Merge bitcoin/bitcoin#27636: kernel: Remove util/system from kernel library, interface_ui from validation.

7d3b35004b039f2bd606bb46a540de7babdbc41e refactor: Move system from util to common library (TheCharlatan)
7eee356c0a7fefd70c8de21689efa335f52a69ba refactor: Split util::AnyPtr into its own file (TheCharlatan)
44de325d95447498036479c3112ba741caf45bf6 refactor: Split util::insert into its own file (TheCharlatan)
9ec5da36b62276ae22e348f26f88aaf646357d6d refactor: Move ScheduleBatchPriority to its own file (TheCharlatan)
f871c69191dfe1331861ebcdbadb6bd47e45c8b1 kernel: Add warning method to notifications (TheCharlatan)
4452707edec91c7d7991f486dd41ef3edb4f7fbf kernel: Add progress method to notifications (TheCharlatan)
84d71457e7250ab25c0a11d1ad1c7657197ffd90 kernel: Add headerTip method to notifications (TheCharlatan)
447761c8228d58f948aae7e73ed079c028cacb97 kernel: Add notification interface (TheCharlatan)

Pull request description:

  This pull request is part of the `libbitcoinkernel` project https://github.com/bitcoin/bitcoin/issues/27587 https://github.com/bitcoin/bitcoin/projects/18 and more specifically its "Step 2: Decouple most non-consensus code from libbitcoinkernel".

  ---

  It removes the kernel library's dependency on `util/system` and `interface_ui`. `util/system` contains networking and shell-related code that should not be part of the kernel library. The following pull requests prepared `util/system` for this final step: https://github.com/bitcoin/bitcoin/pull/27419 https://github.com/bitcoin/bitcoin/pull/27254 https://github.com/bitcoin/bitcoin/pull/27238.

  `interface_ui` defines functions for a more general node interface and has a dependency on `boost/signals2`. After applying the patches from this pull request, the kernel's reliance on boost is down to `boost::multiindex`.

  The approach implemented here introduces some indirection, which makes the code a bit harder to read. Any suggestions for improving or reworking this pull request to make it more concise, or even reworking it into a more proper interface, are appreciated.

ACKs for top commit:
  MarcoFalke:
    re-ACK 7d3b35004b039f2bd606bb46a540de7babdbc41e (no change) 🎋
  stickies-v:
    Code Review ACK 7d3b35004b039f2bd606bb46a540de7babdbc41e
  hebasto:
    re-ACK 7d3b35004b039f2bd606bb46a540de7babdbc41e, only last two commits dropped since my [recent](https://github.com/bitcoin/bitcoin/pull/27636#pullrequestreview-1435394620) review.

Tree-SHA512: c8cfc698dc9d78e20191c444708f2d957501229abe95e5806106d1126fb9c5fbcee686fb55645658c0107ce71f10646f37a2fdf7fde16bbf22cbf1ac885dd08d

2 files changed, 36 insertions, 0 deletions

diff --git a/src/kernel/chainstatemanager_opts.h b/src/kernel/chainstatemanager_opts.h
index 2395f60164..917f7d226c 100644
--- a/src/kernel/chainstatemanager_opts.h
+++ b/src/kernel/chainstatemanager_opts.h
@@ -5,6 +5,8 @@
 #ifndef BITCOIN_KERNEL_CHAINSTATEMANAGER_OPTS_H
 #define BITCOIN_KERNEL_CHAINSTATEMANAGER_OPTS_H
 
+#include <kernel/notifications_interface.h>
+
 #include <arith_uint256.h>
 #include <dbwrapper.h>
 #include <txdb.h>
@@ -42,6 +44,7 @@ struct ChainstateManagerOpts {
     DBOptions block_tree_db{};
     DBOptions coins_db{};
     CoinsViewOptions coins_view{};
+    Notifications& notifications;
 };
 
 } // namespace kernel
diff --git a/src/kernel/notifications_interface.h b/src/kernel/notifications_interface.h
new file mode 100644
index 0000000000..48248e9aa0
--- /dev/null
+++ b/src/kernel/notifications_interface.h
@@ -0,0 +1,33 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H
+#define BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H
+
+#include <cstdint>
+#include <string>
+
+class CBlockIndex;
+enum class SynchronizationState;
+struct bilingual_str;
+
+namespace kernel {
+
+/**
+ * A base class defining functions for notifying about certain kernel
+ * events.
+ */
+class Notifications
+{
+public:
+    virtual ~Notifications(){};
+
+    virtual void blockTip(SynchronizationState state, CBlockIndex& index) {}
+    virtual void headerTip(SynchronizationState state, int64_t height, int64_t timestamp, bool presync) {}
+    virtual void progress(const bilingual_str& title, int progress_percent, bool resume_possible) {}
+    virtual void warning(const bilingual_str& warning) {}
+};
+} // namespace kernel
+
+#endif // BITCOIN_KERNEL_NOTIFICATIONS_INTERFACE_H