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, 17 insertions, 4 deletions

diff --git a/src/tools/tool-options.h b/src/tools/tool-options.h
index 33a631975..46720d203 100644
--- a/src/tools/tool-options.h
+++ b/src/tools/tool-options.h
@@ -22,7 +22,7 @@
 #include "support/command-line.h"
 
 //
-// Shared optimization options for commandline tools
+// Shared options for commandline tools
 //
 
 namespace wasm {
@@ -30,6 +30,8 @@ namespace wasm {
 struct ToolOptions : public Options {
   PassOptions passOptions;
 
+  bool quiet = false;
+
   ToolOptions(const std::string& command, const std::string& description)
     : Options(command, description) {
     (*this)
@@ -60,7 +62,12 @@ struct ToolOptions : public Options {
              detectFeatures = true;
              enabledFeatures.makeMVP();
              disabledFeatures.makeMVP();
-           });
+           })
+      .add("--quiet",
+           "-q",
+           "Emit less verbose output and hide trivial warnings.",
+           Arguments::Zero,
+           [this](Options*, const std::string&) { quiet = true; });
     (*this)
       .addFeature(FeatureSet::SignExt, "sign extension operations")
       .addFeature(FeatureSet::Atomics, "atomic operations")
diff --git a/src/tools/wasm-opt.cpp b/src/tools/wasm-opt.cpp
index 33e9a0396..b2d1f2c14 100644
--- a/src/tools/wasm-opt.cpp
+++ b/src/tools/wasm-opt.cpp
@@ -318,7 +318,11 @@ int main(int argc, const char* argv[]) {
     curr = &other;
   }
 
-  if (options.runningPasses()) {
+  if (!options.runningPasses()) {
+    if (!options.quiet) {
+      std::cerr << "warning: no passes specified, not doing any work\n";
+    }
+  } else {
     if (options.debug) {
       std::cerr << "running passes...\n";
     }
@@ -363,7 +367,9 @@ int main(int argc, const char* argv[]) {
   }
 
   if (options.extra.count("output") == 0) {
-    std::cerr << "no output file specified, not emitting output\n";
+    if (!options.quiet) {
+      std::cerr << "warning: no output file specified, not emitting output\n";
+    }
     return 0;
   }