125_no-space-in-link-text.md

id	125
title	No space inside link text rule
status	✅
summary	New rule MDS049 that flags Markdown links and images whose visible text has leading or trailing whitespace inside the brackets. Closes the gap with markdownlint MD039.
model	sonnet

No space inside link text rule

Goal

Let users forbid stray whitespace inside the visible text of links and images. [ click here ](url) renders the spaces as part of the underlined link text in most renderers, which looks broken. The same applies to image alt text. markdownlint covers this as MD039; mdsmith does not.

Background

What goldmark exposes

Inline links are *ast.Link. Inline images are *ast.Image. The visible text is the node's child sequence, but the rule needs the source bytes inside the [...] brackets to detect whitespace flanking the text — the AST already trims to text nodes that may have lost the whitespace.

The rule reads f.Source between the opening [ and the closing ] for each link/image node and inspects the boundary bytes.

Why a separate rule

MDS012 (no-bare-urls) and MDS027 (cross-file reference integrity) handle URLs and link targets. Neither looks at the text between the brackets. A dedicated rule keeps text-formatting policy independent of URL policy.

Reference-style links are out of scope here — plan 107 forbids them entirely. Until that rule is enabled, MDS049 also applies to reference-link text ([ text ][ref]) because the text portion is still visible.

Design

Configuration

rules:
  no-space-in-link-text:
    check-images: true

Category: link. Disabled by default (opt-in). check-images allows opting out of image alt-text checking when MDS032 (no-empty-alt-text) is doing heavier alt-text work.

Detection

Walk *ast.Link and *ast.Image. For each node:

1. Locate the bytes between the opening [ and the matching closing ] in f.Source.
2. If the first byte is whitespace (space, tab), emit link text has leading whitespace (or image alt text has leading whitespace).
3. If the last byte is whitespace, emit the trailing-whitespace variant.
4. Skip when check-images: false and the node is *ast.Image.

Newlines inside the brackets are not flagged — they often reflect intentional wrapping of long link text.

Auto-fix

Trim leading and trailing whitespace inside the brackets. Keep the brackets and any trailing reference label or URL parenthetical untouched.

Error messages

link text has leading whitespace
link text has trailing whitespace
image alt text has leading whitespace
image alt text has trailing whitespace

Tasks

1. Scaffold internal/rules/nospaceinlinktext/ with rule.go, rule_test.go, and the init() rule.Register call.
2. Implement Check() walking *ast.Link and *ast.Image, locating the bracket span in f.Source.
3. Implement rule.Configurable for check-images.
4. Implement Fix() that trims whitespace inside the brackets.
5. Implement rule.Defaultable returning false.
6. Register as MDS049 in category link.
7. Add fixture tests in internal/rules/MDS049-no-space-in-link-text/ covering: clean link, leading space, trailing space, both, image alt with leading space, reference link with whitespace text, and a link whose text wraps across a newline (not flagged).
8. Add rule README following the MDS012 template.

Acceptance Criteria

• [text](url) emits no diagnostic.
• [ text ](url) emits leading and trailing diagnostics and fixes to [text](url).
• [text ](url) emits one trailing diagnostic.
• ![ alt ](img.png) emits two diagnostics with image alt text wording and fixes to ![alt](img.png).
• ![ alt ](img.png) emits no diagnostic when check-images: false.
• A link whose text spans two source lines (newline between words) emits no diagnostic.
• [ text ][ref] emits diagnostics on the text portion only.
• Rule is disabled by default.
• All tests pass: go test ./...
• go tool golangci-lint run reports no issues
• mdsmith check . passes on the repo with the rule disabled (no regression for existing docs).