Fix indent-sexp of #s(...) (Bug#31984)

* lisp/emacs-lisp/lisp-mode.el (indent-sexp): Look for a sexp that
ends after the current line.
* test/lisp/emacs-lisp/lisp-mode-tests.el (indent-sexp-go): New test.

lisp/emacs-lisp/lisp-mode.el

@@ -1199,8 +1199,14 @@ ENDPOS is encountered."
     (setq endpos (copy-marker
                   (if endpos endpos
                     ;; Get error now if we don't have a complete sexp
-                    ;; after point.
+                    ;; after point.  We actually look for a sexp which
-                    (save-excursion (forward-sexp 1) (point)))))
+                    ;; ends after the current line so that we properly
+                    ;; indent things like #s(...).  This might not be
+                    ;; needed if Bug#15998 is fixed.
+                    (let ((eol (line-end-position)))
+                      (save-excursion (while (and (< (point) eol) (not (eobp)))
+                                        (forward-sexp 1))
+                                      (point))))))
     (save-excursion
       (while (let ((indent (lisp-indent-calc-next parse-state))
                    (ppss (lisp-indent-state-ppss parse-state)))

test/lisp/emacs-lisp/lisp-mode-tests.el

@@ -113,6 +113,18 @@ noindent\" 3
       ;; we're indenting ends on the previous line.
       (should (equal (buffer-string) original)))))
 
+(ert-deftest indent-sexp-go ()
+  "Make sure `indent-sexp' doesn't stop after #s."
+  ;; See https://debbugs.gnu.org/cgi/bugreport.cgi?bug=31984.
+  (with-temp-buffer
+    (emacs-lisp-mode)
+    (insert "#s(foo\nbar)\n")
+    (goto-char (point-min))
+    (indent-sexp)
+    (should (equal (buffer-string) "\
+#s(foo
+   bar)\n"))))
+
 (ert-deftest lisp-indent-region ()
   "Test basics of `lisp-indent-region'."
   (with-temp-buffer