From 4adf5228d6235d1b52da70bd62bdbb6f97a60a18 Mon Sep 17 00:00:00 2001
From: Abhay <abhayjnayakpro@gmail.com>
Date: Sun, 19 Apr 2026 22:47:08 +0530
Subject: [PATCH] Add validation for --line-ranges values in parse_line_ranges

The parse_line_ranges function previously accepted invalid ranges like
'5-3' (start > end) or '0-5' (non-positive line numbers) without
raising an error. This adds proper validation with clear error messages.
---
 src/black/ranges.py  | 10 ++++++++++
 tests/test_ranges.py | 28 +++++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/black/ranges.py b/src/black/ranges.py
index d7e003db83f..a1771f80834 100644
--- a/src/black/ranges.py
+++ b/src/black/ranges.py
@@ -36,6 +36,16 @@ def parse_line_ranges(line_ranges: Sequence[str]) -> list[tuple[int, int]]:
                 f" {lines_str!r}"
             ) from None
         else:
+            if start < 1 or end < 1:
+                raise ValueError(
+                    "Incorrect --line-ranges value, "
+                    f"expect positive integers, found {lines_str!r}"
+                )
+            if start > end:
+                raise ValueError(
+                    "Incorrect --line-ranges value, expect START <= END, "
+                    f"found {lines_str!r}"
+                )
             lines.append((start, end))
     return lines
 
diff --git a/tests/test_ranges.py b/tests/test_ranges.py
index 0ed0e989123..dd85123a574 100644
--- a/tests/test_ranges.py
+++ b/tests/test_ranges.py
@@ -2,7 +2,33 @@
 
 import pytest
 
-from black.ranges import adjusted_lines, sanitized_lines
+from black.ranges import adjusted_lines, parse_line_ranges, sanitized_lines
+
+
+@pytest.mark.parametrize(
+    "lines_str, expected",
+    [
+        (["1-5"], [(1, 5)]),
+        (["1-1"], [(1, 1)]),
+        (["1-3", "5-7"], [(1, 3), (5, 7)]),
+    ],
+)
+def test_parse_line_ranges_valid(lines_str, expected):
+    assert parse_line_ranges(lines_str) == expected
+
+
+@pytest.mark.parametrize(
+    "lines_str",
+    [
+        ["5-3"],
+        ["0-5"],
+        ["-1-5"],
+        ["5-0"],
+    ],
+)
+def test_parse_line_ranges_invalid(lines_str):
+    with pytest.raises(ValueError, match="Incorrect --line-ranges"):
+        parse_line_ranges(lines_str)
 
 
 @pytest.mark.parametrize(