[PATCH v2] Make zpty module work in the cygwin and msys2

[Peiyuan Song <squallatf@gmail.com>]

cygwin have /dev/ptmx, need defined `_GNU_SOURCE 1` to use it, but
configure check /dev/ptmx is usable only defined it for linux.

Another probleam is cygwin upstream have an issue
https://cygwin.com/pipermail/cygwin-developers/2021-January/012030.html,
because of that issue, movefd will broken the fd opened by
posix_openpt, so that we mast disable movefd in zpty until cygwin
fix that issue.

v2 change:  make fdtable[master]

---
 Src/Modules/zpty.c | 28 ++++++++++++++++++++++++++++
 configure.ac       |  2 +-
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/Src/Modules/zpty.c b/Src/Modules/zpty.c
index 45fd15ee0..624da13f1 100644
--- a/Src/Modules/zpty.c
+++ b/Src/Modules/zpty.c
@@ -299,6 +299,29 @@ get_pty(int master, int *retfd)

 #endif /* /dev/ptmx or alternatives */

+#ifdef __CYGWIN__
+/*
+ * Ensure the fdtable is large enough for fd, and that the
+ * maximum fd is set appropriately.
+ */
+static void
+check_fd_table(int fd)
+{
+    if (fd <= max_zsh_fd)
+       return;
+
+    if (fd >= fdtable_size) {
+       int old_size = fdtable_size;
+       while (fd >= fdtable_size)
+           fdtable = zrealloc(fdtable,
+                              (fdtable_size *= 2)*sizeof(*fdtable));
+       memset(fdtable + old_size, 0,
+              (fdtable_size - old_size) * sizeof(*fdtable));
+    }
+    max_zsh_fd = fd;
+}
+#endif
+
 static int
 newptycmd(char *nam, char *pname, char **args, int echo, int nblock)
 {
@@ -428,6 +451,7 @@ newptycmd(char *nam, char *pname, char **args, int
echo, int nblock)
        mypid = 0; /* trick to ensure we _exit() */
        zexit(lastval, ZEXIT_NORMAL);
     }
+#ifndef __CYGWIN__
     master = movefd(master);
     if (master == -1) {
        zerrnam(nam, "cannot duplicate fd %d: %e", master, errno);
@@ -435,6 +459,10 @@ newptycmd(char *nam, char *pname, char **args,
int echo, int nblock)
        ineval = oineval;
        return 1;
     }
+#else
+    check_fd_table(master);
+    fdtable[master] = FDT_INTERNAL;
+#endif

     p = (Ptycmd) zalloc(sizeof(*p));

diff --git a/configure.ac b/configure.ac
index 549cae3d6..16dafac05 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2460,7 +2460,7 @@ if test x$ac_cv_have_dev_ptmx = xyes -o
x$ac_cv_func_posix_openpt = xyes && \
    test x$ac_cv_func_ptsname = xyes; then
    AC_CACHE_CHECK([if /dev/ptmx is usable],
    ac_cv_use_dev_ptmx,
-   [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#ifdef __linux
+   [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#if defined(__linux) ||
defined(__CYGWIN__)
 #define _GNU_SOURCE 1
 #endif
 #include <stdlib.h>
--
2.30.0.windows.1