From fa542c2806311341a001b859fea6f34bd79412aa Mon Sep 17 00:00:00 2001
From: YagUber <dev.yaguber@pm.me>
Date: Mon, 14 Sep 2026 15:16:32 -0500
Subject: [PATCH] fix(parser): do not mangle preprocessor directives

---
 abp/filters/parser.py  |  6 ++++++
 tests/test_parser.py   | 24 ++++++++++++++++++++++++
 tests/test_renderer.py |  9 +++++++++
 3 files changed, 39 insertions(+)

diff --git a/abp/filters/parser.py b/abp/filters/parser.py
index d190e58..be9a8e7 100644
--- a/abp/filters/parser.py
+++ b/abp/filters/parser.py
@@ -184,6 +184,7 @@ def _line_type(name, field_names, format_string):
 Header = _line_type("Header", "version", "[{.version}]")
 EmptyLine = _line_type("EmptyLine", "", "")
 Comment = _line_type("Comment", "text", "! {.text}")
+Preprocessor = _line_type("Preprocessor", "text", "!#{.text}")
 Metadata = _line_type("Metadata", "key value", "! {0.key}: {0.value}")
 Filter = _line_type("Filter", "text selector action options", "{.text}")
 Include = _line_type("Include", "target", "%include {0.target}%")
@@ -414,6 +415,11 @@ def parse_line(line, position="body"):
         if match:
             return Header(match.group(1))
 
+    if stripped.startswith("!#"):
+        directive = stripped[2:]
+        if directive and not directive[:1].isspace():
+            return Preprocessor(directive)
+
     if stripped.startswith("!"):
         match = METADATA_REGEXP.match(line)
         if match:
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 9686024..7d5d075 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -176,6 +176,30 @@ def test_parse_filters(filter_text, expected):
         assert getattr(parsed, attribute) == expected_value
 
 
+@pytest.mark.parametrize("text", [
+    "!#if (foo || bar)",
+    "!#else",
+    "!#endif",
+    "!#include my_filter.txt",
+])
+def test_parse_preprocessor_directive(text):
+    line = parse_line(text)
+    assert line.type == "preprocessor"
+    assert line.to_string() == text
+
+
+def test_parse_bad_preprocessor_directive():
+    line = parse_line("! #if bar")
+    assert line.type == "comment"
+    assert line.to_string() == "! #if bar"
+
+
+def test_parse_bare_directive_as_comment():
+    line = parse_line("!#")
+    assert line.type == "comment"
+    assert line.to_string() == "! #"
+
+
 def test_parse_comment():
     line = parse_line("! Block foo")
     assert line.type == "comment"
diff --git a/tests/test_renderer.py b/tests/test_renderer.py
index 0595031..07fc773 100644
--- a/tests/test_renderer.py
+++ b/tests/test_renderer.py
@@ -122,3 +122,12 @@ def test_remove_checksum(head):
     src = MockSource(fl="[Adblock]\n! Comment\n! Checksum: foo")
     got = render_str("fl", {}, src)
     assert got == head + "! Comment"
+
+
+def test_preprocessor_directives(head):
+    src = MockSource(
+        fl="[Adblock]\n%include fragment%",
+        fragment="!#if foo\n||example.com^\n!#endif",
+    )
+    got = render_str("fl", {}, src)
+    assert "!#if foo\n||example.com^\n!#endif" in got