fix: fallback when xref definition jump is a no-op

modules/tools/lookup/autoload/lookup.el

@@ -185,20 +185,23 @@ This can be passed nil as its second argument to unset handlers for MODES. e.g.
 
 (autoload 'xref--show-defs "xref")
 (defun +lookup--xref-show (fn identifier &optional show-fn)
-  (let ((xrefs (funcall fn
+  (let ((origin (point-marker))
+        (xrefs (funcall fn
                         (xref-find-backend)
                         identifier)))
-    (when xrefs
-      (let* ((jumped nil)
-             (xref-after-jump-hook
-              (cons (lambda () (setq jumped t))
-                    xref-after-jump-hook)))
-        (funcall (or show-fn #'xref--show-defs)
-                 (lambda () xrefs)
-                 nil)
-        (if (cdr xrefs)
-            'deferred
-          jumped)))))
+    (unwind-protect
+        (when xrefs
+          (funcall (or show-fn #'xref--show-defs)
+                   (lambda () xrefs)
+                   nil)
+          ;; Some xref backends may report "success" without moving point (e.g.
+          ;; returning the current location). In that case, allow fallback
+          ;; backends to run.
+          (if (cdr xrefs)
+              'deferred
+            (or (not (eq (marker-buffer origin) (current-buffer)))
+                (/= (marker-position origin) (point)))))
+      (set-marker origin nil))))
 
 (defun +lookup-dictionary-definition-backend-fn (identifier)
   "Look up dictionary definition for IDENTIFIER."

modules/tools/lookup/test/test-lookup.el

@@ -0,0 +1,35 @@
+;; -*- lexical-binding: t; no-byte-compile: t; -*-
+;;; tools/lookup/test/test-lookup.el
+
+(describe "tools/lookup"
+  (before-all
+    (load! "../autoload/lookup"))
+
+  (describe "xref fallback behavior"
+    (it "does not treat a no-op single xref result as success"
+      (with-temp-buffer
+        (insert "foo")
+        (goto-char (point-min))
+        (let ((origin (point-marker))
+              (xref-after-jump-hook nil))
+          (unwind-protect
+              (cl-letf (((symbol-function 'xref-find-backend)
+                         (lambda () 'fake))
+                        ((symbol-function 'xref-backend-definitions)
+                         (lambda (_backend _identifier)
+                           (list (xref-make "here"
+                                            (xref-make-buffer-location
+                                             (current-buffer)
+                                             (point))))))
+                        ;; Simulate a backend that triggers jump hooks without
+                        ;; changing point/buffer.
+                        ((symbol-function 'xref--show-defs)
+                         (lambda (_fetcher _alist)
+                           (run-hooks 'xref-after-jump-hook)
+                           nil)))
+                (expect (+lookup--run-handlers
+                         '+lookup-xref-definitions-backend-fn
+                         "foo"
+                         origin)
+                        :to-be nil))
+            (set-marker origin nil)))))))