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spread.js
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Sat, Feb 8, 07:48

spread.js
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import CompileError from './CompileError.js';
export function isArguments(node) {
return node.type === 'Identifier' && node.name === 'arguments';
}
export function inlineSpreads(
code,
node,
elements
) {
let i = elements.length;
while (i--) {
const element = elements[i];
if (!element || element.type !== 'SpreadElement') {
continue;
}
const argument = element.argument;
if (argument.type !== 'ArrayExpression') {
continue;
}
const subelements = argument.elements;
if (subelements.some(subelement => subelement === null)) {
// Not even going to try inlining spread arrays with holes.
// It's a lot of work (got to be VERY careful in comma counting for
// ArrayExpression, and turn blanks into undefined for
// CallExpression and NewExpression), and probably literally no one
// would ever benefit from it.
continue;
}
// We can inline it: drop the `...[` and `]` and sort out any commas.
const isLast = i === elements.length - 1;
if (subelements.length === 0) {
code.remove(
isLast && i !== 0
? elements[i - 1].end // Take the previous comma too
: element.start,
isLast
? node.end - 1 // Must remove trailing comma; element.end wouldn’t
: elements[i + 1].start);
} else {
// Strip the `...[` and the `]` with a possible trailing comma before it,
// leaving just the possible trailing comma after it.
code.remove(element.start, subelements[0].start);
code.remove(
// Strip a possible trailing comma after the last element
subelements[subelements.length - 1].end,
// And also a possible trailing comma after the spread
isLast
? node.end - 1
: element.end
);
}
elements.splice(i, 1, ...subelements);
i += subelements.length;
}
}
// Returns false if it’s safe to simply append a method call to the node,
// e.g. `a` → `a.concat()`.
//
// Returns true if it may not be and so parentheses should be employed,
// e.g. `a ? b : c` → `a ? b : c.concat()` would be wrong.
//
// This test may be overcautious; if desired it can be refined over time.
export function needsParentheses(node) {
switch (node.type) {
// Currently whitelisted are all relevant ES5 node types ('Literal' and
// 'ObjectExpression' are skipped as irrelevant for array/call spread.)
case 'ArrayExpression':
case 'CallExpression':
case 'Identifier':
case 'ParenthesizedExpression':
case 'ThisExpression':
return false;
default:
return true;
}
}
export default function spread(
code,
elements,
start,
argumentsArrayAlias,
isNew
) {
let i = elements.length;
let firstSpreadIndex = -1;
while (i--) {
const element = elements[i];
if (element && element.type === 'SpreadElement') {
if (isArguments(element.argument)) {
code.overwrite(
element.argument.start,
element.argument.end,
argumentsArrayAlias
);
}
firstSpreadIndex = i;
}
}
if (firstSpreadIndex === -1) return false; // false indicates no spread elements
if (isNew) {
for (i = 0; i < elements.length; i += 1) {
const element = elements[i];
if (element.type === 'SpreadElement') {
code.remove(element.start, element.argument.start);
} else {
code.prependRight(element.start, '[');
code.prependRight(element.end, ']');
}
}
return true; // true indicates some spread elements
}
let element = elements[firstSpreadIndex];
const previousElement = elements[firstSpreadIndex - 1];
if (!previousElement) {
// We may need to parenthesize it to handle ternaries like [...a ? b : c].
let addClosingParen;
if (start !== element.start) {
if ((addClosingParen = needsParentheses(element.argument))) {
code.overwrite(start, element.start, '( ');
} else {
code.remove(start, element.start);
}
} else if (element.parent.type === 'CallExpression') {
// CallExpression inserts `( ` itself, we add the ).
// (Yeah, CallExpression did the needsParentheses call already,
// but we don’t have its result handy, so do it again. It’s cheap.)
addClosingParen = needsParentheses(element.argument);
} else {
// Should be unreachable, but doing this is more robust.
throw new CompileError(
'Unsupported spread construct, please raise an issue at https://github.com/bublejs/buble/issues',
element
);
}
code.overwrite(element.end, elements[1].start,
addClosingParen ? ' ).concat( ' : '.concat( ');
} else {
code.overwrite(previousElement.end, element.start, ' ].concat( ');
}
for (i = firstSpreadIndex; i < elements.length; i += 1) {
element = elements[i];
if (element) {
if (element.type === 'SpreadElement') {
code.remove(element.start, element.argument.start);
} else {
code.appendLeft(element.start, '[');
code.appendLeft(element.end, ']');
}
}
}
return true; // true indicates some spread elements
}

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