Enabling `headerless` creates conflicts with markdown-it-attrs

[SimonEast]

See issue at arve0/markdown-it-attrs#164

I'm using VitePress which comes bundled with markdown-it-attrs. As soon as I enable markdown-it-multimd-table with the headerless option and insert a headerless table, markdown-it-attrs starts spitting out errors.

Not sure if the issue can be fixed within this plugin or if it's specific to markdown-it-attrs but thought I'd mention it here and link the issues.

Simon

[SimonEast]

I developed a fix/workaround with the help of Copilot, which fixes this error:

markdown-it-attrs: Error in pattern 'tables tbody calculate': Cannot read properties of null (reading 'colsnum')

Root cause:
In headerless tables, markdown-it-multimd-table emits tbody without thead metadata. markdown-it-attrs assumes tbody_open.meta exists and reads meta.colsnum, so it crashes when meta is null.

Workaround (patch):
I patched node_modules/markdown-it-multimd-table/index.js to ensure tbody_open.meta is always an object in headerless mode, but did not set colsnum. This avoids the null crash without triggering attrs colspan recalculation (which can hide/drop cells).

diff --git a/index.js b/index.js
--- a/index.js
+++ b/index.js
@@ -298,6 +298,13 @@
       if (trToken.meta.grp & 0x10) {
         tag = (trToken.meta.type === 0x00100) ? 'thead' : 'tbody';
         token     = state.push(tag + '_open', tag, 1);
         token.map = tgroupLines = [ trToken.map[0], 0 ];  // array ref
+        // markdown-it-attrs expects tbody_open.meta to be an object.
+        // For headerless tables there is no thead-derived colsnum metadata,
+        // so only ensure non-null meta to avoid null dereference.
+        if (options.headerless && tag === 'tbody') {
+          token.meta = md.utils.assign({}, token.meta || {});
+        }
         upTokens  = [];
       }

This is a temporary workaround, but appears to work for me so far.

For those who want to manually patch in the meantime, using patch-package is probably recommended rather than manually patching (which may get lost later).