Add some systems that support addchdir.

This will need to be expanded but should support most modern systems.

src/core/os.c

@@ -55,6 +55,7 @@
 #include <sys/utime.h>
 #include <io.h>
 #include <process.h>
+#define JANET_SPAWN_CHDIR
 #else
 #include <spawn.h>
 #include <utime.h>
@@ -73,6 +74,20 @@ extern char **environ;
 #endif
 #endif
 
+/* Detect availability of posix_spawn_file_actions_addchdir_np. Since
+ * this doesn't seem to follow any standard, just a common extension, we
+ * must enumerate supported systems for availability. Define JANET_SPAWN_NO_CHDIR
+ * to disable this. */
+#ifndef JANET_SPAWN_NO_CHDIR
+#ifdef __GLIBC__
+#define JANET_SPAWN_CHDIR
+#elif defined(JANET_APPLE) /* Some older versions may not work here. */
+#define JANET_SPAWN_CHDIR
+#elif defined(__FreeBSD__) /* Not all BSDs work, for example openBSD doesn't seem to support this */
+#define JANET_SPAWN_CHDIR
+#endif
+#endif
+
 /* Not POSIX, but all Unixes but Solaris have this function. */
 #if defined(JANET_POSIX) && !defined(__sun)
 time_t timegm(struct tm *tm);
@@ -1182,6 +1197,21 @@ static Janet os_execute_impl(int32_t argc, Janet *argv, JanetExecuteMode mode) {
         }
     }
 
+    /* Optional working directory. Available for both os/execute and os/spawn. */
+    const char *chdir_path = NULL;
+    if (argc > 2) {
+        JanetDictView tab = janet_getdictionary(argv, 2);
+        Janet workdir = janet_dictionary_get(tab.kvs, tab.cap, janet_ckeywordv("cd"));
+        if (janet_checktype(workdir, JANET_STRING)) {
+            chdir_path = (const char *) janet_unwrap_string(workdir);
+#ifndef JANET_SPAWN_CHDIR
+            janet_panicf(":cd argument not supported on this system - %s", chdir_path);
+#endif
+        } else if (!janet_checktype(workdir, JANET_NIL)) {
+            janet_panicf("expected string for :cd argumnet, got %v", workdir);
+        }
+    }
+
     /* Clean up if any of the pipes have any issues */
     if (pipe_errflag) {
         if (pipe_in != JANET_HANDLE_NONE) close_handle(pipe_in);
@@ -1196,6 +1226,7 @@ static Janet os_execute_impl(int32_t argc, Janet *argv, JanetExecuteMode mode) {
     SECURITY_ATTRIBUTES saAttr;
     PROCESS_INFORMATION processInfo;
     STARTUPINFO startupInfo;
+    LPCSTR lpCurrentDirectory = NULL;
     memset(&saAttr, 0, sizeof(saAttr));
     memset(&processInfo, 0, sizeof(processInfo));
     memset(&startupInfo, 0, sizeof(startupInfo));
@@ -1212,6 +1243,10 @@ static Janet os_execute_impl(int32_t argc, Janet *argv, JanetExecuteMode mode) {
     }
     const char *path = (const char *) janet_unwrap_string(exargs.items[0]);
 
+    if (chdir_path != NULL) {
+        lpCurrentDirectory = chdir_path;
+    }
+
     /* Do IO redirection */
 
     if (pipe_in != JANET_HANDLE_NONE) {
@@ -1248,7 +1283,7 @@ static Janet os_execute_impl(int32_t argc, Janet *argv, JanetExecuteMode mode) {
                        TRUE, /* handle inheritance */
                        0, /* flags */
                        use_environ ? NULL : envp, /* pass in environment */
-                       NULL, /* use parents starting directory */
+                       lpCurrentDirectory,
                        &startupInfo,
                        &processInfo)) {
         cp_failed = 1;
@@ -1305,6 +1340,15 @@ static Janet os_execute_impl(int32_t argc, Janet *argv, JanetExecuteMode mode) {
     /* Posix spawn setup */
     posix_spawn_file_actions_t actions;
     posix_spawn_file_actions_init(&actions);
+#ifdef JANET_SPAWN_CHDIR
+    if (chdir_path != NULL) {
+#ifdef JANET_SPAWN_CHDIR_NO_NP
+        posix_spawn_file_actions_addchdir(&actions, chdir_path);
+#else
+        posix_spawn_file_actions_addchdir_np(&actions, chdir_path);
+#endif
+    }
+#endif
     if (pipe_in != JANET_HANDLE_NONE) {
         posix_spawn_file_actions_adddup2(&actions, pipe_in, 0);
         posix_spawn_file_actions_addclose(&actions, pipe_in);