Merge bitcoin/bitcoin#25727: util, config: error on startup if conf or reindex are set in config file

deba6fe315 test: update feature_config_args.py (josibake)
2e3826cbcd util: warn if reindex is used in conf (josibake)
5e744f4238 util: disallow setting conf in bitcoin.conf (josibake)

Pull request description:

  In help from `bitcoind -h` it specifes that `conf` can only be used from the commandline. However, if `conf` is set in a `bitcoin.conf` file, there is no error and from reading the logs it seems as if the `conf=<other file>` is being used, despite it being ignored. To recreate, you can setup a `bitcoin.conf` file in the default directory, add `conf=<some other file>.conf` and in the separate config file set whichever config value you want and verify that it is being ignored. alternatively, if you set `includeconf=<some other file>.conf` , your config in `<some other file>` will be picked up.

  This PR fixes this by having the node error when reading the config file if `conf=` is set.

  Additionally, it was mentioned in a recent [PR review club](https://bitcoincore.reviews/24858) that if `reindex=1` is set in the config file, the node will reindex on every startup, which is undesirable:
   ```irc
  17:14 <larryruane> michaelfolkson: Reindex is requested by the user (node operator) as a configuration option (command line or in the config file, tho you probably would never put it in the file, or else it would reindex on every startup!)
  ```

  This PR also has a commit to warn if `reindex=1` is set in the config file.

ACKs for top commit:
  hebasto:
    ACK deba6fe315, tested on Ubuntu 22.04.
  aureleoules:
    tACK deba6fe315
  ryanofsky:
    Code review ACK deba6fe315.

Tree-SHA512: 619fd0aa14e98af1166d6beb92651f5ba3f10d38b8ee132957f094f19c3a37313d9f4d7be2e4019f3fc9a2ca5fa42d03eb539ad820e27efec7ee58a26eb520b1

test/functional/feature_config_args.py

@@ -20,11 +20,25 @@ class ConfArgsTest(BitcoinTestFramework):
         self.disable_autoconnect = False
 
     def test_config_file_parser(self):
+        self.log.info('Test config file parser')
         self.stop_node(0)
 
+        # Check that startup fails if conf= is set in bitcoin.conf or in an included conf file
+        bad_conf_file_path = os.path.join(self.options.tmpdir, 'node0', 'bitcoin_bad.conf')
+        util.write_config(bad_conf_file_path, n=0, chain='', extra_config=f'conf=some.conf\n')
+        conf_in_config_file_err = 'Error: Error reading configuration file: conf cannot be set in the configuration file; use includeconf= if you want to include additional config files'
+        self.nodes[0].assert_start_raises_init_error(
+            extra_args=[f'-conf={bad_conf_file_path}'],
+            expected_msg=conf_in_config_file_err,
+        )
         inc_conf_file_path = os.path.join(self.nodes[0].datadir, 'include.conf')
         with open(os.path.join(self.nodes[0].datadir, 'bitcoin.conf'), 'a', encoding='utf-8') as conf:
             conf.write(f'includeconf={inc_conf_file_path}\n')
+        with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
+            conf.write('conf=some.conf\n')
+        self.nodes[0].assert_start_raises_init_error(
+            expected_msg=conf_in_config_file_err,
+        )
 
         self.nodes[0].assert_start_raises_init_error(
             expected_msg='Error: Error parsing command line arguments: Invalid parameter -dash_cli=1',
@@ -32,10 +46,18 @@ class ConfArgsTest(BitcoinTestFramework):
         )
         with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
             conf.write('dash_conf=1\n')
+
         with self.nodes[0].assert_debug_log(expected_msgs=['Ignoring unknown configuration value dash_conf']):
             self.start_node(0)
         self.stop_node(0)
 
+        with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
+            conf.write('reindex=1\n')
+
+        with self.nodes[0].assert_debug_log(expected_msgs=['Warning: reindex=1 is set in the configuration file, which will significantly slow down startup. Consider removing or commenting out this option for better performance, unless there is currently a condition which makes rebuilding the indexes necessary']):
+            self.start_node(0)
+        self.stop_node(0)
+
         with open(inc_conf_file_path, 'w', encoding='utf-8') as conf:
             conf.write('-dash=1\n')
         self.nodes[0].assert_start_raises_init_error(expected_msg='Error: Error reading configuration file: parse error on line 1: -dash=1, options in configuration file must be specified without leading -')