balodesecurity opened a new pull request, #8324:
URL: https://github.com/apache/hadoop/pull/8324
## Summary
`hdfs diskbalancer -help plan` (and `-help execute`, `-help query`, `-help
cancel`, `-help report`) always printed the generic usage summary instead of
the per-command help text. This is a regression compared to Hadoop 3.1.1.
### Root Cause
The `--help` option is declared with `.optionalArg(true)` in Apache Commons
CLI. With that flag, the option value is **only** captured when the equals-sign
form is used (`--help=plan`). A space-separated form (`-help plan`) leaves
`plan` as a positional leftover argument, so `cmd.getOptionValue("help")`
returns `null` and `HelpCommand` falls through to printing generic help.
### Fix
In `HelpCommand.execute()`, after `getOptionValue("help")` returns null,
fall back to the first element of `cmd.getArgs()` as the sub-command name. This
makes the natural `hdfs diskbalancer -help <cmd>` syntax work without requiring
the awkward `--help=<cmd>` form.
### Changes
- `HelpCommand.java`: add fallback to `cmd.getArgs()[0]` when the option
value is null.
- `TestDiskBalancerCommand.java`: add `testHelpCommandWithSubCommand` which
runs `-help <cmd>` for all five sub-commands and asserts the output contains
the expected keyword.
## Test plan
- [ ] `TestDiskBalancerCommand#testHelpCommandWithSubCommand` passes locally
✅
- [ ] Full module build passes (`mvn package ... -DskipTests`) ✅
- [ ] Existing `testHelpCommand` (no sub-command) still passes ✅
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