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add handling of lone commas when destructuring arrays #12772

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add handling of lone commas when destructuring arrays #12772

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30 changes: 18 additions & 12 deletions lib/rules/comma-style.js
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Expand Up @@ -124,10 +124,11 @@ module.exports = {
* @param {Token} commaToken The token representing the comma.
* @param {Token} currentItemToken The first token of the current item.
* @param {Token} reportItem The item to use when reporting an error.
* @param {boolean} arrayLiteral whether the comma is in a destructuring assignment.
* @returns {void}
* @private
*/
function validateCommaItemSpacing(previousItemToken, commaToken, currentItemToken, reportItem) {
function validateCommaItemSpacing(previousItemToken, commaToken, currentItemToken, reportItem, arrayLiteral) {

// if single line
if (astUtils.isTokenOnSameLine(commaToken, currentItemToken) &&
Expand All @@ -144,15 +145,21 @@ module.exports = {
: "between";

// lone comma
context.report({
node: reportItem,
loc: {
line: commaToken.loc.end.line,
column: commaToken.loc.start.column
},
messageId: "unexpectedLineBeforeAndAfterComma",
fix: getFixerFunction(styleType, previousItemToken, commaToken, currentItemToken)
});
if (arrayLiteral) {

// ignored element, move on.
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Place holder in case we may want to report other things later, based on new options.


} else {
context.report({
node: reportItem,
loc: {
line: commaToken.loc.end.line,
column: commaToken.loc.start.column
},
messageId: "unexpectedLineBeforeAndAfterComma",
fix: getFixerFunction(styleType, previousItemToken, commaToken, currentItemToken)
});
}

} else if (style === "first" && !astUtils.isTokenOnSameLine(commaToken, currentItemToken)) {

Expand Down Expand Up @@ -213,7 +220,7 @@ module.exports = {
*/
if (astUtils.isCommaToken(commaToken)) {
validateCommaItemSpacing(previousItemToken, commaToken,
currentItemToken, reportItem);
currentItemToken, reportItem, arrayLiteral);
}

if (item) {
Expand All @@ -232,7 +239,6 @@ module.exports = {
* dangling comma.
*/
if (arrayLiteral) {

const lastToken = sourceCode.getLastToken(node),
nextToLastToken = sourceCode.getTokenBefore(lastToken);

Expand Down
18 changes: 0 additions & 18 deletions tests/lib/rules/comma-style.js
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Expand Up @@ -585,19 +585,6 @@ ruleTester.run("comma-style", rule, {
}],
errors: [{ messageId: "expectedCommaFirst" }]
},
{
code: "var foo = [\n(bar\n)\n,\nbaz\n];",
output: "var foo = [\n(bar\n),\nbaz\n];",
errors: [{
messageId: "unexpectedLineBeforeAndAfterComma",
type: "Identifier"
}]
},
Comment on lines -588 to -595
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This particular test doesn't have empty elements. If it's failing, then the change might be incorrect since it modifies behavior for arrays/patterns that don't have empty elements.

A simplified example, this time with an array pattern that doesn't have empty elements:

/*eslint comma-style: ["error", "last", { 
    "exceptions": { "ArrayPattern": false }
}]*/

var [
  foo
  ,
  bar] = [];

This is invalid code by this rule in the actual version - Online Demo

After this change as it's implemented at the moment, this would be a valid code (I think, it would be nice to add a test case). Is this the desired new behavior, i.e., should we ignore any commas on separate lines?

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Is this the desired new behavior, i.e., should we ignore any commas on separate lines?

If "comma-style" is enabled, that comma in a new line belongs either with foo (as default 'last'), or bar (if set to 'first'). Meaning your example should indeed fail.
My attempted fix is therefor incomplete.
Will revise and amend it... thanks for pointing it out. 👍

{
code: "[(foo),\n,\nbar]",
output: "[(foo),,\nbar]",
errors: [{ messageId: "unexpectedLineBeforeAndAfterComma" }]
},
{
code: "new Foo(a\n,b);",
output: "new Foo(a,\nb);",
Expand All @@ -608,11 +595,6 @@ ruleTester.run("comma-style", rule, {
}],
errors: [{ messageId: "expectedCommaLast" }]
},
{
code: "[\n[foo(3)],\n,\nbar\n];",
output: "[\n[foo(3)],,\nbar\n];",
errors: [{ messageId: "unexpectedLineBeforeAndAfterComma" }]
},
{

// https://github.com/eslint/eslint/issues/10632
Expand Down