Merge bitcoin/bitcoin#23006: multiprocess: Add new bitcoin-gui, bitcoin-qt, bitcoin-wallet init implementations

d5f985e51f multiprocess: Add new bitcoin-gui, bitcoin-qt, bitcoin-wallet init implementations (Russell Yanofsky)

Pull request description:

  Add separate `interfaces::Init` subclasses for `bitcoin-wallet`,  `bitcoin-gui`, and `bitcoin-qt` binaries instead of sharing `bitcoind` and `bitcoin-node` init subclasses in different binaries. After this, the new init subclasses can be customized in #10102, so node and wallet code is dropped from the `bitcoin-gui` binary and wallet code is dropped from into the `bitcoin-node` binary.

  ---

  This PR is part of the [process separation project](https://github.com/bitcoin/bitcoin/projects/10).

ACKs for top commit:
  lsilva01:
    reACK d5f985e
  hebasto:
    re-ACK d5f985e51f, only suggested changes since my [previous](https://github.com/bitcoin/bitcoin/pull/23006#pullrequestreview-787537444) review.

Tree-SHA512: 6784210bd9ce3a6fbc66852680d0e9bc513c072dc538aeb7f48cb6a41580d3f567ccef04f975ee767a714a4b05d4d87273e94a79abda1b9c25d5ac4bbe752006

src/init/bitcoin-gui.cpp

@@ -0,0 +1,47 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <interfaces/chain.h>
+#include <interfaces/echo.h>
+#include <interfaces/init.h>
+#include <interfaces/ipc.h>
+#include <interfaces/node.h>
+#include <interfaces/wallet.h>
+#include <node/context.h>
+#include <util/system.h>
+
+#include <memory>
+
+namespace init {
+namespace {
+const char* EXE_NAME = "bitcoin-gui";
+
+class BitcoinGuiInit : public interfaces::Init
+{
+public:
+    BitcoinGuiInit(const char* arg0) : m_ipc(interfaces::MakeIpc(EXE_NAME, arg0, *this))
+    {
+        m_node.args = &gArgs;
+        m_node.init = this;
+    }
+    std::unique_ptr<interfaces::Node> makeNode() override { return interfaces::MakeNode(m_node); }
+    std::unique_ptr<interfaces::Chain> makeChain() override { return interfaces::MakeChain(m_node); }
+    std::unique_ptr<interfaces::WalletClient> makeWalletClient(interfaces::Chain& chain) override
+    {
+        return MakeWalletClient(chain, *Assert(m_node.args));
+    }
+    std::unique_ptr<interfaces::Echo> makeEcho() override { return interfaces::MakeEcho(); }
+    interfaces::Ipc* ipc() override { return m_ipc.get(); }
+    NodeContext m_node;
+    std::unique_ptr<interfaces::Ipc> m_ipc;
+};
+} // namespace
+} // namespace init
+
+namespace interfaces {
+std::unique_ptr<Init> MakeGuiInit(int argc, char* argv[])
+{
+    return std::make_unique<init::BitcoinGuiInit>(argc > 0 ? argv[0] : "");
+}
+} // namespace interfaces

src/init/bitcoin-qt.cpp

@@ -0,0 +1,42 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <interfaces/chain.h>
+#include <interfaces/echo.h>
+#include <interfaces/init.h>
+#include <interfaces/node.h>
+#include <interfaces/wallet.h>
+#include <node/context.h>
+#include <util/system.h>
+
+#include <memory>
+
+namespace init {
+namespace {
+class BitcoinQtInit : public interfaces::Init
+{
+public:
+    BitcoinQtInit()
+    {
+        m_node.args = &gArgs;
+        m_node.init = this;
+    }
+    std::unique_ptr<interfaces::Node> makeNode() override { return interfaces::MakeNode(m_node); }
+    std::unique_ptr<interfaces::Chain> makeChain() override { return interfaces::MakeChain(m_node); }
+    std::unique_ptr<interfaces::WalletClient> makeWalletClient(interfaces::Chain& chain) override
+    {
+        return MakeWalletClient(chain, *Assert(m_node.args));
+    }
+    std::unique_ptr<interfaces::Echo> makeEcho() override { return interfaces::MakeEcho(); }
+    NodeContext m_node;
+};
+} // namespace
+} // namespace init
+
+namespace interfaces {
+std::unique_ptr<Init> MakeGuiInit(int argc, char* argv[])
+{
+    return std::make_unique<init::BitcoinQtInit>();
+}
+} // namespace interfaces

src/init/bitcoin-wallet.cpp

@@ -0,0 +1,12 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <interfaces/init.h>
+
+namespace interfaces {
+std::unique_ptr<Init> MakeWalletInit(int argc, char* argv[], int& exit_status)
+{
+    return std::make_unique<Init>();
+}
+} // namespace interfaces