Merge pull request #28 from criteo/no-indexed-access-on-enums

Add 'No indexed access on enums' rule

README.md

@@ -182,6 +182,14 @@ Why?
 
 To maintain a coherent user experience, we aim to use the classes and components from the shared component library as much as possible, as opposed to custom styles.
 
+### no-indexed-access-on-enums
+
+_Forbid accessing an enum thanks to an index: Enum[0]._
+
+Why?
+
+The names of the enum values should not be "data" in the context of the application at runtime. This brings a lack of clarity, a lack of readability, maintenance issues, and can be error-prone.
+
 ### no-ngxs-select-decorator
 
 _Forbid using the NGXS `@Select()` decorator: `@ViewSelectSnapshot()` should be preferred._
@@ -218,7 +226,7 @@ When using `.reduce()`, it may be tempting to do something like this for the sak
 const mappedById = myArray.reduce((acc, entity) => ({ ...acc, [entity.id]: entity }), {});
 ```
 
-However, spreading the accumulator at every iteration results in an operation with O(n^2) time & spatial complexity. 
+However, spreading the accumulator at every iteration results in an operation with O(n^2) time & spatial complexity.
 
 This rule helps ensure that `.reduce()` is an O(n) operation. For example:
 

lib/configs/internal/recommended.js

@@ -14,6 +14,7 @@ module.exports = {
     'criteo/filename-match-export': ['error', { removeFromFilename: ['.actions'] }],
     'criteo/no-null-undefined-comparison': 'error',
     'criteo/no-spreading-accumulators': 'error',
+    'criteo/no-indexed-access-on-enums': 'error',
     'criteo/no-todo-without-ticket': 'error',
     'eslint-comments/disable-enable-pair': ['error', { allowWholeFile: true }],
     'eslint-comments/require-description': 'error',

lib/rules/no-indexed-access-on-enums.js

@@ -0,0 +1,48 @@
+/**
+ * @fileoverview no-indexed-access-on-enums
+ * @author Connor Ullman
+ * @author Adam Perea
+ */
+'use strict';
+
+module.exports = {
+    meta: {
+        type: 'suggestion',
+        docs: {
+            description: 'Do not use indexed access on enums',
+            recommended: 'error',
+        },
+        messages: {
+            failure: 'Indexed accesses on an enum are almost always a mistake, as the names of the enum values should not be "data" in the context of the application at runtime.',
+        },
+        schema: [],
+    },
+
+  create(context) {
+    return {
+        MemberExpression(node) {
+            const parserServices = context.parserServices;
+            if (!parserServices) return;
+
+            const checker = parserServices.program?.getTypeChecker();
+            if (!checker) return;
+
+            if (!node.computed) return;
+
+            const objectNode = parserServices.esTreeNodeToTSNodeMap.get(node.object);
+            const objectSymbol = checker.getSymbolAtLocation(objectNode);
+            if (!objectSymbol) return;
+
+            const enumSymbol =
+            ts.SymbolFlags.Alias & objectSymbol.flags ? checker.getAliasedSymbol(objectSymbol) : objectSymbol;
+            const isEnum = ts.SymbolFlags.Enum & enumSymbol.flags;
+            if (!isEnum) return;
+
+            context.report({
+            node,
+            messageId: 'failure',
+            });
+        },
+        };
+  },
+};