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

[Visuwesh]

[வியாழன் ஜூன் 02, 2022] Lars Ingebrigtsen wrote:

> Visuwesh <visuweshm@gmail.com> writes:
>
>> 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.
>
> I think that might make sense, but perhaps Stefan has some comments here
> (added to the CCs).

To no one's surprise, the patch is not the right approach.  IIUC, when I
use braces, *pattern) thingies are not recognised as "case-)" anymore so
sh-indent-for-case-label does not get applied.  I tried a bit more but I
only got it to respect the first line but still it is definitely not the
right approach,

diff --git a/lisp/progmodes/sh-script.el b/lisp/progmodes/sh-script.el
index 4d2554c087..96ff8e8627 100644
--- a/lisp/progmodes/sh-script.el
+++ b/lisp/progmodes/sh-script.el
@@ -1971,9 +1971,9 @@ sh-smie-sh-rules
                              (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 "{") (smie-rule-parent-p "for" "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)
@@ -2021,10 +2021,13 @@ sh-smie-sh-rules
     ('(:after . "in") (sh-var-value 'sh-indent-for-case-label))
     ;; sh-indent-for-continuation: Line continuations are handled differently.
     (`(:after . ,(or "(" "{" "["))
-     (if (not (looking-at ".[ \t]*[^\n \t#]"))
-         (sh-var-value 'sh-indent-after-open)
-       (goto-char (1- (match-end 0)))
-       `(column . ,(current-column))))
+     (cond
+      ((smie-rule-parent-p "case")
+       (sh-var-value 'sh-indent-for-case-label))
+      ((not (looking-at ".[ \t]*[^\n \t#]"))
+       (sh-var-value 'sh-indent-after-open))
+      (t (goto-char (1- (match-end 0)))
+         `(column . ,(current-column)))))
     ;; sh-indent-after-function: we don't handle it differently.
     ))