From dab37a6a1117d690d683121edc4d7c8fb8dd75a7 Mon Sep 17 00:00:00 2001
From: Logan Hunt <39638017+dosisod@users.noreply.github.com>
Date: Wed, 7 Feb 2024 06:55:02 -0800
Subject: [PATCH] Remove redundant parentheses in `case` statement `if` guards
 (#4214)

A follow up to #4024 but for `if` guards in `case` statements. I noticed this
when #4024 was made stable, and noticed I had some code that had extra parens
around the `if` guard.
---
 CHANGES.md                                    |   1 +
 docs/the_black_code_style/future_style.md     |   2 +
 src/black/linegen.py                          |   2 +
 src/black/mode.py                             |   1 +
 src/black/resources/black.schema.json         |   3 +-
 .../remove_redundant_parens_in_case_guard.py  | 114 ++++++++++++++++++
 6 files changed, 122 insertions(+), 1 deletion(-)
 create mode 100644 tests/data/cases/remove_redundant_parens_in_case_guard.py

diff --git a/CHANGES.md b/CHANGES.md
index 5d4858da811..3583348f377 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -20,6 +20,7 @@
   expression (#4154)
 - Checking for newline before adding one on docstring that is almost at the line limit
   (#4185)
+- Remove redundant parentheses in `case` statement `if` guards (#4214).
 
 ### Configuration
 
diff --git a/docs/the_black_code_style/future_style.md b/docs/the_black_code_style/future_style.md
index f4534680645..4ae46cecded 100644
--- a/docs/the_black_code_style/future_style.md
+++ b/docs/the_black_code_style/future_style.md
@@ -32,6 +32,8 @@ Currently, the following features are included in the preview style:
   expressions that involve the power operator
 - `docstring_check_for_newline`: checks if there is a newline before the terminating
   quotes of a docstring
+- `remove_redundant_guard_parens`: Removes redundant parentheses in `if` guards for
+  `case` blocks.
 
 (labels/unstable-features)=
 
diff --git a/src/black/linegen.py b/src/black/linegen.py
index c45a1308013..2b7fbc492cf 100644
--- a/src/black/linegen.py
+++ b/src/black/linegen.py
@@ -529,6 +529,8 @@ def __post_init__(self) -> None:
         # PEP 634
         self.visit_match_stmt = self.visit_match_case
         self.visit_case_block = self.visit_match_case
+        if Preview.remove_redundant_guard_parens in self.mode:
+            self.visit_guard = partial(v, keywords=Ø, parens={"if"})
 
 
 def _hugging_power_ops_line_to_string(
diff --git a/src/black/mode.py b/src/black/mode.py
index f9fad082e03..90c10c324a5 100644
--- a/src/black/mode.py
+++ b/src/black/mode.py
@@ -179,6 +179,7 @@ class Preview(Enum):
     typed_params_trailing_comma = auto()
     is_simple_lookup_for_doublestar_expression = auto()
     docstring_check_for_newline = auto()
+    remove_redundant_guard_parens = auto()
 
 
 UNSTABLE_FEATURES: Set[Preview] = {
diff --git a/src/black/resources/black.schema.json b/src/black/resources/black.schema.json
index 04ddb32e087..8252a6c4bd8 100644
--- a/src/black/resources/black.schema.json
+++ b/src/black/resources/black.schema.json
@@ -87,7 +87,8 @@
           "multiline_string_handling",
           "typed_params_trailing_comma",
           "is_simple_lookup_for_doublestar_expression",
-          "docstring_check_for_newline"
+          "docstring_check_for_newline",
+          "remove_redundant_guard_parens"
         ]
       },
       "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."
diff --git a/tests/data/cases/remove_redundant_parens_in_case_guard.py b/tests/data/cases/remove_redundant_parens_in_case_guard.py
new file mode 100644
index 00000000000..bec4a3c3fcd
--- /dev/null
+++ b/tests/data/cases/remove_redundant_parens_in_case_guard.py
@@ -0,0 +1,114 @@
+# flags: --minimum-version=3.10 --preview --line-length=79
+
+match 1:
+    case _ if (True):
+        pass
+
+
+match 1:
+    case _ if (
+        True
+    ):
+        pass
+
+
+match 1:
+    case _ if (
+        # this is a comment
+        True
+    ):
+        pass
+
+
+match 1:
+    case _ if (
+        True
+        # this is a comment
+    ):
+        pass
+
+
+match 1:
+    case _ if (
+        True  # this is a comment
+    ):
+        pass
+
+
+match 1:
+    case _ if (  # this is a comment
+        True
+    ):
+        pass
+
+
+match 1:
+    case _ if (
+        True
+    ):  # this is a comment
+        pass
+
+
+match 1:
+    case _ if (True):  # comment over the line limit unless parens are removed x
+        pass
+
+
+match 1:
+    case _ if (True):  # comment over the line limit and parens should go to next line
+        pass
+
+
+# output
+
+match 1:
+    case _ if True:
+        pass
+
+
+match 1:
+    case _ if True:
+        pass
+
+
+match 1:
+    case _ if (
+        # this is a comment
+        True
+    ):
+        pass
+
+
+match 1:
+    case _ if (
+        True
+        # this is a comment
+    ):
+        pass
+
+
+match 1:
+    case _ if True:  # this is a comment
+        pass
+
+
+match 1:
+    case _ if True:  # this is a comment
+        pass
+
+
+match 1:
+    case _ if True:  # this is a comment
+        pass
+
+
+match 1:
+    case _ if True:  # comment over the line limit unless parens are removed x
+        pass
+
+
+match 1:
+    case (
+        _
+    ) if True:  # comment over the line limit and parens should go to next line
+        pass