rpc: Make pruneheight also reflect undo data presence

src/rpc/blockchain.cpp

@@ -786,16 +786,24 @@ static RPCHelpMan getblock()
 std::optional<int> GetPruneHeight(const BlockManager& blockman, const CChain& chain) {
     AssertLockHeld(::cs_main);
 
+    // Search for the last block missing block data or undo data. Don't let the
+    // search consider the genesis block, because the genesis block does not
+    // have undo data, but should not be considered pruned.
+    const CBlockIndex* first_block{chain[1]};
     const CBlockIndex* chain_tip{chain.Tip()};
-    if (!(chain_tip->nStatus & BLOCK_HAVE_DATA)) return chain_tip->nHeight;
 
-    // Get first block with data, after the last block without data.
-    // This is the start of the unpruned range of blocks.
-    const auto& first_unpruned{*Assert(blockman.GetFirstBlock(*chain_tip, /*status_mask=*/BLOCK_HAVE_DATA))};
-    if (!first_unpruned.pprev) {
-       // No block before the first unpruned block means nothing is pruned.
-       return std::nullopt;
+    // If there are no blocks after the genesis block, or no blocks at all, nothing is pruned.
+    if (!first_block || !chain_tip) return std::nullopt;
+
+    // If the chain tip is pruned, everything is pruned.
+    if (!((chain_tip->nStatus & BLOCK_HAVE_MASK) == BLOCK_HAVE_MASK)) return chain_tip->nHeight;
+
+    const auto& first_unpruned{*Assert(blockman.GetFirstBlock(*chain_tip, /*status_mask=*/BLOCK_HAVE_MASK, first_block))};
+    if (&first_unpruned == first_block) {
+        // All blocks between first_block and chain_tip have data, so nothing is pruned.
+        return std::nullopt;
     }
+
     // Block before the first unpruned block is the last pruned block.
     return Assert(first_unpruned.pprev)->nHeight;
 }

test/functional/feature_pruning.py

@@ -25,6 +25,7 @@ from test_framework.util import (
     assert_equal,
     assert_greater_than,
     assert_raises_rpc_error,
+    try_rpc,
 )
 
 # Rescans start at the earliest block up to 2 hours before a key timestamp, so
@@ -479,8 +480,12 @@ class PruneTest(BitcoinTestFramework):
         self.log.info("Test invalid pruning command line options")
         self.test_invalid_command_line_options()
 
+        self.log.info("Test scanblocks can not return pruned data")
         self.test_scanblocks_pruned()
 
+        self.log.info("Test pruneheight reflects the presence of block and undo data")
+        self.test_pruneheight_undo_presence()
+
         self.log.info("Done")
 
     def test_scanblocks_pruned(self):
@@ -494,5 +499,18 @@ class PruneTest(BitcoinTestFramework):
         assert_raises_rpc_error(-1, "Block not available (pruned data)", node.scanblocks,
             "start", [{"desc": f"raw({false_positive_spk.hex()})"}], 0, 0, "basic", {"filter_false_positives": True})
 
+    def test_pruneheight_undo_presence(self):
+        node = self.nodes[2]
+        pruneheight = node.getblockchaininfo()["pruneheight"]
+        fetch_block = node.getblockhash(pruneheight - 1)
+
+        self.connect_nodes(1, 2)
+        peers = node.getpeerinfo()
+        node.getblockfrompeer(fetch_block, peers[0]["id"])
+        self.wait_until(lambda: not try_rpc(-1, "Block not available (pruned data)", node.getblock, fetch_block), timeout=5)
+
+        new_pruneheight = node.getblockchaininfo()["pruneheight"]
+        assert_equal(pruneheight, new_pruneheight)
+
 if __name__ == '__main__':
     PruneTest().main()