vim-patch:2307945: runtime(java): Optionally recognise all primitive constants in _switch-case_ labels

Define "g:java_syntax_previews" and include number 455 in
its list to enable this recognition:
------------------------------------------------------------
	let g:java_syntax_previews = [455]
------------------------------------------------------------

Reference:
https://openjdk.org/jeps/455

closes: vim/vim#15698

23079450a8

Co-authored-by: Aliaksei Budavei <0x000c70@gmail.com>

runtime/doc/syntax.txt

@@ -1704,10 +1704,11 @@ cycles for such a feature to become either integrated into the platform or
 withdrawn from this effort.  To cater for early adopters, there is optional
 support in Vim for syntax related preview features that are implemented.  You
 can request it by specifying a list of preview feature numbers as follows: >
-	:let g:java_syntax_previews = [430]
+	:let g:java_syntax_previews = [455]
 
 The supported JEP numbers are to be drawn from this table:
 	`430`: String Templates [JDK 21]
+	`455`: Primitive types in Patterns, instanceof, and switch
 
 Note that as soon as the particular preview feature will have been integrated
 into the Java platform, its entry will be removed from the table and related

runtime/syntax/java.vim

@@ -3,7 +3,7 @@
 " Maintainer:		Aliaksei Budavei <0x000c70 AT gmail DOT com>
 " Former Maintainer:	Claudio Fleiner <claudio@fleiner.com>
 " Repository:		https://github.com/zzzyxwvut/java-vim.git
-" Last Change:		2024 Sep 11
+" Last Change:		2024 Sep 18
 
 " Please check :help java.vim for comments on some of the options available.
 
@@ -283,19 +283,27 @@ if exists("g:java_space_errors")
 endif
 
 exec 'syn match javaUserLabel "^\s*\<\K\k*\>\%(\<default\>\)\@' . s:ff.Peek('7', '') . '<!\s*::\@!"he=e-1'
+
+if s:ff.IsRequestedPreviewFeature(455)
+  syn region  javaLabelRegion	transparent matchgroup=javaLabel start="\<case\>" matchgroup=NONE end=":\|->" contains=javaBoolean,javaNumber,javaCharacter,javaString,javaConstant,@javaClasses,javaGenerics,javaType,javaLabelDefault,javaLabelVarType,javaLabelWhenClause
+else
   syn region  javaLabelRegion	transparent matchgroup=javaLabel start="\<case\>" matchgroup=NONE end=":\|->" contains=javaLabelCastType,javaLabelNumber,javaCharacter,javaString,javaConstant,@javaClasses,javaGenerics,javaLabelDefault,javaLabelVarType,javaLabelWhenClause
+  syn keyword javaLabelCastType	contained char byte short int
+  syn match   javaLabelNumber	contained "\<0\>[lL]\@!"
+  syn match   javaLabelNumber	contained "\<\%(0\%([xX]\x\%(_*\x\)*\|_*\o\%(_*\o\)*\|[bB][01]\%(_*[01]\)*\)\|[1-9]\%(_*\d\)*\)\>[lL]\@!"
+  hi def link javaLabelCastType	javaType
+  hi def link javaLabelNumber	javaNumber
+endif
+
 syn region  javaLabelRegion	transparent matchgroup=javaLabel start="\<default\>\%(\s*\%(:\|->\)\)\@=" matchgroup=NONE end=":\|->" oneline
 " Consider grouped _default_ _case_ labels, i.e.
 " case null, default ->
 " case null: default:
 syn keyword javaLabelDefault	contained default
 syn keyword javaLabelVarType	contained var
-syn keyword javaLabelCastType	contained char byte short int
 " Allow for the contingency of the enclosing region not being able to
 " _keep_ its _end_, e.g. case ':':.
 syn region  javaLabelWhenClause	contained transparent matchgroup=javaLabel start="\<when\>" matchgroup=NONE end=":"me=e-1 end="->"me=e-2 contains=TOP,javaExternal,javaLambdaDef
-syn match   javaLabelNumber	contained "\<0\>[lL]\@!"
-syn match   javaLabelNumber	contained "\<\%(0\%([xX]\x\%(_*\x\)*\|_*\o\%(_*\o\)*\|[bB][01]\%(_*[01]\)*\)\|[1-9]\%(_*\d\)*\)\>[lL]\@!"
 
 " Comments
 syn keyword javaTodo		contained TODO FIXME XXX
@@ -692,8 +700,6 @@ hi def link javaUserLabelRef		javaUserLabel
 hi def link javaLabel			Label
 hi def link javaLabelDefault		javaLabel
 hi def link javaLabelVarType		javaOperator
-hi def link javaLabelNumber		javaNumber
-hi def link javaLabelCastType		javaType
 
 hi def link javaComment			Comment
 hi def link javaCommentStar		javaComment