Print warning when a single-file package fails package-buffer-info

package-build.el

@@ -718,6 +718,10 @@ FILES is a list of (SOURCE . DEST) relative filepath pairs."
           (with-current-buffer (find-file pkg-target)
             (pb/update-or-insert-version version)
             (write-file pkg-target nil)
+            (condition-case err
+                (package-buffer-info)
+              ('error
+               (message "Warning: package is uninstallable - package-buffer-info reports:\n%S" err)))
             (kill-buffer))
 
           (pb/write-pkg-readme (and (> (length pkg-info) 4) (aref pkg-info 4))