Implementation of async-await transformation on js ast.

tests/compiler/dart2js/async_await_js_transform_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "package:expect/expect.dart";
+import "package:compiler/src/js/js.dart";
+import "package:compiler/src/js/rewrite_async.dart";
+
+import "backend_dart/dart_printer_test.dart" show PrintDiagnosticListener;
+
+void testTransform(String source, String expected) {
+  Fun fun = js(source);
+  Fun rewritten = new AsyncRewriter(
+      thenHelper: new VariableUse("thenHelper"),
+      newController: new New(new VariableUse("newCompleter"), []),
+      endOfIteration: new VariableUse("endOfIteration"),
+      newIterable: new New(new VariableUse("newCompleter"), []),
+      safeVariableName: (String name) => "__$name").rewrite(fun);
+  Printer printer = new Printer(new PrintDiagnosticListener(), null);
+  printer.visit(rewritten);
+  Expect.stringEquals(expected, printer.outBuffer.getText());

[floitsch, 2015/02/02 22:00:12]

This is extremely brittle. Any change in the transformer will require changes to
the test.

We will probably revisit, when optimizations are implemented (and there is a lot
of potential for them...)

[sigurdm, 2015/02/03 16:59:33]

True - these tests were mostly useful while developing - to give a clear picture
of exactly what I wanted to generate.

+}
+
+main() {
+  testTransform("""
+function() async {
+  print(this.x); // Ensure `this` is translated in the helper function.
+  await foo();
+}""", """
+function() {
+  var __goto = 0, __completer = new newCompleter(), __self = this;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          print(__self.x);
+          __goto = 1;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 1:
+          // returning from await.
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+
+  testTransform("""
+function() async {
+  try {
+    __outer: while (true) { // Overlapping label name.
+      try {
+        inner: while (true) {
+          break __outer; // Break from untranslated loop to translated target.
+          break; // break to untranslated target.
+        }
+        while (true) {
+          return; // Return via finallies.
+        }
+        var __helper = await foo(); // Overlapping variable name.
+      } finally {
+        foo();
+        continue; // Continue from finally with pending finally.
+        return 2; // Return from finally with pending finally.
+      }
+    }
+  } finally {
+    return 3; // Return from finally with no pending finally.
+  }
+  return 4;
+}""", """
+function() {
+  var __goto = 0, __completer = new newCompleter(), __handler = null, __next, __returnValue, __helper;
+  function __helper1(__result) {
+    while (true)
+      try {
+        __outer1:
+          switch (__goto) {
+            case 0:
+              // Function start
+              __handler = 2;
+            case 6:
+              // continue __outer
+            case 7:
+              // while condition
+              if (!true) {
+                // goto after while
+                __goto = 8;
+                break;
+              }
+              __handler = 9;
+              inner: {
+                while (true) {
+                  __next = [5];
+                  __goto = 10;
+                  break __outer1;
+                  break;
+                }
+              }
+              while (true) {
+                __next = [1, 3];
+                __goto = 10;
+                break __outer1;
+              }
+              __goto = 12;
+              return thenHelper(foo(), __helper1, __completer, function(__error) {
+                __goto = 9;
+                __helper1(__error);
+              });
+            case 12:
+              // returning from await.
+              __helper = __result;
+              __handler = 2;
+              __next = [11];
+              // goto finally
+              __goto = 10;
+              break;
+            case 9:
+              // catch
+              __next = [11];
+            case 10:
+              // finally
+              foo();
+              // goto while condition
+              __goto = 7;
+              break;
+              __returnValue = 2;
+              __next = [1];
+              // goto finally
+              __goto = 3;
+              break;
+              // goto the next finally handler
+              __goto = __next.pop();
+              break;
+            case 11:
+              // after finally
+              // goto while condition
+              __goto = 7;
+              break;
+            case 8:
+              // after while
+            case 5:
+              // break __outer
+              __handler = null;
+              __next = [4];
+              // goto finally
+              __goto = 3;
+              break;
+            case 2:
+              // catch
+              __next = [4];
+            case 3:
+              // finally
+              __returnValue = 3;
+              // goto Return
+              __goto = 1;
+              break;
+              // goto the next finally handler
+              __goto = __next.pop();
+              break;
+            case 4:
+              // after finally
+              __returnValue = 4;
+              // goto Return
+              __goto = 1;
+              break;
+            case 1:
+              // Return
+              return thenHelper(__returnValue, null, __completer, null);
+          }
+      } catch (__error) {
+        if (__handler === null)
+          throw __error;
+        __result = __error;
+        __goto = __handler;
+      }
+
+  }
+  return thenHelper(null, __helper1, __completer, null);
+}""");
+  testTransform("""
+function() async {
+  var a, b, c, d, e, f;
+  a = b++; // post- and preincrements.
+  b = --b;
+  c = (await foo()).a++;
+  d = ++(await foo()).a;
+  e = foo1()[await foo2()]--;
+  f = --foo1()[await foo2()];
+}""", """
+function() {
+  var __goto = 0, __completer = new newCompleter(), a, b, c, d, e, f, __temp1;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          a = b++;
+          b = --b;
+          __goto = 1;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 1:
+          // returning from await.
+          c = __result.a++;
+          __goto = 2;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 2:
+          // returning from await.
+          d = ++__result.a;
+          __temp1 = foo1();
+          __goto = 3;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 3:
+          // returning from await.
+          e = __temp1[__result]--;
+          __temp1 = foo1();
+          __goto = 4;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 4:
+          // returning from await.
+          f = --__temp1[__result];
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+  testTransform("""
+function() async {
+  var a, b, c, d, e, f, g, h; // empty initializer
+  a = foo1() || await foo2(); // short circuiting operators
+  b = await foo1() || foo2();
+  c = await foo1() || foo3(await foo2());
+  d = foo1() || foo2();
+  e = foo1() && await foo2();
+  f = await foo1() && foo2();
+  g = await foo1() && await foo2();
+  h = foo1() && foo2();
+}""", """
+function() {
+  var __goto = 0, __completer = new newCompleter(), a, b, c, d, e, f, g, h, __temp1;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          __temp1 = foo1();
+          if (__temp1) {
+            // goto then
+            __goto = 1;
+            break;
+          } else
+            __result = __temp1;
+          // goto join
+          __goto = 2;
+          break;
+        case 1:
+          // then
+          __goto = 3;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 3:
+          // returning from await.
+        case 2:
+          // join
+          a = __result;
+          __goto = 4;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 4:
+          // returning from await.
+          b = __result || foo2();
+          __goto = 7;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 7:
+          // returning from await.
+          __temp1 = __result;
+          if (__temp1) {
+            // goto then
+            __goto = 5;
+            break;
+          } else
+            __result = __temp1;
+          // goto join
+          __goto = 6;
+          break;
+        case 5:
+          // then
+          __temp1 = foo3;
+          __goto = 8;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 8:
+          // returning from await.
+          __result = __temp1(__result);
+        case 6:
+          // join
+          c = __result;
+          d = foo1() || foo2();
+          __temp1 = foo1();
+          if (__temp1)
+            __result = __temp1;
+          else {
+            // goto then
+            __goto = 9;
+            break;
+          }
+          // goto join
+          __goto = 10;
+          break;
+        case 9:
+          // then
+          __goto = 11;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 11:
+          // returning from await.
+        case 10:
+          // join
+          e = __result;
+          __goto = 12;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 12:
+          // returning from await.
+          f = __result && foo2();
+          __goto = 15;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 15:
+          // returning from await.
+          __temp1 = __result;
+          if (__temp1)
+            __result = __temp1;
+          else {
+            // goto then
+            __goto = 13;
+            break;
+          }
+          // goto join
+          __goto = 14;
+          break;
+        case 13:
+          // then
+          __goto = 16;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 16:
+          // returning from await.
+        case 14:
+          // join
+          g = __result;
+          h = foo1() && foo2();
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+  testTransform("""
+function(x, y) async {
+  while (true) {
+    switch(y) { // Switch with no awaits in case key expressions
+      case 0:
+      case 1: 
+        await foo();
+        continue; // Continue the loop, not the switch
+      case 1: // Duplicate case
+        await foo();
+        break; // Break the switch
+      case 2:
+        foo(); // No default
+    }
+  }
+}""", """
+function(x, y) {
+  var __goto = 0, __completer = new newCompleter();
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+        case 1:
+          // while condition
+          if (!true) {
+            // goto after while
+            __goto = 2;
+            break;
+          }
+        case 3:
+          // switch
+          switch (y) {
+            case 0:
+              // goto case
+              __goto = 5;
+              break;
+            case 1:
+              // goto case
+              __goto = 6;
+              break;
+            case 1:
+              // goto case
+              __goto = 7;
+              break;
+            case 2:
+              // goto case
+              __goto = 8;
+              break;
+          }
+          // goto after switch
+          __goto = 4;
+          break;
+        case 5:
+          // case
+        case 6:
+          // case
+          __goto = 9;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 9:
+          // returning from await.
+          // goto while condition
+          __goto = 1;
+          break;
+        case 7:
+          // case
+          __goto = 10;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 10:
+          // returning from await.
+          // goto after switch
+          __goto = 4;
+          break;
+        case 8:
+          // case
+          foo();
+        case 4:
+          // after switch
+          // goto while condition
+          __goto = 1;
+          break;
+        case 2:
+          // after while
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+  testTransform("""
+function() async {
+  do {
+    var a = await foo();
+    if (a) // If with no awaits in body
+      break;
+    else
+      continue;
+  } while (await foo());
+}
+""", """
+function() {
+  var __goto = 0, __completer = new newCompleter(), a;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+        case 1:
+          // do body
+          __goto = 4;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 4:
+          // returning from await.
+          a = __result;
+          if (a) {
+            // goto after do
+            __goto = 3;
+            break;
+          } else {
+            // goto do condition
+            __goto = 2;
+            break;
+          }
+        case 2:
+          // do condition
+          __goto = 5;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 5:
+          // returning from await.
+          if (__result) {
+            // goto do body
+            __goto = 1;
+            break;
+          }
+        case 3:
+          // after do
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+
+  testTransform("""
+function() async {
+  for (var i = 0; i < await foo1(); i += await foo2()) {
+    if (foo(i))
+      continue;
+    else
+      break;
+    if (!foo(i)) { // If with no else and await in body.
+      await foo();
+      return;
+    }
+    print(await(foo(i)));
+  } 
+}
+""", """
+function() {
+  var __goto = 0, __completer = new newCompleter(), __returnValue, i, __temp1;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          i = 0;
+        case 2:
+          // for condition
+          __temp1 = i;
+          __goto = 5;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 5:
+          // returning from await.
+          if (!(__temp1 < __result)) {
+            // goto after for
+            __goto = 4;
+            break;
+          }
+          if (foo(i)) {
+            // goto for update
+            __goto = 3;
+            break;
+          } else {
+            // goto after for
+            __goto = 4;
+            break;
+          }
+          __goto = !foo(i) ? 6 : 7;
+          break;
+        case 6:
+          // then
+          __goto = 8;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 8:
+          // returning from await.
+          // goto Return
+          __goto = 1;
+          break;
+        case 7:
+          // join
+          __temp1 = print;
+          __goto = 9;
+          return thenHelper(foo(i), __helper, __completer, null);
+        case 9:
+          // returning from await.
+          __temp1(__result);
+        case 3:
+          // for update
+          __goto = 10;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 10:
+          // returning from await.
+          i = __result;
+          // goto for condition
+          __goto = 2;
+          break;
+        case 4:
+          // after for
+        case 1:
+          // Return
+          return thenHelper(__returnValue, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+
+  testTransform("""
+function(a) async {
+  var x = {"a": foo1(), "b": await foo2(), "c": foo3()};
+  x["a"] = 2; // Different assignments
+  (await foo()).a = 3;
+  x[await foo()] = 4;
+  x[(await foo1()).a = await foo2()] = 5;
+  (await foo1())[await foo2()] = await foo3(6);
+}
+""", """
+function(a) {
+  var __goto = 0, __completer = new newCompleter(), x, __temp1, __temp2;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          __temp1 = foo1();
+          __goto = 1;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 1:
+          // returning from await.
+          x = {a: __temp1, b: __result, c: foo3()};
+          x.a = 2;
+          __goto = 2;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 2:
+          // returning from await.
+          __result.a = 3;
+          __temp1 = x;
+          __goto = 3;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 3:
+          // returning from await.
+          __temp1[__result] = 4;
+          __temp1 = x;
+          __goto = 4;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 4:
+          // returning from await.
+          __temp2 = __result;
+          __goto = 5;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 5:
+          // returning from await.
+          __temp1[__temp2.a = __result] = 5;
+          __goto = 6;
+          return thenHelper(foo1(), __helper, __completer, null);
+        case 6:
+          // returning from await.
+          __temp1 = __result;
+          __goto = 7;
+          return thenHelper(foo2(), __helper, __completer, null);
+        case 7:
+          // returning from await.
+          __temp2 = __result;
+          __goto = 8;
+          return thenHelper(foo3(6), __helper, __completer, null);
+        case 8:
+          // returning from await.
+          __temp1[__temp2] = __result;
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+  testTransform("""
+function(c) async {
+  try {
+    var x = c ? await foo() : foo(); // conditional
+    var y = {};
+  } catch (error) {
+    try {
+      x = c ? await fooError(error) : fooError(error);
+    } catch (error) { // nested error handler with overlapping name
+      y.x = foo(error);
+    } finally {
+      foo(x);
+    }
+  }
+}
+""", """
+function(c) {
+  var __goto = 0, __completer = new newCompleter(), __handler = null, x, y, __error1, __error2;
+  function __helper(__result) {
+    while (true)
+      try {
+        switch (__goto) {
+          case 0:
+            // Function start
+            __handler = 1;
+            __goto = c ? 4 : 6;
+            break;
+          case 4:
+            // then
+            __goto = 7;
+            return thenHelper(foo(), __helper, __completer, function(__error) {
+              __goto = 1;
+              __helper(__error);
+            });
+          case 7:
+            // returning from await.
+            // goto join
+            __goto = 5;
+            break;
+          case 6:
+            // else
+            __result = foo();
+          case 5:
+            // join
+            x = __result;
+            y = {};
+            __handler = null;
+            __next = [3];
+            // goto after finally
+            __goto = 3;
+            break;
+          case 1:
+            // catch
+            __handler = null;
+            __error1 = __result;
+            __handler = 8;
+            __goto = c ? 11 : 13;
+            break;
+          case 11:
+            // then
+            __goto = 14;
+            return thenHelper(fooError(__error1), __helper, __completer, function(__error) {
+              __goto = 8;
+              __helper(__error);
+            });
+          case 14:
+            // returning from await.
+            // goto join
+            __goto = 12;
+            break;
+          case 13:
+            // else
+            __result = fooError(__error1);
+          case 12:
+            // join
+            x = __result;
+            __handler = null;
+            __next = [10];
+            // goto finally
+            __goto = 9;
+            break;
+          case 8:
+            // catch
+            __handler = null;
+            __error2 = __result;
+            y.x = foo(__error2);
+            __next = [10];
+          case 9:
+            // finally
+            foo(x);
+            // goto the next finally handler
+            __goto = __next.pop();
+            break;
+          case 10:
+            // after finally
+          case 3:
+            // after finally
+            // implicit return
+            return thenHelper(null, null, __completer, null);
+        }
+      } catch (__error) {
+        if (__handler === null)
+          throw __error;
+        __result = __error;
+        __goto = __handler;
+      }
+
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+  testTransform("""
+function(x, y) async {
+  print(await(foo(x))); // calls
+  (await print)(foo(x));
+  print(foo(await x));
+  await (print(foo(await x)));
+  print(foo(x, await y, z));
+}
+""", """
+function(x, y) {
+  var __goto = 0, __completer = new newCompleter(), __temp1, __temp2, __temp3;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+          __temp1 = print;
+          __goto = 1;
+          return thenHelper(foo(x), __helper, __completer, null);
+        case 1:
+          // returning from await.
+          __temp1(__result);
+          __goto = 2;
+          return thenHelper(print, __helper, __completer, null);
+        case 2:
+          // returning from await.
+          __result(foo(x));
+          __temp1 = print;
+          __temp2 = foo;
+          __goto = 3;
+          return thenHelper(x, __helper, __completer, null);
+        case 3:
+          // returning from await.
+          __temp1(__temp2(__result));
+          __temp1 = print;
+          __temp2 = foo;
+          __goto = 5;
+          return thenHelper(x, __helper, __completer, null);
+        case 5:
+          // returning from await.
+          __goto = 4;
+          return thenHelper(__temp1(__temp2(__result)), __helper, __completer, null);
+        case 4:
+          // returning from await.
+          __temp1 = print;
+          __temp2 = foo;
+          __temp3 = x;
+          __goto = 6;
+          return thenHelper(y, __helper, __completer, null);
+        case 6:
+          // returning from await.
+          __temp1(__temp2(__temp3, __result, z));
+          // implicit return
+          return thenHelper(null, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+  testTransform("""
+function(x, y) async {
+  while (await(foo())) {
+    lab: { // labelled statement
+      switch(y) {
+      case 0:
+        foo();
+      case 0: // Duplicate case
+        print(await foo1(x));
+        return y;
+      case await bar(): // await in case
+        print(await foobar(x));
+        return y;
+      case x:
+        if (a) {
+          throw new Error();
+        } else {
+          continue;
+        }
+      default: // defaul case
+        break lab; // break to label
+      }
+      foo();
+    }
+  }
+}""", """
+function(x, y) {
+  var __goto = 0, __completer = new newCompleter(), __returnValue, __temp1;
+  function __helper(__result) {
+    while (true)
+      switch (__goto) {
+        case 0:
+          // Function start
+        case 2:
+          // while condition
+          __goto = 4;
+          return thenHelper(foo(), __helper, __completer, null);
+        case 4:
+          // returning from await.
+          if (!__result) {
+            // goto after while
+            __goto = 3;
+            break;
+          }
+        case 6:
+          // continue lab
+        case 7:
+          // switch
+          __temp1 = y;
+          if (__temp1 === 0) {
+            // goto case
+            __goto = 9;
+            break;
+          }
+          if (__temp1 === 0) {
+            // goto case
+            __goto = 10;
+            break;
+          }
+          __goto = 12;
+          return thenHelper(bar(), __helper, __completer, null);
+        case 12:
+          // returning from await.
+          if (__temp1 === __result) {
+            // goto case
+            __goto = 11;
+            break;
+          }
+          if (__temp1 === x) {
+            // goto case
+            __goto = 13;
+            break;
+          }
+          // goto default
+          __goto = 14;
+          break;
+        case 9:
+          // case
+          foo();
+        case 10:
+          // case
+          __temp1 = print;
+          __goto = 15;
+          return thenHelper(foo1(x), __helper, __completer, null);
+        case 15:
+          // returning from await.
+          __temp1(__result);
+          __returnValue = y;
+          // goto Return
+          __goto = 1;
+          break;
+        case 11:
+          // case
+          __temp1 = print;
+          __goto = 16;
+          return thenHelper(foobar(x), __helper, __completer, null);
+        case 16:
+          // returning from await.
+          __temp1(__result);
+          __returnValue = y;
+          // goto Return
+          __goto = 1;
+          break;
+        case 13:
+          // case
+          if (a) {
+            throw new Error();
+          } else {
+            // goto while condition
+            __goto = 2;
+            break;
+          }
+        case 14:
+          // default
+          // goto break lab
+          __goto = 5;
+          break;
+        case 8:
+          // after switch
+          foo();
+        case 5:
+          // break lab
+          // goto while condition
+          __goto = 2;
+          break;
+        case 3:
+          // after while
+        case 1:
+          // Return
+          return thenHelper(__returnValue, null, __completer, null);
+      }
+  }
+  return thenHelper(null, __helper, __completer, null);
+}""");
+}