Added complete TCO (tail call optimization).

Works across functions and generates simpler and faster code than #701.
Works even across files when used in conjunction with `runtime` option.

Closes #256.

.editorconfig

@@ -6,6 +6,6 @@ charset = utf-8
 trim_trailing_whitespace = true
 insert_final_newline = true
 
-[*.js]
+[*.{js,json}]
 indent_style = space
 indent_size = 2

lib/6to5/transformation/file.js

@@ -56,7 +56,8 @@ File.helpers = [
   "class-call-check",
   "object-destructuring-empty",
   "temporal-undefined",
-  "temporal-assert-defined"
+  "temporal-assert-defined",
+  "tail-call"
 ];
 
 File.validOptions = [

lib/6to5/transformation/templates/tail-call-body.js

@@ -1,13 +0,0 @@
-{
-  var ARGUMENTS_ID = arguments,
-      THIS_ID = this,
-      SHOULD_CONTINUE_ID,
-      RESULT_ID;
-
-  do {
-    SHOULD_CONTINUE_ID = false;
-    RESULT_ID = FUNCTION.apply(THIS_ID, ARGUMENTS_ID);
-  } while(SHOULD_CONTINUE_ID);
-
-  return RESULT_ID;
-}

lib/6to5/transformation/templates/tail-call.js

@@ -0,0 +1,21 @@
+(function () {
+  function Tail(func, args, context) {
+    this.func = func;
+    this.args = args;
+    this.context = context;
+  }
+
+  var isRunning = false;
+
+  return function (func, args, context) {
+    var result = new Tail(func, args, context);
+    if (!isRunning) {
+      isRunning = true;
+      do {
+        result = result.func.apply(result.context, result.args);
+      } while (result instanceof Tail);
+      isRunning = false;
+    }
+    return result;
+  };
+})()

lib/6to5/transformation/transformers/es6/tail-call.js

@@ -1,6 +1,5 @@
 "use strict";
 
-var util = require("../../../util");
 var t    = require("../../../types");
 
 function returnBlock(expr) {
@@ -27,7 +26,7 @@ function transformExpression(node, scope, state) {
         } else {
           node.alternate = returnBlock(node.alternate);
         }
-        return node;
+        return [node];
 
       case "LogicalExpression":
         // only call in right-value of can be optimized
@@ -36,17 +35,11 @@ function transformExpression(node, scope, state) {
           return;
         }
 
-        // cache left value as it might have side-effects
-        var leftId = state.getLeftId();
-        var testExpr = t.assignmentExpression(
-          "=",
-          leftId,
-          node.left
-        );
+        var test = state.wrapSideEffect(node.left);
         if (node.operator === "&&") {
-          testExpr = t.unaryExpression("!", testExpr);
+          test.expr = t.unaryExpression("!", test.expr);
         }
-        return [t.ifStatement(testExpr, returnBlock(leftId))].concat(callRight);
+        return [t.ifStatement(test.expr, returnBlock(test.ref))].concat(callRight);
 
       case "SequenceExpression":
         var seq = node.expressions;
@@ -66,53 +59,28 @@ function transformExpression(node, scope, state) {
         return [t.expressionStatement(node)].concat(lastCall);
 
       case "CallExpression":
-        var callee = node.callee, prop, thisBinding, args;
+        var callee = node.callee, thisBinding;
+        var args = [callee];
 
-        if (t.isMemberExpression(callee, { computed: false }) &&
-            t.isIdentifier(prop = callee.property)) {
-          switch (prop.name) {
-            case "call":
-              args = t.arrayExpression(node.arguments.slice(1));
-              break;
-
-            case "apply":
-              args = node.arguments[1] || t.identifier("undefined");
-              break;
-
-            default:
-              return;
-          }
-
-          thisBinding = node.arguments[0];
-          callee = callee.object;
+        // bind `this` to object in member expressions
+        if (t.isMemberExpression(callee)) {
+          var object = state.wrapSideEffect(callee.object);
+          callee.object = object.expr;
+          thisBinding = object.ref;
         }
 
-        // only tail recursion can be optimized as for now
-        if (!t.isIdentifier(callee) || !scope.bindingEquals(callee.name, state.ownerId)) {
-          return;
+        if (node.arguments.length > 0 || thisBinding) {
+          args.push(t.arrayExpression(node.arguments));
         }
 
-        state.hasTailRecursion = true;
+        if (thisBinding) {
+          args.push(thisBinding);
+        }
 
-        return [
-          t.expressionStatement(t.assignmentExpression(
-            "=",
-            state.getArgumentsId(),
-            args || t.arrayExpression(node.arguments)
-          )),
-
-          t.expressionStatement(t.assignmentExpression(
-            "=",
-            state.getThisId(),
-            thisBinding || t.identifier("undefined")
-          )),
-
-          t.returnStatement(t.assignmentExpression(
-            "=",
-            state.getShouldContinueId(),
-            t.literal(true)
-          ))
-        ];
+        return [t.returnStatement(t.callExpression(
+          state.getHelperRef(),
+          args
+        ))];
     }
   })(node);
 }
@@ -152,56 +120,34 @@ var functionVisitor = {
 };
 
 exports.FunctionDeclaration =
-exports.FunctionExpression = function (node, parent, scope) {
-  // only tail recursion can be optimized as for now,
-  // so we can skip anonymous functions entirely
-  var ownerId = node.id;
-  if (!ownerId) return;
-
-  var argumentsId, thisId, shouldContinueId, leftId;
+exports.FunctionExpression = function (node, parent, scope, file) {
+  var tempId, helperRef;
 
   var state = {
-    hasTailRecursion: false,
-    ownerId: ownerId,
+    ownerId: node.id,
 
-    getArgumentsId: function () {
-      return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
+    getHelperRef: function () {
+      return helperRef = helperRef || file.addHelper("tail-call");
     },
 
-    getThisId: function () {
-      return thisId = thisId || scope.generateUidIdentifier("this");
-    },
-
-    getShouldContinueId: function () {
-      return shouldContinueId = shouldContinueId || scope.generateUidIdentifier("shouldContinue");
-    },
-
-    getLeftId: function () {
-      return leftId = leftId || scope.generateUidIdentifier("left");
+    wrapSideEffect: function (node) {
+      if (t.isIdentifier(node) || t.isLiteral(node)) {
+        return {expr: node, ref: node};
+      }
+      tempId = tempId || scope.generateUidIdentifier("temp");
+      return {
+        expr: t.assignmentExpression("=", tempId, node),
+        ref: tempId
+      };
     }
   };
 
   // traverse the function and look for tail recursion
   scope.traverse(node, functionVisitor, state);
 
-  if (!state.hasTailRecursion) return;
-
-  var block = t.ensureBlock(node);
-
-  if (leftId) {
-    block.body.unshift(t.variableDeclaration("var", [
-      t.variableDeclarator(leftId)
+  if (tempId) {
+    t.ensureBlock(node).body.unshift(t.variableDeclaration("var", [
+      t.variableDeclarator(tempId)
     ]));
   }
-
-  var resultId = scope.generateUidIdentifier("result");
-  state.getShouldContinueId();
-
-  node.body = util.template("tail-call-body", {
-    SHOULD_CONTINUE_ID: shouldContinueId,
-    ARGUMENTS_ID:       argumentsId,
-    RESULT_ID:          resultId,
-    FUNCTION:           t.functionExpression(null, node.params, block),
-    THIS_ID:            thisId,
-  });
 };

test/fixtures/transformation/es6-arrow-functions/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/es6-classes-loose/options.json

@@ -1,3 +1,4 @@
 {
-  "loose": ["es6.classes"]
+  "loose": ["es6.classes"],
+  "blacklist": ["es6.tailCall"]
 }

test/fixtures/transformation/es6-classes/calling-super-properties/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/es6-destructuring/spread/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/es6-modules-system/hoist-function-exports/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/es6-properties.shorthand/method-self-reference/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/es6-spread/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/es6-tail-call/call-apply/expected.js

@@ -1,27 +1,13 @@
 "use strict";
 
 (function f(n) {
-  var _arguments = arguments,
-      _this = this,
-      _shouldContinue,
-      _result;
-  do {
-    _shouldContinue = false;
-    _result = (function (n) {
-      if (n <= 0) {
-        console.log(this, arguments);
-        return "foo";
-      }
-      if (Math.random() > 0.5) {
-        _arguments = [n - 1];
-        _this = this;
-        return _shouldContinue = true;
-      } else {
-        _arguments = [n - 1];
-        _this = this;
-        return _shouldContinue = true;
-      }
-    }).apply(_this, _arguments);
-  } while (_shouldContinue);
-  return _result;
+  if (n <= 0) {
+    console.log(this, arguments);
+    return "foo";
+  }
+  if (Math.random() > 0.5) {
+    return to5Runtime.tailCall(f.call, [this, n - 1], f);
+  } else {
+    return to5Runtime.tailCall(f.apply, [this, [n - 1]], f);
+  }
 })(1000000) === "foo";

test/fixtures/transformation/es6-tail-call/cross-function/actual.js

@@ -0,0 +1,7 @@
+function f(n) {
+    return n <= 0 ? "foo" : g(n - 1);
+}
+
+function g(n) {
+    return n <= 0 ? "goo" : f(n - 1);
+}

test/fixtures/transformation/es6-tail-call/cross-function/expected.js

@@ -0,0 +1,17 @@
+"use strict";
+
+function f(n) {
+    if (n <= 0) {
+        return "foo";
+    } else {
+        return to5Runtime.tailCall(g, [n - 1]);
+    }
+}
+
+function g(n) {
+    if (n <= 0) {
+        return "goo";
+    } else {
+        return to5Runtime.tailCall(f, [n - 1]);
+    }
+}

test/fixtures/transformation/es6-tail-call/expressions/expected.js

@@ -1,30 +1,18 @@
 "use strict";
 
 (function f(n) {
-  var _arguments = arguments,
-      _this = this,
-      _shouldContinue,
-      _result;
-  do {
-    _shouldContinue = false;
-    _result = (function (n) {
-      var _left;
-      if (n <= 0) {
-        return "foo";
-      } else {
-        doSmth();
+  var _temp;
+  if (n <= 0) {
+    return "foo";
+  } else {
+    doSmth();
 
-        if (!(_left = getTrueValue())) {
-          return _left;
-        }
-        if (_left = getFalseValue()) {
-          return _left;
-        }
-        _arguments = [n - 1];
-        _this = undefined;
-        return _shouldContinue = true;
-      }
-    }).apply(_this, _arguments);
-  } while (_shouldContinue);
-  return _result;
+    if (!(_temp = getTrueValue())) {
+      return _temp;
+    }
+    if (_temp = getFalseValue()) {
+      return _temp;
+    }
+    return to5Runtime.tailCall(f, [n - 1]);
+  }
 })(1000000, true) === "foo";

test/fixtures/transformation/es6-tail-call/options.json

@@ -0,0 +1,4 @@
+{
+  "runtime": true,
+  "blacklist": []
+}

test/fixtures/transformation/es6-tail-call/recursion/expected.js

@@ -1,23 +1,11 @@
 "use strict";
 
 (function f(_x, /* should be undefined after first pass */m) {
-  var _arguments = arguments,
-      _this = this,
-      _shouldContinue,
-      _result;
-  do {
-    _shouldContinue = false;
-    _result = (function (_x, m) {
-      var n = arguments[0] === undefined ? getDefaultValue() : arguments[0];
-      if (n <= 0) {
-        return "foo";
-      }
-      // Should be clean (undefined) on each pass
-      var local;
-      _arguments = [n - 1];
-      _this = undefined;
-      return _shouldContinue = true;
-    }).apply(_this, _arguments);
-  } while (_shouldContinue);
-  return _result;
+  var n = arguments[0] === undefined ? getDefaultValue() : arguments[0];
+  if (n <= 0) {
+    return "foo";
+  }
+  // Should be clean (undefined) on each pass
+  var local;
+  return to5Runtime.tailCall(f, [n - 1]);
 })(1000000, true) === "foo";

test/fixtures/transformation/es6-tail-call/side-effect/actual.js

@@ -0,0 +1,7 @@
+function f() {
+    return getObj().method();
+}
+
+function g() {
+  return getFalseValue() || getValue();
+}

test/fixtures/transformation/es6-tail-call/side-effect/expected.js

@@ -0,0 +1,14 @@
+"use strict";
+
+function f() {
+  var _temp;
+  return to5Runtime.tailCall((_temp = getObj()).method, [], _temp);
+}
+
+function g() {
+  var _temp;
+  if (_temp = getFalseValue()) {
+    return _temp;
+  }
+  return to5Runtime.tailCall(getValue);
+}

test/fixtures/transformation/es6-tail-call/try-catch/expected.js

@@ -10,26 +10,14 @@
 })(1000000) === "foo";
 
 (function f(n) {
-  var _arguments = arguments,
-      _this = this,
-      _shouldContinue,
-      _result;
-  do {
-    _shouldContinue = false;
-    _result = (function (n) {
-      if (n <= 0) {
-        return "foo";
-      }
-      try {
-        throw new Error();
-      } catch (e) {
-        _arguments = [n - 1];
-        _this = undefined;
-        return _shouldContinue = true;
-      }
-    }).apply(_this, _arguments);
-  } while (_shouldContinue);
-  return _result;
+  if (n <= 0) {
+    return "foo";
+  }
+  try {
+    throw new Error();
+  } catch (e) {
+    return to5Runtime.tailCall(f, [n - 1]);
+  }
 })(1000000) === "foo";
 
 (function f(n) {
@@ -44,22 +32,10 @@
 })(1000000) === "foo";
 
 (function f(n) {
-  var _arguments = arguments,
-      _this = this,
-      _shouldContinue,
-      _result;
-  do {
-    _shouldContinue = false;
-    _result = (function (n) {
-      if (n <= 0) {
-        return "foo";
-      }
-      try {} finally {
-        _arguments = [n - 1];
-        _this = undefined;
-        return _shouldContinue = true;
-      }
-    }).apply(_this, _arguments);
-  } while (_shouldContinue);
-  return _result;
+  if (n <= 0) {
+    return "foo";
+  }
+  try {} finally {
+    return to5Runtime.tailCall(f, [n - 1]);
+  }
 })(1000000) === "foo";

test/fixtures/transformation/es7-comprehensions/options.json

@@ -1,3 +1,4 @@
 {
-  "experimental": true
+  "experimental": true,
+  "blacklist": ["es6.tailCall"]
 }

test/fixtures/transformation/playground/method-binding/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["es6.tailCall"]
+}

test/fixtures/transformation/react/arrow-functions/options.json

@@ -0,0 +1,3 @@
+{
+  "blacklist": ["useStrict", "es6.tailCall"]
+}