[PATCH 4/5] installemulation(): restore static state after the option scan

[Imre Péntek <imre@xxxxxxxxxx>]

installemulation() passes its target to setemulate() through the
static variables setemulate_emulation and setemulate_opts.  A trap run
during scanhashtable() that itself uses "emulate" (every powerlevel10k
function starts with "emulate -L zsh") overwrites them with a pointer
into its own, soon dead, stack frame; the outer scan then writes the
option settings there (AddressSanitizer: stack-use-after-return in
setemulate()).

Save the previous values and restore them after the scan.

Co-Authored-By: Claude Opus 5.5 <noreply@xxxxxxxxxxxxx>
---

Notes:
    Reproducer: start "zsh -f", paste the lines below, then hold down
    Ctrl-C for a few seconds.  Without this patch (preceding ones applied),
    AddressSanitizer reports stack-use-after-return in setemulate().
    
        setopt interactivecomments
        # 4: a trap's "emulate" run during another emulate's option scan leaves
        #    the outer scan writing to the finished call's stack frame.
        #    (Builtins run with signals unqueued: the trap runs mid-scan.
        #    The zle -F handler on /dev/zero keeps emulate running.)
        exec {z}</dev/zero
        h() { local c; read -r -u $1 -k 1 c; repeat 20 emulate -L zsh }
        zle -F $z h
        t() { emulate -L zsh -o extendedglob }
        trap 't; return 130' INT

 Src/options.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Src/options.c b/Src/options.c
index 9bf56cf81..b7213ff54 100644
--- a/Src/options.c
+++ b/Src/options.c
@@ -522,10 +522,16 @@ setemulate(HashNode hn, int fully)
 void
 installemulation(int new_emulation, char *new_opts)
 {
+    /* a trap run during the scan may emulate too: restore for our caller */
+    int sav_emulation = setemulate_emulation;
+    char *sav_opts = setemulate_opts;
+
     setemulate_emulation = new_emulation;
     setemulate_opts = new_opts;
     scanhashtable(optiontab, 0, 0, 0, setemulate,
 		  !!(new_emulation & EMULATE_FULLY));
+    setemulate_emulation = sav_emulation;
+    setemulate_opts = sav_opts;
 }
 
 /**/
-- 
2.55.0