Wrap concatenated strings used as function args in parens.

CHANGES.md

@@ -15,6 +15,8 @@
 <!-- Changes that affect Black's preview style -->
 
 - Enforce empty lines before classes and functions with sticky leading comments (#3302)
+- Implicitly concatenated strings used as function args are now wrapped inside
+  parentheses (#3307)
 
 ### Configuration
 

src/black/__init__.py

@@ -497,8 +497,10 @@ def main(  # noqa: C901
             user_level_config = str(find_user_pyproject_toml())
             if config == user_level_config:
                 out(
-                    "Using configuration from user-level config at "
-                    f"'{user_level_config}'.",
+                    (
+                        "Using configuration from user-level config at "
+                        f"'{user_level_config}'."
+                    ),
                     fg="blue",
                 )
             elif config_source in (

src/black/mode.py

@@ -180,8 +180,10 @@ class Mode:
     def __post_init__(self) -> None:
         if self.experimental_string_processing:
             warn(
-                "`experimental string processing` has been included in `preview`"
-                " and deprecated. Use `preview` instead.",
+                (
+                    "`experimental string processing` has been included in `preview`"
+                    " and deprecated. Use `preview` instead."
+                ),
                 Deprecated,
             )
 

src/black/parsing.py

@@ -29,9 +29,11 @@
 except ImportError:
     if sys.version_info < (3, 8) and not _IS_PYPY:
         print(
-            "The typed_ast package is required but not installed.\n"
-            "You can upgrade to Python 3.8+ or install typed_ast with\n"
-            "`python3 -m pip install typed-ast`.",
+            (
+                "The typed_ast package is required but not installed.\n"
+                "You can upgrade to Python 3.8+ or install typed_ast with\n"
+                "`python3 -m pip install typed-ast`."
+            ),
             file=sys.stderr,
         )
         sys.exit(1)

src/black/trans.py

@@ -1058,33 +1058,19 @@ def _prefer_paren_wrap_match(LL: List[Leaf]) -> Optional[int]:
         if LL[0].type != token.STRING:
             return None
 
-        matching_nodes = [
-            syms.listmaker,
-            syms.dictsetmaker,
-            syms.testlist_gexp,
-        ]
-        # If the string is an immediate child of a list/set/tuple literal...
-        if (
-            parent_type(LL[0]) in matching_nodes
-            or parent_type(LL[0].parent) in matching_nodes
+        # If the string is surrounded by commas (or is the first/last child)...
+        prev_sibling = LL[0].prev_sibling
+        next_sibling = LL[0].next_sibling
+        if not prev_sibling and not next_sibling and parent_type(LL[0]) == syms.atom:
+            # If it's an atom string, we need to check the parent atom's siblings.
+            parent = LL[0].parent
+            assert parent is not None  # For type checkers.
+            prev_sibling = parent.prev_sibling
+            next_sibling = parent.next_sibling
+        if (not prev_sibling or prev_sibling.type == token.COMMA) and (
+            not next_sibling or next_sibling.type == token.COMMA
         ):
-            # And the string is surrounded by commas (or is the first/last child)...
-            prev_sibling = LL[0].prev_sibling
-            next_sibling = LL[0].next_sibling
-            if (
-                not prev_sibling
-                and not next_sibling
-                and parent_type(LL[0]) == syms.atom
-            ):
-                # If it's an atom string, we need to check the parent atom's siblings.
-                parent = LL[0].parent
-                assert parent is not None  # For type checkers.
-                prev_sibling = parent.prev_sibling
-                next_sibling = parent.next_sibling
-            if (not prev_sibling or prev_sibling.type == token.COMMA) and (
-                not next_sibling or next_sibling.type == token.COMMA
-            ):
-                return 0
+            return 0
 
         return None
 
@@ -1653,9 +1639,8 @@ class StringParenWrapper(BaseStringSplitter, CustomSplitMapMixin):
         assigned the value of some string.
             OR
         * The line starts with an "atom" string that prefers to be wrapped in
-        parens. It's preferred to be wrapped when it's is an immediate child of
-        a list/set/tuple literal, AND the string is surrounded by commas (or is
-        the first/last child).
+        parens. It's preferred to be wrapped when the string is surrounded by
+        commas (or is the first/last child).
 
     Transformations:
         The chosen string is wrapped in parentheses and then split at the LPAR.

tests/data/preview/cantfit.py

@@ -79,10 +79,14 @@
 )
 # long arguments
 normal_name = normal_function_name(
-    "but with super long string arguments that on their own exceed the line limit so"
-    " there's no way it can ever fit",
-    "eggs with spam and eggs and spam with eggs with spam and eggs and spam with eggs"
-    " with spam and eggs and spam with eggs",
+    (
+        "but with super long string arguments that on their own exceed the line limit"
+        " so there's no way it can ever fit"
+    ),
+    (
+        "eggs with spam and eggs and spam with eggs with spam and eggs and spam with"
+        " eggs with spam and eggs and spam with eggs"
+    ),
     this_is_a_ridiculously_long_name_and_nobody_in_their_right_mind_would_use_one_like_it=0,
 )
 string_variable_name = "a string that is waaaaaaaayyyyyyyy too long, even in parens, there's nothing you can do"  # noqa

tests/data/preview/long_strings.py

@@ -297,8 +297,10 @@ def foo():
 y = "Short string"
 
 print(
-    "This is a really long string inside of a print statement with extra arguments"
-    " attached at the end of it.",
+    (
+        "This is a really long string inside of a print statement with extra arguments"
+        " attached at the end of it."
+    ),
     x,
     y,
     z,
@@ -474,13 +476,15 @@ def foo():
 )
 
 bad_split_func1(
-    "But what should happen when code has already "
-    "been formatted but in the wrong way? Like "
-    "with a space at the end instead of the "
-    "beginning. Or what about when it is split too "
-    "soon? In the case of a split that is too "
-    "short, black will try to honer the custom "
-    "split.",
+    (
+        "But what should happen when code has already "
+        "been formatted but in the wrong way? Like "
+        "with a space at the end instead of the "
+        "beginning. Or what about when it is split too "
+        "soon? In the case of a split that is too "
+        "short, black will try to honer the custom "
+        "split."
+    ),
     xxx,
     yyy,
     zzz,
@@ -583,9 +587,11 @@ def foo():
 )
 
 arg_comment_string = print(
-    "Long lines with inline comments which are apart of (and not the only member of) an"
-    " argument list should have their comments appended to the reformatted string's"
-    " enclosing left parentheses.",  # This comment gets thrown to the top.
+    (  # This comment gets thrown to the top.
+        "Long lines with inline comments which are apart of (and not the only member"
+        " of) an argument list should have their comments appended to the reformatted"
+        " string's enclosing left parentheses."
+    ),
     "Arg #2",
     "Arg #3",
     "Arg #4",
@@ -645,23 +651,31 @@ def foo():
 )
 
 func_with_bad_comma(
-    "This is a really long string argument to a function that has a trailing comma"
-    " which should NOT be there.",
+    (
+        "This is a really long string argument to a function that has a trailing comma"
+        " which should NOT be there."
+    ),
 )
 
 func_with_bad_comma(
-    "This is a really long string argument to a function that has a trailing comma"
-    " which should NOT be there.",  # comment after comma
+    (  # comment after comma
+        "This is a really long string argument to a function that has a trailing comma"
+        " which should NOT be there."
+    ),
 )
 
 func_with_bad_comma(
-    "This is a really long string argument to a function that has a trailing comma"
-    " which should NOT be there.",
+    (
+        "This is a really long string argument to a function that has a trailing comma"
+        " which should NOT be there."
+    ),
 )
 
 func_with_bad_comma(
-    "This is a really long string argument to a function that has a trailing comma"
-    " which should NOT be there.",  # comment after comma
+    (  # comment after comma
+        "This is a really long string argument to a function that has a trailing comma"
+        " which should NOT be there."
+    ),
 )
 
 func_with_bad_parens_that_wont_fit_in_one_line(

tests/data/preview/long_strings__regression.py

@@ -679,9 +679,11 @@ class A:
     def foo():
         some_func_call(
             "xxxxxxxxxx",
-            "xx {xxxxxxxxxxx}/xxxxxxxxxxx.xxx xxxx.xxx && xxxxxx -x "
-            '"xxxx xxxxxxx xxxxxx xxxx; xxxx xxxxxx_xxxxx xxxxxx xxxx; '
-            "xxxx.xxxx_xxxxxx(['xxxx.xxx'], xxxx.xxxxxxx().xxxxxxxxxx)\" ",
+            (
+                "xx {xxxxxxxxxxx}/xxxxxxxxxxx.xxx xxxx.xxx && xxxxxx -x "
+                '"xxxx xxxxxxx xxxxxx xxxx; xxxx xxxxxx_xxxxx xxxxxx xxxx; '
+                "xxxx.xxxx_xxxxxx(['xxxx.xxx'], xxxx.xxxxxxx().xxxxxxxxxx)\" "
+            ),
             None,
             ("xxxxxxxxxxx",),
         ),
@@ -690,9 +692,11 @@ def foo():
 class A:
     def foo():
         some_func_call(
-            "xx {xxxxxxxxxxx}/xxxxxxxxxxx.xxx xxxx.xxx && xxxxxx -x "
-            "xxxx, ('xxxxxxx xxxxxx xxxx, xxxx') xxxxxx_xxxxx xxxxxx xxxx; "
-            "xxxx.xxxx_xxxxxx(['xxxx.xxx'], xxxx.xxxxxxx().xxxxxxxxxx)\" ",
+            (
+                "xx {xxxxxxxxxxx}/xxxxxxxxxxx.xxx xxxx.xxx && xxxxxx -x "
+                "xxxx, ('xxxxxxx xxxxxx xxxx, xxxx') xxxxxx_xxxxx xxxxxx xxxx; "
+                "xxxx.xxxx_xxxxxx(['xxxx.xxx'], xxxx.xxxxxxx().xxxxxxxxxx)\" "
+            ),
             None,
             ("xxxxxxxxxxx",),
         ),
@@ -810,8 +814,10 @@ def foo():
 )
 
 lpar_and_rpar_have_comments = func_call(  # LPAR Comment
-    "Long really ridiculous type of string that shouldn't really even exist at all. I"
-    " mean commmme onnn!!!",  # Comma Comment
+    (  # Comma Comment
+        "Long really ridiculous type of string that shouldn't really even exist at all."
+        " I mean commmme onnn!!!"
+    ),
 )  # RPAR Comment
 
 cmd_fstring = (