In win32, system* shouldn't launch shell when command not found

When system* was called to execute a script/excutable without args, if
that did not exist, it would launch an interactive session. Now it fails
with an error.

* libguile/posix-w32.c (start_child): return when cmd not found
* test-suite/tests/posix.test (system*): system* test should handle errors

libguile/posix-w32.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 2001, 2006, 2008, 2016 Free Software Foundation, Inc.
+/* Copyright (C) 2001, 2006, 2008, 2016, 2018 Free Software Foundation, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public License
@@ -740,8 +740,11 @@ start_child (const char *exec_file, char **argv,
   CloseHandle (herr);
   CloseHandle (pi.hThread);
 
-  /* Posix requires to call the shell if execvp fails to invoke EXEC_FILE.  */
-  if (errno_save == ENOEXEC || errno_save == ENOENT)
+  /* Posix requires to call the shell if execvp fails to invoke EXEC_FILE.
+   * But if there are no arguments, this would just open an interactive
+   * cmd.exe shell, so return in that case. */
+  if ((errno_save == ENOEXEC || errno_save == ENOENT)
+      && (argv[0] != NULL && argv[1] != NULL)
     {
       const char *shell = getenv ("ComSpec");
 

test-suite/tests/posix.test

@@ -235,8 +235,9 @@
     ;; With Guile up to 2.0.7 included, the child process launched by
     ;; `system*' would remain alive after an `execvp' failure.
     (let ((me (getpid)))
-      (and (not (zero? (system* "something-that-does-not-exist")))
-           (= me (getpid))))))
+      (and
+       (not (equal? 0 (false-if-exception (system* "something-that-does-not-exist"))))
+       (= me (getpid))))))
 
 ;;
 ;; crypt
@@ -245,12 +246,16 @@
 (with-test-prefix "crypt"
 
   (pass-if "basic usage"
-    (string? (crypt "pass" "abcdefg")))
+    (if (not (defined? 'crypt))
+        (throw 'unsupported)
+        (string? (crypt "pass" "abcdefg"))))
 
   (pass-if-exception "glibc EINVAL" exception:system-error
     ;; This used to deadlock while trying to throw to 'system-error'.
     ;; This test uses the special interpretation of the salt that glibc
     ;; does; specifically, we pass a syntactically invalid salt here.
-    (if (string-contains %host-type "-gnu")
-        (crypt "pass" "$X$abc")                   ;EINVAL
-        (throw 'unresolved))))
+    (if (not (defined? 'crypt))
+        (throw 'unsupported)
+        (if (string-contains %host-type "-gnu")
+            (crypt "pass" "$X$abc")                   ;EINVAL
+            (throw 'unresolved)))))