Update: add allowElseIf option to no-else-return (fixes #9228) (#9229)

docs/rules/no-else-return.md

@@ -16,6 +16,23 @@ function foo() {
 
 This rule is aimed at highlighting an unnecessary block of code following an `if` containing a return statement. As such, it will warn when it encounters an `else` following a chain of `if`s, all of them containing a `return` statement.
 
+## Options
+
+This rule has an object option:
+
+```json
+{
+    "no-else-return": ["error", { "allowElseIf": true }],
+    // or
+    "no-else-return": ["error", { "allowElseIf": false }]
+}
+```
+
+* `allowElseIf: true` (default) allows `else if` blocks after a return
+* `allowElseIf: false` disallows `else if` blocks after a return
+
+### `allowElseIf: true`
+
 Examples of **incorrect** code for this rule:
 
 ```js
@@ -49,6 +66,16 @@ function foo() {
     return t;
 }
 
+function foo() {
+    if (error) {
+        return 'It failed';
+    } else {
+        if (loading) {
+            return "It's still loading";
+        }
+    }
+}
+
 // Two warnings for nested occurrences
 function foo() {
     if (x) {
@@ -95,4 +122,44 @@ function foo() {
         return z;
     }
 }
+
+function foo() {
+    if (error) {
+        return 'It failed';
+    } else if (loading) {
+        return "It's still loading";
+    }
+}
+```
+
+### `allowElseIf: false`
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint no-else-return: ["error", {allowElseIf: false}]*/
+
+function foo() {
+    if (error) {
+        return 'It failed';
+    } else if (loading) {
+        return "It's still loading";
+    }
+}
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint no-else-return: ["error", {allowElseIf: false}]*/
+
+function foo() {
+    if (error) {
+        return 'It failed';
+    }
+
+    if (loading) {
+        return "It's still loading";
+    }
+}
 ```

lib/ast-utils.js

@@ -1041,7 +1041,8 @@ module.exports = {
         } else if (parent.type === "Property" || parent.type === "MethodDefinition") {
             if (parent.kind === "constructor") {
                 return "constructor";
-            } else if (parent.kind === "get") {
+            }
+            if (parent.kind === "get") {
                 tokens.push("getter");
             } else if (parent.kind === "set") {
                 tokens.push("setter");

lib/cli.js

@@ -152,7 +152,8 @@ const cli = {
             if (files.length) {
                 log.error("The --print-config option must be used with exactly one file name.");
                 return 1;
-            } else if (text) {
+            }
+            if (text) {
                 log.error("The --print-config option is not available for piped-in code.");
                 return 1;
             }

lib/formatters/html.js

@@ -51,7 +51,8 @@ function renderSummary(totalErrors, totalWarnings) {
 function renderColor(totalErrors, totalWarnings) {
     if (totalErrors !== 0) {
         return 2;
-    } else if (totalWarnings !== 0) {
+    }
+    if (totalWarnings !== 0) {
         return 1;
     }
     return 0;

lib/rules/callback-return.js

@@ -60,7 +60,8 @@ module.exports = {
             if (node.type === "MemberExpression") {
                 if (node.object.type === "Identifier") {
                     return true;
-                } else if (node.object.type === "MemberExpression") {
+                }
+                if (node.object.type === "MemberExpression") {
                     return containsOnlyIdentifiers(node.object);
                 }
             }

lib/rules/capitalized-comments.js

@@ -247,7 +247,8 @@ module.exports = {
 
             if (capitalize === "always" && isLowercase) {
                 return false;
-            } else if (capitalize === "never" && isUppercase) {
+            }
+            if (capitalize === "never" && isUppercase) {
                 return false;
             }
 

lib/rules/new-cap.js

@@ -178,7 +178,8 @@ module.exports = {
 
                 // char has no uppercase variant, so it's non-alphabetic
                 return "non-alpha";
-            } else if (firstChar === firstCharLower) {
+            }
+            if (firstChar === firstCharLower) {
                 return "lower";
             }
             return "upper";

lib/rules/newline-before-return.js

@@ -59,9 +59,11 @@ module.exports = {
 
             if (parentType === "IfStatement") {
                 return isPrecededByTokens(node, ["else", ")"]);
-            } else if (parentType === "DoWhileStatement") {
+            }
+            if (parentType === "DoWhileStatement") {
                 return isPrecededByTokens(node, ["do"]);
-            } else if (parentType === "SwitchCase") {
+            }
+            if (parentType === "SwitchCase") {
                 return isPrecededByTokens(node, [":"]);
             }
             return isPrecededByTokens(node, [")"]);

lib/rules/no-alert.js

@@ -71,7 +71,8 @@ function isShadowed(scope, node) {
 function isGlobalThisReferenceOrGlobalWindow(scope, node) {
     if (scope.type === "global" && node.type === "ThisExpression") {
         return true;
-    } else if (node.name === "window") {
+    }
+    if (node.name === "window") {
         return !isShadowed(scope, node);
     }
 

lib/rules/no-control-regex.js

@@ -31,7 +31,8 @@ module.exports = {
         function getRegExp(node) {
             if (node.value instanceof RegExp) {
                 return node.value;
-            } else if (typeof node.value === "string") {
+            }
+            if (typeof node.value === "string") {
 
                 const parent = context.getAncestors().pop();
 

lib/rules/no-else-return.js

@@ -24,8 +24,15 @@ module.exports = {
             recommended: false
         },
 
-        schema: [],
-
+        schema: [{
+            type: "object",
+            properties: {
+                allowElseIf: {
+                    type: "boolean"
+                }
+            },
+            additionalProperties: false
+        }],
         fixable: "code"
     },
 
@@ -134,13 +141,13 @@ module.exports = {
 
         /**
          * Check to see if the node is valid for evaluation,
-         * meaning it has an else and not an else-if
+         * meaning it has an else.
          *
          * @param {Node} node The node being evaluated
          * @returns {boolean} True if the node is valid
          */
         function hasElse(node) {
-            return node.alternate && node.consequent && node.alternate.type !== "IfStatement";
+            return node.alternate && node.consequent;
         }
 
         /**
@@ -189,14 +196,15 @@ module.exports = {
             return checkForReturnOrIf(node);
         }
 
+
         /**
-         * Check the if statement
+         * Check the if statement, but don't catch else-if blocks.
          * @returns {void}
          * @param {Node} node The node for the if statement to check
          * @private
          */
-        function IfStatement(node) {
-            const parent = context.getAncestors().pop();
+        function checkIfWithoutElse(node) {
+            const parent = node.parent;
             let consequents,
                 alternate;
 
@@ -221,13 +229,40 @@ module.exports = {
             }
         }
 
+        /**
+         * Check the if statement
+         * @returns {void}
+         * @param {Node} node The node for the if statement to check
+         * @private
+         */
+        function checkIfWithElse(node) {
+            const parent = node.parent;
+
+
+            /*
+             * Fixing this would require splitting one statement into two, so no error should
+             * be reported if this node is in a position where only one statement is allowed.
+             */
+            if (!astUtils.STATEMENT_LIST_PARENTS.has(parent.type)) {
+                return;
+            }
+
+            const alternate = node.alternate;
+
+            if (alternate && alwaysReturns(node.consequent)) {
+                displayReport(alternate);
+            }
+        }
+
+        const allowElseIf = !(context.options[0] && context.options[0].allowElseIf === false);
+
         //--------------------------------------------------------------------------
         // Public API
         //--------------------------------------------------------------------------
 
         return {
 
-            "IfStatement:exit": IfStatement
+            "IfStatement:exit": allowElseIf ? checkIfWithoutElse : checkIfWithElse
 
         };
 

lib/rules/no-extra-parens.js

@@ -195,10 +195,12 @@ module.exports = {
         function containsAssignment(node) {
             if (node.type === "AssignmentExpression") {
                 return true;
-            } else if (node.type === "ConditionalExpression" &&
+            }
+            if (node.type === "ConditionalExpression" &&
                     (node.consequent.type === "AssignmentExpression" || node.alternate.type === "AssignmentExpression")) {
                 return true;
-            } else if ((node.left && node.left.type === "AssignmentExpression") ||
+            }
+            if ((node.left && node.left.type === "AssignmentExpression") ||
                     (node.right && node.right.type === "AssignmentExpression")) {
                 return true;
             }
@@ -219,7 +221,8 @@ module.exports = {
 
             if (node.type === "ReturnStatement") {
                 return node.argument && containsAssignment(node.argument);
-            } else if (node.type === "ArrowFunctionExpression" && node.body.type !== "BlockStatement") {
+            }
+            if (node.type === "ArrowFunctionExpression" && node.body.type !== "BlockStatement") {
                 return containsAssignment(node.body);
             }
             return containsAssignment(node);

lib/rules/no-mixed-requires.js

@@ -104,14 +104,16 @@ module.exports = {
 
                 // "var x = require('util');"
                 return DECL_REQUIRE;
-            } else if (allowCall &&
+            }
+            if (allowCall &&
                 initExpression.type === "CallExpression" &&
                 initExpression.callee.type === "CallExpression"
             ) {
 
                 // "var x = require('diagnose')('sub-module');"
                 return getDeclarationType(initExpression.callee);
-            } else if (initExpression.type === "MemberExpression") {
+            }
+            if (initExpression.type === "MemberExpression") {
 
                 // "var x = require('glob').Glob;"
                 return getDeclarationType(initExpression.object);
@@ -131,7 +133,8 @@ module.exports = {
 
                 // "var x = require('glob').Glob;"
                 return inferModuleType(initExpression.object);
-            } else if (initExpression.arguments.length === 0) {
+            }
+            if (initExpression.arguments.length === 0) {
 
                 // "var x = require();"
                 return REQ_COMPUTED;
@@ -149,7 +152,8 @@ module.exports = {
 
                 // "var fs = require('fs');"
                 return REQ_CORE;
-            } else if (/^\.{0,2}\//.test(arg.value)) {
+            }
+            if (/^\.{0,2}\//.test(arg.value)) {
 
                 // "var utils = require('./utils');"
                 return REQ_FILE;

lib/rules/sort-imports.js

@@ -67,9 +67,11 @@ module.exports = {
         function usedMemberSyntax(node) {
             if (node.specifiers.length === 0) {
                 return "none";
-            } else if (node.specifiers[0].type === "ImportNamespaceSpecifier") {
+            }
+            if (node.specifiers[0].type === "ImportNamespaceSpecifier") {
                 return "all";
-            } else if (node.specifiers.length === 1) {
+            }
+            if (node.specifiers.length === 1) {
                 return "single";
             }
             return "multiple";

lib/util/source-code.js

@@ -332,7 +332,8 @@ class SourceCode extends TokenStore {
                     }
 
                     return parent && parent.type !== "FunctionDeclaration" && parent.type !== "Program" ? findJSDocComment(parentLeadingComments, parent.loc.start.line) : null;
-                } else if (leadingComments.length) {
+                }
+                if (leadingComments.length) {
                     return findJSDocComment(leadingComments, node.loc.start.line);
                 }
 

packages/eslint-config-eslint/default.yml

@@ -51,7 +51,7 @@ rules:
     no-confusing-arrow: "error"
     no-console: "error"
     no-delete-var: "error"
-    no-else-return: "error"
+    no-else-return: ["error", { allowElseIf: false }]
     no-eval: "error"
     no-extend-native: "error"
     no-extra-bind: "error"

tests/lib/linter.js

@@ -20,7 +20,8 @@
 function compatRequire(name, windowName) {
     if (typeof window === "object") {
         return window[windowName || name];
-    } else if (typeof require === "function") {
+    }
+    if (typeof require === "function") {
         return require(name);
     }
     throw new Error(`Cannot find object '${name}'.`);