include <script/policy.h>
 #include <script/script.h>
 #include <script/signingprovider.h>
 #include <script/solver.h>
@@ -1941,6 +1942,55 @@ std::vector<std::unique_ptr<DescriptorImpl>> ParseScript(uint32_t& key_exp_index
         error = "Can only have addr() at top level";
         return {};
     }
+    if (ctx == ParseScriptContext::TOP && Func("compile_tr", expr)) {
+        auto arg = Expr(expr);
+        auto internal_keys = ParsePubkey(key_exp_index, arg, ParseScriptContext::P2TR, out, error);
+        if (internal_keys.empty()) {
+            error = strprintf("compile_tr(): %s", error);
+            return {};
+        }
+        ++key_exp_index;
+        if (!Const(",", expr)) {
+            error = "compile_tr(): expected ',' after internal key";
+            return {};
+        }
+
+        KeyParser parser(/*out = */&out, /* in = */nullptr, /* ctx = */miniscript::MiniscriptContext::TAPSCRIPT, key_exp_index);
+        auto pol = policy::ParsePolicy<uint32_t>(expr, parser);
+        if (!pol) {
+            error = "compile_tr(): invalid policy expression";
+            if (!parser.m_key_parsing_error.empty()) error = strprintf("compile_tr(): %s", parser.m_key_parsing_error);
+            return {};
+        }
+
+        auto result = policy::CompileTrNative<uint32_t>(*pol);
+        if (!result) {
+            error = "compile_tr(): policy compilation failed (too many leaves or unsupported policy)";
+            return {};
+        }
+
+        auto& [scripts, depths] = *result;
+
+        // Each compiled leaf's Node<uint32_t> uses key indices from parser.m_keys.
+        // Give each MiniscriptDescriptor a clone of all keys so indices resolve correctly.
+        std::vector<std::unique_ptr<DescriptorImpl>> descs;
+        for (size_t i = 0; i < scripts.size(); ++i) {
+            std::vector<std::unique_ptr<PubkeyProvider>> leaf_keys;
+            for (const auto& key_vec : parser.m_keys) {
+                leaf_keys.push_back(key_vec.at(0)->Clone());
+            }
+            descs.push_back(std::make_unique<MiniscriptDescriptor>(
+                std::move(leaf_keys), std::move(scripts[i])));
+        }
+
+        key_exp_index += parser.m_keys.size();
+        ret.emplace_back(std::make_unique<TRDescriptor>(std::move(internal_keys.at(0)), std::move(descs), depths));
+        return ret;
+
+    } else if (Func("compile_tr", expr)) {
+        error = "Can only have compile_tr at top level";
+        return {};
+    }
     if (ctx == ParseScriptContext::TOP && Func("tr", expr)) {
         auto arg = Expr(expr);
         auto internal_keys = ParsePubkey(key_exp_index, arg, ParseScriptContext::P2TR, out, error);

src/script/policy.cpp

@@ -0,0 +1,5 @@
+// Copyright (c) 2026 The Bitcoin Knots developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <script/policy.h>