Add a new tree-sitter query predicate 'pred'

I realized that using an arbitrary function as the predicate in
queries is very helpful for some queries I'm writing for python and
javascript, and presumably most other languages[1].

Granted, we can already filter out unwanted nodes by using a function
instead of a face for the capture name, and (1) determine whether the
captured node is valid and (2) fontify that node if it's valid.

However, such approach is a bit more cumbersome and more importantly
gets in the way of another potential use of the fontification queries:
context extraction.

For example, I could use the query for the 'variable' feature to get
all the variables in a certain region.  In this use-case, we want the
filtering happen before returning the captured nodes.

Besides, the change is relatively small and straightforward: most code
are already there, I just need to add some boilerplate.

[1] For a code like aa.bb(cc), we want bb to be in function face,
because obviously its a function.  But for aa.bb, we want bb to be in
property face, because it's a property.  In the AST, bb is always a
property, the difference between the two cases is the enclosing node:
in the first case, aa.bb is in a "call_expression" node, indicating
that bb is used as a function (a method).  So we want a predicate
function that checks whether bb is used as a function or a property,
and determine whether it should be in function or property face.

* doc/lispref/parsing.texi (Pattern Matching): Update manual.
* src/treesit.c (Ftreesit_pattern_expand): Handle :pred.
(treesit_predicate_capture_name_to_node): A new function extracted
from treesit_predicate_capture_name_to_text.
(treesit_predicate_capture_name_to_text): Use the newly extracted
function.
(treesit_predicate_pred): New predicate function.
(treesit_eval_predicates): Add new predicate.  Also fix a bug: we want
to AND the results of each predicate.
* test/src/treesit-tests.el (treesit--ert-pred-last-sibling): New
helper function.
(treesit-query-api): Test #pred predicate.

doc/lispref/parsing.texi

@@ -1266,10 +1266,11 @@ example, with the following pattern:
 @end example
 
 @noindent
-tree-sitter only matches arrays where the first element equals to
+tree-sitter only matches arrays where the first element equals to the
-the last element.  To attach a predicate to a pattern, we need to
+last element.  To attach a predicate to a pattern, we need to group
-group them together.  A predicate always starts with a @samp{#}.
+them together.  A predicate always starts with a @samp{#}.  Currently
-Currently there are two predicates, @code{#equal} and @code{#match}.
+there are three predicates, @code{#equal}, @code{#match}, and
+@code{#pred}.
 
 @deffn Predicate equal arg1 arg2
 Matches if @var{arg1} equals to @var{arg2}.  Arguments can be either
@@ -1282,6 +1283,11 @@ Matches if the text that @var{capture-name}'s node spans in the buffer
 matches regular expression @var{regexp}.  Matching is case-sensitive.
 @end deffn
 
+@deffn Predicate pred fn &rest nodes
+Matches if function @var{fn} returns non-@code{nil} when passed each
+node in @var{nodes} as arguments.
+@end deffn
+
 Note that a predicate can only refer to capture names that appear in
 the same pattern.  Indeed, it makes little sense to refer to capture
 names in other patterns.

src/treesit.c

@@ -2170,6 +2170,8 @@ See Info node `(elisp)Pattern Matching' for detailed explanation.  */)
     return build_pure_c_string ("#equal");
   if (EQ (pattern, QCmatch))
     return build_pure_c_string ("#match");
+  if (EQ (pattern, QCpred))
+    return build_pure_c_string ("#pred");
   Lisp_Object opening_delimeter
     = build_pure_c_string (VECTORP (pattern) ? "[" : "(");
   Lisp_Object closing_delimiter
@@ -2269,10 +2271,10 @@ treesit_predicates_for_pattern (TSQuery *query, uint32_t pattern_index)
   return Fnreverse (result);
 }
 
-/* Translate a capture NAME (symbol) to the text of the captured node.
+/* Translate a capture NAME (symbol) to a node.
    Signals treesit-query-error if such node is not captured.  */
 static Lisp_Object
-treesit_predicate_capture_name_to_text (Lisp_Object name,
+treesit_predicate_capture_name_to_node (Lisp_Object name,
 					struct capture_range captures)
 {
   Lisp_Object node = Qnil;
@@ -2292,6 +2294,16 @@ treesit_predicate_capture_name_to_text (Lisp_Object name,
 	      name, build_pure_c_string ("A predicate can only refer"
 					 " to captured nodes in the "
 					 "same pattern"));
+  return node;
+}
+
+/* Translate a capture NAME (symbol) to the text of the captured node.
+   Signals treesit-query-error if such node is not captured.  */
+static Lisp_Object
+treesit_predicate_capture_name_to_text (Lisp_Object name,
+					struct capture_range captures)
+{
+  Lisp_Object node = treesit_predicate_capture_name_to_node (name, captures);
 
   struct buffer *old_buffer = current_buffer;
   set_buffer_internal (XBUFFER (XTS_PARSER (XTS_NODE (node)->parser)->buffer));
@@ -2365,13 +2377,30 @@ treesit_predicate_match (Lisp_Object args, struct capture_range captures)
     return false;
 }
 
-/* About predicates: I decide to hard-code predicates in C instead of
+/* Handles predicate (#pred FN ARG...).  Return true if FN returns
-   implementing an extensible system where predicates are translated
+   non-nil; return false otherwise.  The arity of FN must match the
-   to Lisp functions, and new predicates can be added by extending a
+   number of ARGs  */
-   list of functions, because I really couldn't imagine any useful
+static bool
-   predicates besides equal and match.  If we later found out that
+treesit_predicate_pred (Lisp_Object args, struct capture_range captures)
-   such system is indeed useful and necessary, it can be easily
+{
-   added.  */
+  if (XFIXNUM (Flength (args)) < 2)
+    xsignal2 (Qtreesit_query_error,
+	      build_pure_c_string ("Predicate `pred' requires "
+				   "at least two arguments, "
+				   "but was only given"),
+	      Flength (args));
+
+  Lisp_Object fn = Fintern (XCAR (args), Qnil);
+  Lisp_Object nodes = Qnil;
+  Lisp_Object tail = XCDR (args);
+  FOR_EACH_TAIL (tail)
+    nodes = Fcons (treesit_predicate_capture_name_to_node (XCAR (tail),
+							   captures),
+		   nodes);
+  nodes = Fnreverse (nodes);
+
+  return !NILP (CALLN (Fapply, fn, nodes));
+}
 
 /* If all predicates in PREDICATES passes, return true; otherwise
    return false.  */
@@ -2387,14 +2416,17 @@ treesit_eval_predicates (struct capture_range captures, Lisp_Object predicates)
       Lisp_Object fn = XCAR (predicate);
       Lisp_Object args = XCDR (predicate);
       if (!NILP (Fstring_equal (fn, build_pure_c_string ("equal"))))
-	pass = treesit_predicate_equal (args, captures);
+	pass &= treesit_predicate_equal (args, captures);
       else if (!NILP (Fstring_equal (fn, build_pure_c_string ("match"))))
-	pass = treesit_predicate_match (args, captures);
+	pass &= treesit_predicate_match (args, captures);
+      else if (!NILP (Fstring_equal (fn, build_pure_c_string ("pred"))))
+	pass &= treesit_predicate_pred (args, captures);
       else
 	xsignal3 (Qtreesit_query_error,
 		  build_pure_c_string ("Invalid predicate"),
 		  fn, build_pure_c_string ("Currently Emacs only supports"
-					   " equal and match predicate"));
+					   " equal, match, and pred"
+					   " predicate"));
     }
   /* If all predicates passed, add captures to result list.  */
   return pass;
@@ -3217,6 +3249,7 @@ syms_of_treesit (void)
   DEFSYM (QCanchor, ":anchor");
   DEFSYM (QCequal, ":equal");
   DEFSYM (QCmatch, ":match");
+  DEFSYM (QCpred, ":pred");
 
   DEFSYM (Qnot_found, "not-found");
   DEFSYM (Qsymbol_error, "symbol-error");

test/src/treesit-tests.el

@@ -335,6 +335,9 @@ BODY is the test body."
 
 ;;; Query
 
+(defun treesit--ert-pred-last-sibling (node)
+  (null (treesit-node-next-sibling node t)))
+
 (ert-deftest treesit-query-api ()
   "Tests for query API."
   (skip-unless (treesit-language-available-p 'json))
@@ -357,13 +360,16 @@ BODY is the test body."
 (pair key: (_) @keyword)
 ((_) @bob (#match \"^B.b$\" @bob))
 (number) @number
-((number) @n3 (#equal \"3\" @n3)) "
+((number) @n3 (#equal \"3\" @n3))
+((number) @n3p (#pred treesit--ert-pred-last-sibling @n3p))"
                  ;; Sexp query.
                  ((string) @string
                   (pair key: (_) @keyword)
                   ((_) @bob (:match "^B.b$" @bob))
                   (number) @number
-                  ((number) @n3 (:equal "3" @n3)))))
+                  ((number) @n3 (:equal "3" @n3))
+                  ((number) @n3p (:pred treesit--ert-pred-last-sibling
+                                        @n3p)))))
         ;; Test `treesit-query-compile'.
         (dolist (query (list query1
                              (treesit-query-compile 'json query1)))
@@ -375,7 +381,8 @@ BODY is the test body."
               (string . "\"Bob\"")
               (bob . "Bob")
               (number . "3")
-              (n3 . "3"))
+              (n3 . "3")
+              (n3p . "3"))
             (mapcar (lambda (entry)
                       (cons (car entry)
                             (treesit-node-text