afv-library/skills/dx-code-analyzer-custom-rule-create/references/eslint-rules-discovery.md

ESLint Rules Discovery & Configuration

READ THIS FIRST for ANY ESLint request. 90% of ESLint rules already exist — this guide shows you how to find and configure them instead of creating custom plugins.

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Three Tiers of ESLint Rules

Tier	What It Is	When to Use	Effort	Coverage
Tier 1: Built-In Rules	200+ core ESLint rules	First choice — check here FIRST	LOW (enable in config)	70% of requests
Tier 2: Configurable Rules	no-restricted-syntax, no-restricted-globals, no-restricted-properties	When no built-in rule exists but pattern is generic	MEDIUM (AST selector)	20% of requests
Tier 3: Custom Plugins	Write your own ESLint plugin	LAST RESORT — domain-specific multi-node patterns only	HIGH (Node code, testing)	10% of requests

Always start at Tier 1 and work down.

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Tier 1: Discover Built-In Rules

Discovery Workflow (MANDATORY)

Before creating ANY custom ESLint rule:

1. Run: sf code-analyzer rules --rule-selector eslint
2. Search output for keywords from the user's request:
   • User says "ban console.log" → search for "console"
   • User says "enforce ===" → search for "equal" or "strict"
   • User says "no unused variables" → search for "unused"
3. Check naming patterns:
   • no-* — Disallow something (no-console, no-debugger, no-eval)
   • prefer-* — Prefer one style (prefer-const, prefer-arrow-callback)
   • require-* — Require something (require-await, require-yield)
   • @lwc/lwc/* — LWC-specific rules (no-inner-html, no-document-query)
4. If found: Configure it (see "Configuration Workflow" below). STOP — do NOT create a custom plugin.
5. If NOT found: Proceed to Tier 2.

Common Built-In Rules by Category

Code Quality

User Request	Rule Name	Config Example
"No unused variables"	no-unused-vars	"no-unused-vars": "error"
"No unused imports"	no-unused-vars	Same rule covers imports
"Require await in async functions"	require-await	"require-await": "error"
"No empty blocks"	no-empty	"no-empty": "error"
"No unreachable code"	no-unreachable	"no-unreachable": "error"

Security

User Request	Rule Name	Config Example
"Ban eval()"	no-eval	"no-eval": "error"
"Ban debugger"	no-debugger	"no-debugger": "error"
"No implied eval"	no-implied-eval	"no-implied-eval": "error"
"Ban alert()"	no-alert	"no-alert": "error"

Best Practices

User Request	Rule Name	Config Example
"Enforce ==="	eqeqeq	"eqeqeq": ["error", "always"]
"Prefer const"	prefer-const	"prefer-const": "error"
"No var"	no-var	"no-var": "error"
"Prefer arrow functions"	prefer-arrow-callback	"prefer-arrow-callback": "error"
"Require default in switch"	default-case	"default-case": "error"

Logging/Debugging

User Request	Rule Name	Config Example
"Ban console.log"	no-console	"no-console": "error"
"Ban console.* except error"	no-console	"no-console": ["error", { "allow": ["error", "warn"] }]

LWC Plugin Rules (Check if Available)

If Code Analyzer has @lwc/eslint-plugin-lwc enabled:

User Request	Rule Name	Notes
"Ban innerHTML"	@lwc/lwc/no-inner-html	XSS prevention
"No document.querySelector"	@lwc/lwc/no-document-query	Use template queries
"Validate @api usage"	@lwc/lwc/no-api-reassignments	Prevents reassigning @api properties
"Validate @wire syntax"	@lwc/lwc/valid-wire	Built-in
"No async in getters"	@lwc/lwc/no-async-operation	Lifecycle hook validation

Check availability:

sf code-analyzer rules --rule-selector eslint | grep -i "@lwc"

External Documentation

• All ESLint built-in rules: https://eslint.org/docs/latest/rules/
• LWC ESLint plugin: https://github.com/salesforce/eslint-plugin-lwc
• Salesforce Lightning plugin: https://github.com/forcedotcom/eslint-plugin-lightning

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Configuration Workflow (Tier 1)

When a built-in rule exists:

1. Create eslint.config.js if it doesn't exist:

   module.exports = [
     {
       files: ["**/lwc/**/*.js"],  // or ["**/*.js"] for all JS files
       rules: {
         // Rules go here
       }
     }
   ];
   

2. Add the rule with desired severity:

   rules: {
     "no-console": "error",              // Ban completely
     "eqeqeq": ["error", "always"],      // With options
     "no-unused-vars": ["warn"]          // Warning instead of error
   }
   

3. Update code-analyzer.yml (AFTER file exists):

   engines:
     eslint:
       eslint_config_file: "eslint.config.js"
   

4. Validate:

   sf code-analyzer rules --rule-selector eslint:no-console
   

   If the rule does NOT appear in the output, the config is wrong. Do NOT proceed to testing.

5. Test positive:

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

6. Test negative: Run against clean code, confirm 0 violations.

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Tier 2 and Tier 3: Configurable Rules and Custom Plugins

For detailed information on these tiers:

Tier	File	When to Use
Tier 2: Configurable Rules	eslint-tier2-configurable.md	no-restricted-globals, no-restricted-syntax, no-restricted-properties — ban specific patterns without writing plugins
Tier 3: Custom Plugins	eslint-tier3-custom-plugins.md	Complete examples for all tiers + when to create custom plugins (LAST RESORT)

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Decision Tree

User asks for ESLint rule
    ↓
Run: sf code-analyzer rules --rule-selector eslint
    ↓
Search output for keywords
    ↓
    ├─ Built-in rule found? → Configure it (Tier 1) → DONE ✅
    │
    ├─ Pattern is "ban function X"? → Use no-restricted-globals (Tier 2) → DONE ✅
    │
    ├─ Pattern is "ban syntax Y"? → Use no-restricted-syntax (Tier 2) → DONE ✅
    │
    └─ Complex multi-node pattern? → Create custom plugin (Tier 3) → See eslint-custom-plugins.md

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Key Rules

1. ALWAYS run discovery FIRST — 90% of requests are Tier 1 or Tier 2
2. NEVER create a custom plugin without checking built-in rules — this is a skill failure
3. VALIDATE after configuration — sf code-analyzer rules --rule-selector eslint:<name> must show the rule
4. TEST both positive and negative samples — confirm violations are caught AND clean code passes

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When to Read Other References

• All ESLint requests start here (discovery)
• If Tier 3 custom plugin needed: Read references/eslint-custom-plugins.md
• If troubleshooting config issues: Read references/troubleshooting.md (ESLint section)