codeconsole opened a new pull request, #16089:
URL: https://github.com/apache/grails-core/pull/16089
## Problem
`DirectoryWatcher` probes for JNA to decide whether the native macOS
FSEvents watcher is usable:
```java
Class.forName("com.sun.jna.Pointer");
```
JNA is not what that watcher needs. `MacOsWatchServiceDirectoryWatcher`
needs `io.methvin:directory-watcher`, which `grails-bootstrap` declares
`compileOnly` and therefore never puts on an application's runtime classpath.
Applications routinely acquire JNA transitively —
`org.testcontainers:testcontainers` →
`com.github.docker-java:docker-java-transport-zerodep` → `net.java.dev.jna:jna`
is a common path. On macOS those applications are sent down a load of
`MacOsWatchServiceDirectoryWatcher` that cannot succeed. The resulting
`NoClassDefFoundError` is caught by a single catch-all that drops straight to
`PollingDirectoryWatcher`, so they silently poll every watched directory on a
1s timer instead of receiving file system events:
```
Exception while trying to load WatchServiceDirectoryWatcher (this is
probably Java 6
and WatchService isn't available). Falling back to PollingDirectoryWatcher.
Caused by: java.lang.NoClassDefFoundError:
io/methvin/watchservice/MacOSXListeningWatchService
```
The fallback ordering makes this worse than having no JNA at all: without
JNA the `else` branch selects `WatchServiceDirectoryWatcher` and works
correctly. Adding an unrelated dependency downgrades file watching.
## Change
Probe for `io.methvin.watchservice.MacOSXListeningWatchService` — the class
that actually backs the native watcher — and degrade in steps: native macOS →
JDK `WatchService` → polling.
Polling is now only reached if the JDK cannot supply a `WatchService`, which
cannot happen on the Java 21 baseline. The message no longer claims Java 6.
Absence of the optional dependency is logged at debug rather than warn, since
it is an opt-in performance improvement rather than a fault.
## Verification
Selected delegate, comparing this branch against `8.0.x` under three
classpaths on macOS:
| classpath | before | after |
|---|---|---|
| JNA present, `directory-watcher` absent | `PollingDirectoryWatcher` |
`WatchServiceDirectoryWatcher` |
| neither present | `WatchServiceDirectoryWatcher` | unchanged |
| both present | `MacOsWatchServiceDirectoryWatcher` | unchanged |
The broken case is fixed and both already-working cases are untouched.
`DirectoryWatcherSpec` covers the three outcomes and fails on the current
implementation (2 of 3 cases). Reproducing the reported shape needs JNA present
and `directory-watcher` absent, so JNA is added to the test runtime classpath.
`:grails-bootstrap:test` (142 tests), `codeStyle` and `rat` all pass.
## Note
An alternative fix would be promoting `io.methvin:directory-watcher` to a
real runtime dependency of `grails-bootstrap`, giving every macOS application
native watching. That adds JNA and a native library to all application
classpaths, so I kept the dependency optional here and fixed only the selection
logic. Happy to take that route instead if preferred.
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