bug#67142: 29.1; with-sqlite-transaction commits on exception rather than rolling back

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 16 Nov 2023 21:25:53 +0100
> From: Vasilij Schneidermann <mail@vasilij.de>
> Cc: 67142@debbugs.gnu.org
> 
> > Does the change below look correct?  (I'm not an expert on SQLite or
> > DB programming in general.)
> 
> The `unwind-protect` part does not look correct since the rollback is
> always performed, even after the body form completed successfully and a
> commit was done. Either a commit or a rollback should be done, not both.

Oops.  Is the below better?

> A minor mistake is the result variable not using an uninterned symbol
> (or alternatively, `prog1` could replace the use of the result variable).

I don't understand this part, sorry.  Why do we need a symbol to
return the result of the body?

diff --git a/lisp/sqlite.el b/lisp/sqlite.el
index aad0aa4..4488896 100644
--- a/lisp/sqlite.el
+++ b/lisp/sqlite.el
@@ -24,18 +24,25 @@
 ;;; Code:
 
 (defmacro with-sqlite-transaction (db &rest body)
-  "Execute BODY while holding a transaction for DB."
+  "Execute BODY while holding a transaction for DB.
+If BODY completes normally, commit the changes and return
+the value of BODY.
+If BODY signals an error, or transaction commit fails, roll
+back the transaction changes."
   (declare (indent 1) (debug (form body)))
   (let ((db-var (gensym))
         (func-var (gensym)))
     `(let ((,db-var ,db)
            (,func-var (lambda () ,@body)))
        (if (sqlite-available-p)
-           (unwind-protect
-               (progn
-                 (sqlite-transaction ,db-var)
-                 (funcall ,func-var))
-             (sqlite-commit ,db-var))
+           (let (result commit)
+             (unwind-protect
+                 (progn
+                   (sqlite-transaction ,db-var)
+                   (setq result (funcall ,func-var))
+                   (setq commit (sqlite-commit ,db-var))
+                   result)
+             (or commit (sqlite-rollback ,db-var))))
          (funcall ,func-var)))))
 
 (provide 'sqlite)