Add a new way to mark async imports in library files.

Allow library functions to be asyncify'd with either an `async` function or adding
`$name_async`.

Author: brendandahl

emcc.py

@@ -101,7 +101,7 @@
 }
 
 DEFAULT_ASYNCIFY_IMPORTS = [
-  'emscripten_sleep', 'emscripten_wget', 'emscripten_wget_data', 'emscripten_idb_load',
+  'emscripten_wget', 'emscripten_wget_data', 'emscripten_idb_load',
   'emscripten_idb_store', 'emscripten_idb_delete', 'emscripten_idb_exists',
   'emscripten_idb_load_blob', 'emscripten_idb_store_blob', 'SDL_Delay',
   'emscripten_scan_registers', 'emscripten_lazy_load_code',

emscripten.py

@@ -393,6 +393,9 @@ def emscript(in_wasm, out_wasm, outfile_js, memfile):
 
   report_missing_symbols(forwarded_json['librarySymbols'])
 
+  if settings.ASYNCIFY:
+    settings.ASYNCIFY_IMPORTS += ['env.' + x for x in forwarded_json['asyncFuncs']]
+
   if not outfile_js:
     logger.debug('emscript: skipping remaining js glue generation')
     return

src/jsifier.js

@@ -69,6 +69,7 @@ function isDefined(symName) {
 function runJSify() {
   const libraryItems = [];
   const symbolDeps = {};
+  const asyncFuncs = [];
   let postSets = [];
 
   LibraryManager.load();
@@ -335,6 +336,7 @@ function ${name}(${args}) {
         }
       });
       let isFunction = false;
+      let isAsyncFunction = false;
 
       if (typeof snippet == 'string') {
         if (snippet[0] != '=') {
@@ -352,6 +354,7 @@ function ${name}(${args}) {
         addImplicitDeps(snippet, deps);
       } else if (typeof snippet == 'function') {
         isFunction = true;
+        isAsyncFunction = snippet.constructor.name == 'AsyncFunction';
         snippet = processLibraryFunction(snippet, symbol, mangled, deps);
         addImplicitDeps(snippet, deps);
       }
@@ -410,6 +413,10 @@ function ${name}(${args}) {
         contentText = `var ${mangled} = ${snippet};`;
       }
       const sig = LibraryManager.library[symbol + '__sig'];
+      isAsyncFunction = LibraryManager.library[symbol + '__async'] ?? isAsyncFunction;
+      if (isAsyncFunction) {
+        asyncFuncs.push(symbol);
+      }
       // asm module exports are done in emscripten.py, after the asm module is ready. Here
       // we also export library methods as necessary.
       if ((EXPORT_ALL || EXPORTED_FUNCTIONS.has(mangled)) && !isStub) {
@@ -423,6 +430,9 @@ function ${name}(${args}) {
       if (sig && (RELOCATABLE || ASYNCIFY == 2)) {
         contentText += `\n${mangled}.sig = '${sig}';`;
       }
+      if (isAsyncFunction) {
+        contentText += `\n${mangled}.isAsync = true;`;
+      }
       if (isStub) {
         contentText += `\n${mangled}.stub = true;`;
         if (ASYNCIFY) {
@@ -529,6 +539,7 @@ function ${name}(${args}) {
     print('//FORWARDED_DATA:' + JSON.stringify({
       librarySymbols: librarySymbols,
       warnings: warnings,
+      asyncFuncs,
       ATINITS: ATINITS.join('\n'),
       ATMAINS: ATMAINS.join('\n'),
       ATEXITS: ATEXITS.join('\n'),

src/library_async.js

@@ -40,7 +40,8 @@ mergeInto(LibraryManager.library, {
           var original = imports[x];
           var sig = original.sig;
           if (typeof original == 'function') {
-            var isAsyncifyImport = ASYNCIFY_IMPORTS.indexOf(x) >= 0 ||
+            var isAsyncifyImport = original.isAsync ||
+                                   ASYNCIFY_IMPORTS.indexOf(x) >= 0 ||
                                    x.startsWith('__asyncjs__');
 #if ASYNCIFY == 2
             // Wrap async imports with a suspending WebAssembly function.
@@ -452,6 +453,7 @@ mergeInto(LibraryManager.library, {
 
   emscripten_sleep__sig: 'vi',
   emscripten_sleep__deps: ['$safeSetTimeout'],
+  emscripten_sleep__async: true,
   emscripten_sleep: function(ms) {
     // emscripten_sleep() does not return a value, but we still need a |return|
     // here for stack switching support (ASYNCIFY=2). In that mode this function

src/utility.js

@@ -168,6 +168,7 @@ function isJsLibraryConfigIdentifier(ident) {
     '__noleakcheck',
     '__internal',
     '__user',
+    '__async',
   ];
   return suffixes.some((suffix) => ident.endsWith(suffix));
 }