Fix trailing line comment classified as enclosed in validators

[DylanPiercey]

Description

Fixes isValidAttrValue (and isValidStatement / isValidScriptlet) reporting enclosed for a value that ends in a trailing // line comment, e.g. "hello" // note.

isValid only downgraded enclosed → valid when it scanned a literal newline byte. A line comment that runs to EOF contains no newline, so hadUnguardedNewline never tripped and the value stayed enclosed. But a trailing line comment consumes everything that would follow it on the line, so the value is not safe to emit verbatim.

The fix flags the enclosing expression as having an unguarded newline when a line comment reaches EOF while no group is open — mirroring the existing unguarded-newline handling. It lives in EXPRESSION.return, so it only affects line comments whose parent is a JS expression (not the same state entered from tag/HTML contexts).

input	before	after
"hello" // c	enclosed	valid
foo // c	enclosed	valid
1 + 2 // c	enclosed	valid
"hello" /* c */ // d	enclosed	valid
"hello" /* c */	enclosed	enclosed (block comment self-closes)
("hello" // c\n)	enclosed	enclosed (guarded by parens)
"hello"\n// c	valid	valid

Motivation and Context

Regression introduced in 5.11.0 (last good: 5.10.2). enclosed promises consumers "safe to emit verbatim, no wrapping needed" — so prettier-plugin-marko emitted such values bare, ejecting the comment and commenting out the tag close:

<!-- input -->
<custom-tag id=("hello" // this comment should not be removed")/>

<!-- broken output: comment ejected, would comment out the tag close -->
<custom-tag id="hello"/> // this comment should not be removed

Checklist:

• I have updated/added documentation affected by my changes.
• I have added tests to cover my changes.

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Generated by Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 4b97e68

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
htmljs-parser	Patch

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.95%. Comparing base (16f453a) to head (4b97e68).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #227   +/-   ##
=======================================
  Coverage   99.95%   99.95%           
=======================================
  Files          34       34           
  Lines        4261     4270    +9     
  Branches      792      793    +1     
=======================================
+ Hits         4259     4268    +9     
  Misses          2        2           

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Plan: Pro

Run ID: 9ef8cb99-fa5d-47ae-8779-d7fa0a83b7a7

📥 Commits

Reviewing files that changed from the base of the PR and between 16f453a and 4b97e68.

📒 Files selected for processing (3)

• .changeset/tidy-carrots-repair.md
• src/__tests__/validate.test.ts
• src/states/EXPRESSION.ts

---

Walkthrough

This change fixes validation logic for inline JavaScript-in-HTML values ending with a trailing // line comment. EXPRESSION.ts now marks expressions as having an unguarded newline when a line comment reaches end-of-input without an active group, preventing incorrect "enclosed" classification. Tests were added covering isValidAttrValue, isValidStatement, and isValidScriptlet behavior with trailing, grouped, and block comments. A changeset documents the patch and clarifies classification rules for line comments.

Changes

Area	Change
src/states/EXPRESSION.ts	Sets hadUnguardedNewline = true for // comments reaching end-of-input with no active group stack
src/__tests__/validate.test.ts	Adds tests for trailing/grouped/block comment classification across isValidAttrValue, isValidStatement, isValidScriptlet
.changeset/tidy-carrots-repair.md	Documents patch fix for htmljs-parser validation reporting

Sequence Diagram(s)

sequenceDiagram
  participant Parser
  participant EXPRESSION
  participant Expression
  Parser->>EXPRESSION: return(child, expression) for JS_COMMENT_LINE
  EXPRESSION->>EXPRESSION: check pos === maxPos and no groupStack
  EXPRESSION->>Expression: set hadUnguardedNewline = true

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Estimated code review effort: Low

Related PRs: None identified

Suggested labels: patch, bug fix

Suggested reviewers: None identified

🐰 A comment that trails off at the end,
No longer confused as "enclosed," my friend,
A newline unguarded, EOF in sight,
Now classified properly, validation's delight!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: trailing line comments being misclassified as enclosed.
Description check	✅ Passed	The description is directly related to the changeset and accurately explains the validation fix and tests.
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

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• Create PR with unit tests
• Commit unit tests in branch claude/htmljs-parser-regression-pgpr2x

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