hush: fix `trap`

function                                             old     new   delta
expand_variables                                    2217    2280     +63
static.argv                                            -       8      +8

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

3 files changed, 52 insertions, 1 deletions

diff --git a/shell/hush.c b/shell/hush.c
index 6b176c388..eaf911458 100644
--- a/shell/hush.c
+++ b/shell/hush.c
@@ -5180,6 +5180,47 @@ static FILE *generate_stream_from_string(const char *s)
                 xmove_fd(channel[1], 1);
                 /* Prevent it from trying to handle ctrl-z etc */
                 IF_HUSH_JOB(G.run_list_level = 1;)
+                /* Awful hack for `trap` or $(trap).
+                 *
+                 * http://www.opengroup.org/onlinepubs/009695399/utilities/trap.html
+                 * contains an example where "trap" is executed in a subshell:
+                 *
+                 * save_traps=$(trap)
+                 * ...
+                 * eval "$save_traps"
+                 *
+                 * Standard does not say that "trap" in subshell shall print
+                 * parent shell's traps. It only says that its output
+                 * must have suitable form, but then, in the above example
+                 * (which is not supposed to be normative), it implies that.
+                 *
+                 * bash (and probably other shell) does implement it
+                 * (traps are reset to defaults, but "trap" still shows them),
+                 * but as a result, "trap" logic is hopelessly messed up:
+                 *
+                 * # trap
+                 * trap -- 'echo Ho' SIGWINCH  <--- we have a handler
+                 * # (trap)        <--- trap is in subshell - no output (correct, traps are reset)
+                 * # true | trap   <--- trap is in subshell - no output (ditto)
+                 * # echo `true | trap`    <--- in subshell - output (but traps are reset!)
+                 * trap -- 'echo Ho' SIGWINCH
+                 * # echo `(trap)`         <--- in subshell in subshell - output
+                 * trap -- 'echo Ho' SIGWINCH
+                 * # echo `true | (trap)`  <--- in subshell in subshell in subshell - output!
+                 * trap -- 'echo Ho' SIGWINCH
+                 *
+                 * The rules when to forget and when to not forget traps
+                 * get really complex and nonsensical.
+                 *
+                 * Our solution: ONLY bare $(trap) or `trap` is special.
+                 */
+                s = skip_whitespace(s);
+                if (strncmp(s, "trap", 4) == 0 && (*skip_whitespace(s + 4) == '\0'))
+                {
+                        static const char *const argv[] = { NULL, NULL };
+                        builtin_trap((char**)argv);
+                        exit(0); /* not _exit() - we need to fflush */
+                }
 #if BB_MMU
                 reset_traps_to_defaults();
                 parse_and_run_string(s);
@@ -7057,7 +7098,8 @@ static int FAST_FUNC builtin_trap(char **argv)
                         if (G.traps[i]) {
                                 printf("trap -- ");
                                 print_escaped(G.traps[i]);
-                                printf(" %s\n", get_signame(i));
+                                /* bash compat: it says SIGxxx, not just xxx */
+                                printf(" SIG%s\n", get_signame(i));
                         }
                 }
                 /*fflush(stdout); - done after each builtin anyway */
diff --git a/shell/hush_test/hush-trap/savetrap.right b/shell/hush_test/hush-trap/savetrap.right
new file mode 100644
index 000000000..2d33427aa
--- /dev/null
+++ b/shell/hush_test/hush-trap/savetrap.right
@@ -0,0 +1,3 @@
+trap -- 'echo WINCH!' SIGWINCH
+trap -- 'echo WINCH!' SIGWINCH
+Done
diff --git a/shell/hush_test/hush-trap/savetrap.tests b/shell/hush_test/hush-trap/savetrap.tests
new file mode 100755
index 000000000..6492e86a2
--- /dev/null
+++ b/shell/hush_test/hush-trap/savetrap.tests
@@ -0,0 +1,6 @@
+trap 'echo WINCH!' SIGWINCH
+v=` trap   `
+echo $v
+v=`trap`
+echo $v
+echo Done