B912: check if map calls have strict flag (#517)

* B912: check if map calls have strict flag

* Fix

* Update README.rst

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Fix

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: kasium

README.rst

@@ -367,6 +367,11 @@ This is meant to be enabled by developers writing visitors using the ``ast`` mod
 
 The ``strict=`` argument was added in Python 3.13, so don't enable this flag for code that should work on <3.13.
 
+.. _B912:
+
+**B912**: ``map()`` without an explicit `strict=` parameter set. ``strict=True`` causes the resulting iterator
+to raise a ``ValueError`` if the arguments are exhausted at differing lengths.
+
 .. _B950:
 
 **B950**: Line too long. This is a pragmatic equivalent of
@@ -480,6 +485,7 @@ UNRELEASED
 * B042: New check for reminding to call super().__init__ in custom exceptions
 * flake8-bugbear now requires at least Python 3.9, like flake8>=7.2.0
 * B028: Skip if skip_file_prefixes is used (#503)
+* Add B912: `map()` without an explicit `strict=` parameter. (#516)
 
 24.12.12
 ~~~~~~~~

bugbear.py

@@ -531,6 +531,7 @@ def visit_Call(self, node) -> None:
         self.check_for_b905(node)
         self.check_for_b910(node)
         self.check_for_b911(node)
+        self.check_for_b912(node)
 
         # no need for copying, if used in nested calls it will be set to None
         current_b040_caught_exception = self.b040_caught_exception
@@ -1536,6 +1537,16 @@ def check_for_b905(self, node) -> None:
         if not any(kw.arg == "strict" for kw in node.keywords):
             self.add_error("B905", node)
 
+    def check_for_b912(self, node) -> None:
+        if not (
+            isinstance(node.func, ast.Name)
+            and node.func.id == "map"
+            and len(node.args) > 2
+        ):
+            return
+        if not any(kw.arg == "strict" for kw in node.keywords):
+            self.add_error("B912", node)
+
     def check_for_b906(self, node: ast.FunctionDef) -> None:
         if not node.name.startswith("visit_"):
             return
@@ -2465,6 +2476,7 @@ def __call__(self, lineno: int, col: int, vars: tuple[object, ...] = ()) -> erro
     "B911": Error(
         message="B911 `itertools.batched()` without an explicit `strict=` parameter."
     ),
+    "B912": Error(message="B912 `map()` without an explicit `strict=` parameter."),
     "B950": Error(message="B950 line too long ({} > {} characters)"),
 }
 
@@ -2480,5 +2492,6 @@ def __call__(self, lineno: int, col: int, vars: tuple[object, ...] = ()) -> erro
     "B909",
     "B910",
     "B911",
+    "B912",
     "B950",
 ]

tests/eval_files/b912_py314.py

@@ -0,0 +1,8 @@
+map(lambda x: x, "a", "b")  # B912: 0
+map(lambda x: x, "a", "b", *map("c"))  # B912: 0
+map(lambda x: x, "a", map(lambda x: x, "a"), strict=True)  # B912: 22
+
+map()
+map(lambda x: x, "a")
+map(lambda x: x, "a", "b", strict=False)
+map(lambda x: x, "a", "b", "c", strict=True)