mempool: add AssumeCalculateMemPoolAncestors helper function

There are quite a few places that assume CalculateMemPoolAncestors
will return a value without raising an error. This helper function
adds logging (and Assume for debug builds) that ensures robustness
but increases visibility in case of unexpected failures

src/txmempool.cpp

@@ -254,6 +254,20 @@ util::Result<CTxMemPool::setEntries> CTxMemPool::CalculateMemPoolAncestors(
                                             limits);
 }
 
+CTxMemPool::setEntries CTxMemPool::AssumeCalculateMemPoolAncestors(
+    std::string_view calling_fn_name,
+    const CTxMemPoolEntry &entry,
+    const Limits& limits,
+    bool fSearchForParents /* = true */) const
+{
+    auto result{Assume(CalculateMemPoolAncestors(entry, limits, fSearchForParents))};
+    if (!result) {
+        LogPrintLevel(BCLog::MEMPOOL, BCLog::Level::Error, "%s: CalculateMemPoolAncestors failed unexpectedly, continuing with empty ancestor set (%s)\n",
+                      calling_fn_name, util::ErrorString(result).original);
+    }
+    return std::move(result).value_or(CTxMemPool::setEntries{});
+}
+
 void CTxMemPool::UpdateAncestorsOf(bool add, txiter it, setEntries &setAncestors)
 {
     const CTxMemPoolEntry::Parents& parents = it->GetMemPoolParentsConst();

src/txmempool.h

@@ -11,6 +11,7 @@
 #include <optional>
 #include <set>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <vector>
 
@@ -566,6 +567,26 @@ public:
                                    const Limits& limits,
                                    bool fSearchForParents = true) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
+    /**
+     * Same as CalculateMemPoolAncestors, but always returns a (non-optional) setEntries.
+     * Should only be used when it is assumed CalculateMemPoolAncestors would not fail. If
+     * CalculateMemPoolAncestors does unexpectedly fail, an empty setEntries is returned and the
+     * error is logged to BCLog::MEMPOOL with level BCLog::Level::Error. In debug builds, failure
+     * of CalculateMemPoolAncestors will lead to shutdown due to assertion failure.
+     *
+     * @param[in]   calling_fn_name     Name of calling function so we can properly log the call site
+     *
+     * @return a setEntries corresponding to the result of CalculateMemPoolAncestors or an empty
+     *         setEntries if it failed
+     *
+     * @see CTXMemPool::CalculateMemPoolAncestors()
+     */
+    setEntries AssumeCalculateMemPoolAncestors(
+        std::string_view calling_fn_name,
+        const CTxMemPoolEntry &entry,
+        const Limits& limits,
+        bool fSearchForParents = true) const EXCLUSIVE_LOCKS_REQUIRED(cs);
+
     /** Calculate all in-mempool ancestors of a set of transactions not already in the mempool and
      * check ancestor and descendant limits. Heuristics are used to estimate the ancestor and
      * descendant count of all entries if the package were to be added to the mempool.  The limits