Parsing a GFM table with rows of unequal cell counts, then stringifying and re-parsing, changes the `tableRow` cell counts to match the header width.

[ChristianMurphy]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected package

mdast-util-gfm 3.1.0, mdast-util-gfm-table (via mdast-util-gfm), mdast-util-to-markdown 2.1.2

Steps to reproduce

Parsing a GFM table with rows of unequal cell counts, then stringifying and
re-parsing, changes the tableRow cell counts to match the header width.

a||
-|-
|

round-trips through structure:

tree1: table > [row(cells=2), row(cells=1)]
tree2: table > [row(cells=2), row(cells=2)]

---

parse

a||
-|-
|

tree₁:

{
  "type": "table",
  "children": [
    { "type": "tableRow", "children": [
      { "type": "tableCell", "children": [{ "type": "text" }] },
      { "type": "tableCell", "children": [] }
    ]},
    { "type": "tableRow", "children": [
      { "type": "tableCell", "children": [] }
    ]}
  ]
}

stringify it:

| a |   |
| - | - |
|   |   |

tree₂ has two cells in the second body row (padded to header width):

{
  "type": "table",
  "children": [
    { "type": "tableRow", "children": [
      { "type": "tableCell", "children": [{ "type": "text" }] },
      { "type": "tableCell", "children": [] }
    ]},
    { "type": "tableRow", "children": [
      { "type": "tableCell", "children": [] },
      { "type": "tableCell", "children": [] }
    ]}
  ]
}

Two other fixtures in micromark-extension-gfm-table's suite minimize to the
same shape (||\n-|\n|||, ||||||\n-|-|-|-|-\n|) with the same signature.

📓 GFM §4.10 says short rows render as padded. The AST preserves real
widths though, and the serializer emits them padded, so a re-parse sees the
padded widths and the tree structure drifts. Either (a) the parser should
normalize row widths to header width at parse time, or (b) the serializer
should not pad short rows. Round-trip stability requires picking one.

Actual behavior

Short body rows are padded to match the header width on stringify, so the
re-parsed tree has more cells than the original.

Expected behavior

parse → stringify → parse preserves tableRow cell counts.

Runtime

No response

Package manager

No response

Operating system

No response

Build and bundle tools

No response