Unify a codepath in typevarlike semanal (#12480)

mypy/semanal.py

@@ -3093,14 +3093,8 @@ def process_typevar_declaration(self, s: AssignmentStmt) -> bool:
         if not call:
             return False
 
-        lvalue = s.lvalues[0]
-        assert isinstance(lvalue, NameExpr)
-        if s.type:
-            self.fail("Cannot declare the type of a type variable", s)
-            return False
-
-        name = lvalue.name
-        if not self.check_typevarlike_name(call, name, s):
+        name = self.extract_typevarlike_name(s, call)
+        if name is None:
             return False
 
         # Constraining types
@@ -3279,6 +3273,20 @@ def process_typevar_parameters(self, args: List[Expression],
             variance = INVARIANT
         return variance, upper_bound
 
+    def extract_typevarlike_name(self, s: AssignmentStmt, call: CallExpr) -> Optional[str]:
+        if not call:
+            return None
+
+        lvalue = s.lvalues[0]
+        assert isinstance(lvalue, NameExpr)
+        if s.type:
+            self.fail("Cannot declare the type of a TypeVar or similar construct", s)
+            return None
+
+        if not self.check_typevarlike_name(call, lvalue.name, s):
+            return None
+        return lvalue.name
+
     def process_paramspec_declaration(self, s: AssignmentStmt) -> bool:
         """Checks if s declares a ParamSpec; if yes, store it in symbol table.
 
@@ -3293,14 +3301,8 @@ def process_paramspec_declaration(self, s: AssignmentStmt) -> bool:
         if not call:
             return False
 
-        lvalue = s.lvalues[0]
-        assert isinstance(lvalue, NameExpr)
-        if s.type:
-            self.fail("Cannot declare the type of a parameter specification", s)
-            return False
-
-        name = lvalue.name
-        if not self.check_typevarlike_name(call, name, s):
+        name = self.extract_typevarlike_name(s, call)
+        if name is None:
             return False
 
         # ParamSpec is different from a regular TypeVar:

test-data/unit/semanal-errors.test

@@ -1081,7 +1081,7 @@ x = TypeVar('x') # E: Cannot redefine "x" as a type variable
 
 [case testTypevarWithType]
 from typing import TypeVar
-x = TypeVar('x') # type: int # E: Cannot declare the type of a type variable
+x = TypeVar('x') # type: int # E: Cannot declare the type of a TypeVar or similar construct
 [out]
 
 [case testRedefineTypevar]
@@ -1432,7 +1432,7 @@ from typing_extensions import ParamSpec
 
 TParams = ParamSpec('TParams')
 TP = ParamSpec('?')  # E: String argument 1 "?" to ParamSpec(...) does not match variable name "TP"
-TP2: int = ParamSpec('TP2')  # E: Cannot declare the type of a parameter specification
+TP2: int = ParamSpec('TP2')  # E: Cannot declare the type of a TypeVar or similar construct
 
 [out]