bin: run additional validation for --dry-run

There are certain kinds of invalid configurations that pass the
`--dry-run` check, but fail to start at run time. This commit addresses
the issue by re-using some of the hot reload validation logic.

For example, this config is trivially invalid, passes `--dry-run`, and
fails at runtime:

```
pipeline:
  inputs:
  - name: dummy
    tag: test
    invalid_property_that_does_not_exist: some_value
  outputs:
  - name: stdout
    match: '*'
```

```
zsh ❮ fluent-bit --dry-run -c ~/tmp/fbconfig-bad-property.yaml
Fluent Bit v4.1.1
* Copyright (C) 2015-2025 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _             ___   __
|  ___| |                | |   | ___ (_) |           /   | /  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __/ /| | `| |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / / /_| |  | |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /\___  |__| |_
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/     |_(_)___/

configuration test is successful

zsh ❮ fluent-bit -c ~/tmp/fbconfig-bad-property.yaml
Fluent Bit v4.1.1
* Copyright (C) 2015-2025 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _             ___   __
|  ___| |                | |   | ___ (_) |           /   | /  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __/ /| | `| |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / / /_| |  | |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /\___  |__| |_
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/     |_(_)___/

[2025/10/31 16:05:55.268532000] [ info] [fluent bit] version=4.1.1, commit=, pid=21037
[2025/10/31 16:05:55.268808000] [ info] [storage] ver=1.5.3, type=memory, sync=normal, checksum=off, max_chunks_up=128
[2025/10/31 16:05:55.269140000] [ info] [simd    ] disabled
[2025/10/31 16:05:55.269147000] [ info] [cmetrics] version=1.0.5
[2025/10/31 16:05:55.269407000] [ info] [ctraces ] version=0.6.6
[2025/10/31 16:05:55.269476000] [error] [config] dummy: unknown configuration property 'invalid_property_that_does_not_exist'. The following properties are allowed: samples, dummy, metadata, rate, interval_sec, interval_nsec, copies, start_time_sec, start_time_nsec, fixed_timestamp, flush_on_startup, and test_hang_on_exit.
[2025/10/31 16:05:55.269486000] [ help] try the command: fluent-bit -i dummy -h

[2025/10/31 16:05:55.269515000] [error] [engine] input initialization failed
```

With this commit, we can see that the additional validation from hot
reload catches the error right away:

```
zsh ❯ bin/fluent-bit --dry-run -c ~/tmp/fbconfig-bad-property.yaml
Fluent Bit v4.2.0
* Copyright (C) 2015-2025 The Fluent Bit Authors
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

______ _                  _    ______ _ _             ___   __
|  ___| |                | |   | ___ (_) |           /   | /  |
| |_  | |_   _  ___ _ __ | |_  | |_/ /_| |_  __   __/ /| | `| |
|  _| | | | | |/ _ \ '_ \| __| | ___ \ | __| \ \ / / /_| |  | |
| |   | | |_| |  __/ | | | |_  | |_/ / | |_   \ V /\___  |__| |_
\_|   |_|\__,_|\___|_| |_|\__| \____/|_|\__|   \_/     |_(_)___/

[2025/10/31 16:07:50.402568000] [error] [config] dummy: unknown configuration property 'invalid_property_that_does_not_exist'. The following properties are allowed: samples, dummy, metadata, rate, interval_sec, interval_nsec, copies, start_time_sec, start_time_nsec, fixed_timestamp, flush_on_startup, and test_hang_on_exit.
[2025/10/31 16:07:50.402792000] [ help] try the command: bin/fluent-bit -i dummy -h

[2025/10/31 16:07:50.402800000] [error] [reload] check properties for input plugins is failed
```

(The logs of course now say `[reload]`, which is a little misleading...
we can clean that up, if desired).

Signed-off-by: Andrew Hayworth <[email protected]>

Author: ahayworth

src/fluent-bit.c

@@ -1430,6 +1430,11 @@ static int flb_main_run(int argc, char **argv)
 #endif
 
     if (config->dry_run == FLB_TRUE) {
+        ret = flb_reload_property_check_all(config);
+        if (ret != 0) {
+            exit(EXIT_FAILURE);
+        }
+
         fprintf(stderr, "configuration test is successful\n");
         flb_init_env();
         flb_cf_destroy(cf_opts);