Prevent await inside janet_call - address #1531

This was partially implemented before, but not in the case where the
await or other signal itself was created by a C function. We have to
separate code paths for generating signals - one via normal returns in
janet_vm_continue, and the other via longjump. This adds handling for
the longjump case, as well as improved messaging.

Author: bakpakin

src/core/capi.c

@@ -62,6 +62,13 @@ JANET_NO_RETURN static void janet_top_level_signal(const char *msg) {
 
 void janet_signalv(JanetSignal sig, Janet message) {
     if (janet_vm.return_reg != NULL) {
+        /* Should match logic in janet_call for coercing everything not ok to an error (no awaits, yields, etc.) */
+        if (janet_vm.coerce_error && sig != JANET_SIGNAL_OK) {
+            if (sig != JANET_SIGNAL_ERROR) {
+                message = janet_wrap_string(janet_formatc("%v coerced from %s to error", message, janet_signal_names[sig]));
+            }
+            sig = JANET_SIGNAL_ERROR;
+        }
         *janet_vm.return_reg = message;
         if (NULL != janet_vm.fiber) {
             janet_vm.fiber->flags |= JANET_FIBER_DID_LONGJUMP;

src/core/state.h

@@ -100,6 +100,7 @@ struct JanetVM {
      * return point for panics. */
     jmp_buf *signal_buf;
     Janet *return_reg;
+    int coerce_error;
 
     /* The global registry for c functions. Used to store meta-data
      * along with otherwise bare c function pointers. */

src/core/vm.c

@@ -1373,7 +1373,10 @@ Janet janet_call(JanetFunction *fun, int32_t argc, const Janet *argv) {
 
     /* Run vm */
     janet_vm.fiber->flags |= JANET_FIBER_RESUME_NO_USEVAL | JANET_FIBER_RESUME_NO_SKIP;
+    int old_coerce_error = janet_vm.coerce_error;
+    janet_vm.coerce_error = 1;
     JanetSignal signal = run_vm(janet_vm.fiber, janet_wrap_nil());
+    janet_vm.coerce_error = old_coerce_error;
 
     /* Teardown */
     janet_vm.stackn = oldn;
@@ -1384,6 +1387,10 @@ Janet janet_call(JanetFunction *fun, int32_t argc, const Janet *argv) {
     }
 
     if (signal != JANET_SIGNAL_OK) {
+        /* Should match logic in janet_signalv */
+        if (signal != JANET_SIGNAL_ERROR) {
+            *janet_vm.return_reg = janet_wrap_string(janet_formatc("%v coerced from %s to error", *janet_vm.return_reg, janet_signal_names[signal]));
+        }
         janet_panicv(*janet_vm.return_reg);
     }
 
@@ -1430,8 +1437,10 @@ void janet_try_init(JanetTryState *state) {
     state->vm_fiber = janet_vm.fiber;
     state->vm_jmp_buf = janet_vm.signal_buf;
     state->vm_return_reg = janet_vm.return_reg;
+    state->coerce_error = janet_vm.coerce_error;
     janet_vm.return_reg = &(state->payload);
     janet_vm.signal_buf = &(state->buf);
+    janet_vm.coerce_error = 0;
 }
 
 void janet_restore(JanetTryState *state) {
@@ -1440,6 +1449,7 @@ void janet_restore(JanetTryState *state) {
     janet_vm.fiber = state->vm_fiber;
     janet_vm.signal_buf = state->vm_jmp_buf;
     janet_vm.return_reg = state->vm_return_reg;
+    janet_vm.coerce_error = state->coerce_error;
 }
 
 static JanetSignal janet_continue_no_check(JanetFiber *fiber, Janet in, Janet *out) {

src/include/janet.h

@@ -1261,6 +1261,7 @@ typedef struct {
     /* new state */
     jmp_buf buf;
     Janet payload;
+    int coerce_error;
 } JanetTryState;
 
 /***** END SECTION TYPES *****/

test/suite-ev.janet

@@ -465,4 +465,13 @@
 # Close chat server
 (:close chat-server)
 
+# Issue #1531
+(def c (ev/chan 0))
+(ev/spawn (while (def x (ev/take c))))
+(defn print-to-chan [x] (ev/give c x))
+(assert-error "coerce await inside janet_call to error"
+              (with-dyns [*out* print-to-chan]
+                (pp :foo)))
+(ev/chan-close c)
+
 (end-suite)