Warning improvements (#2438)

If wasm-opt is run with no passes, warn, as we've gotten reports that people
assume a tool called "wasm-opt" should optimize automatically (but we follow
llvm's opt convention of not doing so).

Add a --quiet (-q) flag that suppresses this minor warning, and the other minor
warning where there is no output file.

2 files changed, 19 insertions, 1 deletions

diff --git a/test/unit/test_asyncify.py b/test/unit/test_asyncify.py
index 9b7c403c0..052dedb0e 100644
--- a/test/unit/test_asyncify.py
+++ b/test/unit/test_asyncify.py
@@ -45,7 +45,7 @@ class AsyncifyTest(BinaryenTestCase):
             ('--pass-arg=asyncify-whitelist@DOS_ReadFile(unsigned short, unsigned char*, unsigned short*, bool)', None),
         ]:
             print(arg, warning)
-            err = run_process(WASM_OPT + [self.input_path('asyncify-pure.wast'), '--asyncify', arg], stdout=subprocess.PIPE, stderr=subprocess.PIPE).stderr.strip()
+            err = run_process(WASM_OPT + ['-q', self.input_path('asyncify-pure.wast'), '--asyncify', arg], stdout=subprocess.PIPE, stderr=subprocess.PIPE).stderr.strip()
             if warning:
                 self.assertIn('warning', err)
                 self.assertIn(warning, err)
diff --git a/test/unit/test_warnings.py b/test/unit/test_warnings.py
new file mode 100644
index 000000000..9fb43a12b
--- /dev/null
+++ b/test/unit/test_warnings.py
@@ -0,0 +1,18 @@
+import subprocess
+
+from scripts.test.shared import WASM_OPT, run_process
+from .utils import BinaryenTestCase
+
+
+class WarningsText(BinaryenTestCase):
+    def test_warn_on_no_passes(self):
+        err = run_process(WASM_OPT + [self.input_path('asyncify-pure.wast'), '-o', 'a.wasm'], stderr=subprocess.PIPE).stderr
+        self.assertIn('warning: no passes specified, not doing any work', err)
+
+    def test_warn_on_no_output(self):
+        err = run_process(WASM_OPT + [self.input_path('asyncify-pure.wast'), '-O1'], stderr=subprocess.PIPE).stderr
+        self.assertIn('warning: no output file specified, not emitting output', err)
+
+    def test_quiet_suppresses_warnings(self):
+        err = run_process(WASM_OPT + [self.input_path('asyncify-pure.wast'), '-q'], stderr=subprocess.PIPE).stderr
+        self.assertNotIn('warning', err)