Simplify callUserCallback. NFC (#17440)

This moves the fetch-specific behaviour into the fetch library.

Author: sbc100

src/Fetch.js

@@ -454,43 +454,51 @@ function startFetch(fetch, successcb, errorcb, progresscb, readystatechangecb) {
   var fetchAttrReplace = !!(fetchAttributes & {{{ cDefine('EMSCRIPTEN_FETCH_REPLACE') }}});
   var fetchAttrSynchronous = !!(fetchAttributes & {{{ cDefine('EMSCRIPTEN_FETCH_SYNCHRONOUS') }}});
 
+  function doCallback(f) {
+    if (fetchAttrSynchronous) {
+      f();
+    } else {
+      callUserCallback(f);
+    }
+  }
+
   var reportSuccess = (fetch, xhr, e) => {
 #if FETCH_DEBUG
     console.log('fetch: operation success. e: ' + e);
 #endif
     {{{ runtimeKeepalivePop() }}}
-    callUserCallback(() => {
+    doCallback(() => {
       if (onsuccess) {{{ makeDynCall('vp', 'onsuccess') }}}(fetch);
       else if (successcb) successcb(fetch);
-    }, fetchAttrSynchronous);
+    });
   };
 
   var reportProgress = (fetch, xhr, e) => {
-    callUserCallback(() => {
+    doCallback(() => {
       if (onprogress) {{{ makeDynCall('vp', 'onprogress') }}}(fetch);
       else if (progresscb) progresscb(fetch);
-    }, fetchAttrSynchronous);
+    });
   };
 
   var reportError = (fetch, xhr, e) => {
 #if FETCH_DEBUG
     console.error('fetch: operation failed: ' + e);
 #endif
     {{{ runtimeKeepalivePop() }}}
-    callUserCallback(() => {
+    doCallback(() => {
       if (onerror) {{{ makeDynCall('vp', 'onerror') }}}(fetch);
       else if (errorcb) errorcb(fetch);
-    }, fetchAttrSynchronous);
+    });
   };
 
   var reportReadyStateChange = (fetch, xhr, e) => {
 #if FETCH_DEBUG
     console.log('fetch: ready state change. e: ' + e);
 #endif
-    callUserCallback(() => {
+    doCallback(() => {
       if (onreadystatechange) {{{ makeDynCall('vp', 'onreadystatechange') }}}(fetch);
       else if (readystatechangecb) readystatechangecb(fetch);
-    }, fetchAttrSynchronous);
+    });
   };
 
   var performUncachedXhr = (fetch, xhr, e) => {
@@ -510,20 +518,20 @@ function startFetch(fetch, successcb, errorcb, progresscb, readystatechangecb) {
       console.log('fetch: IndexedDB store succeeded.');
 #endif
       {{{ runtimeKeepalivePop() }}}
-      callUserCallback(() => {
+      doCallback(() => {
         if (onsuccess) {{{ makeDynCall('vp', 'onsuccess') }}}(fetch);
         else if (successcb) successcb(fetch);
-      }, fetchAttrSynchronous);
+      });
     };
     var storeError = (fetch, xhr, e) => {
 #if FETCH_DEBUG
       console.error('fetch: IndexedDB store failed.');
 #endif
       {{{ runtimeKeepalivePop() }}}
-      callUserCallback(() => {
+      doCallback(() => {
         if (onsuccess) {{{ makeDynCall('vp', 'onsuccess') }}}(fetch);
         else if (successcb) successcb(fetch);
-      }, fetchAttrSynchronous);
+      });
     };
     fetchCacheData(Fetch.dbInstance, fetch, xhr.response, storeSuccess, storeError);
   };

src/library.js

@@ -3488,8 +3488,7 @@ mergeInto(LibraryManager.library, {
     '$maybeExit',
 #endif
   ],
-  $callUserCallback__docs: '/** @param {boolean=} synchronous */',
-  $callUserCallback: function(func, synchronous) {
+  $callUserCallback: function(func) {
 #if EXIT_RUNTIME
     if (runtimeExited || ABORT) {
 #else
@@ -3500,11 +3499,6 @@ mergeInto(LibraryManager.library, {
 #endif
       return;
     }
-    // For synchronous calls, let any exceptions propagate, and don't let the runtime exit.
-    if (synchronous) {
-      func();
-      return;
-    }
     try {
       func();
 #if EXIT_RUNTIME || USE_PTHREADS