From b677a643c5322b6af2dbca1f8f7a4f8c98e732aa Mon Sep 17 00:00:00 2001
From: Tushar Sadhwani <tushar.sadhwani000@gmail.com>
Date: Sun, 2 Jun 2024 01:31:36 +0530
Subject: [PATCH] tokenizer: skip lines that are just slash and whitespace
 (#4343)

---
 AUTHORS.md                                    |  1 +
 CHANGES.md                                    |  2 ++
 src/blib2to3/pgen2/tokenize.py                |  6 +++++
 tests/data/cases/backslash_before_indent.py   | 24 +++++++++++++++++++
 .../cases/comment_after_escaped_newline.py    |  4 +++-
 tests/data/cases/form_feeds.py                |  1 +
 6 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 tests/data/cases/backslash_before_indent.py

diff --git a/AUTHORS.md b/AUTHORS.md
index e0511bb9b7c..fa1ce8f7112 100644
--- a/AUTHORS.md
+++ b/AUTHORS.md
@@ -181,6 +181,7 @@ Multiple contributions by:
 - [Tony Narlock](mailto:tony@git-pull.com)
 - [Tsuyoshi Hombashi](mailto:tsuyoshi.hombashi@gmail.com)
 - [Tushar Chandra](mailto:tusharchandra2018@u.northwestern.edu)
+- [Tushar Sadhwani](mailto:tushar.sadhwani000@gmail.com)
 - [Tzu-ping Chung](mailto:uranusjr@gmail.com)
 - [Utsav Shah](mailto:ukshah2@illinois.edu)
 - utsav-dbx
diff --git a/CHANGES.md b/CHANGES.md
index 68a2fe35205..a63503d539a 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -34,6 +34,8 @@
 - Fix regression where Black failed to parse a multiline f-string containing another
   multiline string (#4339)
 
+- Fix bug with Black incorrectly parsing empty lines with a backslash (#4343)
+
 ### Performance
 
 <!-- Changes that improve Black's performance. -->
diff --git a/src/blib2to3/pgen2/tokenize.py b/src/blib2to3/pgen2/tokenize.py
index b86b91ed37f..28972a9bd78 100644
--- a/src/blib2to3/pgen2/tokenize.py
+++ b/src/blib2to3/pgen2/tokenize.py
@@ -608,6 +608,12 @@ def generate_tokens(
         except StopIteration:
             line = ""
         lnum += 1
+
+        # skip lines that are just indent characters ending with a slash
+        # to avoid storing that line's indent information.
+        if not contstr and line.rstrip("\n").strip(" \t\f") == "\\":
+            continue
+
         pos, max = 0, len(line)
 
         if contstr:  # continued string
diff --git a/tests/data/cases/backslash_before_indent.py b/tests/data/cases/backslash_before_indent.py
new file mode 100644
index 00000000000..2d126a945e4
--- /dev/null
+++ b/tests/data/cases/backslash_before_indent.py
@@ -0,0 +1,24 @@
+# flags: --minimum-version=3.10
+class Plotter:
+\
+    pass
+
+class AnotherCase:
+  \
+    """Some
+    \
+    Docstring
+    """
+
+# output
+
+class Plotter:
+
+    pass
+
+
+class AnotherCase:
+    """Some
+    \
+    Docstring
+    """
diff --git a/tests/data/cases/comment_after_escaped_newline.py b/tests/data/cases/comment_after_escaped_newline.py
index 133f4898a47..133c230a3a8 100644
--- a/tests/data/cases/comment_after_escaped_newline.py
+++ b/tests/data/cases/comment_after_escaped_newline.py
@@ -14,5 +14,7 @@ def bob():  # pylint: disable=W9016
     pass
 
 
-def bobtwo():  # some comment here
+def bobtwo():
+
+    # some comment here
     pass
diff --git a/tests/data/cases/form_feeds.py b/tests/data/cases/form_feeds.py
index 48ffc98106b..957b4a1db95 100644
--- a/tests/data/cases/form_feeds.py
+++ b/tests/data/cases/form_feeds.py
@@ -156,6 +156,7 @@ def something(self):
 
 #
 
+
 #
 pass