introduce and use the generalized `node::Warnings` interface

Instead of having separate warning functions (and globals) for each
different warning that can be raised, encapsulate this logic into
a single class and allow to (un)set any number of warnings.

Introduces behaviour change:
- the `-alertnotify` command is executed for all
  `KernelNotifications::warningSet` calls, which now also covers the
  `LARGE_WORK_INVALID_CHAIN` warning.
- previously, warnings were returned based on a predetermined order,
  e.g. with the "pre-release test build" warning always first. This
  is no longer the case, and Warnings::GetMessages() will return
  messages sorted by the id of the warning.

Removes warnings.cpp from kernel.

7 files changed, 117 insertions, 70 deletions

diff --git a/src/node/abort.cpp b/src/node/abort.cpp
index 6f836824b2..68c09f0ef7 100644
--- a/src/node/abort.cpp
+++ b/src/node/abort.cpp
@@ -12,13 +12,12 @@
 
 #include <atomic>
 #include <cstdlib>
-#include <string>
 
 namespace node {
 
 void AbortNode(util::SignalInterrupt* shutdown, std::atomic<int>& exit_status, const bilingual_str& message)
 {
-    SetMiscWarning(message);
+    g_warnings.Set(Warning::FATAL_INTERNAL_ERROR, message);
     InitError(_("A fatal internal error occurred, see debug.log for details: ") + message);
     exit_status.store(EXIT_FAILURE);
     if (shutdown && !(*shutdown)()) {
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index 88af9dadbc..9ea3f63fdf 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -93,7 +93,7 @@ public:
     explicit NodeImpl(NodeContext& context) { setContext(&context); }
     void initLogging() override { InitLogging(args()); }
     void initParameterInteraction() override { InitParameterInteraction(args()); }
-    bilingual_str getWarnings() override { return Join(GetWarnings(), Untranslated("<hr />")); }
+    bilingual_str getWarnings() override { return Join(node::g_warnings.GetMessages(), Untranslated("<hr />")); }
     int getExitStatus() override { return Assert(m_context)->exit_status.load(); }
     uint32_t getLogCategories() override { return LogInstance().GetCategoryMask(); }
     bool baseInitialize() override
diff --git a/src/node/kernel_notifications.cpp b/src/node/kernel_notifications.cpp
index 1900ac3117..e18919f503 100644
--- a/src/node/kernel_notifications.cpp
+++ b/src/node/kernel_notifications.cpp
@@ -10,6 +10,7 @@
 #include <common/args.h>
 #include <common/system.h>
 #include <kernel/context.h>
+#include <kernel/warning.h>
 #include <logging.h>
 #include <node/abort.h>
 #include <node/interface_ui.h>
@@ -46,16 +47,6 @@ static void AlertNotify(const std::string& strMessage)
 #endif
 }
 
-static void DoWarning(const bilingual_str& warning)
-{
-    static bool fWarned = false;
-    node::SetMiscWarning(warning);
-    if (!fWarned) {
-        AlertNotify(warning.original);
-        fWarned = true;
-    }
-}
-
 namespace node {
 
 kernel::InterruptResult KernelNotifications::blockTip(SynchronizationState state, CBlockIndex& index)
@@ -80,9 +71,16 @@ void KernelNotifications::progress(const bilingual_str& title, int progress_perc
     uiInterface.ShowProgress(title.translated, progress_percent, resume_possible);
 }
 
-void KernelNotifications::warning(const bilingual_str& warning)
+void KernelNotifications::warningSet(kernel::Warning id, const bilingual_str& message)
+{
+    if (node::g_warnings.Set(id, message)) {
+        AlertNotify(message.original);
+    }
+}
+
+void KernelNotifications::warningUnset(kernel::Warning id)
 {
-    DoWarning(warning);
+    g_warnings.Unset(id);
 }
 
 void KernelNotifications::flushError(const bilingual_str& message)
diff --git a/src/node/kernel_notifications.h b/src/node/kernel_notifications.h
index f4d97a0fff..96f09be453 100644
--- a/src/node/kernel_notifications.h
+++ b/src/node/kernel_notifications.h
@@ -15,6 +15,10 @@ class CBlockIndex;
 enum class SynchronizationState;
 struct bilingual_str;
 
+namespace kernel {
+enum class Warning;
+} // namespace kernel
+
 namespace util {
 class SignalInterrupt;
 } // namespace util
@@ -34,7 +38,9 @@ public:
 
     void progress(const bilingual_str& title, int progress_percent, bool resume_possible) override;
 
-    void warning(const bilingual_str& warning) override;
+    void warningSet(kernel::Warning id, const bilingual_str& message) override;
+
+    void warningUnset(kernel::Warning id) override;
 
     void flushError(const bilingual_str& message) override;
 
diff --git a/src/node/timeoffsets.cpp b/src/node/timeoffsets.cpp
index 17ee44a92c..b839b60565 100644
--- a/src/node/timeoffsets.cpp
+++ b/src/node/timeoffsets.cpp
@@ -49,7 +49,7 @@ bool TimeOffsets::WarnIfOutOfSync() const
     // when median == std::numeric_limits<int64_t>::min(), calling std::chrono::abs is UB
     auto median{std::max(Median(), std::chrono::seconds(std::numeric_limits<int64_t>::min() + 1))};
     if (std::chrono::abs(median) <= WARN_THRESHOLD) {
-        node::SetMedianTimeOffsetWarning(std::nullopt);
+        node::g_warnings.Unset(node::Warning::CLOCK_OUT_OF_SYNC);
         uiInterface.NotifyAlertChanged();
         return false;
     }
@@ -63,7 +63,7 @@ bool TimeOffsets::WarnIfOutOfSync() const
         "RPC methods to get more info."
     ), Ticks<std::chrono::minutes>(WARN_THRESHOLD))};
     LogWarning("%s\n", msg.original);
-    node::SetMedianTimeOffsetWarning(msg);
+    node::g_warnings.Set(node::Warning::CLOCK_OUT_OF_SYNC, msg);
     uiInterface.NotifyAlertChanged();
     return true;
 }
diff --git a/src/node/warnings.cpp b/src/node/warnings.cpp
index 9d2239e64a..8a94eb0bd2 100644
--- a/src/node/warnings.cpp
+++ b/src/node/warnings.cpp
@@ -12,69 +12,53 @@
 #include <univalue.h>
 #include <util/translation.h>
 
-#include <optional>
+#include <utility>
 #include <vector>
 
-static GlobalMutex g_warnings_mutex;
-static bilingual_str g_misc_warnings GUARDED_BY(g_warnings_mutex);
-static bool fLargeWorkInvalidChainFound GUARDED_BY(g_warnings_mutex) = false;
-static std::optional<bilingual_str> g_timeoffset_warning GUARDED_BY(g_warnings_mutex){};
-
 namespace node {
-void SetMiscWarning(const bilingual_str& warning)
+Warnings g_warnings;
+
+Warnings::Warnings()
 {
-    LOCK(g_warnings_mutex);
-    g_misc_warnings = warning;
+    // Pre-release build warning
+    if (!CLIENT_VERSION_IS_RELEASE) {
+        m_warnings.insert(
+            {Warning::PRE_RELEASE_TEST_BUILD,
+             _("This is a pre-release test build - use at your own risk - do not use for mining or merchant applications")});
+    }
 }
-
-void SetfLargeWorkInvalidChainFound(bool flag)
+bool Warnings::Set(warning_type id, bilingual_str message)
 {
-    LOCK(g_warnings_mutex);
-    fLargeWorkInvalidChainFound = flag;
+    LOCK(m_mutex);
+    const auto& [_, inserted]{m_warnings.insert({id, std::move(message)})};
+    return inserted;
 }
 
-void SetMedianTimeOffsetWarning(std::optional<bilingual_str> warning)
+bool Warnings::Unset(warning_type id)
 {
-    LOCK(g_warnings_mutex);
-    g_timeoffset_warning = warning;
+    return WITH_LOCK(m_mutex, return m_warnings.erase(id));
 }
 
-std::vector<bilingual_str> GetWarnings()
+std::vector<bilingual_str> Warnings::GetMessages() const
 {
-    std::vector<bilingual_str> warnings;
-
-    LOCK(g_warnings_mutex);
-
-    // Pre-release build warning
-    if (!CLIENT_VERSION_IS_RELEASE) {
-        warnings.emplace_back(_("This is a pre-release test build - use at your own risk - do not use for mining or merchant applications"));
-    }
-
-    // Misc warnings like out of disk space and clock is wrong
-    if (!g_misc_warnings.empty()) {
-        warnings.emplace_back(g_misc_warnings);
-    }
-
-    if (fLargeWorkInvalidChainFound) {
-        warnings.emplace_back(_("Warning: We do not appear to fully agree with our peers! You may need to upgrade, or other nodes may need to upgrade."));
+    LOCK(m_mutex);
+    std::vector<bilingual_str> messages;
+    messages.reserve(m_warnings.size());
+    for (const auto& [id, msg] : m_warnings) {
+        messages.push_back(msg);
     }
-
-    if (g_timeoffset_warning) {
-        warnings.emplace_back(g_timeoffset_warning.value());
-    }
-
-    return warnings;
+    return messages;
 }
 
 UniValue GetWarningsForRpc(bool use_deprecated)
 {
     if (use_deprecated) {
-        const auto all_warnings{GetWarnings()};
+        const auto all_warnings{g_warnings.GetMessages()};
         return all_warnings.empty() ? "" : all_warnings.back().original;
     }
 
     UniValue warnings{UniValue::VARR};
-    for (auto&& warning : GetWarnings()) {
+    for (auto&& warning : g_warnings.GetMessages()) {
         warnings.push_back(std::move(warning.original));
     }
     return warnings;
diff --git a/src/node/warnings.h b/src/node/warnings.h
index 7766f1dbc9..c85e8a16a9 100644
--- a/src/node/warnings.h
+++ b/src/node/warnings.h
@@ -6,26 +6,86 @@
 #ifndef BITCOIN_NODE_WARNINGS_H
 #define BITCOIN_NODE_WARNINGS_H
 
-#include <optional>
-#include <string>
+#include <sync.h>
+
+#include <map>
+#include <variant>
 #include <vector>
 
 class UniValue;
 struct bilingual_str;
 
+namespace kernel {
+enum class Warning;
+} // namespace kernel
+
 namespace node {
-void SetMiscWarning(const bilingual_str& warning);
-void SetfLargeWorkInvalidChainFound(bool flag);
-/** Pass std::nullopt to disable the warning */
-void SetMedianTimeOffsetWarning(std::optional<bilingual_str> warning);
-/** Return potential problems detected by the node. */
-std::vector<bilingual_str> GetWarnings();
+enum class Warning {
+    CLOCK_OUT_OF_SYNC,
+    PRE_RELEASE_TEST_BUILD,
+    FATAL_INTERNAL_ERROR,
+};
+
 /**
- * RPC helper function that wraps GetWarnings. Returns a UniValue::VSTR
- * with the latest warning if use_deprecated is set to true, or a
- * UniValue::VARR with all warnings otherwise.
+ * @class Warnings
+ * @brief Manages warning messages within a node.
+ *
+ * The Warnings class provides mechanisms to set, unset, and retrieve
+ * warning messages.
+ *
+ * This class is designed to be non-copyable to ensure warnings
+ * are managed centrally.
+ */
+class Warnings
+{
+    typedef std::variant<kernel::Warning, node::Warning> warning_type;
+
+    mutable Mutex m_mutex;
+    std::map<warning_type, bilingual_str> m_warnings GUARDED_BY(m_mutex);
+
+public:
+    Warnings();
+    //! A warnings instance should always be passed by reference, never copied.
+    Warnings(const Warnings&) = delete;
+    Warnings& operator=(const Warnings&) = delete;
+    /**
+     * @brief Set a warning message. If a warning with the specified
+     *        `id` is already active, false is returned and the new
+     *        warning is ignored. If `id` does not yet exist, the
+     *        warning is set, and true is returned.
+     *
+     * @param[in]   id  Unique identifier of the warning.
+     * @param[in]   message Warning message to be shown.
+     *
+     * @returns true if the warning was indeed set (i.e. there is no
+     *          active warning with this `id`), otherwise false.
+     */
+    bool Set(warning_type id, bilingual_str message) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
+    /**
+     * @brief Unset a warning message. If a warning with the specified
+     *        `id` is active, it is unset, and true is returned.
+     *        Otherwise, no warning is unset and false is returned.
+     *
+     * @param[in]   id  Unique identifier of the warning.
+     *
+     * @returns true if the warning was indeed unset (i.e. there is an
+     *          active warning with this `id`), otherwise false.
+     */
+    bool Unset(warning_type id) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
+    /** Return potential problems detected by the node, sorted by the
+     * warning_type id */
+    std::vector<bilingual_str> GetMessages() const EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);
+};
+
+/**
+ * RPC helper function that wraps g_warnings.GetMessages().
+ *
+ * Returns a UniValue::VSTR with the latest warning if use_deprecated is
+ * set to true, or a UniValue::VARR with all warnings otherwise.
  */
 UniValue GetWarningsForRpc(bool use_deprecated);
+
+extern Warnings g_warnings;
 } // namespace node
 
 #endif // BITCOIN_NODE_WARNINGS_H