Update: improve canFix() logic and add more tests (refs eslint#5958)

lib/rules/newline-before-return.js

@@ -15,9 +15,7 @@ module.exports = {
             category: "Stylistic Issues",
             recommended: false
         },
-
         fixable: "whitespace",
-
         schema: []
     },
 
@@ -106,8 +104,9 @@ module.exports = {
 
         /**
          * Returns the line number of the token before the node that is passed in as an argument
-         * @param {ASTNode} node - node from
+         * @param {ASTNode} node - The node to use as the start of the calculation
          * @returns {number} Line number of the token before `node`
+         * @private
          */
         function getLineNumberOfTokenBefore(node) {
             const tokenBefore = sourceCode.getTokenBefore(node);
@@ -154,16 +153,30 @@ module.exports = {
          *
          * @param {ASTNode} node - The return statement node to check.
          * @returns {boolean} `true` if it can fix the node.
+         * @private
          */
         function canFix(node) {
-            const lineNumTokenBefore = getLineNumberOfTokenBefore(node);
-            const tokenHasComments = calcCommentLines(node, lineNumTokenBefore) > 0;
+            const leadingComments = sourceCode.getComments(node).leading;
+            const lastLeadingComment = leadingComments[leadingComments.length - 1];
+            const tokenBefore = sourceCode.getTokenBefore(node);
+
+            if (leadingComments.length === 0) {
+                return true;
+            }
 
-            if (tokenHasComments) {
-                return false;
+            // 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 true;
+            return false;
         }
 
         //--------------------------------------------------------------------------

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

@@ -110,6 +110,11 @@ 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; \nreturn;\n}"
+        },
         {
             code: "function a() {\nvar b;\nreturn;\n}",
             errors: ["Expected newline before return statement."],
@@ -174,7 +179,7 @@ ruleTester.run("newline-before-return", rule, {
         {
             code: "function a() {\nif (b) { return; } /*multi-line\ncomment*/ return c;\n}",
             errors: ["Expected newline before return statement."],
-            output: "function a() {\nif (b) { return; } /*multi-line\ncomment*/ \nreturn c;\n}"
+            output: "function a() {\nif (b) { return; } /*multi-line\ncomment*/ return c;\n}"
         },
         {
             code: "var a;\nreturn;",
@@ -196,6 +201,59 @@ ruleTester.run("newline-before-return", rule, {
             code: "function a() {\nfor (var b; b < c; b++) {\nif (d) {\nbreak; //comment\n}\nreturn;\n}\n}",
             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}"
         }
     ]
 });