From 721dff549362f54930ecc038218dcc40e599a875 Mon Sep 17 00:00:00 2001
From: Tushar Sadhwani <tushar.sadhwani000@gmail.com>
Date: Thu, 11 Jul 2024 08:22:37 +0530
Subject: [PATCH] fix: avoid formatting backslash strings inside f-strings
 (#4401)

---
 CHANGES.md                  | 3 +++
 src/black/linegen.py        | 9 +++++++++
 tests/data/cases/pep_701.py | 6 ++++++
 3 files changed, 18 insertions(+)

diff --git a/CHANGES.md b/CHANGES.md
index a63503d539a..e3e37484a59 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -34,6 +34,9 @@
 - Fix regression where Black failed to parse a multiline f-string containing another
   multiline string (#4339)
 
+- Fix regression where Black failed to parse an escaped single quote inside an f-string
+  (#4401)
+
 - Fix bug with Black incorrectly parsing empty lines with a backslash (#4343)
 
 ### Performance
diff --git a/src/black/linegen.py b/src/black/linegen.py
index 9d22a7e7854..46945ca2a14 100644
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -510,6 +510,15 @@ def visit_fstring(self, node: Node) -> Iterator[Line]:
         # currently we don't want to format and split f-strings at all.
         string_leaf = fstring_to_string(node)
         node.replace(string_leaf)
+        if "\\" in string_leaf.value and any(
+            "\\" in str(child)
+            for child in node.children
+            if child.type == syms.fstring_replacement_field
+        ):
+            # string normalization doesn't account for nested quotes,
+            # causing breakages. skip normalization when nested quotes exist
+            yield from self.visit_default(string_leaf)
+            return
         yield from self.visit_STRING(string_leaf)
 
         # TODO: Uncomment Implementation to format f-string children
diff --git a/tests/data/cases/pep_701.py b/tests/data/cases/pep_701.py
index d72d91c6799..717927d206d 100644
--- a/tests/data/cases/pep_701.py
+++ b/tests/data/cases/pep_701.py
@@ -128,6 +128,9 @@
 f"""{'''
 '''}"""
 
+f"{'\''}"
+f"{f'\''}"
+
 # output
 
 x = f"foo"
@@ -258,3 +261,6 @@
 
 f"""{'''
 '''}"""
+
+f"{'\''}"
+f"{f'\''}"