hush: fix corner cases with exec in empty expansions

Cases like these:

var=val exec >redir

var=val `` >redir

function                                             old     new   delta
run_pipe                                            1701    1723     +22
redirect_and_varexp_helper                            56      55      -1
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 22/-1)              Total: 21 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

5 files changed, 35 insertions, 17 deletions

diff --git a/shell/ash_test/ash-redir/redir_exec1.right b/shell/ash_test/ash-redir/redir_exec1.right
new file mode 100644
index 000000000..d4393d10c
--- /dev/null
+++ b/shell/ash_test/ash-redir/redir_exec1.right
@@ -0,0 +1,2 @@
+redir_exec1.tests: line 1: can't create /cant/be/created: nonexistent directory
+First
diff --git a/shell/ash_test/ash-redir/redir_exec1.tests b/shell/ash_test/ash-redir/redir_exec1.tests
new file mode 100755
index 000000000..290e1cb39
--- /dev/null
+++ b/shell/ash_test/ash-redir/redir_exec1.tests
@@ -0,0 +1,2 @@
+v=`echo First >&2` exec >/cant/be/created
+echo One:$?
diff --git a/shell/hush.c b/shell/hush.c
index 24ae237d7..43702360a 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -8200,19 +8200,21 @@ static int redirect_and_varexp_helper(
                 struct squirrel **sqp,
                 char **argv_expanded)
 {
+        /* Assignments occur before redirects. Try:
+         * a=`sleep 1` sleep 2 3>/qwe/rty
+         */
+
+        char **new_env = expand_assignments(command->argv, command->assignment_cnt);
+        dump_cmd_in_x_mode(new_env);
+        dump_cmd_in_x_mode(argv_expanded);
+        /* this takes ownership of new_env[i] elements, and frees new_env: */
+        set_vars_and_save_old(new_env);
+
         /* setup_redirects acts on file descriptors, not FILEs.
          * This is perfect for work that comes after exec().
          * Is it really safe for inline use?  Experimentally,
          * things seem to work. */
-        int rcode = setup_redirects(command, sqp);
-        if (rcode == 0) {
-                char **new_env = expand_assignments(command->argv, command->assignment_cnt);
-                dump_cmd_in_x_mode(new_env);
-                dump_cmd_in_x_mode(argv_expanded);
-                /* this takes ownership of new_env[i] elements, and frees new_env: */
-                set_vars_and_save_old(new_env);
-        }
-        return rcode;
+        return setup_redirects(command, sqp);
 }
 static NOINLINE int run_pipe(struct pipe *pi)
 {
@@ -8315,6 +8317,7 @@ static NOINLINE int run_pipe(struct pipe *pi)
                          * Ensure redirects take effect (that is, create files).
                          * Try "a=t >file"
                          */
+ only_assignments:
                         G.expand_exitcode = 0;
 
                         rcode = setup_redirects(command, &squirrel);
@@ -8359,12 +8362,10 @@ static NOINLINE int run_pipe(struct pipe *pi)
 #endif
                         argv_expanded = expand_strvec_to_strvec(argv + command->assignment_cnt);
 
-                /* if someone gives us an empty string: `cmd with empty output` */
-//TODO: what about: var=EXPR `` >FILE ? will var be set? Will FILE be created?
+                /* If someone gives us an empty string: `cmd with empty output` */
                 if (!argv_expanded[0]) {
                         free(argv_expanded);
-                        debug_leave();
-                        return G.last_exitcode;
+                        goto only_assignments;
                 }
 
                 old_vars = NULL;
@@ -8378,9 +8379,17 @@ static NOINLINE int run_pipe(struct pipe *pi)
                 if (x || funcp) {
                         if (x && x->b_function == builtin_exec && argv_expanded[1] == NULL) {
                                 debug_printf("exec with redirects only\n");
-                                rcode = setup_redirects(command, NULL);
-//TODO: what about: var=EXPR exec >FILE ? will var be set?
+                                /*
+                                 * Variable assignments are executed, but then "forgotten":
+                                 *  a=`sleep 1;echo A` exec 3>&-; echo $a
+                                 * sleeps, but prints nothing.
+                                 */
+                                enter_var_nest_level();
+                                G.shadowed_vars_pp = &old_vars;
+                                rcode = redirect_and_varexp_helper(command, /*squirrel:*/ NULL, argv_expanded);
+                                G.shadowed_vars_pp = sv_shadowed;
                                 /* rcode=1 can be if redir file can't be opened */
+
                                 goto clean_up_and_ret1;
                         }
 
@@ -8452,9 +8461,10 @@ static NOINLINE int run_pipe(struct pipe *pi)
                 } else
                         goto must_fork;
 
+                restore_redirects(squirrel);
+ clean_up_and_ret1:
                 leave_var_nest_level();
                 add_vars(old_vars);
-                restore_redirects(squirrel);
 
                 /*
                  * Try "usleep 99999999" + ^C + "echo $?"
@@ -8474,7 +8484,6 @@ static NOINLINE int run_pipe(struct pipe *pi)
                         if (sigismember(&G.pending_set, SIGINT))
                                 rcode = 128 + SIGINT;
                 }
- clean_up_and_ret1:
                 free(argv_expanded);
                 IF_HAS_KEYWORDS(if (pi->pi_inverted) rcode = !rcode;)
                 debug_leave();
diff --git a/shell/hush_test/hush-redir/redir_exec1.right b/shell/hush_test/hush-redir/redir_exec1.right
new file mode 100644
index 000000000..6ff8fc832
--- /dev/null
+++ b/shell/hush_test/hush-redir/redir_exec1.right
@@ -0,0 +1,3 @@
+First
+hush: can't open '/cant/be/created': No such file or directory
+One:1
diff --git a/shell/hush_test/hush-redir/redir_exec1.tests b/shell/hush_test/hush-redir/redir_exec1.tests
new file mode 100755
index 000000000..290e1cb39
--- /dev/null
+++ b/shell/hush_test/hush-redir/redir_exec1.tests
@@ -0,0 +1,2 @@
+v=`echo First >&2` exec >/cant/be/created
+echo One:$?