Fix escaped-mustache highlighting for odd backslash runs

[daaain]

Background

Follow-up to #116, which added highlighting for escaped mustaches (\{{foo}}). A review comment on that PR pointed out that it fails on \\\{{foo}} and asked for a rule for escaped backslashes.

The bug

The escaped_expression rule used a negative lookbehind (?<!\\) to avoid treating a double backslash (\\{{foo}}) as a mustache escape. That handles one-vs-two backslashes, but whether a mustache is escaped actually depends on the parity of the whole backslash run in front of it — because backslashes escape each other too:

Input	Backslashes	Meaning	Before
\{{foo}}	1 (odd)	escaped mustache	✅ escaped
\\{{foo}}	2 (even)	escaped backslash, mustache evaluates	✅ evaluates
\\\{{foo}}	3 (odd)	escaped backslash + escaped mustache	❌ wrongly evaluated
\\\\{{foo}}	4 (even)	two escaped backslashes, mustache evaluates	✅ evaluates

So \\\{{foo}} was highlighted as a live expression when it should render literally.

The fix

Add an escaped_backslash rule that matches each \\ pair leading up to a mustache and scopes it as constant.character.escape.handlebars. Since those pairs are consumed first, escaped_expression only ever sees the lone leftover backslash of an odd-length run:

• odd run → a backslash is left over → mustache is escaped
• even run → no backslash left → mustache evaluates

This matches Handlebars semantics for any number of backslashes, so the lookbehind is no longer needed and is dropped. The new rule's lookahead ((?=\\*\{{2,3})) keeps bare backslashes in plain text — e.g. Windows paths — from being highlighted as escapes.

Wired into the main patterns and the inline <script> template body across all three grammar files (Handlebars.json, Handlebars.sublime-syntax, Handlebars.tmLanguage).

Tests

Extends test/escaping.test.js with coverage for three- and four-backslash runs, escaped-backslash highlighting, and bare backslashes in text. Full suite passes (57 tests).

🤖 Generated with Claude Code

https://claude.ai/code/session_011RgLiYPtaei9qTBqYbAGeN

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Generated by Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Improved syntax highlighting for Handlebars expressions preceded by backslashes.
  • Correctly distinguishes escaped mustaches from literal backslash pairs.
  • Handles odd and even backslash sequences consistently, including within inline scripts.

• Tests

  • Expanded coverage for single, double, triple, and quadruple backslash escape scenarios.
  • Verified that unrelated backslashes are not incorrectly highlighted.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 105148a1-7b19-452f-9c8d-566105ca83c2

📥 Commits

Reviewing files that changed from the base of the PR and between a5aa65d and 0ffd0a2.

📒 Files selected for processing (4)

• grammars/Handlebars.json
• grammars/Handlebars.sublime-syntax
• grammars/Handlebars.tmLanguage
• test/escaping.test.js

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📝 Walkthrough

Walkthrough

The Handlebars grammars now parse escaped backslash pairs separately from escaped mustaches across JSON, Sublime, and TextMate formats. Escaping tests cover odd and even backslash parity, escape scopes, and unrelated backslashes.

Changes

Handlebars escaping

Layer / File(s)	Summary
Separate escaped backslash parsing grammars/Handlebars.json, grammars/Handlebars.sublime-syntax, grammars/Handlebars.tmLanguage	Adds escaped_backslash handling before escaped_expression in top-level and embedded inline-script parsing, replacing the previous negative-lookbehind behavior.
Backslash parity coverage test/escaping.test.js	Tests double-, triple-, and quadruple-backslash runs, escaped-backslash scopes, mustache tokenization, and backslashes not preceding mustaches.

Estimated code review effort: 2 (Simple) | ~15 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: fixing escaped-mustache highlighting for odd backslash runs.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/handlebars-escaped-backslashes-xirrma

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