Disallow single-line implicit concatenated strings (#13928)

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

@@ -138,3 +138,60 @@ a = f"""\x1F"""
 a = """\x1F"""
 a = """\\x1F"""
 a = """\\\x1F"""
+
+
+##############################################################################
+# Implicit concatenated strings
+##############################################################################
+
+# In preview, don't collapse implicit concatenated strings that can't be joined into a single string
+# and that are multiline in the source.
+
+(
+    r"aaaaaaaaa"
+    r"bbbbbbbbbbbbbbbbbbbb"
+)
+
+(
+    r"aaaaaaaaa" r"bbbbbbbbbbbbbbbbbbbb"
+    "cccccccccccccccccccccc"
+)
+
+(
+    """aaaaaaaaa"""
+    """bbbbbbbbbbbbbbbbbbbb"""
+)
+
+(
+    f"""aaaa{
+    10}aaaaa"""
+    fr"""bbbbbbbbbbbbbbbbbbbb"""
+)
+
+if (
+       r"aaaaaaaaa"
+       r"bbbbbbbbbbbbbbbbbbbb"
+   ) + ["aaaaaaaaaa", "bbbbbbbbbbbbbbbb"]: ...
+
+
+
+# In preview, keep implicit concatenated strings on a single line if they fit and are not separate by line breaks in the source
+(
+    r"aaaaaaaaa" r"bbbbbbbbbbbbbbbbbbbb"
+)
+
+r"aaaaaaaaa" r"bbbbbbbbbbbbbbbbbbbb"
+
+(
+    f"aaaa{
+    10}aaaaa" fr"bbbbbbbbbbbbbbbbbbbb"
+)
+
+(
+    r"""aaaaaaaaa""" r"""bbbbbbbbbbbbbbbbbbbb"""
+)
+
+(
+    f"""aaaa{
+    10}aaaaa""" fr"""bbbbbbbbbbbbbbbbbbbb"""
+)