Add heading-max, code-block-max, and stern mode to line-length rule

[jeduden]

Summary

This PR extends the line-length rule (TM001) with three new configuration options that provide more granular control over line length checking:

1. Per-category limits: heading-max and code-block-max allow different maximum lengths for heading and code block lines
2. Stern mode: A new stern option that only flags lines exceeding the limit if they contain a space character past the limit column

Key Changes

• New Rule fields:

  • HeadingMax *int: Optional maximum length for heading lines
  • CodeBlockMax *int: Optional maximum length for code block lines
  • Stern bool: Enable strict space-based flagging

• Enhanced line classification:

  • Added collectHeadingLines() to identify heading lines via AST walking
  • Refactored line categorization into lineCategories struct for cleaner organization
  • Added buildCategories() to pre-compute line classifications

• Improved checking logic:

  • activeMax() determines the effective limit for each line based on its type
  • isSkipped() consolidates all skip conditions including new stern mode logic
  • hasSpacePastLimit() implements stern mode detection

• Settings handling:

  • Refactored ApplySettings() into smaller focused methods (applyMax(), applyPositiveIntPtr(), applyStern(), etc.)
  • Added validation that heading-max and code-block-max must be positive integers
  • Updated DefaultSettings() to include stern: false

• Documentation and tests:

  • Updated README with new settings, examples, and use cases
  • Added 30+ comprehensive test cases covering all new features and their interactions
  • Added example markdown files demonstrating good/bad cases for each feature

Implementation Details

• Per-category limits inherit from max when unset, maintaining backward compatibility
• Per-category limits and exclude compose correctly: excluded lines are still skipped even when a category-specific limit is set
• Stern mode applies independently of exclusions and respects per-category limits
• Heading detection uses AST walking to reliably identify heading nodes regardless of syntax style

https://claude.ai/code/session_01PNAbRKSSUqz9rtkM37eKiM

[jeduden]

@copilot fix ci

[Copilot]

@jeduden I've opened a new pull request, #2, to work on those changes. Once the pull request is ready, I'll request review from you.

[Copilot]

Pull request overview

This PR enhances the line-length rule (TM001) with three new configuration options to provide finer-grained control over line length checking: per-category limits for headings and code blocks, and a "stern mode" that only flags lines with spaces past the limit.

Changes:

• Added heading-max, code-block-max, and stern settings to the Rule struct with corresponding validation and application logic
• Refactored line checking to pre-compute line categories and determine active limits based on line type
• Added comprehensive test coverage with 30+ unit tests and example markdown files demonstrating the new features

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
internal/rules/linelength/rule.go	Implements per-category limits and stern mode logic; refactors settings application into focused helper methods; adds AST-based heading detection and category-based limit selection
internal/rules/linelength/rule_test.go	Adds comprehensive test coverage for heading-max, code-block-max, and stern mode features with tests for inheritance, composition, and edge cases
rules/TM001-line-length/README.md	Documents the new settings with descriptions, configuration examples, and usage examples for each feature
rules/TM001-line-length/good/stern-no-spaces-past-limit.md	Example demonstrating stern mode allowing long URLs without spaces past limit
rules/TM001-line-length/good/heading-within-limit.md	Example showing heading within heading-max limit
rules/TM001-line-length/good/code-block-within-limit.md	Example showing code block within code-block-max limit
rules/TM001-line-length/bad/stern-spaces-past-limit.md	Example showing stern mode flagging lines with spaces past limit
rules/TM001-line-length/bad/heading-over-limit.md	Example showing heading exceeding heading-max

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[Copilot]

The comment describing the test case is misleading. It states "space at position 60" when using a heading-max of 60, but the space is actually at 0-indexed position 60, which is the 61st character (1-indexed). Since the limit is 60, this space is indeed past the limit. Consider clarifying: "# " (2 chars) + 58 'h' chars = 60 chars total, then space at 0-indexed byte 60 (past the limit), then 5 'x' chars, totaling 66 chars."

Suggested change

	// "# " (2) + 58 'h' chars + space at position 60 + 5 'x' chars = 66 total.
	// heading-max=60, so the space at position 60 is past the limit.
	// "# " (2 chars) + 58 'h' chars = 60 chars total, then a space at 0-indexed position 60
	// (the 61st character, i.e., past heading-max=60), then 5 'x' chars, for 66 chars total.