runtime(java): Search type and method declarations with "&inc" and "&def"

=============== LIMITATIONS AND OBSERVATIONS ===============

* Remember that external-type names can only be found when
  they match filenames resolvable in "&path" with "import"
  declarations; load the source file of an external type to
  look up its nested types and sibling top types, if any.

* Strive to narrow the search by assigning only relevant
  pathnames for directories *or* an archive to "&path", e.g.
  ":set path-=/usr/include".

* Use "{Visual}gf" on fully-qualified names.

* Accept the fact that "&define" cannot contain end-of-line
  characters (":help definition-search").  A declaration
  whose matchable header is not contained within a line can
  be found iff all of its non-optional components belong to
  the same line; for types, such components are a keyword,
  e.g. "class", followed by a run of blank characters and
  an identifier, e.g. "Test"; for methods: a return type,
  e.g. "String", or a keyword "void", followed by a run of
  blank characters and an identifier, e.g. "toString", that
  is followed by "(".

* The members of the "java.lang" package are usually not
  associated with "import" declarations; to look up their
  declarations, load a source file for a member of that
  package, and then use, on a simple name of interest for
  a member, either "[-Ctrl-d" etc. for local declarations
  or "gf" for external declarations, assuming that "." *or*
  the appropriate pathname for a JDK archive is assigned to
  "&path".

* Follow the above instruction made for the "java.lang"
  members for any type whose simple name is not associated
  with an "import" declaration, i.e. a member type of the
  same package that is declared in another compilation unit.

* Append the "$" character to "&iskeyword" when looking up
  declarations of generated code.

See zzzyxwvut/java-vim#4.

closes: #17281

Co-authored-by: Konfekt <Konfekt@users.noreply.github.com>
Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/ftplugin/java.vim

@@ -3,9 +3,7 @@
 " Maintainer:		Aliaksei Budavei <0x000c70 AT gmail DOT com>
 " Former Maintainer:	Dan Sharp
 " Repository:		https://github.com/zzzyxwvut/java-vim.git
-" Last Change:		2024 Dec 25
-"			2024 Jan 14 by Vim Project (browsefilter)
-"			2024 May 23 by Riley Bruins <ribru17@gmail.com> ('commentstring')
+" Last Change:		2025 May 08
 
 " Make sure the continuation lines below do not cause problems in
 " compatibility mode.
@@ -30,6 +28,32 @@ let b:did_ftplugin = 1
 " extension.
 set suffixes+=.class
 
+" Set up "&define" and "&include".
+let s:peek = ''
+
+try
+    " Since v7.3.1037.
+    if 'ab' !~ 'a\@1<!b'
+	let s:peek = string(strlen('instanceof') + 8)
+    endif
+catch /\<E59:/
+endtry
+
+" Treat "s:common" as a non-backtracking unit to avoid matching constructor
+" declarations whose package-private headers are indistinguishable from method
+" invocation.  Note that "[@-]" must not and "$" may not be in "&l:iskeyword".
+let s:common = '\%(\%(\%(@\%(interface\)\@!\%(\K\k*\.\)*\K\k*\)\s\+\)*' .
+	\ '\%(p\%(rivate\|rotected\|ublic\)\s\+\)\=\)\@>'
+let s:types = '\%(\%(abstract\|final\|non-sealed\|s\%(ealed\|tatic\|trictfp\)\)\s\+\)*' .
+	\ '\%(class\|enum\|@\=interface\|record\)\s\+\ze\K\k*\>'
+let s:methods = '\%(\%(abstract\|default\|final\|native\|s\%(tatic\|trictfp\|ynchronized\)\)\s\+\)*' .
+	\ '\%(<.\{-1,}>\s\+\)\=\%(\K\k*\.\)*\K\k*\s*\%(<.\{-1,}>\%(\s\|\[\)\@=\)\=\s*\%(\[\]\s*\)*' .
+	\ '\s\+\ze\%(\<\%(assert\|case\|instanceof\|new\|return\|throw\|when\)\s\+\)\@' .
+	\ s:peek . '<!\K\k*\s*('
+let &l:define = printf('\C\m^\s*%s\%%(%s\|%s\)', s:common, s:types, s:methods)
+let &l:include = '\C\m^\s*import\s\+\ze\%(\K\k*\.\)\+\K\k*;'
+unlet s:methods s:types s:common s:peek
+
 " Enable gf on import statements.  Convert . in the package
 " name to / and append .java to the name, then search the path.
 setlocal includeexpr=substitute(v:fname,'\\.','/','g')
@@ -341,7 +365,7 @@ if (!empty(get(g:, 'spotbugs_properties', {})) ||
 endif
 
 function! JavaFileTypeCleanUp() abort
-    setlocal suffixes< suffixesadd< formatoptions< comments< commentstring< path< includeexpr<
+    setlocal suffixes< suffixesadd< formatoptions< comments< commentstring< path< includeexpr< include< define<
     unlet! b:browsefilter
 
     " The concatenated ":autocmd" removals may be misparsed as an ":autocmd".