Avoid incrementing McCabe complexity for class methods (#857)

resources/test/fixtures/C901.py

@@ -106,3 +106,33 @@ async def foobar(a, b, c):
 # Complexity = 1
 def annotated_assign():
     x: Any = None
+
+
+# Complexity = 9
+class Class:
+    def handle(self, *args, **options):
+        if args:
+            return
+
+        class ServiceProvider:
+            def a(self):
+                pass
+
+            def b(self, data):
+                if not args:
+                    pass
+
+        class Logger:
+            def c(*args, **kwargs):
+                pass
+
+            def error(self, message):
+                pass
+
+            def info(self, message):
+                pass
+
+            def exception(self):
+                pass
+
+        return ServiceProvider(Logger())

src/mccabe/checks.rs

@@ -46,7 +46,6 @@ fn get_complexity_number(stmts: &[Stmt]) -> usize {
                 complexity += get_complexity_number(body);
             }
             StmtKind::ClassDef { body, .. } => {
-                complexity += 1;
                 complexity += get_complexity_number(body);
             }
             _ => {}

src/mccabe/snapshots/ruff__mccabe__tests__max_complexity_0.snap

@@ -164,7 +164,84 @@ expression: checks
     row: 107
     column: 0
   end_location:
-    row: 109
+    row: 112
     column: 0
   fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - handle
+      - 9
+  location:
+    row: 113
+    column: 4
+  end_location:
+    row: 139
+    column: 0
+  fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - a
+      - 1
+  location:
+    row: 118
+    column: 12
+  end_location:
+    row: 121
+    column: 12
+  fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - b
+      - 2
+  location:
+    row: 121
+    column: 12
+  end_location:
+    row: 125
+    column: 8
+  fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - c
+      - 1
+  location:
+    row: 126
+    column: 12
+  end_location:
+    row: 129
+    column: 12
+  fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - error
+      - 1
+  location:
+    row: 129
+    column: 12
+  end_location:
+    row: 132
+    column: 12
+  fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - info
+      - 1
+  location:
+    row: 132
+    column: 12
+  end_location:
+    row: 135
+    column: 12
+  fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - exception
+      - 1
+  location:
+    row: 135
+    column: 12
+  end_location:
+    row: 138
+    column: 8
+  fix: ~
 

src/mccabe/snapshots/ruff__mccabe__tests__max_complexity_3.snap

@@ -13,4 +13,15 @@ expression: checks
     row: 85
     column: 0
   fix: ~
+- kind:
+    FunctionIsTooComplex:
+      - handle
+      - 9
+  location:
+    row: 113
+    column: 4
+  end_location:
+    row: 139
+    column: 0
+  fix: ~