Merge #16757: doc: CChainState return values

fa912a8 doc: move-only ActivateBestChain doxygen comment to header (MarcoFalke)
fa99efd doc: ActivateBestChainStep return value (MarcoFalke)

Pull request description:

  It will always return true, unless a system error such as #15305 occurred

ACKs for top commit:
  laanwj:
    ACK fa912a8

Tree-SHA512: d439da844a467f9705014b946d7d987fb62cb63fe6a325b2fdbbb73a6578fc0ade3f60892044f02face43948204fc4e3c9fa70d108233d4ca8eef27984059689

Author: laanwj

src/validation.cpp

@@ -2508,6 +2508,8 @@ void CChainState::PruneBlockIndexCandidates() {
 /**
  * Try to make some progress towards making pindexMostWork the active block.
  * pblock is either nullptr or a pointer to a CBlock corresponding to pindexMostWork.
+ *
+ * @returns true unless a system error occurred
  */
 bool CChainState::ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace)
 {
@@ -2627,15 +2629,6 @@ static void LimitValidationInterfaceQueue() LOCKS_EXCLUDED(cs_main) {
     }
 }
 
-/**
- * Make the best chain active, in multiple steps. The result is either failure
- * or an activated best chain. pblock is either nullptr or a pointer to a block
- * that is already loaded (to avoid loading it again from disk).
- *
- * ActivateBestChain is split into steps (see ActivateBestChainStep) so that
- * we avoid holding cs_main for an extended period of time; the length of this
- * call may be quite long during reindexing or a substantial reorg.
- */
 bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock) {
     // Note that while we're often called here from ProcessNewBlock, this is
     // far from a guarantee. Things in the P2P/RPC will often end up calling
@@ -2683,8 +2676,10 @@ bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams&
 
                 bool fInvalidFound = false;
                 std::shared_ptr<const CBlock> nullBlockPtr;
-                if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : nullBlockPtr, fInvalidFound, connectTrace))
+                if (!ActivateBestChainStep(state, chainparams, pindexMostWork, pblock && pblock->GetHash() == pindexMostWork->GetBlockHash() ? pblock : nullBlockPtr, fInvalidFound, connectTrace)) {
+                    // A system error occurred
                     return false;
+                }
                 blocks_connected = true;
 
                 if (fInvalidFound) {

src/validation.h

@@ -211,7 +211,7 @@ static const uint64_t MIN_DISK_SPACE_FOR_BLOCK_FILES = 550 * 1024 * 1024;
  * @param[in]   pblock  The block we want to process.
  * @param[in]   fForceProcessing Process this block even if unrequested; used for non-network block sources and whitelisted peers.
  * @param[out]  fNewBlock A boolean which is set to indicate if the block was first received via this call
- * @return True if state.IsValid()
+ * @returns     If the block was processed, independently of block validity
  */
 bool ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr<const CBlock> pblock, bool fForceProcessing, bool* fNewBlock) LOCKS_EXCLUDED(cs_main);
 
@@ -653,6 +653,8 @@ class CChainState {
      *
      * If FlushStateMode::NONE is used, then FlushStateToDisk(...) won't do anything
      * besides checking if we need to prune.
+     *
+     * @returns true unless a system error occurred
      */
     bool FlushStateToDisk(
         const CChainParams& chainparams,
@@ -667,7 +669,20 @@ class CChainState {
     //! if we pruned.
     void PruneAndFlush();
 
-    bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock) LOCKS_EXCLUDED(cs_main);
+    /**
+     * Make the best chain active, in multiple steps. The result is either failure
+     * or an activated best chain. pblock is either nullptr or a pointer to a block
+     * that is already loaded (to avoid loading it again from disk).
+     *
+     * ActivateBestChain is split into steps (see ActivateBestChainStep) so that
+     * we avoid holding cs_main for an extended period of time; the length of this
+     * call may be quite long during reindexing or a substantial reorg.
+     *
+     * @returns true unless a system error occurred
+     */
+    bool ActivateBestChain(CValidationState& state,
+        const CChainParams& chainparams,
+        std::shared_ptr<const CBlock> pblock) LOCKS_EXCLUDED(cs_main);
 
     bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock) EXCLUSIVE_LOCKS_REQUIRED(cs_main);