Why pad inlineCode's value with spaces?

[vvenv]

No idea of these:

  // If this is not just spaces or eols (tabs don’t count), and either the
  // first or last character are a space, eol, or tick, then pad with spaces.
  if (
    /[^ \r\n]/.test(value) &&
    (/[ \r\n`]/.test(value.charAt(0)) ||
      /[ \r\n`]/.test(value.charAt(value.length - 1)))
  ) {
    value = ' ' + value + ' '
  }

https://github.com/syntax-tree/mdast-util-to-markdown/blob/main/lib/handle/inline-code.js#L28-L34

A inline-code with value inline code (space+inline+space+code) will transform to inline code (space+space+inline+space+code+space), with unexpected extra spaces.

[wooorm]

This behavior is needed to roundtrip the value (see the comment above it): https://spec.commonmark.org/0.30/#code-span.
The padding has to be done on both sides: it doesn’t work if it’s only on one side, then it changes the code.

As you can see from your example, they are equivalent: the spaces around it are dropped.

See some example: https://spec.commonmark.org/dingus/?text=1.%20%60%20%60%20one%20space%20(persists)%0A1.%20%60%20%20%20%20%60%20four%20spaces%20(persists)%0A1.%20%60a%20%60%20final%20space%20(persists)%0A1.%20%60%20a%60%20initial%20space%20(persists)%0A1.%20%60%20a%20%60%20initial%20and%20final%20space%20(dropped)%0A1.%20%60%60%20%60a%60%20%60%60%20spaces%20around%20ticks%20(dropped)%0A1.%20%60%20%60%60a%60%60%20%60%20spaces%20around%20ticks%2C%20inverted%20(dropped)%0A

[wooorm]

It sounds like that is a bug in your md->html->md pipeline.

Otherwise, no, we can’t change it, doing so changes the value of the code.

Try roundtripping with both mdast-util-from-markdown and mdast-util-to-markdown to see that it changes the AST.

[wooorm]

We might be able to leave it as-is if there’s a [ \r\n] on one side but not both, perhaps?
It’s definitely needed if there’s a space on both sides or a tick on one or both sides 🤔

[wooorm]

Like this?

if (
  /[^ \r\n]/.test(value) &&
  ((/^[ \r\n]/.test(value) && /[ \r\n]$/.test(value)) ||
    /^`|`$/.test(value))
) {
  // Pad
}

[vvenv]

https://github.com/commonmark/commonmark-spec-web/blob/gh-pages/js/commonmark.js#L7824-L7833

if (
    contents.length > 0 &&
    contents.match(/[^ ]/) !== null &&
    contents[0] == " " &&
    contents[contents.length - 1] == " "
) {
    node._literal = contents.slice(1, contents.length - 1);
} else {
    node._literal = contents;
}

There is no whitespace padding in spec, just dropping and persisting

[wooorm]

Indeed, parsing drops or persists. So micromark/mdast-util-to-markdown do that.
Because mdast-util-to-markdown serializes, we need to prevent important information from being removed:

import assert from 'node:assert'
import {fromMarkdown} from 'mdast-util-from-markdown'
import {toMarkdown} from 'mdast-util-to-markdown'
import {removePosition} from 'unist-util-remove-position'

const input = 'a `  b  ` c'

const treeA = removePosition(fromMarkdown(input))
const treeB = removePosition(fromMarkdown(toMarkdown(treeA)))

assert.deepStrictEqual(treeA, treeB)
console.dir(treeA, {depth: null})