Fix emphasis delimiters inside link URLs

src/Parser/InlineParser.php

@@ -972,6 +972,16 @@ protected function parseDelimited(string $text, int $pos, string $delimiter, str
                 }
             }
 
+            // Skip over link/image constructs [...](...) and [...][]  or ![...](...) etc.
+            if ($char === '[' || ($char === '!' && ($text[$searchPos + 1] ?? '') === '[')) {
+                $linkEnd = $this->findLinkEnd($text, $char === '!' ? $searchPos + 1 : $searchPos);
+                if ($linkEnd !== null) {
+                    $searchPos = $linkEnd;
+
+                    continue;
+                }
+            }
+
             // Skip escape sequences
             if ($char === '\\' && $searchPos + 1 < $length) {
                 $searchPos += 2;
@@ -1535,6 +1545,79 @@ protected function findAutolinkEnd(string $text, int $pos): ?int
         return null;
     }
 
+    /**
+     * Find the end of a link/image construct starting at $pos (which points to '[').
+     * Handles [text](url), [text][ref], and [text][] forms.
+     *
+     * @return int|null Position after the link construct, or null if not a valid link
+     */
+    protected function findLinkEnd(string $text, int $pos): ?int
+    {
+        $length = strlen($text);
+        if ($pos >= $length || $text[$pos] !== '[') {
+            return null;
+        }
+
+        // Find matching ]
+        $bracketDepth = 1;
+        $i = $pos + 1;
+        while ($i < $length && $bracketDepth > 0) {
+            if ($text[$i] === '[') {
+                $bracketDepth++;
+            } elseif ($text[$i] === ']') {
+                $bracketDepth--;
+            } elseif ($text[$i] === '\\' && $i + 1 < $length) {
+                $i++;
+            }
+            if ($bracketDepth > 0) {
+                $i++;
+            }
+        }
+
+        if ($bracketDepth !== 0) {
+            return null;
+        }
+
+        // $i is now at the closing ]
+        $afterBracket = $i + 1;
+
+        // Inline link: [text](url)
+        if ($afterBracket < $length && $text[$afterBracket] === '(') {
+            $parenDepth = 1;
+            $j = $afterBracket + 1;
+            while ($j < $length && $parenDepth > 0) {
+                if ($text[$j] === '(') {
+                    $parenDepth++;
+                } elseif ($text[$j] === ')') {
+                    $parenDepth--;
+                } elseif ($text[$j] === '\\' && $j + 1 < $length) {
+                    $j++;
+                }
+                if ($parenDepth > 0) {
+                    $j++;
+                }
+            }
+
+            if ($parenDepth === 0) {
+                return $j + 1;
+            }
+
+            return null;
+        }
+
+        // Reference link: [text][ref] or [text][]
+        if ($afterBracket < $length && $text[$afterBracket] === '[') {
+            $refEnd = strpos($text, ']', $afterBracket + 1);
+            if ($refEnd !== false) {
+                return $refEnd + 1;
+            }
+
+            return null;
+        }
+
+        return null;
+    }
+
     /**
      * Remove comments from attribute string: % ... % or % to end
      */

tests/TestCase/Parser/InlineParserTest.php

@@ -374,6 +374,47 @@ public function testAutolinkPrecedenceOverEmphasis(): void
         $this->assertSame('http://example.com/a_b', $children[1]->getDestination());
     }
 
+    public function testEmphasisWithUnderscoreInLinkUrl(): void
+    {
+        // Issue #70: underscores in link URLs should not break emphasis
+        $para = $this->parseInline('_[link](http://example.com?foo_bar=1), more text_');
+
+        $children = $para->getChildren();
+        $this->assertCount(1, $children);
+        $this->assertInstanceOf(Emphasis::class, $children[0]);
+
+        $emChildren = $children[0]->getChildren();
+        // Should contain a link node followed by text
+        $this->assertInstanceOf(Link::class, $emChildren[0]);
+        $this->assertSame('http://example.com?foo_bar=1', $emChildren[0]->getDestination());
+    }
+
+    public function testEmphasisWithUnderscoreInLinkUrlMoreCases(): void
+    {
+        // _hello [link](a_b) world_
+        $para = $this->parseInline('_hello [link](a_b) world_');
+
+        $children = $para->getChildren();
+        $this->assertCount(1, $children);
+        $this->assertInstanceOf(Emphasis::class, $children[0]);
+
+        $emChildren = $children[0]->getChildren();
+        $this->assertInstanceOf(Text::class, $emChildren[0]);
+        $this->assertSame('hello ', $emChildren[0]->getContent());
+        $this->assertInstanceOf(Link::class, $emChildren[1]);
+        $this->assertSame('a_b', $emChildren[1]->getDestination());
+    }
+
+    public function testStrongWithStarInLinkUrl(): void
+    {
+        // *[closed](hello*) - star in URL should not break strong
+        $para = $this->parseInline('*[link](http://example.com?q=a*b) text*');
+
+        $children = $para->getChildren();
+        $this->assertCount(1, $children);
+        $this->assertInstanceOf(Strong::class, $children[0]);
+    }
+
     public function testEmphasisFollowedByCloseBrace(): void
     {
         // Emphasis opener cannot be followed by } (closer marker)

tests/official/emphasis.test

@@ -213,7 +213,7 @@ _ab\_c_
 ```
 _[bar_](url)
 .
-<p><em>[bar</em>](url)</p>
+<p>_<a href="url">bar_</a></p>
 ```
 
 ```

tests/official/links_and_images.test

@@ -179,7 +179,7 @@ starts first:
 ```
 *[closed](hello*)
 .
-<p><strong>[closed](hello</strong>)</p>
+<p>*<a href="hello*">closed</a></p>
 ```
 
 Avoid this with a backslash escape: