vim-patch:e73e5b8: runtime(java): Optionally highlight the :: token for method references

This token will be highlighted, similar to the arrow of
lambda expressions, whenever "g:java_highlight_functions" is
defined.

Also:

- Improve the recognition of _switch-case_ labels
  (D-Cysteine).
- Remove insignificant empty statements in syntax test
  files.

closes: vim/vim#15322

References:
https://docs.oracle.com/javase/specs/jls/se21/html/jls-15.html#jls-15.13
https://github.com/fleiner/vim/pull/1

e73e5b889b

Co-authored-by: Aliaksei Budavei <0x000c70@gmail.com>
Co-authored-by: D-Cysteine <54219287+D-Cysteine@users.noreply.github.com>

runtime/doc/syntax.txt

@@ -1574,11 +1574,11 @@ use the following: >
 	:let java_highlight_java_io=1
 Check the javaid.vim file for a list of all the packages that are supported.
 
-Function names are not highlighted, as the way to find functions depends on
-how you write Java code.  The syntax file knows two possible ways to highlight
-headers of function declarations:
+Headers of indented function declarations can be highlighted (along with parts
+of lambda expressions and method reference expressions), but it depends on how
+you write Java code.  Two formats are recognized:
 
-If you write function declarations that are consistently indented by either
+1) If you write function declarations that are consistently indented by either
 a tab, or a space . . . or eight space character(s), you may want to set >
 	:let java_highlight_functions="indent"
 	:let java_highlight_functions="indent1"
@@ -1590,10 +1590,12 @@ a tab, or a space . . . or eight space character(s), you may want to set >
 	:let java_highlight_functions="indent7"
 	:let java_highlight_functions="indent8"
 Note that in terms of 'shiftwidth', this is the leftmost step of indentation.
-However, if you follow the Java guidelines about how functions and classes are
-supposed to be named (with respect to upper- and lowercase) and there is any
-amount of indentation, you may want to set >
+
+2) However, if you follow the Java guidelines about how functions and types
+are supposed to be named (with respect to upper- and lowercase) and there is
+any amount of indentation, you may want to set >
 	:let java_highlight_functions="style"
+
 In addition, you can combine any value of "java_highlight_functions" with >
 	:let java_highlight_signature=1
 to have the name of a function with its parameter list parens distinctly

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 Jun 22
+" Last Change:		2024 Jul 23
 
 " Please check :help java.vim for comments on some of the options available.
 
@@ -260,7 +260,7 @@ if exists("java_space_errors")
   endif
 endif
 
-exec 'syn match javaUserLabel "^\s*\<\K\k*\>\%(\<default\>\)\@' . s:ff.Peek('7', '') . '<!\s*:"he=e-1'
+exec 'syn match javaUserLabel "^\s*\<\K\k*\>\%(\<default\>\)\@' . s:ff.Peek('7', '') . '<!\s*::\@!"he=e-1'
 syn region  javaLabelRegion	transparent matchgroup=javaLabel start="\<case\>" matchgroup=NONE end=":\|->" contains=javaLabelCastType,javaLabelNumber,javaCharacter,javaString,javaConstant,@javaClasses,javaGenerics,javaLabelDefault,javaLabelVarType,javaLabelWhenClause
 syn region  javaLabelRegion	transparent matchgroup=javaLabel start="\<default\>\%(\s*\%(:\|->\)\)\@=" matchgroup=NONE end=":\|->" oneline
 " Consider grouped _default_ _case_ labels, i.e.
@@ -497,8 +497,12 @@ syn match   javaParenError	 "\]"
 
 hi def link javaParenError	javaError
 
-" Lambda expressions (JLS-17, §15.27).
+" Lambda expressions (JLS-17, §15.27) and method references (JLS-17,
+" §15.13).
 if exists("java_highlight_functions")
+  syn match javaMethodRef ":::\@!"
+  hi def link javaMethodRef javaFuncDef
+
   if exists("java_highlight_signature")
     let s:ff.LambdaDef = s:ff.LeftConstant
   else