Fix crash due to checking type variable values too early

Move type variable checks which use subtype and type sameness
checks to happen at the end of semantic analysis.

The implementation also adds the concept of priorities to
semantic analysis patch callbacks. Callback calls are
sorted by the priority. We resolve forward references and
calculate fallbacks before checking type variable values,
as otherwise the latter could see incomplete types and crash.

Fixes #4200.

Author: JukkaL

mypy/build.py

@@ -1853,14 +1853,14 @@ def parse_file(self) -> None:
 
     def semantic_analysis(self) -> None:
         assert self.tree is not None, "Internal error: method must be called on parsed file only"
-        patches = []  # type: List[Callable[[], None]]
+        patches = []  # type: List[Tuple[int, Callable[[], None]]]
         with self.wrap_context():
             self.manager.semantic_analyzer.visit_file(self.tree, self.xpath, self.options, patches)
         self.patches = patches
 
     def semantic_analysis_pass_three(self) -> None:
         assert self.tree is not None, "Internal error: method must be called on parsed file only"
-        patches = []  # type: List[Callable[[], None]]
+        patches = []  # type: List[Tuple[int, Callable[[], None]]]
         with self.wrap_context():
             self.manager.semantic_analyzer_pass3.visit_file(self.tree, self.xpath,
                                                             self.options, patches)
@@ -1869,7 +1869,8 @@ def semantic_analysis_pass_three(self) -> None:
         self.patches = patches + self.patches
 
     def semantic_analysis_apply_patches(self) -> None:
-        for patch_func in self.patches:
+        patches_by_priority = sorted(self.patches, key=lambda x: x[0])
+        for priority, patch_func in patches_by_priority:
             patch_func()
 
     def type_check_first_pass(self) -> None:

mypy/semanal.py

@@ -84,6 +84,7 @@
 from mypy.plugin import Plugin, ClassDefContext, SemanticAnalyzerPluginInterface
 from mypy import join
 from mypy.util import get_prefix
+from mypy.semanal_shared import PRIORITY_FALLBACKS
 
 
 T = TypeVar('T')
@@ -258,11 +259,12 @@ def __init__(self,
         self.recurse_into_functions = True
 
     def visit_file(self, file_node: MypyFile, fnam: str, options: Options,
-                   patches: List[Callable[[], None]]) -> None:
+                   patches: List[Tuple[int, Callable[[], None]]]) -> None:
         """Run semantic analysis phase 2 over a file.
 
-        Add callbacks by mutating the patches list argument. They will be called
-        after all semantic analysis phases but before type checking.
+        Add (priority, callback) pairs by mutating the 'patches' list argument. They
+        will be called after all semantic analysis phases but before type checking,
+        lowest priority values first.
         """
         self.recurse_into_functions = True
         self.options = options
@@ -2454,7 +2456,7 @@ def patch() -> None:
         # We can't calculate the complete fallback type until after semantic
         # analysis, since otherwise MROs might be incomplete. Postpone a callback
         # function that patches the fallback.
-        self.patches.append(patch)
+        self.patches.append((PRIORITY_FALLBACKS, patch))
 
         def add_field(var: Var, is_initialized_in_class: bool = False,
                       is_property: bool = False) -> None:
@@ -2693,7 +2695,7 @@ def patch() -> None:
         # We can't calculate the complete fallback type until after semantic
         # analysis, since otherwise MROs might be incomplete. Postpone a callback
         # function that patches the fallback.
-        self.patches.append(patch)
+        self.patches.append((PRIORITY_FALLBACKS, patch))
         return info
 
     def check_classvar(self, s: AssignmentStmt) -> None:

mypy/semanal_pass3.py

@@ -10,7 +10,7 @@
 """
 
 from collections import OrderedDict
-from typing import Dict, List, Callable, Optional, Union, Set, cast
+from typing import Dict, List, Callable, Optional, Union, Set, cast, Tuple
 
 from mypy import messages, experiments
 from mypy.nodes import (
@@ -26,8 +26,9 @@
 from mypy.errors import Errors, report_internal_error
 from mypy.options import Options
 from mypy.traverser import TraverserVisitor
-from mypy.typeanal import TypeAnalyserPass3, collect_any_types
+from mypy.typeanal import TypeAnalyserPass3, collect_any_types, TypeVariableChecker
 from mypy.typevars import has_no_typevars
+from mypy.semanal_shared import PRIORITY_FORWARD_REF, PRIORITY_TYPEVAR_VALUES
 import mypy.semanal
 
 
@@ -48,7 +49,7 @@ def __init__(self, modules: Dict[str, MypyFile], errors: Errors,
         self.recurse_into_functions = True
 
     def visit_file(self, file_node: MypyFile, fnam: str, options: Options,
-                   patches: List[Callable[[], None]]) -> None:
+                   patches: List[Tuple[int, Callable[[], None]]]) -> None:
         self.recurse_into_functions = True
         self.errors.set_file(fnam, file_node.fullname())
         self.options = options
@@ -349,12 +350,7 @@ def analyze(self, type: Optional[Type], node: Union[Node, SymbolTableNode],
             analyzer = self.make_type_analyzer(indicator)
             type.accept(analyzer)
             self.check_for_omitted_generics(type)
-            if indicator.get('forward') or indicator.get('synthetic'):
-                def patch() -> None:
-                    self.perform_transform(node,
-                        lambda tp: tp.accept(ForwardReferenceResolver(self.fail,
-                                                                      node, warn)))
-                self.patches.append(patch)
+            self.generate_type_patches(node, indicator, warn)
 
     def analyze_types(self, types: List[Type], node: Node) -> None:
         # Similar to above but for nodes with multiple types.
@@ -363,12 +359,24 @@ def analyze_types(self, types: List[Type], node: Node) -> None:
             analyzer = self.make_type_analyzer(indicator)
             type.accept(analyzer)
             self.check_for_omitted_generics(type)
+        self.generate_type_patches(node, indicator, warn=False)
+
+    def generate_type_patches(self,
+                              node: Union[Node, SymbolTableNode],
+                              indicator: Dict[str, bool],
+                              warn: bool) -> None:
         if indicator.get('forward') or indicator.get('synthetic'):
             def patch() -> None:
                 self.perform_transform(node,
                     lambda tp: tp.accept(ForwardReferenceResolver(self.fail,
-                                                                  node, warn=False)))
-            self.patches.append(patch)
+                                                                  node, warn)))
+            self.patches.append((PRIORITY_FORWARD_REF, patch))
+        if indicator.get('typevar'):
+            def patch() -> None:
+                self.perform_transform(node,
+                    lambda tp: tp.accept(TypeVariableChecker(self.fail)))
+
+            self.patches.append((PRIORITY_TYPEVAR_VALUES, patch))
 
     def analyze_info(self, info: TypeInfo) -> None:
         # Similar to above but for nodes with synthetic TypeInfos (NamedTuple and NewType).
@@ -387,7 +395,8 @@ def make_type_analyzer(self, indicator: Dict[str, bool]) -> TypeAnalyserPass3:
                                  self.sem.plugin,
                                  self.options,
                                  self.is_typeshed_file,
-                                 indicator)
+                                 indicator,
+                                 self.patches)
 
     def check_for_omitted_generics(self, typ: Type) -> None:
         if not self.options.disallow_any_generics or self.is_typeshed_file:

mypy/semanal_shared.py

@@ -0,0 +1,11 @@
+"""Shared definitions used by different parts of semantic analysis."""
+
+# Priorities for ordering of patches within the final "patch" phase of semantic analysis
+# (after pass 3):
+
+# Fix forward references (needs to happen first)
+PRIORITY_FORWARD_REF = 0
+# Fix fallbacks (does joins)
+PRIORITY_FALLBACKS = 1
+# Checks type var values (does subtype checks)
+PRIORITY_TYPEVAR_VALUES = 2

mypy/typeanal.py

@@ -1,7 +1,7 @@
 """Semantic analysis of types"""
 
 from collections import OrderedDict
-from typing import Callable, List, Optional, Set, Tuple, Iterator, TypeVar, Iterable, Dict
+from typing import Callable, List, Optional, Set, Tuple, Iterator, TypeVar, Iterable, Dict, Union
 from itertools import chain
 
 from contextlib import contextmanager
@@ -14,14 +14,15 @@
     Type, UnboundType, TypeVarType, TupleType, TypedDictType, UnionType, Instance, AnyType,
     CallableType, NoneTyp, DeletedType, TypeList, TypeVarDef, TypeVisitor, SyntheticTypeVisitor,
     StarType, PartialType, EllipsisType, UninhabitedType, TypeType, get_typ_args, set_typ_args,
-    CallableArgument, get_type_vars, TypeQuery, union_items, TypeOfAny, ForwardRef, Overloaded
+    CallableArgument, get_type_vars, TypeQuery, union_items, TypeOfAny, ForwardRef, Overloaded,
+    TypeTranslator
 )
 
 from mypy.nodes import (
     TVAR, TYPE_ALIAS, UNBOUND_IMPORTED, TypeInfo, Context, SymbolTableNode, Var, Expression,
     IndexExpr, RefExpr, nongen_builtins, check_arg_names, check_arg_kinds, ARG_POS, ARG_NAMED,
     ARG_OPT, ARG_NAMED_OPT, ARG_STAR, ARG_STAR2, TypeVarExpr, FuncDef, CallExpr, NameExpr,
-    Decorator
+    Decorator, Node
 )
 from mypy.tvar_scope import TypeVarScope
 from mypy.sametypes import is_same_type
@@ -656,7 +657,8 @@ def __init__(self,
                  plugin: Plugin,
                  options: Options,
                  is_typeshed_stub: bool,
-                 indicator: Dict[str, bool]) -> None:
+                 indicator: Dict[str, bool],
+                 patches: List[Tuple[int, Callable[[], None]]]) -> None:
         self.lookup_func = lookup_func
         self.lookup_fqn_func = lookup_fqn_func
         self.fail = fail_func
@@ -665,6 +667,7 @@ def __init__(self,
         self.plugin = plugin
         self.is_typeshed_stub = is_typeshed_stub
         self.indicator = indicator
+        self.patches = patches
 
     def visit_instance(self, t: Instance) -> None:
         info = t.type
@@ -707,64 +710,21 @@ def visit_instance(self, t: Instance) -> None:
             t.args = [AnyType(TypeOfAny.from_error) for _ in info.type_vars]
             t.invalid = True
         elif info.defn.type_vars:
-            # Check type argument values.
-            # TODO: Calling is_subtype and is_same_types in semantic analysis is a bad idea
-            for (i, arg), tvar in zip(enumerate(t.args), info.defn.type_vars):
-                if tvar.values:
-                    if isinstance(arg, TypeVarType):
-                        arg_values = arg.values
-                        if not arg_values:
-                            self.fail('Type variable "{}" not valid as type '
-                                      'argument value for "{}"'.format(
-                                          arg.name, info.name()), t)
-                            continue
-                    else:
-                        arg_values = [arg]
-                    self.check_type_var_values(info, arg_values, tvar.name, tvar.values, i + 1, t)
-                # TODO: These hacks will be not necessary when this will be moved to later stage.
-                arg = self.resolve_type(arg)
-                bound = self.resolve_type(tvar.upper_bound)
-                if not is_subtype(arg, bound):
-                    self.fail('Type argument "{}" of "{}" must be '
-                              'a subtype of "{}"'.format(
-                                  arg, info.name(), bound), t)
+            # Check type argument values. This is postponed to the end of semantic analysis
+            # since we need full MROs and resolved forward references.
+            for tvar in info.defn.type_vars:
+                if (tvar.values
+                        or not isinstance(tvar.upper_bound, Instance)
+                        or tvar.upper_bound.type.fullname() != 'builtins.object'):
+                    # Some restrictions on type variable. These can only be checked later
+                    # after we have final MROs and forward references have been resolved.
+                    self.indicator['typevar'] = True
         for arg in t.args:
             arg.accept(self)
         if info.is_newtype:
             for base in info.bases:
                 base.accept(self)
 
-    def check_type_var_values(self, type: TypeInfo, actuals: List[Type], arg_name: str,
-                              valids: List[Type], arg_number: int, context: Context) -> None:
-        for actual in actuals:
-            actual = self.resolve_type(actual)
-            if (not isinstance(actual, AnyType) and
-                    not any(is_same_type(actual, self.resolve_type(value))
-                            for value in valids)):
-                if len(actuals) > 1 or not isinstance(actual, Instance):
-                    self.fail('Invalid type argument value for "{}"'.format(
-                        type.name()), context)
-                else:
-                    class_name = '"{}"'.format(type.name())
-                    actual_type_name = '"{}"'.format(actual.type.name())
-                    self.fail(messages.INCOMPATIBLE_TYPEVAR_VALUE.format(
-                        arg_name, class_name, actual_type_name), context)
-
-    def resolve_type(self, tp: Type) -> Type:
-        # This helper is only needed while is_subtype and is_same_type are
-        # called in third pass. This can be removed when TODO in visit_instance is fixed.
-        if isinstance(tp, ForwardRef):
-            if tp.resolved is None:
-                return tp.unbound
-            tp = tp.resolved
-        if isinstance(tp, Instance) and tp.type.replaced:
-            replaced = tp.type.replaced
-            if replaced.tuple_type:
-                tp = replaced.tuple_type
-            if replaced.typeddict_type:
-                tp = replaced.typeddict_type
-        return tp
-
     def visit_callable_type(self, t: CallableType) -> None:
         t.ret_type.accept(self)
         for arg_type in t.arg_types:
@@ -1036,3 +996,58 @@ def make_optional_type(t: Type) -> Type:
         return UnionType(items + [NoneTyp()], t.line, t.column)
     else:
         return UnionType([t, NoneTyp()], t.line, t.column)
+
+
+class TypeVariableChecker(TypeTranslator):
+    """Visitor that checks that type variables in generic types have valid values.
+
+    Note: This must be run at the end of semantic analysis when MROs are
+    complete and forward references have been resolved.
+
+    This does two things:
+
+    - If type variable in C has a value restriction, check that X in C[X] conforms
+      to the restriction.
+    - If type variable in C has a non-default upper bound, check that X in C[X]
+      conforms to the upper bound.
+
+    (This doesn't need to be a type translator, but it simplifies the implementation.)
+    """
+
+    def __init__(self, fail: Callable[[str, Context], None]) -> None:
+        self.fail = fail
+
+    def visit_instance(self, t: Instance) -> Type:
+        info = t.type
+        for (i, arg), tvar in zip(enumerate(t.args), info.defn.type_vars):
+            if tvar.values:
+                if isinstance(arg, TypeVarType):
+                    arg_values = arg.values
+                    if not arg_values:
+                        self.fail('Type variable "{}" not valid as type '
+                                  'argument value for "{}"'.format(
+                                      arg.name, info.name()), t)
+                        continue
+                else:
+                    arg_values = [arg]
+                self.check_type_var_values(info, arg_values, tvar.name, tvar.values, i + 1, t)
+            if not is_subtype(arg, tvar.upper_bound):
+                self.fail('Type argument "{}" of "{}" must be '
+                          'a subtype of "{}"'.format(
+                              arg, info.name(), tvar.upper_bound), t)
+        return t
+
+    def check_type_var_values(self, type: TypeInfo, actuals: List[Type], arg_name: str,
+                              valids: List[Type], arg_number: int, context: Context) -> None:
+        for actual in actuals:
+            if (not isinstance(actual, AnyType) and
+                    not any(is_same_type(actual, value)
+                            for value in valids)):
+                if len(actuals) > 1 or not isinstance(actual, Instance):
+                    self.fail('Invalid type argument value for "{}"'.format(
+                        type.name()), context)
+                else:
+                    class_name = '"{}"'.format(type.name())
+                    actual_type_name = '"{}"'.format(actual.type.name())
+                    self.fail(messages.INCOMPATIBLE_TYPEVAR_VALUE.format(
+                        arg_name, class_name, actual_type_name), context)

test-data/unit/check-newtype.test

@@ -360,3 +360,10 @@ d: object
 if isinstance(d, T):  # E: Cannot use isinstance() with a NewType type
     reveal_type(d) # E: Revealed type is '__main__.T'
 [builtins fixtures/isinstancelist.pyi]
+
+[case testInvalidNewTypeCrash]
+from typing import List, NewType, Union
+N = NewType('N', XXX)  # E: Argument 2 to NewType(...) must be subclassable (got "Any") \
+                       # E: Name 'XXX' is not defined
+x: List[Union[N, int]]  # E: Invalid type "__main__.N"
+[builtins fixtures/list.pyi]

test-data/unit/check-typeddict.test

@@ -1333,7 +1333,7 @@ T = TypeVar('T', bound='M')
 class G(Generic[T]):
     x: T
 
-yb: G[int] # E: Type argument "builtins.int" of "G" must be a subtype of "TypedDict({'x': builtins.int}, fallback=typing.Mapping[builtins.str, builtins.object])"
+yb: G[int] # E: Type argument "builtins.int" of "G" must be a subtype of "TypedDict('__main__.M', {'x': builtins.int})"
 yg: G[M]
 z: int = G[M]().x['x']
 

test-data/unit/check-unions.test

@@ -940,3 +940,10 @@ x: Union[ExtremelyLongTypeNameWhichIsGenericSoWeCanUseItMultipleTimes[int],
 def takes_int(arg: int) -> None: pass
 
 takes_int(x)  # E: Argument 1 to "takes_int" has incompatible type <union: 6 items>; expected "int"
+
+[case testRecursiveForwardReferenceInUnion]
+from typing import List, Union
+MYTYPE = List[Union[str, "MYTYPE"]]
+[builtins fixtures/list.pyi]
+[out]
+main:2: error: Recursive types not fully supported yet, nested types replaced with "Any"