Fix formatting for if clauses in match-case blocks (#4269)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

CHANGES.md

@@ -14,6 +14,9 @@
 
 <!-- Changes that affect Black's preview style -->
 
+- `if` guards in `case` blocks are now wrapped in parentheses when the line is too long.
+  (#4269)
+
 ### Configuration
 
 <!-- Changes to how Black can be configured -->

docs/the_black_code_style/future_style.md

@@ -34,6 +34,8 @@ Currently, the following features are included in the preview style:
   quotes of a docstring
 - `remove_redundant_guard_parens`: Removes redundant parentheses in `if` guards for
   `case` blocks.
+- `parens_for_long_if_clauses_in_case_block`: Adds parentheses to `if` clauses in `case`
+  blocks when the the line is too long
 
 (labels/unstable-features)=
 

src/black/linegen.py

@@ -1310,6 +1310,16 @@ def normalize_invisible_parens(  # noqa: C901
                 child, parens_after={"case"}, mode=mode, features=features
             )
 
+        # Add parentheses around if guards in case blocks
+        if (
+            isinstance(child, Node)
+            and child.type == syms.guard
+            and Preview.parens_for_long_if_clauses_in_case_block in mode
+        ):
+            normalize_invisible_parens(
+                child, parens_after={"if"}, mode=mode, features=features
+            )
+
         # Add parentheses around long tuple unpacking in assignments.
         if (
             index == 0

src/black/mode.py

@@ -180,6 +180,7 @@ class Preview(Enum):
     is_simple_lookup_for_doublestar_expression = auto()
     docstring_check_for_newline = auto()
     remove_redundant_guard_parens = auto()
+    parens_for_long_if_clauses_in_case_block = auto()
 
 
 UNSTABLE_FEATURES: Set[Preview] = {

src/black/resources/black.schema.json

@@ -88,7 +88,8 @@
           "typed_params_trailing_comma",
           "is_simple_lookup_for_doublestar_expression",
           "docstring_check_for_newline",
-          "remove_redundant_guard_parens"
+          "remove_redundant_guard_parens",
+          "parens_for_long_if_clauses_in_case_block"
         ]
       },
       "description": "Enable specific features included in the `--unstable` style. Requires `--preview`. No compatibility guarantees are provided on the behavior or existence of any unstable features."

tests/data/cases/pattern_matching_complex.py

@@ -83,7 +83,7 @@
 match x:
     case [0]:
         y = 0
-    case [1, 0] if (x := x[:0]):
+    case [1, 0] if x := x[:0]:
         y = 1
     case [1, 0]:
         y = 2

tests/data/cases/pattern_matching_with_if_stmt.py

@@ -0,0 +1,72 @@
+# flags: --preview --minimum-version=3.10
+match match:
+    case "test" if case != "not very loooooooooooooog condition":  # comment
+        pass
+
+match smth:
+    case "test" if "any long condition" != "another long condition" and "this is a long condition":
+        pass
+    case test if "any long condition" != "another long condition" and "this is a looooong condition":
+        pass
+    case test if "any long condition" != "another long condition" and "this is a looooong condition":  # some additional comments
+        pass
+    case test if (True): # some comment
+        pass
+    case test if (False
+        ): # some comment
+        pass
+    case test if (True  # some comment
+        ):
+        pass  # some comment
+    case cases if (True  # some comment
+                   ): # some other comment
+        pass  # some comment
+    case match if (True  # some comment
+                   ):
+        pass  # some comment
+
+# case black_test_patma_052 (originally in the pattern_matching_complex test case)
+match x:
+    case [1, 0] if x := x[:0]:
+        y = 1
+    case [1, 0] if (x := x[:0]):
+        y = 1
+
+# output
+
+match match:
+    case "test" if case != "not very loooooooooooooog condition":  # comment
+        pass
+
+match smth:
+    case "test" if (
+        "any long condition" != "another long condition" and "this is a long condition"
+    ):
+        pass
+    case test if (
+        "any long condition" != "another long condition"
+        and "this is a looooong condition"
+    ):
+        pass
+    case test if (
+        "any long condition" != "another long condition"
+        and "this is a looooong condition"
+    ):  # some additional comments
+        pass
+    case test if True:  # some comment
+        pass
+    case test if False:  # some comment
+        pass
+    case test if True:  # some comment
+        pass  # some comment
+    case cases if True:  # some comment  # some other comment
+        pass  # some comment
+    case match if True:  # some comment
+        pass  # some comment
+
+# case black_test_patma_052 (originally in the pattern_matching_complex test case)
+match x:
+    case [1, 0] if x := x[:0]:
+        y = 1
+    case [1, 0] if x := x[:0]:
+        y = 1