fix: don't strip spaces from all-space code spans

Closes #1180

src/rules_inline/backticks.ts

@@ -54,9 +54,14 @@ export default function backtick (state: StateInline, silent: boolean): boolean
         if (!silent) {
           const token = state.push('code_inline', 'code', 0)
           token.markup = marker
-          token.content = state.src.slice(pos, matchStart)
-            .replace(/\n/g, ' ')
-            .replace(/^ (.+) $/, '$1')
+          let content = state.src.slice(pos, matchStart).replace(/\n/g, ' ')
+
+          // Strip one space from each side, unless the content is all spaces
+          if (content.startsWith(' ') && content.endsWith(' ') && /[^ ]/.test(content)) {
+            content = content.slice(1, -1)
+          }
+
+          token.content = content
         }
         state.pos = matchEnd
         return true

test/fixtures/markdown-it/commonmark_extras.txt

@@ -916,3 +916,10 @@ the label cancels the link (CommonMark 0.31.2 6.1).
 .
 <p>[foo <code>bar](/url)</code> baz</p>
 .
+
+No stripping when a code span is all spaces (CommonMark 0.31.2 6.1).
+.
+`   `
+.
+<p><code>   </code></p>
+.