bug#55764: 29.0.50; sh-mode: Support mksh's alternate case brace syntax

[Visuwesh]

mksh and OpenBSD's ksh support an alternative case syntax for historical
reasons [1],

    case $i {
    *pattern) do ;;
    *pattern2) do2 ;;
    }


Currently, sh-mode cannot handle this and the easy way out of writing a
semicolon after $i is out since,

   % case "foo"; { *o) echo 1;; }
   /bin/mksh: syntax error: unexpected ';'

I came with the attached patch after a bit of trial and error but I'm
not sure if it is the right way to do it.

diff --git a/lisp/progmodes/sh-script.el b/lisp/progmodes/sh-script.el
index 4d2554c087..588d9038e5 100644
--- a/lisp/progmodes/sh-script.el
+++ b/lisp/progmodes/sh-script.el
@@ -1971,9 +1971,10 @@
                              (sh-var-value 'sh-indent-for-case-label)))
     (`(:before . ,(or "(" "{" "[" "while" "if" "for" "case"))
      (cond
-      ((and (equal token "{") (smie-rule-parent-p "for"))
+      ((and (equal token "{") (or (smie-rule-parent-p "for")
+                                  (smie-rule-parent-p "case")))
        (let ((data (smie-backward-sexp "in")))
-         (when (equal (nth 2 data) "for")
+         (when (member (nth 2 data) '("for" "case"))
            `(column . ,(smie-indent-virtual)))))
       ((not (smie-rule-prev-p "&&" "||" "|"))
        (when (smie-rule-hanging-p)

--

[1] Here's what the mksh manual says,

    For historical reasons, open and close braces may be used instead
    of in and esac, for example: “case $foo { (ba[rz]|blah) date ;; }”

and OpenBSD's ksh manual says,

    For historical reasons, open and close braces may be used instead of
    in and esac e.g. case $foo { *) echo bar; }.