RFR: 8354216: Small cleanups relating to Log.DiagnosticHandler

[Maurizio Cimadamore]

On Wed, 9 Apr 2025 15:45:23 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

> This is split off as a sub-task of [JDK-8224228](https://bugs.openjdk.org/browse/JDK-8224228), which seeks to add `@SuppressWarnings` support for lexical features. 
> 
> There are a few of small refactoring cleanups possible relating to the nested class `Log.DiagnosticHandler`.
> 
> First, this class is currently declared as a static inner class with an explicit field reference to its outer class (`Log`) instance. Although protected and non final, this field really should never be changed. Therefore, there is no reason not to just make `DiagnosticHandler` a non-static inner class. This will slightly simplify the code and eliminate an obscure corner case by which a bug could possibly occur someday.
> 
> Secondly, the deferred diagnostics are currently stored in a linked list, and in cases where they must be sorted before being reported, they have to be copied into an array first. A simpler and more space efficient approach would be to just use an `ArrayList`. Then the sorting variant of the method can just sort the list in place and delegate directly to the non-sorting variant.
> 
> Finally, the code can be simplified by replacing a null `filter` predicate with an always true predicate at construction time instead of at filter time.

src/jdk.compiler/share/classes/com/sun/tools/javac/util/Log.java line 184:

> 182:         /** Report all deferred diagnostics in the specified order. */
> 183:         public void reportDeferredDiagnostics(Comparator<JCDiagnostic> order) {
> 184:             deferred.sort(order);

So, here there would seem to be a difference in behavior, in that `sort` has a permanent side-effect on `deferred`. But I think this is fine, because at the end of this method we end up setting `deferred = null` anyway, right?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24553#discussion_r2035817640