🐛 FIX: texmath infinite loop on block math closed outside blockquote

CHANGELOG.md

@@ -1,5 +1,14 @@
 # Change Log
 
+## Unreleased
+
+- 🐛 FIX: `texmath` no longer loops forever on block math opened inside a blockquote and closed after it (#156)
+
+  The block rules matched their regex against the rest of the source, so the closing
+  delimiter could lie outside the current block; the rule then reported a match
+  without advancing `state.line`. The closing line is now searched within the current
+  block only, otherwise the rule does not match (no auto-closing, as in `amsmath`).
+
 ## 0.7.0 - 2026-07-19
 
 - ✨ NEW: Add section reference plugin (`section_ref`) (#144)

mdit_py_plugins/texmath/index.py

@@ -128,25 +128,28 @@ def make_block_func(rule: RuleDictType) -> Callable[[StateBlock, int, int, bool]
     def _func(state: StateBlock, begLine: int, endLine: int, silent: bool) -> bool:
         begin = state.bMarks[begLine] + state.tShift[begLine]
         res = applyRule(rule, state.src, begin, state.parentType == "blockquote")
-        if res:
-            if not silent:
-                token = state.push(rule["name"], "math", 0)
-                token.block = True
-                token.content = res[1]
-                token.info = res[len(res.groups())]
-                token.markup = rule["tag"]
-
-            line = begLine
-            endpos = begin + res.end() - 1
-
-            while line < endLine:
-                if endpos >= state.bMarks[line] and endpos <= state.eMarks[line]:
-                    # line for end of block math found ...
-                    state.line = line + 1
-                    break
-                line += 1
-
-        return bool(res)
+        if not res:
+            return False
+
+        # find the line holding the end of the match, within this block only
+        endpos = begin + res.end() - 1
+        line = begLine
+        while line < endLine and endpos > state.eMarks[line]:
+            line += 1
+        if line >= endLine or endpos < state.bMarks[line]:
+            # the closing delimiter lies outside the current block,
+            # e.g. math opened inside a blockquote and closed after it
+            return False
+
+        if not silent:
+            token = state.push(rule["name"], "math", 0)
+            token.block = True
+            token.content = res[1]
+            token.info = res[len(res.groups())]
+            token.markup = rule["tag"]
+
+        state.line = line + 1
+        return True
 
     return _func
 

tests/fixtures/texmath_bracket.md

@@ -410,3 +410,15 @@ Indented by 4 spaces, DISABLE-CODEBLOCKS
     </eqn>
 </section>
 .
+
+display equation opened in blockquote and closed outside it (valid=False)
+.
+> \[ a=1
+
+\]
+.
+<blockquote>
+<p>[ a=1</p>
+</blockquote>
+<p>]</p>
+.

tests/fixtures/texmath_dollar.md

@@ -454,3 +454,31 @@ Indented by 4 spaces, DISABLE-CODEBLOCKS
 <eqn>a</eqn>
 </section>
 .
+
+display equation opened in blockquote and closed outside it (valid=False)
+.
+> $$ a=1
+
+$$
+.
+<blockquote>
+<p>$$ a=1</p>
+</blockquote>
+<p>$$</p>
+.
+
+display equation opened in nested blockquote and closed outside it (valid=False)
+.
+- > $$ a=1
+
+$$ (1)
+.
+<ul>
+<li>
+<blockquote>
+<p>$$ a=1</p>
+</blockquote>
+</li>
+</ul>
+<p>$$ (1)</p>
+.

tests/test_texmath.py

@@ -80,6 +80,23 @@ def test_plugin_parse(data_regression):
     data_regression.check([t.as_dict() for t in tokens])
 
 
+@pytest.mark.parametrize(
+    "delimiters,opening,closing",
+    [
+        ("brackets", "\\[", "\\]"),
+        ("dollars", "$$", "$$"),
+        ("kramdown", "$$", "$$"),
+        ("gitlab", "```math", "```"),
+        ("julia", "```math", "```"),
+    ],
+)
+def test_block_closed_outside_blockquote(delimiters, opening, closing):
+    """A math block opened inside a blockquote cannot close after it."""
+    md = MarkdownIt("commonmark").use(texmath_plugin, delimiters=delimiters)
+    tokens = md.parse(f"> {opening} a=1\n\n{closing}\n")
+    assert not [t for t in tokens if t.type.startswith("math_block")]
+
+
 @pytest.mark.parametrize(
     "line,title,input,expected",
     read_fixture_file(FIXTURE_PATH.joinpath("texmath_dollar.md")),