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Shorten assignments to itself #230

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merged 16 commits into from
Nov 13, 2016
Merged

Shorten assignments to itself #230

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3344baa
Simplify assignments to same identifier
kangax Oct 27, 2016
a4d10bc
Add tests
kangax Oct 27, 2016
c666da1
Bump versions
kangax Oct 27, 2016
c6ec99d
Remove versioning
kangax Oct 27, 2016
6b913fe
Remove version
kangax Oct 27, 2016
c1aa0ca
Add support for optimizing member expressions
kangax Nov 1, 2016
6dfe218
Fix test name
kangax Nov 1, 2016
6813842
Remove comment
kangax Nov 1, 2016
5ddc5f8
Simplify ternary
kangax Nov 1, 2016
2c7a0d5
Fix bugs, simplify check
kangax Nov 1, 2016
4f7e8eb
Change postfix to prefix
kangax Nov 1, 2016
64ed8d9
Merge master
kangax Nov 10, 2016
8c0a456
Exclude operators for member expressions too
kangax Nov 10, 2016
6eaded6
includes -> indexOf
kangax Nov 11, 2016
edd236f
Fix lint
boopathi Nov 11, 2016
b058bd0
Improve method name
kangax Nov 13, 2016
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53 changes: 53 additions & 0 deletions packages/babel-plugin-minify-simplify/__tests__/simplify-test.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2136,4 +2136,57 @@ describe("simplify-plugin", () => {
const expected = source;
expect(transform(source)).toBe(expected);
});

it("should transform assignments to the same identifier", () => {

const actual = [
'x = x + 1;',
'x = x - 1;',
'x = x * 1;',
'x = x % 1;',
'x = x << 1;',
'x = x >> 1;',
'x = x >>> 1;',
'x = x & 1;',
'x = x | 1;',
'x = x ^ 1;',
'x = x / 1;',
'x = x ** 1;',
'foo = foo + bar;',
'foo = foo * function(){};',
'foo += 123;',
'foo = 1 + foo;',
'x = x = x + 1;',
'foo = foo + bar + baz;',
'window.foo = window.foo + 1;',
'window.foo.bar = window.foo.baz + 1;',
];

const expected = [
'x++;',
'x--;',
'x *= 1;',
'x %= 1;',
'x <<= 1;',
'x >>= 1;',
'x >>>= 1;',
'x &= 1;',
'x |= 1;',
'x ^= 1;',
'x /= 1;',
'x **= 1;',
'foo += bar;',
'foo *= function () {};',
'foo += 123;',
'foo = 1 + foo;',
'x = x++;',
'foo = foo + bar + baz;',
'window.foo = window.foo + 1;',
'window.foo.bar = window.foo.baz + 1;',
];

actual.forEach((test, index) => {
expect(transform(test)).toBe(expected[index]);
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expect(actual.map((s) => transform(s))).toEqual(expected);

here you compare two arrays and even if one fails in the list, the others still run. But when you do forEach when one of them fails, all else that follows won't be run at all.

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So you're thinking to wrap them in try/catch?

});
});
});
54 changes: 54 additions & 0 deletions packages/babel-plugin-minify-simplify/src/index.js
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Expand Up @@ -28,6 +28,17 @@ module.exports = ({ types: t }) => {
const or = (a, b) => t.logicalExpression("||", a, b);
const and = (a, b) => t.logicalExpression("&&", a, b);

const operators = new Set([
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We need to consider splitting plugins into multiple modules. This kind of mixing of helpers and supplemental stuff is not great ^. I think we could even strive for 1 type-of-transform per file.

'+', '-', '*', '%',
'<<', '>>', '>>>',
'&', '|', '^', '/',
'**'
]);

const updateOperators = new Set([
'+', '-'
]);

return {
name: "minify-simplify",
visitor: {
Expand Down Expand Up @@ -124,6 +135,49 @@ module.exports = ({ types: t }) => {
],
},

AssignmentExpression(path) {

const right = path.get('right');
const left = path.get('left');

const canShorten = (
right.type === 'BinaryExpression' &&
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right.isBinaryExpression()

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Good to know, thanks!

operators.has(right.node.operator) &&
left.node.name === right.node.left.name
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requires isIdentifier check. if left.node and right.node.left are not identifiers, it can end up in undefined === undefined check and canShorten will be true - eg: [a,b] = foo() + 1 - canShorten will be true for this.

);

if (!canShorten) return;

const canBeUpdateExpression = (
right.node.right.type === 'NumericLiteral' &&
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right.get("right").isNumericLiteral() or t.isNumericLiteral(right.node.right)

right.node.right.value === 1 &&
updateOperators.has(right.node.operator));

if (left.node.name === undefined) {
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left.isMemberExpression() is better IMO, rather than depending on left not being an identifier.

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I wasn't sure if it's always going to be member expression. This felt like a broader/safer check. But sure, probably ok to change it.

// TODO: transform MemberExpressions as well
// e.g. foo.bar = foo.bar + 123;
return;
}

if (canBeUpdateExpression) {

const newExpression = t.updateExpression(
right.node.operator + right.node.operator,
t.identifier(left.node.name));
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probably needs to handle member expression here ?

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Wonder if we can make a generic utility for handling both Identifier/MemberExpression?


path.replaceWith(newExpression);
}
else {

const newExpression = t.assignmentExpression(
right.node.operator + '=',
t.identifier(left.node.name),
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handle memberExpressions

t.clone(right.node.right));

path.replaceWith(newExpression);
}
},

ConditionalExpression: {
enter: [
// !foo ? 'foo' : 'bar' -> foo ? 'bar' : 'foo'
Expand Down