Fix Closure compile of small builds that use legacy DYNCALLS mode (#1…

…3883)

* Fix Closure compile of small builds that use legacy DYNCALLS mode but do not export any wasm function with signature 'v' or 'vi'.

* Address review

* Update tests/test_other.py

* Address review

* Remove duplicate hasExportedFunction

* Use hasExportedFunction()

* Generalize closure optimization to makeDynCall macro

* Clean up Closure warnings

Co-authored-by: Alon Zakai <alonzakai@gmail.com>

src/library.js

@@ -3276,8 +3276,13 @@ LibraryManager.library = {
       var func = callback.func;
       if (typeof func == 'number') {
         if (callback.arg === undefined) {
+          // Run the wasm function ptr with signature 'v'. If no function
+          // with such signature was exported, this call does not need
+          // to be emitted (and would confuse Closure)
           {{{ makeDynCall('v', 'func') }}}();
         } else {
+          // If any function with signature 'vi' was exported, run
+          // the callback with that signature.
           {{{ makeDynCall('vi', 'func') }}}(callback.arg);
         }
       } else {

src/parseTools.js

@@ -832,13 +832,28 @@ New syntax is {{{ makeDynCall("${sig}", "funcPtr") }}}(arg1, arg2, ...). \
 Please update to new syntax.`);
 
     if (DYNCALLS) {
+      if (!hasExportedFunction(`dynCall_${sig}`)) {
+        if (ASSERTIONS) {
+          return `(function(${args}) { throw 'Internal Error! Attempted to invoke wasm function pointer with signature "${sig}", but no such functions have gotten exported!'; })`;
+        } else {
+          return `(function(${args}) { /* a dynamic function call to signature ${sig}, but there are no exported function pointers with that signature, so this path should never be taken. Build with ASSERTIONS enabled to validate. */ })`;
+        }
+      }
       return `(function(cb, ${args}) { ${returnExpr} getDynCaller("${sig}", cb)(${args}) })`;
     } else {
       return `(function(cb, ${args}) { ${returnExpr} getWasmTableEntry(cb)(${args}) })`;
     }
   }
 
   if (DYNCALLS) {
+    if (!hasExportedFunction(`dynCall_${sig}`)) {
+      if (ASSERTIONS) {
+        return `(function(${args}) { throw 'Internal Error! Attempted to invoke wasm function pointer with signature "${sig}", but no such functions have gotten exported!'; })`;
+      } else {
+        return `(function(${args}) { /* a dynamic function call to signature ${sig}, but there are no exported function pointers with that signature, so this path should never be taken. Build with ASSERTIONS enabled to validate. */ })`;
+      }
+    }
+
     const dyncall = exportedAsmFunc(`dynCall_${sig}`);
     if (sig.length > 1) {
       return `(function(${args}) { ${returnExpr} ${dyncall}.apply(null, [${funcPtr}, ${args}]); })`;
@@ -1058,6 +1073,9 @@ function _asmjsDemangle(symbol) {
   if (symbol in WASM_SYSTEM_EXPORTS) {
     return symbol;
   }
+  if (symbol.startsWith('dynCall_')) {
+    return symbol;
+  }
   // Strip leading "_"
   assert(symbol.startsWith('_'));
   return symbol.substr(1);

tests/test_other.py

@@ -10815,6 +10815,14 @@ def test_old_makeDynCall_syntax(self):
     err = self.run_process([EMCC, test_file('test_old_dyncall_format.c'), '--js-library', test_file('library_test_old_dyncall_format.js')], stderr=PIPE).stderr
     self.assertContained('syntax for makeDynCall has changed', err)
 
+  # Tests that dynCalls are produced in Closure-safe way in DYNCALLS mode when no actual dynCalls are used
+  @parameterized({
+    'plain': [[]],
+    'asyncify': [['-sASYNCIFY']],
+    'asyncify_bigint': [['-sASYNCIFY', '-sWASM_BIGINT']]})
+  def test_closure_safe(self, args):
+    self.run_process([EMCC, test_file('hello_world.c'), '--closure=1'] + args)
+
   def test_post_link(self):
     err = self.run_process([EMCC, test_file('hello_world.c'), '--oformat=bare', '-o', 'bare.wasm'], stderr=PIPE).stderr
     self.assertContained('--oformat=bare/--post-link are experimental and subject to change', err)