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Avoid adding unnecessary closure for block scoping (#5246)

Browse Source 
When you write

```
for (const x of l) {
  setTimeout(() => x);
}
```

we need to add a closure because the variable is meant to be block-scoped and recreated each time the block runs. We do this.

However, we also add the closure when no loop is present. This isn't necessary, because if no loop is present then each piece of code runs at most once. I changed the transform to only add a closure if a variable is referenced from within a loop.
This commit is contained in:
Ben Alpert 2017-02-13 13:46:00 -08:00 committed by Logan Smyth
parent 2985597d40
commit 14d3c2e256
16 changed files with 217 additions and 103 deletions
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2
packages/babel-core/test/fixtures/transformation/misc/regression-2364/actual.js vendored
View File

@ -1,6 +1,6 @@
function wrapper(fn) {
return (...args) => {
if (someCondition) {
while (someCondition) {
const val = fn(...args);
return val.test(() => {
console.log(val);

22
packages/babel-core/test/fixtures/transformation/misc/regression-2364/expected.js vendored
View File

@ -2,17 +2,19 @@ function wrapper(fn) {
return function () {
var _arguments = arguments;
if (someCondition) {
var _ret = function () {
var val = fn(..._arguments);
return {
v: val.test(function () {
console.log(val);
})
};
}();
var _loop = function () {
var val = fn(..._arguments);
return {
v: val.test(function () {
console.log(val);
})
};
};
while (someCondition) {
var _ret = _loop();
if (typeof _ret === "object") return _ret.v;
}
};
}
}

27
packages/babel-plugin-transform-es2015-block-scoping/src/index.js
View File

@ -112,8 +112,21 @@ function isVar(node) {
}
const letReferenceBlockVisitor = traverse.visitors.merge([{
Loop: {
enter(path, state) {
state.loopDepth++;
},
exit(path, state) {
state.loopDepth--;
},
},
Function(path, state) {
path.traverse(letReferenceFunctionVisitor, state);
// References to block-scoped variables only require added closures if it's
// possible for the code to run more than once -- otherwise it is safe to
// simply rename the variables.
if (state.loopDepth > 0) {
path.traverse(letReferenceFunctionVisitor, state);
}
return path.skip();
}
}, tdzVisitor]);
@ -549,9 +562,19 @@ class BlockScoping {
const state = {
letReferences: this.letReferences,
closurify: false,
file: this.file
file: this.file,
loopDepth: 0,
};
const loopOrFunctionParent = this.blockPath.find(
(path) => path.isLoop() || path.isFunction()
);
if (loopOrFunctionParent && loopOrFunctionParent.isLoop()) {
// There is a loop ancestor closer than the closest function, so we
// consider ourselves to be in a loop.
state.loopDepth++;
}
// traverse through this block, stopping on functions and checking if they
// contain any local let references
this.blockPath.traverse(letReferenceBlockVisitor, state);

14
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/issue-2174/expected.js vendored
View File

@ -1,11 +1,9 @@
if (true) {
var x;
var foo = function () {};
(function () {
function foo() {}
function bar() {
return foo;
}
for (x in {}) {}
})();
var bar = function () {
return foo;
};
for (var x in {}) {}
}

34
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/actual.js vendored Normal file
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@ -0,0 +1,34 @@
function foo() {
const x = 5;
console.log(x);
{
const x = 7;
setTimeout(() => x, 0);
}
}
function bar() {
const x = 5;
console.log(x);
for (let i = 0; i < 7; i++) {
{
const x = i;
setTimeout(() => x, 0);
}
}
}
function baz() {
const x = 5;
console.log(x);
for (let i = 0; i < 7; i++) {
var qux = function qux(y) {
const x = y;
setTimeout(() => x, 0);
};
qux(i);
}
}

42
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loops-and-no-loops/expected.js vendored Normal file
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@ -0,0 +1,42 @@
function foo() {
var x = 5;
console.log(x);
{
var _x = 7;
setTimeout(function () {
return _x;
}, 0);
}
}
function bar() {
var x = 5;
console.log(x);
for (var i = 0; i < 7; i++) {
{
(function () {
var x = i;
setTimeout(function () {
return x;
}, 0);
})();
}
}
}
function baz() {
var x = 5;
console.log(x);
for (var i = 0; i < 7; i++) {
var qux = function qux(y) {
var x = y;
setTimeout(function () {
return x;
}, 0);
};
qux(i);
}
}

11
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/actual.js vendored Normal file
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@ -0,0 +1,11 @@
var f1, f2;
{
let z = 'z1 value';
f1 = function() { return z; };
}
{
let z = 'z2 value';
f2 = function() { return z; };
}
f1();
f2();

15
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/sibling-scopes/expected.js vendored Normal file
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@ -0,0 +1,15 @@
var f1, f2;
{
var z = 'z1 value';
f1 = function () {
return z;
};
}
{
var _z = 'z2 value';
f2 = function () {
return _z;
};
}
f1();
f2();

24
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/actual.js vendored
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@ -1,16 +1,18 @@
function foo() {
switch (2) {
case 0: {
if (true) {
return;
}
while (true) {
switch (2) {
case 0: {
if (true) {
return;
}
const stuff = new Map();
const data = 0;
stuff.forEach(() => {
const d = data;
});
break;
const stuff = new Map();
const data = 0;
stuff.forEach(() => {
const d = data;
});
break;
}
}
}
}

50
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/superswitch/expected.js vendored
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@ -1,29 +1,31 @@
function foo() {
switch (2) {
case 0:
{
var _ret = function () {
if (true) {
return {
v: void 0
};
while (true) {
switch (2) {
case 0:
{
var _ret = function () {
if (true) {
return {
v: void 0
};
}
var stuff = new Map();
var data = 0;
stuff.forEach(function () {
var d = data;
});
return "break";
}();
switch (_ret) {
case "break":
break;
default:
if (typeof _ret === "object") return _ret.v;
}
var stuff = new Map();
var data = 0;
stuff.forEach(function () {
var d = data;
});
return "break";
}();
switch (_ret) {
case "break":
break;
default:
if (typeof _ret === "object") return _ret.v;
}
}
}
}
}

14
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/actual.js vendored
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@ -1,10 +1,12 @@
function fn() {
switch (true) {
default:
let foo = 4;
if (true) {
let bar = () => foo;
console.log(bar());
while (true) {
switch (true) {
default:
let foo = 4;
if (true) {
let bar = () => foo;
console.log(bar());
}
}
}
}

26
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/switch-callbacks/expected.js vendored
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@ -1,14 +1,16 @@
function fn() {
(function () {
switch (true) {
default:
var foo = 4;
if (true) {
var bar = function () {
return foo;
};
console.log(bar());
}
}
})();
while (true) {
(function () {
switch (true) {
default:
var foo = 4;
if (true) {
var bar = function () {
return foo;
};
console.log(bar());
}
}
})();
}
}

6
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/for-const-closure/expected.js vendored Normal file
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@ -0,0 +1,6 @@
for (var i = 0; i < 5; i++) {
var l = i;
setTimeout(function () {
console.log(l);
}, 1);
}

16
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/actual.js vendored
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@ -1,16 +0,0 @@
function foo() {
switch (2) {
case 0: {
if (true) {
return;
}
const stuff = new Map();
const data = 0;
stuff.forEach(() => {
const d = data;
});
break;
}
}
}

3
packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/throwIfClosureRequired/superswitch/options.json vendored
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@ -1,3 +0,0 @@
{
"throws": "Compiling let/const in this block would add a closure (throwIfClosureRequired)."
}

14
packages/babel-plugin-transform-react-constant-elements/test/fixtures/constant-elements/dont-hoist-block-scoped-variables/expected.js vendored
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@ -1,17 +1,11 @@
function render(flag) {
if (flag) {
var _ret = function () {
var bar = "bar";
var bar = "bar";
[].map(() => bar);
[].map(() => bar);
return {
v: <foo bar={bar} />
};
}();
if (typeof _ret === "object") return _ret.v;
return <foo bar={bar} />;
}
return null;
}
}