Fix: (org-ql--define-query-preamble-fn) Pcase pattern for Emacs 30

Now all tests and lints pass on Emacs versions 27.1-29.4.  But on the
current Emacs snapshot build used in CI, Buttercup is hanging
indefinitely, which may be the same problem that led Guix to disable
the tests in
<https://git.savannah.gnu.org/cgit/guix.git/commit/gnu/packages/emacs-xyz.scm?id=3add97c7761e6c58a1d7405f417a49dda5f0a742>.
But I've no way of knowing whether that's a problem in org-ql (seems
unlikely), Emacs snapshot, or Buttercup.  It would be nice to solve
this before Emacs 30.1 is released, but I don't know how to peer
inside Buttercup to find out what it's hanging on.

Fixes #433.

Reported-by: Akira Komamura <akira.komamura@gmail.com>
Co-developed-by: Stefan Monnier <monnier@iro.umontreal.ca>

Author: alphapapa

README.org

@@ -556,7 +556,8 @@ Simple links may also be written manually in either sexp or non-sexp form, like:
 
 ** 0.9-pre
 
-Nothing new yet.
+*Compatibility*
++ Fix compilation error on Emacs 30.  ([[https://github.com/alphapapa/org-ql/issues/433][#433]].  Thanks to [[https://github.com/akirak][Akira Komamura]] and [[https://github.com/monnier][Stefan Monnier]].)
 
 *** helm-org-ql
 

org-ql.el

@@ -1118,10 +1118,10 @@ defined in `org-ql-predicates' by calling `org-ql-defpred'."
                                         ;; Only one preamble is allowed
                                         element)
                                       (pcase element
-                                        ;; FIXME: Should the pattern below be "`(or . ,_)"?  It
-                                        ;; seems to work fine either way, but it seems like it
-                                        ;; should be changed.
-                                        (`(or _) element)
+                                        (`(or ,element)
+                                         ;; A predicate with a single name: unwrap the OR.  (Pcase doesn't like
+                                         ;; "one-armed ORs", giving a "Please avoid it" compilation error.)
+                                         element)
 
                                         ,@preamble-patterns
 

org-ql.info

@@ -1091,7 +1091,11 @@ File: README.info,  Node: 09-pre,  Next: 087,  Up: Changelog
 5.1 0.9-pre
 ===========
 
-Nothing new yet.
+*Compatibility*
+   • Fix compilation error on Emacs 30.  (#433
+     (https://github.com/alphapapa/org-ql/issues/433).  Thanks to Akira
+     Komamura (https://github.com/akirak) and Stefan Monnier
+     (https://github.com/monnier).)
 
 * Menu:
 
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