Don't emit the 'no output file specified' warning when using a pass that emits to stdout (#7696)

Author: dschuff

src/tools/wasm-opt.cpp

@@ -436,7 +436,15 @@ For more on how to optimize effectively, see
 
   if (options.extra.count("output") == 0) {
     if (!options.quiet) {
-      std::cerr << "warning: no output file specified, not emitting output\n";
+      bool printsToStdout = std::any_of(
+        options.passes.begin(),
+        options.passes.end(),
+        [](const OptimizationOptions::PassInfo& info) {
+          return info.name == "print" || info.name == "print-function-map";
+        });
+      if (!printsToStdout) {
+        std::cerr << "warning: no output file specified, not emitting output\n";
+      }
     }
     return 0;
   }

test/unit/test_warnings.py

@@ -16,3 +16,11 @@ def test_warn_on_no_output(self):
     def test_quiet_suppresses_warnings(self):
         err = shared.run_process(shared.WASM_OPT + [self.input_path('asyncify-pure.wat'), '-q'], stderr=subprocess.PIPE).stderr
         self.assertNotIn('warning', err)
+
+    def test_no_warn_on_print(self):
+        err = shared.run_process(shared.WASM_OPT + [self.input_path('asyncify-pure.wat'), '--print'], stderr=subprocess.PIPE).stderr
+        self.assertNotIn('warning: no output file specified, not emitting output', err)
+
+    def test_no_warn_on_print_function_map(self):
+        err = shared.run_process(shared.WASM_OPT + [self.input_path('asyncify-pure.wat'), '--print-function-map'], stderr=subprocess.PIPE).stderr
+        self.assertNotIn('warning: no output file specified, not emitting output', err)