Use new wast parser in wasm2js

When generating assertions, traverse the `WASTScript` data structure rather than
interleaving assertion parsing with emitting.

src/emscripten-optimizer/simple_ast.h

@@ -38,9 +38,8 @@
 #include "snprintf.h"
 #include "support/safe_integer.h"
 
-#define err(str) fprintf(stderr, str "\n");
 #define errv(str, ...) fprintf(stderr, str "\n", __VA_ARGS__);
-#define printErr err
+#define printErr(str) fprintf(stderr, str "\n");
 
 namespace cashew {
 

src/parser/wast-parser.cpp

@@ -397,11 +397,15 @@ Result<WASTScript> wast(Lexer& in) {
   while (!in.empty()) {
     size_t line = in.position().line;
     auto cmd = command(in);
-    if (cmd.getErr() && cmds.empty()) {
+    if (auto* err = cmd.getErr(); err && cmds.empty()) {
       // The entire script might be a single module comprising a sequence of
       // module fields with a top-level `(module ...)`.
       auto wasm = std::make_shared<Module>();
-      CHECK_ERR(parseModule(*wasm, in.buffer));
+      auto parsed = parseModule(*wasm, in.buffer);
+      if (parsed.getErr()) {
+        // No, that wasn't the problem. Return the original error.
+        return Err{err->msg};
+      }
       cmds.push_back({WASTModule{std::move(wasm)}, line});
       return cmds;
     }