Update: add fixer for newline-before-return (fixes #5958)

lib/rules/newline-before-return.js

@@ -15,7 +15,7 @@ module.exports = {
             category: "Stylistic Issues",
             recommended: false
         },
-
+        fixable: "whitespace",
         schema: []
     },
 
@@ -103,35 +103,81 @@ module.exports = {
         }
 
         /**
-         * Checks whether node is preceded by a newline
-         * @param {ASTNode} node - node to check
-         * @returns {boolean} Whether or not the node is preceded by a newline
+         * Returns the line number of the token before the node that is passed in as an argument
+         * @param {ASTNode} node - The node to use as the start of the calculation
+         * @returns {number} Line number of the token before `node`
          * @private
          */
-        function hasNewlineBefore(node) {
-            const tokenBefore = sourceCode.getTokenBefore(node),
-                lineNumNode = node.loc.start.line;
+        function getLineNumberOfTokenBefore(node) {
+            const tokenBefore = sourceCode.getTokenBefore(node);
             let lineNumTokenBefore;
 
             /**
-             * Global return (at the beginning of a script) is a special case.
-             * If there is no token before `return`, then we expect no line
-             * break before the return. Comments are allowed to occupy lines
-             * before the global return, just no blank lines.
-             * Setting lineNumTokenBefore to zero in that case results in the
-             * desired behavior.
-             */
+            * Global return (at the beginning of a script) is a special case.
+            * If there is no token before `return`, then we expect no line
+            * break before the return. Comments are allowed to occupy lines
+            * before the global return, just no blank lines.
+            * Setting lineNumTokenBefore to zero in that case results in the
+            * desired behavior.
+            */
             if (tokenBefore) {
                 lineNumTokenBefore = tokenBefore.loc.end.line;
             } else {
                 lineNumTokenBefore = 0;     // global return at beginning of script
             }
 
+            return lineNumTokenBefore;
+        }
+
+        /**
+         * Checks whether node is preceded by a newline
+         * @param {ASTNode} node - node to check
+         * @returns {boolean} Whether or not the node is preceded by a newline
+         * @private
+         */
+        function hasNewlineBefore(node) {
+            const lineNumNode = node.loc.start.line;
+            const lineNumTokenBefore = getLineNumberOfTokenBefore(node);
             const commentLines = calcCommentLines(node, lineNumTokenBefore);
 
             return (lineNumNode - lineNumTokenBefore - commentLines) > 1;
         }
 
+        /**
+         * Checks whether it is safe to apply a fix to a given return statement.
+         *
+         * The fix is not considered safe if the given return statement has leading comments,
+         * as we cannot safely determine if the newline should be added before or after the comments.
+         * For more information, see: https://github.com/eslint/eslint/issues/5958#issuecomment-222767211
+         *
+         * @param {ASTNode} node - The return statement node to check.
+         * @returns {boolean} `true` if it can fix the node.
+         * @private
+         */
+        function canFix(node) {
+            const leadingComments = sourceCode.getComments(node).leading;
+            const lastLeadingComment = leadingComments[leadingComments.length - 1];
+            const tokenBefore = sourceCode.getTokenBefore(node);
+
+            if (leadingComments.length === 0) {
+                return true;
+            }
+
+            // if the last leading comment ends in the same line as the previous token and
+            // does not share a line with the `return` node, we can consider it safe to fix.
+            // Example:
+            // function a() {
+            //     var b; //comment
+            //     return;
+            // }
+            if (lastLeadingComment.loc.end.line === tokenBefore.loc.end.line &&
+                lastLeadingComment.loc.end.line !== node.loc.start.line) {
+                return true;
+            }
+
+            return false;
+        }
+
         //--------------------------------------------------------------------------
         // Public
         //--------------------------------------------------------------------------
@@ -141,7 +187,16 @@ module.exports = {
                 if (!isFirstNode(node) && !hasNewlineBefore(node)) {
                     context.report({
                         node,
-                        message: "Expected newline before return statement."
+                        message: "Expected newline before return statement.",
+                        fix(fixer) {
+                            if (canFix(node)) {
+                                const tokenBefore = sourceCode.getTokenBefore(node);
+                                const newlines = node.loc.start.line === tokenBefore.loc.end.line ? "\n\n" : "\n";
+
+                                return fixer.insertTextBefore(node, newlines);
+                            }
+                            return null;
+                        }
                     });
                 }
             }

tests/lib/rules/newline-before-return.js

@@ -110,79 +110,171 @@ ruleTester.run("newline-before-return", rule, {
     ],
 
     invalid: [
+        {
+            code: "function a() {\nvar b; return;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; \n\nreturn;\n}"
+        },
         {
             code: "function a() {\nvar b;\nreturn;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b;\n\nreturn;\n}"
         },
         {
             code: "function a() {\nif (b) return b;\nelse if (c) return c;\nelse {\ne();\nreturn d;\n}\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) return b;\nelse if (c) return c;\nelse {\ne();\n\nreturn d;\n}\n}"
+        },
+        {
+            code: "function a() {\nif (b) return b;\nelse if (c) return c;\nelse {\ne(); return d;\n}\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) return b;\nelse if (c) return c;\nelse {\ne(); \n\nreturn d;\n}\n}"
         },
         {
             code: "function a() {\n while (b) {\nc();\nreturn;\n}\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\n while (b) {\nc();\n\nreturn;\n}\n}"
         },
         {
             code: "function a() {\ndo {\nc();\nreturn;\n} while (b);\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\ndo {\nc();\n\nreturn;\n} while (b);\n}"
         },
         {
             code: "function a() {\nfor (var b; b < c; b++) {\nc();\nreturn;\n}\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nfor (var b; b < c; b++) {\nc();\n\nreturn;\n}\n}"
         },
         {
             code: "function a() {\nfor (b in c) {\nd();\nreturn;\n}\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nfor (b in c) {\nd();\n\nreturn;\n}\n}"
         },
         {
             code: "function a() {\nfor (b of c) {\nd();\nreturn;\n}\n}",
             parserOptions: { ecmaVersion: 6 },
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nfor (b of c) {\nd();\n\nreturn;\n}\n}"
         },
         {
             code: "function a() {\nif (b) {\nc();\n}\n//comment\nreturn b;\n}",
-            errors: ["Expected newline before return statement."]
-        },
-        {
-            code: "function a() {\nif (b) {\nc();\n}\n//comment\nreturn b;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) {\nc();\n}\n//comment\nreturn b;\n}"
         },
         {
             code: "function a() {\n/*comment\ncomment*/\nif (b) {\nc();\nreturn b;\n} else {\n//comment\n\nreturn d;\n}\n/*multi-line\ncomment*/\nreturn e;\n}",
-            errors: ["Expected newline before return statement.", "Expected newline before return statement."]
+            errors: ["Expected newline before return statement.", "Expected newline before return statement."],
+            output: "function a() {\n/*comment\ncomment*/\nif (b) {\nc();\n\nreturn b;\n} else {\n//comment\n\nreturn d;\n}\n/*multi-line\ncomment*/\nreturn e;\n}"
         },
         {
             code: "function a() {\nif (b) { return; } //comment\nreturn c;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) { return; } //comment\n\nreturn c;\n}"
         },
         {
             code: "function a() {\nif (b) { return; } /*multi-line\ncomment*/\nreturn c;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) { return; } /*multi-line\ncomment*/\nreturn c;\n}"
         },
         {
             code: "function a() {\nif (b) { return; }\n/*multi-line\ncomment*/ return c;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) { return; }\n/*multi-line\ncomment*/ return c;\n}"
         },
         {
             code: "function a() {\nif (b) { return; } /*multi-line\ncomment*/ return c;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nif (b) { return; } /*multi-line\ncomment*/ return c;\n}"
         },
         {
             code: "var a;\nreturn;",
             parserOptions: { ecmaFeatures: { globalReturn: true } },
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "var a;\n\nreturn;"
+        },
+        {
+            code: "var a; return;",
+            parserOptions: { ecmaFeatures: { globalReturn: true } },
+            errors: ["Expected newline before return statement."],
+            output: "var a; \n\nreturn;"
         },
         {
             code: "function a() {\n{\n//comment\n}\nreturn\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\n{\n//comment\n}\n\nreturn\n}"
+        },
+        {
+            code: "function a() {\n{\n//comment\n} return\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\n{\n//comment\n} \n\nreturn\n}"
         },
         {
             code: "function a() {\nvar c;\nwhile (b) {\n c = d; //comment\n}\nreturn c;\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar c;\nwhile (b) {\n c = d; //comment\n}\n\nreturn c;\n}"
         },
         {
             code: "function a() {\nfor (var b; b < c; b++) {\nif (d) {\nbreak; //comment\n}\nreturn;\n}\n}",
-            errors: ["Expected newline before return statement."]
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nfor (var b; b < c; b++) {\nif (d) {\nbreak; //comment\n}\n\nreturn;\n}\n}"
+        },
+
+        // Testing edge cases of the fixer when the `return` statement has leading comments.
+        // https://github.com/eslint/eslint/issues/5958
+        {
+            code: "function a() {\nvar b; /*multi-line\ncomment*/\nreturn c;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; /*multi-line\ncomment*/\nreturn c;\n}"
+        },
+        {
+            code: "function a() {\nvar b;\n/*multi-line\ncomment*/ return c;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b;\n/*multi-line\ncomment*/ return c;\n}"
+        },
+        {
+            code: "function a() {\nvar b; /*multi-line\ncomment*/ return c;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; /*multi-line\ncomment*/ return c;\n}"
+        },
+        {
+            code: "function a() {\nvar b;\n//comment\nreturn;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b;\n//comment\nreturn;\n}"
+        },
+        {
+            code: "function a() {\nvar b; //comment\nreturn;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; //comment\n\nreturn;\n}"
+        },
+        {
+            code: "function a() {\nvar b;\n/* comment */ return;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b;\n/* comment */ return;\n}"
+        },
+        {
+            code: "function a() {\nvar b;\n//comment\n/* comment */ return;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b;\n//comment\n/* comment */ return;\n}"
+        },
+        {
+            code: "function a() {\nvar b; /* comment */ return;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; /* comment */ return;\n}"
+        },
+        {
+            code: "function a() {\nvar b; /* comment */\nreturn;\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; /* comment */\n\nreturn;\n}"
+        },
+        {
+            code: "function a() {\nvar b;\nreturn; //comment\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b;\n\nreturn; //comment\n}"
+        },
+        {
+            code: "function a() {\nvar b; return; //comment\n}",
+            errors: ["Expected newline before return statement."],
+            output: "function a() {\nvar b; \n\nreturn; //comment\n}"
         }
     ]
 });