Fix: add comma-style handling of lone commas when destructuring arrays

This handles ignored elements as per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Ignoring_some_returned_values Closes eslint#12756
justincorrigible · Jan 11, 2020 · 832f906 · 832f906
1 parent 9dfc850
commit 832f906
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Showing 2 changed files with 18 additions and 30 deletions.
diff --git a/lib/rules/comma-style.js b/lib/rules/comma-style.js
@@ -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) &&
@@ -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.
+
+                } 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)) {
 
@@ -213,7 +220,7 @@ module.exports = {
                      */
                     if (astUtils.isCommaToken(commaToken)) {
                         validateCommaItemSpacing(previousItemToken, commaToken,
-                            currentItemToken, reportItem);
+                            currentItemToken, reportItem, arrayLiteral);
                     }
 
                     if (item) {
@@ -232,7 +239,6 @@ module.exports = {
                  * dangling comma.
                  */
                 if (arrayLiteral) {
-
                     const lastToken = sourceCode.getLastToken(node),
                         nextToLastToken = sourceCode.getTokenBefore(lastToken);
 

diff --git a/tests/lib/rules/comma-style.js b/tests/lib/rules/comma-style.js
@@ -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"
-            }]
-        },
-        {
-            code: "[(foo),\n,\nbar]",
-            output: "[(foo),,\nbar]",
-            errors: [{ messageId: "unexpectedLineBeforeAndAfterComma" }]
-        },
         {
             code: "new Foo(a\n,b);",
             output: "new Foo(a,\nb);",
@@ -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