Merge bitcoin/bitcoin#29130: wallet: Add `createwalletdescriptor` and `gethdkeys` RPCs for adding new automatically generated descriptors

746b6d88395607abbd3c13bbdcdd4ca83e9bc9e4 test: Add test for createwalletdescriptor (Ava Chow)
2402b6306215a9ee8d5f4068ea81f4e7f324adeb wallet: Test upgrade of pre-taproot wallet to have tr() descriptors (Ava Chow)
460ae1bf67c0051033c1802d44787d173abb9248 wallet, rpc: Add createwalletdescriptor RPC (Ava Chow)
8e1a475062e62321e58a0624385cc3fa0885aa12 wallet: Be able to retrieve single key from descriptors (Ava Chow)
85b1fb19dd3a3f3c68da1c5e60a6eb911e1119a6 wallet: Add GetActiveHDPubKeys to retrieve xpubs from active descriptors (Ava Chow)
73926f2d31b61ff78d5f0c8f9b5e3130fb1f9620 wallet, descspkm: Refactor wallet descriptor generation to standalone func (Andrew Chow)
54e74f46ea10e479be682750c1279165f29bb2f4 wallet: Refactor function for single DescSPKM setup (Andrew Chow)
3b09d0eb7f2c1d6ebdab73d18db28e5bf7d74f18 tests: Test for gethdkeys (Ava Chow)
5febe28c9e131fb93fac9c35f80c42759654f150 wallet, rpc: Add gethdkeys RPC (Ava Chow)
66632e5c24c1b59afef1e89b562fbd0117ab6ef5 wallet: Add IsActiveScriptPubKeyMan (Ava Chow)
fa6a259985b61235ebc21eae2a76014cc9437d5f desc spkm: Add functions to retrieve specific private keys (Ava Chow)
fe67841464cc0f970a1c233caba92cb78e9c78dc descriptor: Be able to get the pubkeys involved in a descriptor (Ava Chow)
ef6745879d87cdb6f1061337867a689167e965a1 key: Add constructor for CExtKey that takes CExtPubKey and CKey (Ava Chow)

Pull request description:

  This PR adds a `createwalletdescriptor` RPC which allows users to add new automatically generated descriptors to their wallet, e.g. to upgrade a 0.21.x wallet to contain a taproot descriptor. This RPC takes 3 arguments: the output type to create a descriptor for, whether the descriptor will be internal or external, and the HD key to use if the user wishes to use a specific key. The HD key is an optional parameter. If it is not specified, the wallet will use the key shared by the active descriptors, if they are all single key. For most users in the expected upgrade scenario, this should be sufficient. In more advanced cases, the user must specify the HD key to use.

  Currently, specified HD keys must already exist in the wallet. To make it easier for the user to know, `gethdkeys` is also added to list out the HD keys in use by all of the descriptors in the wallet. This will include all HD keys, whether we have the private key, for it, which descriptors use it and their activeness, and optionally the extended private key. In this way, users with more complex wallets will be still be able to get HD keys from their wallet for use in other scenarios, and if they want to use `createwalletdescriptor`, they can easily get the keys that they can specify to it.

  See also https://github.com/bitcoin/bitcoin/pull/26728#issuecomment-1866961865

ACKs for top commit:
  Sjors:
    re-utACK 746b6d88395607abbd3c13bbdcdd4ca83e9bc9e4
  furszy:
    ACK 746b6d8
  ryanofsky:
    Code review ACK 746b6d88395607abbd3c13bbdcdd4ca83e9bc9e4, and this looks ready to merge. There were various suggested changes since last review where main change seems to be switching `gethdkeys` output to use normalized descriptors (removing hardened path components).

Tree-SHA512: f2849101e6fbf1f59cb031eaaaee97af5b1ae92aaab54c5716940d210f08ab4fc952df2725b636596cd5747b8f5beb1a7a533425bc10d09da02659473516fbda

2 files changed, 49 insertions, 0 deletions

diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index c6bc5f8f1d..a0e755afac 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -212,6 +212,11 @@ public:
 
     /** Derive a private key, if private data is available in arg. */
     virtual bool GetPrivKey(int pos, const SigningProvider& arg, CKey& key) const = 0;
+
+    /** Return the non-extended public key for this PubkeyProvider, if it has one. */
+    virtual std::optional<CPubKey> GetRootPubKey() const = 0;
+    /** Return the extended public key for this PubkeyProvider, if it has one. */
+    virtual std::optional<CExtPubKey> GetRootExtPubKey() const = 0;
 };
 
 class OriginPubkeyProvider final : public PubkeyProvider
@@ -265,6 +270,14 @@ public:
     {
         return m_provider->GetPrivKey(pos, arg, key);
     }
+    std::optional<CPubKey> GetRootPubKey() const override
+    {
+        return m_provider->GetRootPubKey();
+    }
+    std::optional<CExtPubKey> GetRootExtPubKey() const override
+    {
+        return m_provider->GetRootExtPubKey();
+    }
 };
 
 /** An object representing a parsed constant public key in a descriptor. */
@@ -310,6 +323,14 @@ public:
     {
         return arg.GetKey(m_pubkey.GetID(), key);
     }
+    std::optional<CPubKey> GetRootPubKey() const override
+    {
+        return m_pubkey;
+    }
+    std::optional<CExtPubKey> GetRootExtPubKey() const override
+    {
+        return std::nullopt;
+    }
 };
 
 enum class DeriveType {
@@ -525,6 +546,14 @@ public:
         key = extkey.key;
         return true;
     }
+    std::optional<CPubKey> GetRootPubKey() const override
+    {
+        return std::nullopt;
+    }
+    std::optional<CExtPubKey> GetRootExtPubKey() const override
+    {
+        return m_root_extkey;
+    }
 };
 
 /** Base class for all Descriptor implementations. */
@@ -720,6 +749,19 @@ public:
     std::optional<int64_t> MaxSatisfactionWeight(bool) const override { return {}; }
 
     std::optional<int64_t> MaxSatisfactionElems() const override { return {}; }
+
+    void GetPubKeys(std::set<CPubKey>& pubkeys, std::set<CExtPubKey>& ext_pubs) const override
+    {
+        for (const auto& p : m_pubkey_args) {
+            std::optional<CPubKey> pub = p->GetRootPubKey();
+            if (pub) pubkeys.insert(*pub);
+            std::optional<CExtPubKey> ext_pub = p->GetRootExtPubKey();
+            if (ext_pub) ext_pubs.insert(*ext_pub);
+        }
+        for (const auto& arg : m_subdescriptor_args) {
+            arg->GetPubKeys(pubkeys, ext_pubs);
+        }
+    }
 };
 
 /** A parsed addr(A) descriptor. */
diff --git a/src/script/descriptor.h b/src/script/descriptor.h
index caa5d1608d..e78a775330 100644
--- a/src/script/descriptor.h
+++ b/src/script/descriptor.h
@@ -158,6 +158,13 @@ struct Descriptor {
 
     /** Get the maximum size number of stack elements for satisfying this descriptor. */
     virtual std::optional<int64_t> MaxSatisfactionElems() const = 0;
+
+    /** Return all (extended) public keys for this descriptor, including any from subdescriptors.
+     *
+     * @param[out] pubkeys Any public keys
+     * @param[out] ext_pubs Any extended public keys
+     */
+    virtual void GetPubKeys(std::set<CPubKey>& pubkeys, std::set<CExtPubKey>& ext_pubs) const = 0;
 };
 
 /** Parse a `descriptor` string. Included private keys are put in `out`.