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no-chain-coalescence-mixture

Disallow mixing optional chaining and nullish coalescing in one expression.

Targeted pattern scope​

This rule reports LogicalExpression nodes using ?? where the left-hand side is an optional chain (ChainExpression).

In practice, it flags patterns like obj?.value ?? fallback.

What this rule reports​

This rule reports expressions like foo?.bar ?? fallback.

Why this rule exists​

Combining optional chaining and nullish coalescing inline can hide intent and make intermediate values harder to debug. Splitting steps improves readability.

❌ Incorrect​

foo?.bar ?? fallback;

✅ Correct​

foo?.bar;
foo ?? fallback;
const value = foo?.bar;
const result = value ?? fallback;

Behavior and migration notes​

This rule reports only and does not provide an autofix.

Typical migration is introducing an intermediate variable before applying ??.

Options​

This rule has no options.

Additional examples​

const title = config?.labels?.title ?? "Untitled";
// ❌ reported

const maybeTitle = config?.labels?.title;
const titleSafe = maybeTitle ?? "Untitled";
// ✅ valid

ESLint flat config example​

import etcMisc from "eslint-plugin-etc-misc";

export default [
 {
  plugins: { "etc-misc": etcMisc },
  rules: {
   "etc-misc/no-chain-coalescence-mixture": "error",
  },
 },
];

When not to use it​

Disable this rule if your project permits ?. and ?? in the same expression.

Package documentation​

Rule catalog ID: R019

Further reading​

Adoption resources​

  • Start at warning level in CI, then move to error after cleanup.
  • Use focused codemods/autofix batches per package or directory.