Complete shorthands to longhands for symbol-completing tablesscratch/bug-50959-fix

Shorthands aren't symbols, they're text forms that 'read' into
symbols.  As such, shorthands aren't candidates in these tables of
symbols.  But in some situations, if no other candidates match the
pattern, we can e.g. complete "x-foo" to "xavier-foo" if the shorthand

  (("x-" . "xavier-"))

is set up in the buffer of origin.

bug#50959

* lisp/help-fns.el (help--symbol-completion-table): Report
`symbol-help' category.

* lisp/minibuffer.el (completion-styles-alist): New 'shorthand'
style.
(completion-category-defaults): Link 'symbol-help' category with
'shorthand' style.
(minibuffer--original-buffer): New variable.
(completing-read-default): Setup minibuffer--original-buffer.
(completion-shorthand-try-completion)
(completion-shorthand-all-completions): New helpers.

1 files changed, 5 insertions, 2 deletions

diff --git a/lisp/help-fns.el b/lisp/help-fns.el
index 6be5cd4a501..03bbc979a9c 100644
--- a/lisp/help-fns.el
+++ b/lisp/help-fns.el
@@ -176,8 +176,11 @@ with the current prefix.  The files are chosen according to
           completions))
 
 (defun help--symbol-completion-table (string pred action)
-  (if (and completions-detailed (eq action 'metadata))
-      '(metadata (affixation-function . help--symbol-completion-table-affixation))
+  (if (eq action 'metadata)
+      `(metadata
+        ,@(when completions-detailed
+            '((affixation-function . help--symbol-completion-table-affixation)))
+        (category . symbol-help))
     (when help-enable-completion-autoload
       (let ((prefixes (radix-tree-prefixes (help-definition-prefixes) string)))
         (help--load-prefixes prefixes)))