Merge bitcoin/bitcoin#26567: Wallet: estimate the size of signed inputs using descriptors

10546a569c wallet: accurately account for the size of the witness stack (Antoine Poinsot)
9b7ec393b8 wallet: use descriptor satisfaction size to estimate inputs size (Antoine Poinsot)
8d870a9873 script/signingprovider: introduce a MultiSigningProvider (Antoine Poinsot)
fa7c46b503 descriptor: introduce a method to get the satisfaction size (Antoine Poinsot)
bdba7667d2 miniscript: introduce a helper to get the maximum witness size (Antoine Poinsot)
4ab382c2cd miniscript: make GetStackSize independent of P2WSH context (Antoine Poinsot)

Pull request description:

  The wallet currently estimates the size of a signed input by doing a dry run of the signing logic. This is unnecessary since all outputs we can sign for can be represented by a descriptor, and we can derive the size of a satisfaction ("signature") directly from the descriptor itself.
  In addition, the current approach does not generalize well: dry runs of the signing logic are only possible for the most basic scripts. See for instance the discussion in #24149 around that.

  This introduces a method to get the maximum size of a satisfaction from a descriptor, and makes the wallet use that instead of the dry-run.

ACKs for top commit:
  sipa:
    utACK 10546a569c
  achow101:
    re-ACK 10546a569c

Tree-SHA512: 43ed1529fbd30af709d903c8c5063235e8c6a03b500bc8f144273d6184e23a53edf0fea9ef898ed57d8a40d73208b5d935cc73b94a24fad3ad3c63b3b2027174

src/test/fuzz/descriptor_parse.cpp

@@ -112,7 +112,7 @@ static void TestDescriptor(const Descriptor& desc, FlatSigningProvider& sig_prov
 {
     // Trivial helpers.
     (void)desc.IsRange();
-    (void)desc.IsSolvable();
+    const bool is_solvable{desc.IsSolvable()};
     (void)desc.IsSingleType();
     (void)desc.GetOutputType();
 
@@ -131,7 +131,19 @@ static void TestDescriptor(const Descriptor& desc, FlatSigningProvider& sig_prov
     // If we could serialize to script we must be able to infer using the same provider.
     if (!out_scripts.empty()) {
         assert(InferDescriptor(out_scripts.back(), sig_provider));
+
+        // The ScriptSize() must match the size of the serialized Script. (ScriptSize() is set for all descs but 'combo()'.)
+        const bool is_combo{!desc.IsSingleType()};
+        assert(is_combo || desc.ScriptSize() == out_scripts.back().size());
     }
+
+    const auto max_sat_maxsig{desc.MaxSatisfactionWeight(true)};
+    const auto max_sat_nonmaxsig{desc.MaxSatisfactionWeight(true)};
+    const auto max_elems{desc.MaxSatisfactionElems()};
+    // We must be able to estimate the max satisfaction size for any solvable descriptor (but combo).
+    const bool is_nontop_or_nonsolvable{!is_solvable || !desc.GetOutputType()};
+    const bool is_input_size_info_set{max_sat_maxsig && max_sat_nonmaxsig && max_elems};
+    assert(is_input_size_info_set || is_nontop_or_nonsolvable);
 }
 
 void initialize_descriptor_parse()

src/test/fuzz/miniscript.cpp

@@ -973,7 +973,7 @@ void TestNode(const NodeRef& node, FuzzedDataProvider& provider)
 
     if (nonmal_success) {
         // Non-malleable satisfactions are bounded by GetStackSize().
-        assert(witness_nonmal.stack.size() <= *node->GetStackSize());
+        assert(witness_nonmal.stack.size() <= *node->GetStackSize() + 1);
         // If a non-malleable satisfaction exists, the malleable one must also exist, and be identical to it.
         assert(mal_success);
         assert(witness_nonmal.stack == witness_mal.stack);