Merge bitcoin/bitcoin#24626: init: disallow reindex-chainstate when pruning

b2813980b8 init: disallow reindex-chainstate when pruning (Martin Zumsande)

Pull request description:

  The combination of `-reindex-chainstate` and `-prune` currently makes the node stuck in an endless loop:

  - `LoadChainstate()` will wipe the existing chainstate (so we have no genesis block anymore). It won't clean up unusable block files by calling `CleanupBlockRevFiles()` as for full `-reindex`.
  - `ThreadImport()` has [logic](https://github.com/bitcoin/bitcoin/blob/91d12344b1e51809c1ef6b630b631a6da00267c3/src/node/blockstorage.cpp#L855) of reloading Genesis after reindexing. This is what makes full `-reindex` work with `-prune` but it's not executed for `-reindex-chainstate`.
  - Since we still don't have a genesis block, init will wait for it forever in an endless loop ([code](https://github.com/bitcoin/bitcoin/blob/91d12344b1e51809c1ef6b630b631a6da00267c3/src/init.cpp#L1630-L1640)).

  Fix this by disallowing `-reindex-chainstate` together with `-prune`. This is discouraged in the help for `-reindex-chainstate` anyway ("When in pruning mode or if blocks on disk might be corrupted, use full -reindex instead.") but wasn't enforced.

  Fixes #24242

ACKs for top commit:
  MarcoFalke:
    cr ACK b2813980b8

Tree-SHA512: 7220842daaf9a4f972d82b13b81fdeac2833bf5e665c5b0f8eaf6a4bcd0725c8e97d19ec956ca4b730065a983475bb3a2732713d338f4caf8666ccbf63d4d988

src/init.cpp

@@ -853,12 +853,14 @@ bool AppInitParameterInteraction(const ArgsManager& args)
         nLocalServices = ServiceFlags(nLocalServices | NODE_COMPACT_FILTERS);
     }
 
-    // if using block pruning, then disallow txindex and coinstatsindex
     if (args.GetIntArg("-prune", 0)) {
         if (args.GetBoolArg("-txindex", DEFAULT_TXINDEX))
             return InitError(_("Prune mode is incompatible with -txindex."));
         if (args.GetBoolArg("-coinstatsindex", DEFAULT_COINSTATSINDEX))
             return InitError(_("Prune mode is incompatible with -coinstatsindex."));
+        if (args.GetBoolArg("-reindex-chainstate", false)) {
+            return InitError(_("Prune mode is incompatible with -reindex-chainstate. Use full -reindex instead."));
+        }
     }
 
     // If -forcednsseed is set to true, ensure -dnsseed has not been set to false

test/functional/feature_pruning.py

@@ -141,6 +141,10 @@ class PruneTest(BitcoinTestFramework):
             expected_msg='Error: Prune mode is incompatible with -coinstatsindex.',
             extra_args=['-prune=550', '-coinstatsindex'],
         )
+        self.nodes[0].assert_start_raises_init_error(
+            expected_msg='Error: Prune mode is incompatible with -reindex-chainstate. Use full -reindex instead.',
+            extra_args=['-prune=550', '-reindex-chainstate'],
+        )
 
     def test_height_min(self):
         assert os.path.isfile(os.path.join(self.prunedir, "blk00000.dat")), "blk00000.dat is missing, pruning too early"