fix(comark): harden auto-close for code spans, math, escapes, and link text

packages/comark/src/internal/parse/auto-close/index.ts

@@ -254,10 +254,34 @@ function closeInlineMarkersLinear(line: string): string {
   let inAttributes = 0
   let inLinkText = 0
   let inLinkUrl = 0
+  let linkTextBacktickCount = 0
+  // Markers inside an inline code span (`...`) or math ($...$) are literal text
+  let inCode = false
+  let inMath = false
   for (let i = 0; i < len; i++) {
     const prevCh = i > 0 ? line[i - 1] : ''
     const ch = line[i]
 
+    if (ch === '\\') {
+      i++ // Backslash escapes the next char, so neither is a delimiter
+      continue
+    }
+
+    if (inCode) {
+      if (ch === '`') {
+        backtickCount++
+        inCode = false
+      }
+      continue
+    }
+    if (inMath) {
+      if (ch === '$' && !(i + 1 < len && line[i + 1] === '$')) {
+        dollarCount++
+        inMath = false
+      }
+      continue
+    }
+
     if (ch === '{' && prevCh !== ' ') {
       inAttributes++
       continue
@@ -295,7 +319,28 @@ function closeInlineMarkersLinear(line: string): string {
       continue
     }
 
-    if (inLinkText > 0 || inLinkUrl > 0) continue
+    if (inLinkText > 0) {
+      if (ch === '`') linkTextBacktickCount++
+      continue
+    }
+    if (inLinkUrl > 0) continue
+
+    if (ch === '`') {
+      backtickCount++
+      inCode = true
+      continue
+    }
+    if (ch === '$') {
+      if (i + 1 < len && line[i + 1] === '$') {
+        dollarPairCount++ // `$$` is block math, counted as a pair
+        dollarCount += 2
+        i++
+      } else {
+        dollarCount++
+        inMath = true
+      }
+      continue
+    }
 
     if (ch === '*') {
       asteriskCount++
@@ -327,20 +372,17 @@ function closeInlineMarkersLinear(line: string): string {
       } else {
         singleTildeCount++
       }
-    } else if (ch === '`') {
-      backtickCount++
-    } else if (ch === '$' && prevCh !== '\\') {
-      // Count $$ pairs for block/display math
-      if (i + 1 < len && line[i + 1] === '$') {
-        dollarPairCount++
-        dollarCount += 2 // Count both dollars in the pair
-        i++ // Skip next $ since we counted the pair
-      } else {
-        dollarCount++ // Single $ for inline math
-      }
     }
   }
 
+  // Open code/math region: close only it; everything after the opener is literal
+  if (inCode) {
+    return line + '`'
+  }
+  if (inMath) {
+    return line.trim() === '$$' ? line : line + '$'
+  }
+
   // Check for complete ** pairs in O(1) - pairs are matched left to right
   const hasCompleteBoldPair = doubleAsteriskPositions.length >= 2
 
@@ -550,7 +592,9 @@ function closeInlineMarkersLinear(line: string): string {
 
   // Check [ ] (brackets)
   if (!closingSuffix && bracketBalance > 0) {
-    closingSuffix = ']'
+    // An odd backtick opened inside the unclosed link text is an unclosed
+    // inline code span; close it before the bracket so `]` stays outside it.
+    closingSuffix = linkTextBacktickCount % 2 === 1 ? '`]' : ']'
   }
 
   // Check ( ) (parens)

packages/comark/test/auto-close.test.ts

@@ -560,6 +560,14 @@ describe('link', () => {
     const expected = 'https://errors.pydantic.dev/2.13/v/value_error'
     expect(autoCloseMarkdown(input)).toBe(expected)
   })
+
+  it('should close inline code inside unclosed link text', () => {
+    // Backtick must close before the bracket, else `]` lands inside the
+    // unclosed code span and renders as literal "`foo]" not a code link.
+    const input = '[`foo'
+    const expected = '[`foo`]'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
 })
 describe('attributes scope', () => {
   it('should ignore $ in inline attributes', () => {
@@ -610,3 +618,91 @@ describe('attributes scope', () => {
     expect(autoCloseMarkdown(input)).toBe(expected)
   })
 })
+
+describe('inline code spans as literal regions', () => {
+  it('should not count asterisks inside a closed code span', () => {
+    const input = 'text `a*b` and **bold'
+    const expected = 'text `a*b` and **bold**'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should not count underscores inside a closed code span', () => {
+    const input = 'see `a_b_c` then __bold'
+    const expected = 'see `a_b_c` then __bold__'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should close an open code span without leaking an asterisk', () => {
+    const input = '`x * y'
+    const expected = '`x * y`'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should close only the code span when bold wraps an open code span', () => {
+    const input = '**bold `code'
+    const expected = '**bold `code`'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should treat an underscore inside an open code span as literal', () => {
+    const input = '`snake_case'
+    const expected = '`snake_case`'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+})
+
+describe('inline math as literal regions', () => {
+  it('should not count asterisks inside closed inline math', () => {
+    const input = '$a * b$ and *italic'
+    const expected = '$a * b$ and *italic*'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should not count an underscore inside an open math region', () => {
+    const input = 'value $x_0'
+    const expected = 'value $x_0$'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should close inline math without leaking an asterisk', () => {
+    const input = '$a * b'
+    const expected = '$a * b$'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+})
+
+describe('escaped markers', () => {
+  it('should not count an escaped asterisk as a delimiter', () => {
+    const input = 'a \\* b *it'
+    const expected = 'a \\* b *it*'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should not count an escaped underscore as a delimiter', () => {
+    const input = 'a \\_ b _it'
+    const expected = 'a \\_ b _it_'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should not count an escaped backtick as a code span', () => {
+    const input = 'literal \\` then `code'
+    const expected = 'literal \\` then `code`'
+    expect(autoCloseMarkdown(input)).toBe(expected)
+  })
+
+  it('should leave a fully escaped marker untouched', () => {
+    const input = 'just a \\* star'
+    expect(autoCloseMarkdown(input)).toBe(input)
+  })
+})
+
+describe('nested emphasis (known limitations)', () => {
+  // Mixed-marker nesting needs CommonMark flanking resolution, out of scope here
+  it.todo('should close nested bold + underscore-italic (**_text -> **_text_**)', () => {
+    expect(autoCloseMarkdown('**_text')).toBe('**_text_**')
+  })
+
+  it.todo('should close nested italic + bold (*a **b -> *a **b***)', () => {
+    expect(autoCloseMarkdown('*a **b')).toBe('*a **b***')
+  })
+})