wasm: clarify qtloader onExit behavior

onExit is called whenever the application exits, i.e.
when the app canvas should no longer be displayed and
the loader/embedder code should take some action.

Emscripten provides two callbacks which can be used
here:
  - onExit, called when the app exits (but see EXIT_RUNTIME)
  - onAbort, called on abort errors.

These map to the two cases Qt's onExit supports. onExit
is not called when EXIT_RUNTIME is disabled, which means
we don't need the special case for exit code 0.

In addition call onExit on any exception. The second
call to showUi() in html_shell.html is then not needed
any more and we avoid duplicating the UI state handling
in user code.

Update the qtloader_integration test to handle changes in
behavior (we no longer set the error text on exit). Use
emscripten_force_exit() to simulate application exit -
using this function makes Emscripten call onExit even
when EXIT_RUNTIME is disabled.

Change-Id: I72b5463c1836e8d5054e594abbd304fbc67032b7
Reviewed-by: Piotr Wierciński <piotr.wiercinski@qt.io>
Reviewed-by: Mikołaj Boc <Mikolaj.Boc@qt.io>
(cherry picked from commit a4d1c30a1b52e797cce504f90bcf20d7943dd1f9)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/platforms/wasm/qtloader.js

@@ -9,9 +9,14 @@
  * - environment: { [name:string] : string }
  *      environment variables set on the instance
  * - onExit: (exitStatus: { text: string, code?: number, crashed: bool }) => void
- *      called when the application has exited for any reason. exitStatus.code is defined in
+ *      called when the application has exited for any reason. There are two cases:
- *      case of a normal application exit. This is not called on exit with return code 0, as
+ *      aborted: crashed is true, text contains an error message.
- *      the program does not shutdown its runtime and technically keeps running async.
+ *      exited: crashed is false, code contians the exit code.
+ *
+ *      Note that by default Emscripten does not exit when main() returns. This behavior
+ *      is controlled by the EXIT_RUNTIME linker flag; set "-s EXIT_RUNTIME=1" to make
+ *      Emscripten tear down the runtime and exit when main() returns.
+ *
  * - containerElements: HTMLDivElement[]
  *      Array of host elements for Qt screens. Each of these elements is mapped to a QScreen on
  *      launch.
@@ -161,26 +166,14 @@ async function qtLoad(config)
         return originalLocatedFilename;
     }
 
-    // This is needed for errors which occur right after resolving the instance promise but
+    const originalOnExit = config.onExit;
-    // before exiting the function (i.e. on call to main before stack unwinding).
+    config.onExit = code => {
-    let loadTimeException = undefined;
+        originalOnExit?.();
-    // We don't want to issue onExit when aborted
-    let aborted = false;
-    const originalQuit = config.quit;
-    config.quit = (code, exception) =>
-    {
-        originalQuit?.(code, exception);
-
-        if (exception)
-            loadTimeException = exception;
-        if (!aborted && code !== 0) {
         config.qt.onExit?.({
-                text: exception.message,
             code,
             crashed: false
         });
     }
-    };
 
     const originalOnAbort = config.onAbort;
     config.onAbort = text =>
@@ -212,10 +205,17 @@ async function qtLoad(config)
 
     // Call app/emscripten module entry function. It may either come from the emscripten
     // runtime script or be customized as needed.
-    const instance = await Promise.race(
+    let instance;
+    try {
+        instance = await Promise.race(
             [circuitBreaker, config.qt.entryFunction(config)]);
-    if (loadTimeException && loadTimeException.name !== 'ExitStatus')
+    } catch (e) {
-        throw loadTimeException;
+        config.qt.onExit?.({
+            text: e.message,
+            crashed: true
+        });
+        throw e;
+    }
 
     return instance;
 }

src/plugins/platforms/wasm/wasm_shell.html

@@ -65,8 +65,6 @@
             } catch (e) {
                 console.error(e);
                 console.error(e.stack);
-                status.innerHTML = e.message;
-                showUi(spinner);
             }
         }
     </script>

tests/manual/wasm/qtloader_integration/main.cpp

@@ -71,7 +71,7 @@ void crash()
 
 void exitApp()
 {
-    exit(ExitValueFromExitApp);
+    emscripten_force_exit(ExitValueFromExitApp);
 }
 
 void produceOutput()
@@ -135,7 +135,7 @@ int main(int argc, char **argv)
             std::find(arguments.begin(), arguments.end(), QStringLiteral("--exit-immediately"))
             != arguments.end();
     if (exitImmediately)
-        return ExitValueImmediateReturn;
+        emscripten_force_exit(ExitValueImmediateReturn);
 
     const bool crashImmediately =
             std::find(arguments.begin(), arguments.end(), QStringLiteral("--crash-immediately"))

tests/manual/wasm/qtloader_integration/test_body.js

@@ -323,9 +323,7 @@ export class QtLoaderIntegrationTests
             caughtException = e;
         }
 
-        // An exception should have been thrown from load()
+        assert.isUndefined(caughtException);
-        assert.equal('RuntimeError', caughtException.name);
-
         assert.equal(1, onExitMock.calls.length);
         const exitStatus = onExitMock.calls[0][0];
         assert.isTrue(exitStatus.crashed);
@@ -373,7 +371,7 @@ export class QtLoaderIntegrationTests
         const exitStatus = onExitMock.calls[0][0];
         assert.isFalse(exitStatus.crashed);
         assert.equal(instance.EXIT_VALUE_FROM_EXIT_APP, exitStatus.code);
-        assert.isNotUndefined(exitStatus.text);
+        assert.isUndefined(exitStatus.text);
     }
 
     async exitImmediately()
@@ -392,7 +390,7 @@ export class QtLoaderIntegrationTests
 
         assert.isFalse(exitStatusFromOnExit.crashed);
         assert.equal(instance.EXIT_VALUE_IMMEDIATE_RETURN, exitStatusFromOnExit.code);
-        assert.isNotUndefined(exitStatusFromOnExit.text);
+        assert.isUndefined(exitStatusFromOnExit.text);
     }
 
     async userQuitCallbackCalled()