miniscript: add a helper to find the first insane sub with no child

This is helpful for finer grained descriptor parsing error: when there
are multiple errors to report in a Miniscript descriptor start with the
"smallest" fragments: the ones closer to be a leaf.

Co-Authored-By: Pieter Wuille <pieter@wuille.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/test/miniscript_tests.cpp b/src/test/miniscript_tests.cpp
index 6a5bee1d1b..bc5c49ef63 100644
--- a/src/test/miniscript_tests.cpp
+++ b/src/test/miniscript_tests.cpp
@@ -111,6 +111,10 @@ struct KeyConverter {
         assert(it != g_testdata->pkmap.end());
         return it->second;
     }
+
+    std::optional<std::string> ToString(const Key& key) const {
+        return HexStr(ToPKBytes(key));
+    }
 };
 
 //! Singleton instance of KeyConverter.
@@ -290,6 +294,15 @@ BOOST_AUTO_TEST_CASE(fixed_tests)
     // Same when the duplicates are on different levels in the tree
     const auto ms_dup4 = miniscript::FromString("thresh(2,pkh(03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65),s:pk(03fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556),a:and_b(dv:older(1),s:pk(03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65)))", CONVERTER);
     BOOST_CHECK(ms_dup4 && !ms_dup4->IsSane() && !ms_dup4->CheckDuplicateKey());
+    // Test we find the first insane sub closer to be a leaf node. This fragment is insane for two reasons:
+    // 1. It can be spent without a signature
+    // 2. It contains timelock mixes
+    // We'll report the timelock mix error, as it's "deeper" (closer to be a leaf node) than the "no 's' property"
+    // error is.
+    const auto ms_ins = miniscript::FromString("or_i(and_b(after(1),a:after(1000000000)),pk(03cdabb7f2dce7bfbd8a0b9570c6fd1e712e5d64045e9d6b517b3d5072251dc204))", CONVERTER);
+    BOOST_CHECK(ms_ins && ms_ins->IsValid() && !ms_ins->IsSane());
+    const auto insane_sub = ms_ins->FindInsaneSub();
+    BOOST_CHECK(insane_sub && *insane_sub->ToString(CONVERTER) == "and_b(after(1),a:after(1000000000))");
 
     // Timelock tests
     Test("after(100)", "?", TESTMODE_VALID | TESTMODE_NONMAL); // only heightlock