Add error requiring an explicit calling convention for foreign procedures

src/checker.cpp

@@ -3889,6 +3889,14 @@ gb_internal void check_collect_value_decl(CheckerContext *c, Ast *decl) {
 					GB_ASSERT(pl->type->kind == Ast_ProcType);
 					auto cc = pl->type->ProcType.calling_convention;
 					if (cc == ProcCC_ForeignBlockDefault) {
+						if (is_arch_wasm()) {
+							begin_error_block();
+							error(init, "For wasm related targets, it is required that you either define the"
+							            " @(default_calling_convention=<string>) on the foreign block or"
+							            " explicitly assign it on the procedure signature");
+							error_line("\tSuggestion: when dealing with normal Odin code (e.g. js_wasm32), use \"contextless\"; when dealing with Emscripten like code, use \"c\"\n");
+							end_error_block();
+						}
 						cc = ProcCC_CDecl;
 						if (c->foreign_context.default_cc > 0) {
 							cc = c->foreign_context.default_cc;