feat: implement unnecessaryTemplateExpressions rule (TypeScript)

[Copilot]

Implements unnecessaryTemplateExpressions rule to detect template literals containing only a single substitution with no surrounding text.

Rule Behavior

Flags template expressions like `${value}` that add unnecessary syntax noise:

// ❌ Flagged
const name = "Alice";
const greeting = `${name}`;

const count = 42;
const message = `${count}`;

// ✅ Valid
const greeting = `Hello, ${name}!`;
const fullName = `${first} ${last}`;

Changes

• Rule implementation: packages/ts/src/rules/unnecessaryTemplateExpressions.ts - visitor on TemplateExpression nodes checking for single span with empty head and tail
• Tests: packages/ts/src/rules/unnecessaryTemplateExpressions.test.ts - 12 test cases covering variables, function calls, and edge cases
• Documentation: packages/site/src/content/docs/rules/ts/unnecessaryTemplateExpressions.mdx
• Plugin registration: Added to packages/ts/src/plugin.ts in alphabetical order
• Comparisons data: Marked as "status": "implemented" in packages/comparisons/src/data.json
• Dogfooding: Fixed 2 violations in packages/typescript-language/src/convertTypeScriptDiagnosticToLanguageFileDiagnostic.ts

Rule preset: logical and logicalStrict

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:

• typescript-eslint.io
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (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>🚀 Feature: Implement unnecessaryTemplateExpressions rule (TypeScript)</issue_title>
<issue_description>### Feature Request Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Per flint.fyi/rules, Flint is intended to have a unnecessaryTemplateExpressions rule in the TypeScript plugin (ts). It'll behave roughly equivalently to the existing implementations in other linters to start. This issue tracks adding that rule.

Adding this rule will entail creating the following new source files:

• packages/ts/src/rules/unnecessaryTemplateExpressions.ts: implementation of the rule itself
• packages/ts/src/rules/unnecessaryTemplateExpressions.test.ts: tests for the rule
• packages/site/src/content/docs/rules/ts/unnecessaryTemplateExpressions.mdx: documentation of the rule

Additionally, the following files will need to be edited:

• packages/comparisons/src/data.json: Comparisons data will need to mention the rule is now "status": "implemented"
• packages/ts/src/plugin.ts: Included rules should have the new one inserted in alphabetical order

Additional Info

Existing rules in other linters:

• Biome: noUnusedTemplateLiteral
• ESLint: @typescript-eslint/no-unnecessary-template-expression
• Oxlint: typescript/no-unnecessary-template-expression

❤️‍🔥</issue_description>

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

• Fixes 🚀 Feature: Implement unnecessaryTemplateExpressions rule (TypeScript) #2237

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Project	Deployment	Actions	Updated (UTC)
flint	Ready	Preview, Comment	Feb 1, 2026 9:18pm

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