MDXTab VS Code Extension (Spike)

Markdown Extended Tables

• Command: MDXTab: Render Preview (mdxtab.renderPreview) — renders the active Markdown file through the MDXTab compiler into a preview document.
• Command: MDXTab: Validate Document (mdxtab.validateDocument) — validates the active Markdown file and reports diagnostic count/status.
• Command: MDXTab: Show Table Schema (mdxtab.showTableSchema) — opens a markdown view with parsed tables, report_tables, and pivot_tables frontmatter schema as JSON.
• Diagnostics: recompiles on open/change/save; errors surface as markdown diagnostics at the top of the file.
• Preview scheme: mdxtab-preview: opens a virtual document with the rendered output (frontmatter + interpolated aggregates).
• Computed column preview: columns defined in frontmatter computed are rendered in the Markdown preview with their evaluated per-row values. Columns already authored as headers have their empty cells filled in; columns not in the source table are appended automatically.
• Summary row preview: rows defined in frontmatter summary_rows are rendered as synthetic rows appended at the bottom of the table preview.
• Synthetic report table preview: frontmatter report_tables render as derived Markdown tables at matching headings such as ## category_balances.
• Synthetic pivot table preview: frontmatter pivot_tables render as derived matrix tables at matching headings such as ## liquidity.
• Heading completion + hover for synthetic tables: completion suggests report_tables and pivot_tables names when editing Markdown headings, and hover shows quick details on matching synthetic-table headings.
• Expression guardrails: validation rejects pathological computed/aggregate expressions with E_LIMIT diagnostics before they can trigger stack overflow or excessive work.
• Finite-number semantics: validation rejects arithmetic that would produce NaN or Infinity with E_NUMBER diagnostics.

Settings

Summary Rows (summary_rows)

MDXTab supports summary rows defined in table frontmatter. Summary row cells are expressions evaluated left-to-right and can reference prior cells in the same summary row via self.<column>.

tables:
  expenses:
    key: category
    columns: [category, p1, p2, p3, row_total]
    computed:
      row_total: p1 + p2 + p3
    summary_rows:
      running_balance:
        label: Running Balance
        cells:
          p1: sum(p1)
          p2: self.p1 + sum(p2)
          p3: self.p2 + sum(p3)

In preview, the synthetic row is appended after the last data row.

Report Tables (report_tables)

MDXTab supports synthetic report tables defined in frontmatter. A report table uses rows_from to choose the driving source table, then evaluates one cell expression per output column for each generated row.

report_tables:
  category_balances:
    rows_from: categories
    columns: [label, monthly_delta]
    cells:
      label: row.label
      monthly_delta: transactions.total_by_category[row.id]

When the Markdown body contains a matching heading such as ## category_balances, the extension renders a normal Markdown table at that location in preview/output.

Expression Limits

The current compiler applies explicit limits to expressions:

If one of these limits is exceeded, the extension surfaces an E_LIMIT diagnostic through the normal MDXTab validation path.

The core compiler also supports configurable limits via compile options, and the extension maps the settings above to those compile options for validation and preview rendering.

This is a spike; packaging, icons, and richer error mapping are still TBD.