afv-library/skills/dx-code-analyzer-custom-rule-create/references/eslint-tier3-custom-plugins.md

ESLint Tier 3: Custom Plugins

← Back to ESLint Rules Discovery

Tier 3: Custom Plugins (LAST RESORT)

Only create a custom ESLint plugin when:

• ❌ No built-in rule exists (checked Tier 1)
• ❌ No configurable rule can express the pattern (checked Tier 2 — see eslint-tier2-configurable.md)
• ✅ The pattern requires checking multiple AST nodes with complex logic
• ✅ The pattern is domain-specific to your codebase

Examples that justify custom plugins:

• "Flag LWC components with @api properties but no input validation in connectedCallback"
• "Detect imperative Apex calls without error handling (import + .then() without .catch())"
• "Enforce naming conventions on specific decorator patterns"

See: eslint-custom-plugins.md for the plugin creation guide.

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Tier-by-Tier Worked Examples

Tier 2 worked examples (banning globals, restricting syntax, restricting properties) live in eslint-tier2-configurable.md. The examples below cover Tier 1 (built-in rules and the LWC plugin) so the discovery → configure → validate flow is documented end-to-end.

Example 1: "Ban console.log" (Tier 1 — built-in)

User Request: "Create a rule to ban console.log in LWC"

Discovery:

$ sf code-analyzer rules --rule-selector eslint | grep -i console
eslint:no-console  disallow the use of console

Result: Built-in rule exists. ✅

Configuration:

// eslint.config.js
module.exports = [
  {
    files: ["**/lwc/**/*.js"],
    rules: {
      "no-console": "error"
    }
  }
];

Validation:

sf code-analyzer rules --rule-selector eslint:no-console
# Should show: eslint:no-console | error | ...

Test:

sf code-analyzer run --rule-selector eslint:no-console --target lwc/

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Example 2: "Ban innerHTML" (Tier 1 — LWC plugin)

User Request: "Ban innerHTML in LWC for XSS prevention"

Discovery:

$ sf code-analyzer rules --rule-selector eslint | grep -i inner
@lwc/lwc/no-inner-html  disallow use of innerHTML

Result: LWC plugin rule exists. ✅

Configuration:

// eslint.config.js
module.exports = [
  {
    files: ["**/lwc/**/*.js"],
    rules: {
      "@lwc/lwc/no-inner-html": "error"
    }
  }
];

Validation:

sf code-analyzer rules --rule-selector eslint:@lwc/lwc/no-inner-html

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Example 3: "Enforce === over ==" (Tier 1 — built-in)

User Request: "Enforce strict equality checks"

Discovery:

$ sf code-analyzer rules --rule-selector eslint | grep -i equal
eslint:eqeqeq  require the use of === and !==

Result: Built-in rule eqeqeq exists. ✅

Configuration:

rules: {
  "eqeqeq": ["error", "always"]
}