Honor the GFM delimiter row's column alignment in tables by lukebradford · Pull Request #166 · microsoft/SwiftStreamingMarkdown

lukebradford · 2026-08-12T00:20:00Z

The README lists :---, :---: and ---: column alignment as supported, but every table cell renders .leading regardless.

Markdown.Table exposes columnAlignments and Table+.convert has it in hand — there was simply nowhere to put it, since MarkdownRenderable.table carried only headers, rows and the raw markdown. The alignment is dropped at conversion time, so TableView never gets a chance to apply it.

Changes

MarkdownRenderable.table gains alignments: [MarkdownColumnAlignment], a small internal enum so the model keeps its current imports (no Markdown dependency added to the model layer).
Table+.convert maps swift-markdown's columnAlignments onto it, padding absent or short declarations with .leading.
TableView applies both multilineTextAlignment and the cell frame alignment per column — for the header row and both body-cell variants (text and attachment).

Compatibility

A table that declares no alignment still renders .leading, which is the GFM default, so existing output is unchanged. TableView's new alignments parameter is defaulted, so direct constructions — including the ones in TableViewTests — compile untouched.

Why it matters

Numeric columns. A currency or percentage column declared ---: currently reads as a ragged left edge, which is what sent me looking: we render financial tables into a chat transcript, and left-aligned money is genuinely harder to scan.

Note for CI

TableViewSnapshotTests.testTableCellWithOnlyCitation and the UnorderedListViewTests snapshots already fail for me at unmodified main — reference mismatches under macOS-standard-light / macOS-standard-dark, seemingly recorded on different hardware. So I could verify "no new failures" but not "green"; you may want to re-record those independently of this PR.

Happy to add snapshot coverage for a right-aligned table if you'd like it, once the reference situation is sorted.

🤖 Generated with Claude Code

The README lists `:---`, `:---:` and `---:` column alignment as supported, but every cell rendered `.leading` regardless. `Markdown.Table` exposes `columnAlignments`, and `Table+.convert` had it in hand — there was simply nowhere to put it, since `MarkdownRenderable.table` carried only headers, rows and the raw markdown. The alignment was dropped at conversion time and `TableView` never had a chance to apply it. - `MarkdownRenderable.table` gains `alignments: [MarkdownColumnAlignment]`, a small internal enum so the model keeps its current imports. - `Table+.convert` maps swift-markdown's `columnAlignments` onto it, padding short/absent declarations with `.leading`. - `TableView` applies both `multilineTextAlignment` and the cell's frame alignment per column, for the header row and both body-cell variants. A table that declares no alignment still renders `.leading` — the GFM default — so existing output is unchanged. `TableView`'s new `alignments` parameter is defaulted, so direct constructions (including the ones in `TableViewTests`) still compile untouched. This matters most for numeric columns: a currency or percentage column declared `---:` currently reads as a ragged left edge, which is what sent me looking. (Heads up for CI: `TableViewSnapshotTests.testTableCellWithOnlyCitation` and the `UnorderedListViewTests` snapshots already fail on my machine at unmodified `main` — reference mismatches under `macOS-standard-*`, seemingly recorded on different hardware — so I could only verify "no new failures" rather than green.)

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Pull request overview

This PR fixes a gap in the rendering pipeline where GitHub-Flavored Markdown (GFM) table column alignment declared in the delimiter row (:---, :---:, ---:) was being dropped during conversion, causing all table columns to render as leading-aligned in SwiftUI.

Changes:

Extend the render model (MarkdownRenderable.table) to carry per-column alignments via an internal MarkdownColumnAlignment enum.
Map Markdown.Table.columnAlignments to the render model in Table+.convert, defaulting unspecified/short declarations to .leading.
Apply per-column alignment in TableView for header and text cells (and begin applying it for attachment-backed cells).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Sources/MarkdownText/UI/TableView.swift	Accepts per-column alignments and uses them to set `multilineTextAlignment` / frame alignment when rendering cells.
Sources/MarkdownText/UI/BlockView.swift	Threads the new alignments payload from the render model into `TableView`.
Sources/MarkdownText/Models/RenderableDocument.swift	Updates `.table` pattern matches to account for the new alignments payload when extracting plain text / attributed strings.
Sources/MarkdownText/Models/MarkdownRenderable.swift	Adds `MarkdownColumnAlignment` and extends the `.table` case to persist alignments through rendering.
Sources/MarkdownText/Block/Table+.swift	Converts swift-markdown’s `columnAlignments` into the internal model enum, padding missing values with `.leading`.

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    case .containsAttachment(let nsAttributedString):
      HStack(spacing: 0) {
        ParagraphView(contents: applyTypographyThemingAndGetContent(nsAttributedString))
-          .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
+          .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: frameAlignment(forColumn: colIdx))
          .accessibilityValue(String.itemPositionInTable(rowIndex: rowIdx + 2, totalRow: numOfRows + 1, columnIndex: colIdx + 1, totalColumn: headings.count))


+    let alignments = (0..<headerCells.count).map { index -> MarkdownColumnAlignment in
+      guard index < self.columnAlignments.count else { return .leading }
+      switch self.columnAlignments[index] {
+      case .left: return .leading
+      case .center: return .center


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Honor the GFM delimiter row's column alignment in tables - #166

Honor the GFM delimiter row's column alignment in tables#166
lukebradford wants to merge 1 commit into
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yoshi-ai-dev:upstream-table-column-alignment

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lukebradford commented Aug 12, 2026

Changes

Compatibility

Why it matters

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