issue #7442 : markdown tables not rendered

[mattcasters]

Issue #7442 — Markdown preview: GFM table rendering

Recap for code reviewers.

Summary

The Markdown file preview in the Hop file explorer (MarkDownExplorerFileTypeHandler.previewMarkdown()) did not render GFM pipe tables correctly. Tables appeared as plain paragraphs with literal | characters instead of HTML <table> elements.

This change adds the required CommonMark extensions, registers them on the parser and renderer, and adds table-specific CSS for both light and dark mode previews.

Problem

previewMarkdown() used the base CommonMark parser with no extensions:

Parser parser = Parser.builder().build();
HtmlRenderer renderer = HtmlRenderer.builder().build();

CommonMark core does not support GFM tables. A report such as retail-dv-initial-report.md (pipe tables with alignment markers like ---:) was parsed into eight <p>| ... |</p> blocks and zero <table> elements.

Headings, bold text, inline code, and lists rendered correctly; only GFM-specific syntax was broken.

Solution

1. Dependencies (plugins/transforms/textfile/pom.xml)

Three CommonMark extensions were added (all provided scope, version ${commonmark.version} = 0.29.0):

Artifact	Purpose
commonmark-ext-gfm-tables	Pipe tables and column alignment
commonmark-ext-task-list-items	- [x] / - [ ] task lists
commonmark-ext-footnotes	[^1] footnotes

These match the existing pattern for commonmark core in the textfile plugin.

2. Extension registration (MarkDownExplorerFileTypeHandler.java)

Extensions are configured once in a static list and passed to both builder instances:

private static final List<Extension> MARKDOWN_EXTENSIONS =
    List.of(
        TablesExtension.create(),
        TaskListItemsExtension.create(),
        FootnotesExtension.create());

Parser parser = Parser.builder().extensions(MARKDOWN_EXTENSIONS).build();
HtmlRenderer renderer = HtmlRenderer.builder().extensions(MARKDOWN_EXTENSIONS).build();

Parser and HtmlRenderer are thread-safe when built this way, so the static list is appropriate.

3. Table CSS in preview HTML

The inline preview stylesheet had no table rules. Shared layout rules were added (full width, collapsed borders, padding, rounded corners), plus mode-specific colors:

Light mode

• Table background: #ffffff
• Header background: #f1f5f9
• Borders: #e2e8f0
• Alternating rows: #f8fafc

Dark mode

• Table background: #0f172a
• Header background: #1e293b
• Borders: #334155
• Alternating rows: #111827

Colors follow the existing slate palette already used for body, code blocks, and blockquotes.

Files changed

File	Change
plugins/transforms/textfile/pom.xml	+3 CommonMark extension dependencies
plugins/transforms/textfile/src/main/java/.../MarkDownExplorerFileTypeHandler.java	Extension registration + table CSS

Diff size: 2 files, +71 / −2 lines.

Review focus

1. Classpath / assembly — Extension JARs use provided scope like commonmark core. Confirm they are bundled into the Hop client distribution at runtime (same mechanism as the existing commonmark dependency via the textfile plugin).
2. LICENSE — If ASF release policy requires it, the static LICENSE file may need entries for the three new extension artifacts (currently only commonmark core is listed).
3. Scope — Only the explorer Markdown preview is updated. DocBuilder.markdownToHtml() in plugins/misc/documentation still uses the bare parser and would have the same table limitation if HTML doc generation is expected to handle GFM tables.
4. No new tests — Existing MarkDownExplorerFileTypeTest covers file-type metadata only, not preview rendering. Consider whether a small unit test asserting <table> output for a pipe-table snippet is worth adding in a follow-up.

Manual verification

1. Build and start Hop GUI.
2. Open a .md file with GFM tables (e.g. a data-vault load report).
3. Click the preview toolbar button.
4. Confirm:
   • Tables render as bordered HTML tables, not pipe-separated paragraphs.
   • Header row has a distinct background.
   • Alternating row shading is visible.
   • Appearance is correct in both light and dark mode.

Out of scope / known limitations

• No syntax highlighting for fenced code blocks (would need a separate JS/CSS library).
• No commonmark-ext-autolink or commonmark-ext-gfm-strikethrough — bare URLs and ~~strikethrough~~ still render as literal text.
• No ul/ol list styling added (lists were already readable).
• Documentation plugin HTML generation unchanged.