Consider quotes inside format-specs when choosing the quotes for an f-string (#14493)

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/fstring_py312.py

@@ -15,3 +15,31 @@ f'{"""other " """ + "more"}'
 f'{b"""other " """}'
 f'{f"""other " """}'
 
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/13935
+f'{1: hy "user"}'
+f'{1:hy "user"}'
+f'{1: abcd "{1}" }'
+f'{1: abcd "{'aa'}" }'
+f'{1=: "abcd {'aa'}}'
+f'{x:a{z:hy "user"}} \'\'\''
+
+# Changing the outer quotes is fine because the format-spec is in a nested expression.
+f'{f'{z=:hy "user"}'} \'\'\''
+
+
+#  We have to be careful about changing the quotes if the f-string has a debug expression because it is inserted verbatim.
+f'{1=: "abcd \'\'}'  # Don't change the outer quotes, or it results in a syntax error
+f'{1=: abcd \'\'}'  # Changing the quotes here is fine because the inner quotes aren't the opposite quotes
+f'{1=: abcd \"\"}'  # Changing the quotes here is fine because the inner quotes are escaped
+# Don't change the quotes in the following cases:
+f'{x=:hy "user"} \'\'\''
+f'{x=:a{y:hy "user"}} \'\'\''
+f'{x=:a{y:{z:hy "user"}}} \'\'\''
+f'{x:a{y=:{z:hy "user"}}} \'\'\''
+
+# This is fine because the debug expression and format spec are in a nested expression
+
+f"""{1=: "this" is fine}"""
+f'''{1=: "this" is fine}'''  # Change quotes to double quotes because they're preferred
+f'{1=: {'ab"cd"'}}'  # It's okay if the quotes are in an expression part.

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/join_implicit_concatenated_string.py

@@ -319,3 +319,10 @@ assert False, "Implicit concatenated stringuses {} layout on {} format"[
 assert False, +"Implicit concatenated string" "uses {} layout on {} format".format(
     "Multiline", "first"
 )
+
+
+# Regression tests for https://github.com/astral-sh/ruff/issues/13935
+
+"a" f'{1=: "abcd \'\'}'
+f'{1=: "abcd \'\'}' "a"
+f'{1=: "abcd \'\'}' f"{1=: 'abcd \"\"}"