[Backport maintenance/4.0.x] Fix too-many-locals counting PEP 695 type parameters as local variables (#11142)

Fix `too-many-locals` counting PEP 695 type parameters as local variables (#11138)

Fix too-many-locals counting PEP 695 type parameters as locals

astroid places PEP 695 type-param names in node.locals, so R0914 over-counted (def f[T1..T16](x) reported 17/15 for one real local). Exclude type params from the count. Closes #11136


(cherry picked from commit e628929)

Co-authored-by: Hibi <hibin.m@gmail.com>
Co-authored-by: Synvoya <16019863+Synvoya@users.noreply.github.com>

Author: pylint-backport[bot]

doc/whatsnew/fragments/11136.bugfix

@@ -0,0 +1,3 @@
+Fix a false positive for ``too-many-locals`` (``R0914``): PEP 695 type parameters (e.g. ``def f[T1, T2](...)``) were counted as local variables. They are type-system constructs, not runtime locals, and are now excluded from the local-variable count.
+
+Closes #11136

pylint/checkers/design_analysis.py

@@ -577,7 +577,10 @@ def visit_functiondef(self, node: nodes.FunctionDef) -> None:
                 )
 
         # check number of local variables
-        locnum = len(node.locals) - ignored_args_num
+        # PEP 695 type parameters live in the function's ``locals`` but are
+        # type-system constructs, not runtime local variables, so exclude them.
+        type_param_names = {param.name.name for param in node.type_params}
+        locnum = len(set(node.locals) - type_param_names) - ignored_args_num
 
         # decrement number of local variables if '_' is one of them
         if "_" in node.locals:

tests/functional/t/too/too_many_locals_py312.py

@@ -0,0 +1,31 @@
+# pylint: disable=missing-docstring,unused-variable,line-too-long
+
+
+# PEP 695 type parameters live in the function's locals but are type-system
+# constructs, not runtime local variables, so they must not be counted towards
+# ``too-many-locals``. This function has 16 type parameters but only one real
+# local variable, so it must NOT emit ``too-many-locals``.
+def build[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16](arg):
+    result = arg
+    return result
+
+
+# Mixed case: 16 type parameters plus 16 genuine local variables. Only the real
+# locals are counted, so this emits ``too-many-locals`` at 16/15 (not 32/15).
+def mixed[T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16](start):  # [too-many-locals]
+    loc0 = start
+    loc1 = loc0 * 1
+    loc2 = loc1 * 2
+    loc3 = loc2 * 3
+    loc4 = loc3 * 4
+    loc5 = loc4 * 5
+    loc6 = loc5 * 6
+    loc7 = loc6 * 7
+    loc8 = loc7 * 8
+    loc9 = loc8 * 9
+    loc10 = loc9 * 10
+    loc11 = loc10 * 11
+    loc12 = loc11 * 12
+    loc13 = loc12 * 13
+    loc14 = loc13 * 14
+    return loc14

tests/functional/t/too/too_many_locals_py312.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.12

tests/functional/t/too/too_many_locals_py312.txt

@@ -0,0 +1 @@
+too-many-locals:15:0:15:9:mixed:Too many local variables (16/15):UNDEFINED