Add better type deduction to use-startswith-endswith-tuple check:

Also do some sanity checks to ensure that `startswith` and `endswith` calls are
called with exactly one argument.

refurb/checks/string/startswith.py

@@ -1,8 +1,8 @@
 from dataclasses import dataclass
 
-from mypy.nodes import CallExpr, Expression, MemberExpr, NameExpr, OpExpr, UnaryExpr, Var
+from mypy.nodes import CallExpr, Expression, MemberExpr, OpExpr, UnaryExpr
 
-from refurb.checks.common import extract_binary_oper, is_same_type
+from refurb.checks.common import extract_binary_oper, get_mypy_type, is_equivalent, is_same_type
 from refurb.error import Error
 
 
@@ -40,19 +40,15 @@ def are_startswith_or_endswith_calls(
 ) -> tuple[str, Expression] | None:
     match lhs, rhs:
         case (
-            CallExpr(
-                callee=MemberExpr(expr=NameExpr(node=Var(type=ty)) as lhs, name=lhs_func),
-                args=args,
-            ),
-            CallExpr(callee=MemberExpr(expr=NameExpr() as rhs, name=rhs_func)),
+            CallExpr(callee=MemberExpr(expr=lhs, name=lhs_func), args=[first_arg]),
+            CallExpr(callee=MemberExpr(expr=rhs, name=rhs_func), args=[_]),
         ) if (
-            lhs.fullname == rhs.fullname
-            and is_same_type(ty, str, bytes)
+            is_equivalent(lhs, rhs)
+            and is_same_type(get_mypy_type(lhs), str, bytes)
             and lhs_func == rhs_func
             and lhs_func in {"startswith", "endswith"}
-            and args
         ):
-            return lhs_func, args[0]
+            return lhs_func, first_arg
 
     return None
 
@@ -77,9 +73,4 @@ def check(node: OpExpr, errors: list[Error]) -> None:
             old = f"not x.{func}(y) and not x.{func}(z)"
             new = f"not x.{func}((y, z))"
 
-            errors.append(
-                ErrorInfo.from_node(
-                    arg,
-                    msg=f"Replace `{old}` with `{new}`",
-                )
-            )
+            errors.append(ErrorInfo.from_node(arg, msg=f"Replace `{old}` with `{new}`"))

test/data/err_102.py

@@ -9,6 +9,16 @@
 
 _ = not name.startswith("a") and not name.startswith("b")
 
+class C:
+    s: str
+
+c = C()
+
+_ = c.s.startswith("a") or c.s.startswith("b")
+
+# TODO: disallow this because C() differs between branches
+_ = C().s.startswith("a") or C().s.startswith("b")
+
 
 # these should not match
 _ = name.startswith("a") and name.startswith("b")
@@ -23,3 +33,6 @@
 _ = not name.startswith("a") or not name.startswith("b")
 _ = not name.startswith("a") and name.startswith("b")
 _ = name.startswith("a") and not name.startswith("b")
+
+_ = name.startswith("a", "b") or name.startswith("b")  # type: ignore
+_ = name.startswith("a") or name.startswith()  # type: ignore

test/data/err_102.txt

@@ -3,3 +3,5 @@ test/data/err_102.py:6:19 [FURB102]: Replace `x.endswith(y) or x.endswith(z)` wi
 test/data/err_102.py:7:26 [FURB102]: Replace `x.startswith(y) or x.startswith(z)` with `x.startswith((y, z))`
 test/data/err_102.py:8:21 [FURB102]: Replace `x.startswith(y) or x.startswith(z)` with `x.startswith((y, z))`
 test/data/err_102.py:10:25 [FURB102]: Replace `not x.startswith(y) and not x.startswith(z)` with `not x.startswith((y, z))`
+test/data/err_102.py:17:20 [FURB102]: Replace `x.startswith(y) or x.startswith(z)` with `x.startswith((y, z))`
+test/data/err_102.py:20:22 [FURB102]: Replace `x.startswith(y) or x.startswith(z)` with `x.startswith((y, z))`