Keep event faults out of view evaluation

A view that failed (for example on a missing list item) overwrote the
app's fault, so a host saw a fault after a successful event. A view now
reports failure only by its result.

2 files changed, 8 insertions, 1 deletions

diff --git a/prototypes/connections/module.c b/prototypes/connections/module.c
index c07b1e8..2e5375c 100644
--- a/prototypes/connections/module.c
+++ b/prototypes/connections/module.c
@@ -1132,12 +1132,18 @@ PureResult pure_app_reply(const PureApp *app, bool (*visit)(void *, PureSpan), v
     return visit_value(app, &app->arena, app->reply, visit, context);
 }
 
+/* A view that fails reports it by its result; the fault stays the last event's. */
 static PureResult evaluate(PureApp *app, uint32_t view, Slot *out) {
     double values[PURE_MODULE_STATES];
     memcpy(values, app->values, sizeof(values));
     app->view_arena.used = 0;
     Event ev = {.app = app, .arena = &app->view_arena};
-    return run(app->module, values, app->module->view_code[view], &ev, out);
+    PureFault fault = app->fault;
+    uint32_t fault_pc = app->fault_pc;
+    PureResult result = run(app->module, values, app->module->view_code[view], &ev, out);
+    app->fault = fault;
+    app->fault_pc = fault_pc;
+    return result;
 }
 
 bool pure_app_view(PureApp *app, uint32_t view, double *out) {
diff --git a/prototypes/connections/test-module.c b/prototypes/connections/test-module.c
index eb61521..8867e0a 100644
--- a/prototypes/connections/test-module.c
+++ b/prototypes/connections/test-module.c
@@ -916,6 +916,7 @@ static void lists(void) {
     double value;
     CHECK(number_view(&app, 0) == 0 && number_view(&app, 1) == 0 && !pure_app_view(&app, 2, &value));
     CHECK(pure_app_view_text(&app, 3, text_span, &(Text){{0}, 0}) == PURE_NOT_FOUND);  /* no item yet */
+    CHECK(app.fault == PURE_FAULT_NONE);                                                /* views leave faults alone */
     CHECK(pure_app_text(&app, 0, (PureSpan){(const unsigned char *)"a", 1}) == PURE_OK);
     CHECK(pure_app_text(&app, 0, (PureSpan){(const unsigned char *)"b", 1}) == PURE_OK);
     CHECK(pure_list_count(app.lists[1]) == 2 && app.values[2] == 1 && app.values[0] == 2);