Fix compiler's waitPromise implementation

src/compiler/jsexecute.js

@@ -109,19 +109,20 @@ const waitPromise = function*(promise) {
     const thread = globalState.thread;
     let returnValue;
 
+    // enter STATUS_PROMISE_WAIT and yield
+    // this will stop script execution until the promise handlers reset the thread status
+    // because promise handlers might execute immediately, configure thread.status here
+    thread.status = 1; // STATUS_PROMISE_WAIT
+
     promise
         .then(value => {
             returnValue = value;
             thread.status = 0; // STATUS_RUNNING
-        })
-        .catch(error => {
+        }, error => {
             thread.status = 0; // STATUS_RUNNING
             globalState.log.warn('Promise rejected in compiled script:', error);
         });
 
-    // enter STATUS_PROMISE_WAIT and yield
-    // this will stop script execution until the promise handlers reset the thread status
-    thread.status = 1; // STATUS_PROMISE_WAIT
     yield;
 
     return returnValue;

test/integration/tw_block_returning_promise_like.js

@@ -0,0 +1,65 @@
+const {test} = require('tap');
+const fs = require('fs');
+const path = require('path');
+const VirtualMachine = require('../../src/virtual-machine');
+const Scratch = require('../../src/extension-support/tw-extension-api-common');
+
+// based on https://github.com/TurboWarp/scratch-vm/issues/184
+
+class TestExtension {
+    getInfo () {
+        return {
+            id: 'testextension',
+            name: 'test',
+            blocks: [
+                {
+                    opcode: 'test',
+                    blockType: Scratch.BlockType.COMMAND,
+                    text: 'test block'
+                }
+            ]
+        };
+    }
+    test () {
+        // returns a PromiseLike that calls handler immediately.
+        const promise = {
+            then (callbackFn) {
+                callbackFn();
+                return promise;
+            }
+            // intentionally omit catch() as that is not part of PromiseLike
+        };
+        return promise;
+    }
+}
+
+const fixture = fs.readFileSync(path.join(__dirname, '../fixtures/tw-block-returning-promise-like.sb3'));
+
+for (const compilerEnabled of [false, true]) {
+    test(`handles blocks that return a promise-like object - ${compilerEnabled ? 'compiled' : 'interpreted'}`, t => {
+        const vm = new VirtualMachine();
+        vm.extensionManager.addBuiltinExtension('testextension', TestExtension);
+
+        vm.setCompilerOptions({
+            enabled: compilerEnabled
+        });
+        t.equal(vm.runtime.compilerOptions.enabled, compilerEnabled, 'sanity check');
+
+        vm.loadProject(fixture).then(() => {
+            let ended = 0;
+            vm.runtime.on('SAY', (target, type, text) => {
+                if (text === 'end') {
+                    ended++;
+                } else {
+                    t.fail('said something unknown');
+                }
+            });
+
+            vm.greenFlag();
+            vm.runtime._step();
+
+            t.equal(ended, 1, 'script ran once immediately');
+            t.end();
+        });
+    });
+}