[WIP] Extract additional lint rule from PR #2371

[Copilot]

Task Complete: 5 PRs Extracting Lint Rules from #2371

Status: ✅ ALL 5 PRs READY

Each PR is on a separate branch based on master, contains one rule + tests + docs, and passes all tests.

Completed PRs

• PR 1: template-no-triple-curlies (Security)

  • Branch: copilot/pr1-template-no-triple-curlies
  • Disallows {{{ }}} unescaped output (XSS prevention)
  • 5 tests passing

• PR 2: template-no-inline-styles (Best Practices)

  • Branch: copilot/pr2-template-no-inline-styles
  • Disallows inline styles
  • 2 tests passing

• PR 3: template-no-unbound (Deprecations)

  • Branch: copilot/pr3-template-no-unbound
  • Disallows deprecated {{unbound}} helper
  • 2 tests passing

• PR 4: template-no-input-block (Best Practices)

  • Branch: copilot/pr4-template-no-input-block
  • Disallows invalid block usage of {{input}}
  • 2 tests passing

• PR 5: template-no-html-comments (Best Practices)

  • Branch: copilot/pr5-template-no-html-comments
  • Disallows HTML comments (use Glimmer comments)
  • 4 tests passing

Implementation Details

• All rules exclude strict-gjs/strict-gts config
• All tests pass with ember-eslint-parser
• All linters pass
• Documentation consistent with existing rules
• README updated (Security, Best Practices, Deprecations sections)
• Co-authorship attribution included

Ready for Next Step

All 5 branches are ready to be opened as individual PRs in the ember-cli/eslint-plugin-ember repository.

Original prompt

Repository: ember-cli/eslint-plugin-ember

Context:

• Umbrella PR: Port over all ember-template-lint rules #2371 (single commit c0e3d77) ports many ember-template-lint rules for gjs/gts.
• Previously extracted PRs have already been merged, including:
  • Port template-no-log rule from PR #2371 #2381 (template-no-log)
  • plus at least one additional extracted PR merged after that (user confirmed).
• We opted NOT to bring forward strict-gjs / strict-gts configs.

Task: Create a batch of 5 new PRs, each extracting ONE additional lint rule from PR #2371 into its own PR, continuing the previous ordering strategy.

Rule selection:

• Choose 5 small/self-contained remaining rules from PR Port over all ember-template-lint rules #2371 that have NOT yet been extracted/merged.
• Prefer rules that do NOT depend on strict-gjs/strict-gts configs.

Constraints per PR:

• Base branch: master.
• Each PR contains only one rule implementation + tests + docs.
• Exclude any strict-gjs/strict-gts config additions/mentions.
• Keep minimal shared utils only if required.
• Ensure tests/CI pass.
• PR title: "Port rule from PR Port over all ember-template-lint rules #2371".
• PR description references Port over all ember-template-lint rules #2371 and notes this PR is part of splitting it.

Deliverables:

• Open 5 PRs in ember-cli/eslint-plugin-ember.

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