Start removing special cased assert False

Author: A5rocks

mypy/checker.py

@@ -150,6 +150,7 @@
 from mypy.patterns import AsPattern, StarredPattern
 from mypy.plugin import Plugin
 from mypy.plugins import dataclasses as dataclasses_plugin
+from mypy.reachability import assert_will_always_fail
 from mypy.scope import Scope
 from mypy.semanal import is_trivial_body, refers_to_fullname, set_callable_name
 from mypy.semanal_enum import ENUM_BASES, ENUM_SPECIAL_PROPS
@@ -5136,7 +5137,11 @@ def visit_assert_stmt(self, s: AssertStmt) -> None:
             self.expr_checker.analyze_cond_branch(
                 else_map, s.msg, None, suppress_unreachable_errors=False
             )
-        self.push_type_map(true_map)
+        if assert_will_always_fail(s, self.options):
+            # TODO: move this logic into `find_isinstance_check`
+            self.push_type_map(None)
+        else:
+            self.push_type_map(true_map)
 
     def visit_raise_stmt(self, s: RaiseStmt) -> None:
         """Type check a raise statement."""

mypy/semanal_pass1.py

@@ -66,6 +66,9 @@ def visit_file(self, file: MypyFile, fnam: str, mod_id: str, options: Options) -
         for i, defn in enumerate(file.defs):
             defn.accept(self)
             if isinstance(defn, AssertStmt) and assert_will_always_fail(defn, options):
+                # TODO: remove this by passing through unreachability info to semanal
+                # for top-level definitions. (testUnreachableAfterToplevelAssertImport)
+
                 # We've encountered an assert that's always false,
                 # e.g. assert sys.platform == 'lol'.  Truncate the
                 # list of statements.  This mutates file.defs too.

test-data/unit/check-unreachable-code.test

@@ -795,11 +795,12 @@ main:3: error: Cannot find implementation or library stub for module named "bad"
 main:3: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
 
 [case testUnreachableAfterToplevelAssertNotInsideIf]
+# flags: --warn-unreachable --platform unknown
 import sys
 if sys.version_info[0] >= 2:
     assert sys.platform == 'lol'
-    reveal_type('')  # N: Revealed type is "Literal['']?"
-reveal_type('')  # N: Revealed type is "Literal['']?"
+    reveal_type('')  # E: Statement is unreachable
+reveal_type('')  # E: Statement is unreachable
 [builtins fixtures/ops.pyi]
 
 [case testUnreachableFlagWithBadControlFlow1]