Map bare autolinks from their end, not their start column

[hebertialmeida]

Follow-up to #10, reported against 1.4.0 from a wrapped paragraph holding two links: the second URL was highlighted from partway through — e.com in the link colour, https://www.exampl as plain text.

cmark's GFM autolink extension gets a bare URL's start wrong in two different ways, and its end right in both. Both are now handled by measuring back from the end, which needs no knowledge of where the line began.

1. Wrong by the length of the preceding lines

The start is reported as an offset into the paragraph's content buffer, not a column on its line. On a single-line paragraph the two coincide to within one character — which is exactly why the +1 adjustment in #10 looked correct. After a soft line break the error grows by every byte of the preceding lines:

link	actual column	reported	error
https://one.example.com	3	12	+9 ("line one" + newline)
https://two.example.com	31	40	+9

So highlighting painted a suffix of each URL and left the front as plain text.

2. Missing entirely

A URL that opens a paragraph is reported at column 0. position(in:) is all-or-nothing by design — it is used by every node type — so it mapped neither end, and the URL went unhighlighted anywhere. This was called out as a known gap in the 1.4.0 notes.

Bare autolinks are now adjusted before that check, and the end is mapped from its own line and column when position(in:) declined to.

The fix

The start is derived by walking back the length of the URL as written in the source. The source length matters, and is pinned by a test: GFM expands www.example.com to http://www.example.com, so measuring the destination would walk back too far.

The two text nodes around the link were wrong for the same reason and are repaired with it — the autolink's own child takes the link's whole position, and the run in front of it stops where the link starts. Where the URL opens the line, cmark emits a leading text node with an empty literal whose span cannot be clamped without inverting it; that one is left alone and documented, since it carries no text and every consumer reads the literal rather than the span.

Tests

Tests/MarkdownSyntaxTests/BareAutolinkLineOffsetTests.swift — 14 cases: the reported two-links-on-a-wrapped-line shape, a URL alone on a later line, two bare links after a soft break, a link on line 5, www. expansion, both text-node repairs, paragraph-opening URLs (document-initial and later), and four that pin the single-line and inline/angle-link behaviour that was already right.

CI=true swift test → 130 passed, 1 skipped.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a4e066e) to head (f75dd87).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #11   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files            1         1           
  Lines          133       133           
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  Hits           133       133           

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