Added a rule to R.cond warning if the last condition is not a R.T.

README.md

@@ -34,6 +34,7 @@ Configure it in `package.json`.
       "ramda/complement-simplification": "error",
       "ramda/compose-pipe-style": "error",
       "ramda/compose-simplification": "error",
+      "ramda/cond-default": "error",
       "ramda/cond-simplification": "error",
       "ramda/either-simplification": "error",
       "ramda/eq-by-simplification": "error",
@@ -67,6 +68,7 @@ Configure it in `package.json`.
 - `complement-simplification` - Forbids confusing `complement`, suggesting a better one
 - `compose-pipe-style` - Enforces `compose` for single line expression and `pipe` for multiline
 - `compose-simplification` - Detects when a function that has the same behavior already exists
+- `cond-default` - Enforces `cond` having `R.T` as the last condition
 - `cond-simplification` - Forbids using `cond` when `ifElse`, `either` or `both` fits
 - `either-simplification` - Suggests transforming negated `either` conditions on negated `both`
 - `eq-by-simplification` - Forbids `eqBy(prop(_))` and suggests `eqProps`

rules/cond-default.js

@@ -0,0 +1,43 @@
+'use strict';
+const R = require('ramda');
+const ast = require('../ast-helper');
+
+const isCalling = ast.isCalling;
+const isRamdaMethod = ast.isRamdaMethod;
+
+const create = context => ({
+    CallExpression(node) {
+        const match = isCalling({
+            name: 'cond',
+            arguments: R.tryCatch(
+                R.pipe(
+                    R.head,
+                    R.prop('elements'),
+                    R.last,
+                    R.prop('elements'),
+                    R.head,
+                    isRamdaMethod('T'),
+                    R.not
+                ),
+                R.F
+            )
+        });
+
+        if (match(node)) {
+            context.report({
+                node,
+                message: '`cond` should finish with a `T` condition so it returns a default value'
+            });
+        }
+    }
+});
+
+module.exports = {
+    create,
+    meta: {
+        docs: {
+            description: '`cond` default, like suggesting returning a default value',
+            recommended: 'error'
+        }
+    }
+};

test/cond-default.js

@@ -0,0 +1,37 @@
+import test from 'ava';
+import avaRuleTester from 'eslint-ava-rule-tester';
+import rule from '../rules/cond-default';
+
+const ruleTester = avaRuleTester(test, {
+    env: {
+        es6: true
+    },
+    parserOptions: {
+        sourceType: 'module'
+    }
+});
+
+const error = {
+    ruleId: 'cond-default',
+    message: '`cond` should finish with a `T` condition so it returns a default value'
+};
+
+ruleTester.run('cond-default', rule, {
+    valid: [
+        'cond([[a, b], [T, d]])',
+        'R.cond([[a, b], [R.T, d]])',
+        'cond([[a, b], [c, d], [T, f]])',
+        'R.cond([[a, b], [c, d], [R.T, f]])',
+        'cond(anything)'
+    ],
+    invalid: [
+        {
+            code: 'cond([[a, b], [c, d]])',
+            errors: [error]
+        },
+        {
+            code: 'cond([[a, b], [c, d], [e, f]])',
+            errors: [error]
+        }
+    ]
+});