Configure ESLint for WebComponents templates to allow underscore-prefixed unused variables

[Copilot]

CLI-generated WebComponents apps fail lint with @typescript-eslint/no-unused-vars errors. The default @typescript-eslint/recommended config doesn't account for common Lit/WebComponents patterns where underscore-prefixed variables indicate intentional non-use.

Changes

ESLint Configuration (eslint.config.mjs)

• Added @typescript-eslint/no-unused-vars rule with argsIgnorePattern: '^_' and varsIgnorePattern: '^_' (matches Lit framework convention)
• Enabled eslint-plugin-lit with rules: no-legacy-template-syntax, no-invalid-html, no-useless-template-literals
• Replaced inline globals with globals package for browser and es2021 environments
• Updated ecmaVersion from 12 to latest

Dependencies (package.json)

• Added @eslint/eslintrc@^3.2.0 (required for FlatCompat)
• Added globals@^15.14.0

Applied to both _base and _base_with_home project templates.

Example

// ✅ Now allowed - underscore indicates intentional non-use
private _cache: Map<string, any> = new Map();
private handleEvent(_event: Event): void { /* ... */ }

// ❌ Still caught - missing underscore prefix
const unusedVar = 1;  // error: 'unusedVar' is assigned but never used

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• www.google-analytics.com
  • Triggering command: Ignite UI CLI (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Lint errors in CLI generated app for WebComponents</issue_title>
<issue_description>### Description
When you create a WC app through the CLI and you run lint test, no-unused-vars errors occur.

Steps to reproduce

1. Create a WebComponents application through the CLI
2. Install the modules
3. Run lint tests

Result

no-unused-vars errors are shown

Expected result

There should be no errors when you run the lint tests.

Attachments

</issue_description>

<agent_instructions>Let's first investigate which is the most common tool for linting a web components project. Then define which are the recommended lint rules to be set.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Lint errors in CLI generated app for WebComponents #1291

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[coveralls]

coverage: 70.369%. remained the same
when pulling 936277e on copilot/fix-lint-errors-webcomponents-app
into 549f80a on master.