Fix: prevent fixing to incorrect code (fixes #11069)

lib/rules/no-else-return.js

@@ -12,6 +12,35 @@
 const astUtils = require("../util/ast-utils");
 const FixTracker = require("../util/fix-tracker");
 
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+const BLOCK_SCOPED_DECLARATION = /^(?:VariableDeclarator|ClassDeclaration)$/;
+
+/**
+ *
+ * @param {*} scope  current scope
+ * @param {Token} startToken s
+ * @param {Token} endToken s
+ * @returns {boolean} s
+ */
+function blockScopeDeclaration(scope, startToken, endToken) {
+
+    return scope.childScopes.some(childScope => {
+        const {
+            start,
+            end
+        } = childScope.block;
+
+        const elseBranch =
+            start === startToken.start && end === endToken.end;
+
+        return elseBranch ? childScope.variables.some(variable => BLOCK_SCOPED_DECLARATION.test(variable.defs[0].node.type)) : false;
+    });
+}
+
+
 //------------------------------------------------------------------------------
 // Rule Definition
 //------------------------------------------------------------------------------
@@ -88,6 +117,11 @@ module.exports = {
                     }
 
                     const endToken = sourceCode.getLastToken(node);
+
+                    if (blockScopeDeclaration(context.getScope(), startToken, endToken)) {
+                        return null;
+                    }
+
                     const lastTokenOfElseBlock = sourceCode.getTokenBefore(endToken);
 
                     if (lastTokenOfElseBlock.value !== ";") {

tests/lib/rules/no-else-return.js

@@ -182,6 +182,32 @@ ruleTester.run("no-else-return", rule, {
             output: "function foo21() { var x = true; if (x) { return x; } if (x === false) { return false; } }",
             options: [{ allowElseIf: false }],
             errors: [{ messageId: "unexpected", type: "IfStatement" }]
+        },
+        {
+            code: "function foo() { if (true) { return bar; } else { const baz = 1;  return baz; } }",
+            output: null,
+            parserOptions: { ecmaVersion: 6 },
+            errors: [{ messageId: "unexpected", type: "BlockStatement" }]
+        },
+        {
+            code: "function foo() { if (true) { return bar; } else { let baz = 1;  return baz; } }",
+            output: null,
+            parserOptions: { ecmaVersion: 6 },
+            errors: [{ messageId: "unexpected", type: "BlockStatement" }]
+        },
+        {
+            code: "function foo() { let bar = true; if (baz) { return; } else { let bar = false;  return; } }",
+            output: null,
+            parserOptions: { ecmaVersion: 6 },
+            errors: [{ messageId: "unexpected", type: "BlockStatement" }]
+        },
+        {
+            code: "function foo() { let bar = true; if (baz) { return baz; } else { { let bar = false; }  return bar; } }",
+            output: "function foo() { let bar = true; if (baz) { return baz; }  { let bar = false; }  return bar;  }",
+            parserOptions: { ecmaVersion: 6 },
+            errors: [
+                { messageId: "unexpected", type: "BlockStatement" }
+            ]
         }
     ]
 });