Fix bug which causes f-expressions to be split (#1809)

Closes #1807.

diff --git a/src/black/__init__.py b/src/black/__init__.py
index e09838d866a1f3071079858fc12afc70575cdff8..7a7456ad78b7217c93a5f85993b998bdb281c6d7 100644 (file)
--- a/src/black/__init__.py
+++ b/src/black/__init__.py
@@ -3611,13 +3611,14 @@ class StringSplitter(CustomSplitMapMixin, BaseStringSplitter):
     MIN_SUBSTR_SIZE = 6
     # Matches an "f-expression" (e.g. {var}) that might be found in an f-string.
     RE_FEXPR = r"""
-    (?<!\{)\{
+    (?<!\{) (?:\{\{)* \{ (?!\{)
         (?:
             [^\{\}]
             | \{\{
             | \}\}
+            | (?R)
         )+?
-    (?<!\})(?:\}\})*\}(?!\})
+    (?<!\}) \} (?:\}\})* (?!\})
     """
 
     def do_splitter_match(self, line: Line) -> TMatchResult:

diff --git a/tests/data/long_strings__regression.py b/tests/data/long_strings__regression.py
index 9bfb1eedd5aaef71c73c5c19790b61e014b12d54..7065b2fcef85220f0a8d3a9c4c53a18f1c3c6a5b 100644 (file)
--- a/tests/data/long_strings__regression.py
+++ b/tests/data/long_strings__regression.py
@@ -371,6 +371,10 @@ RE_THREE_BACKSLASHES = {
     ),
 }
 
+# We do NOT split on f-string expressions.
+print(f"Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam. {[f'{i}' for i in range(10)]}")
+x = f"This is a long string which contains an f-expr that should not split {{{[i for i in range(5)]}}}."
+
 # output
 
 
@@ -830,3 +834,13 @@ RE_THREE_BACKSLASHES = {
         r"(?<!([0-9]\ ))(?<=(^|\ ))([A-Z]+(\ )?|[0-9](\ )|[a-z](\\\ )){4,7}([A-Z]|[0-9]|[a-z])($|\b)(?!(\ ?([0-9]\ )|(\.)))"
     ),
 }
+
+# We do NOT split on f-string expressions.
+print(
+    "Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam."
+    f" {[f'{i}' for i in range(10)]}"
+)
+x = (
+    "This is a long string which contains an f-expr that should not split"
+    f" {{{[i for i in range(5)]}}}."
+)