python · gvanrossum · Mar 27, 2017 · Dec 22, 2016 · Dec 23, 2016 · Dec 23, 2016
diff --git a/mypy/build.py b/mypy/build.py
@@ -1397,7 +1397,8 @@ def parse_file(self) -> None:
         # this before processing imports, since this may mark some
         # import statements as unreachable.
         first = FirstPass(manager.semantic_analyzer)
-        first.visit_file(self.tree, self.xpath, self.id, self.options)
+        with self.wrap_context():
+            first.visit_file(self.tree, self.xpath, self.id, self.options)
 
         # Initialize module symbol table, which was populated by the
         # semantic analyzer.

diff --git a/mypy/checker.py b/mypy/checker.py
@@ -36,7 +36,8 @@
 from mypy import messages
 from mypy.subtypes import (
     is_subtype, is_equivalent, is_proper_subtype, is_more_precise,
-    restrict_subtype_away, is_subtype_ignoring_tvars
+    restrict_subtype_away, is_subtype_ignoring_tvars, is_callable_subtype,
+    unify_generic_callable,
 )
 from mypy.maptype import map_instance_to_supertype
 from mypy.typevars import fill_typevars, has_no_typevars
@@ -261,29 +262,70 @@ def accept_loop(self, body: Statement, else_body: Statement = None, *,
 
     def visit_overloaded_func_def(self, defn: OverloadedFuncDef) -> None:
         num_abstract = 0
+        if not defn.items:
+            # In this case we have already complained about none of these being
+            # valid overloads.
+            return None
+        if len(defn.items) == 1:
+            self.fail('Single overload definition, multiple required', defn)
+
         if defn.is_property:
             # HACK: Infer the type of the property.
-            self.visit_decorator(defn.items[0])
+            self.visit_decorator(cast(Decorator, defn.items[0]))
         for fdef in defn.items:
+            assert isinstance(fdef, Decorator)
             self.check_func_item(fdef.func, name=fdef.func.name())
             if fdef.func.is_abstract:
                 num_abstract += 1
         if num_abstract not in (0, len(defn.items)):
             self.fail(messages.INCONSISTENT_ABSTRACT_OVERLOAD, defn)
+        if defn.impl:
+            defn.impl.accept(self)
         if defn.info:
             self.check_method_override(defn)
             self.check_inplace_operator_method(defn)
         self.check_overlapping_overloads(defn)
+        return None
 
     def check_overlapping_overloads(self, defn: OverloadedFuncDef) -> None:
+        # At this point we should have set the impl already, and all remaining
+        # items are decorators
         for i, item in enumerate(defn.items):
+            assert isinstance(item, Decorator)
+            sig1 = self.function_type(item.func)
             for j, item2 in enumerate(defn.items[i + 1:]):
                 # TODO overloads involving decorators
-                sig1 = self.function_type(item.func)
+                assert isinstance(item2, Decorator)
                 sig2 = self.function_type(item2.func)
                 if is_unsafe_overlapping_signatures(sig1, sig2):
                     self.msg.overloaded_signatures_overlap(i + 1, i + j + 2,
                                                            item.func)
+            if defn.impl:
+                if isinstance(defn.impl, FuncDef):
+                    impl_type = defn.impl.type
+                elif isinstance(defn.impl, Decorator):
+                    impl_type = defn.impl.var.type
+                else:
+                    assert False, "Impl isn't the right type"
+                # This can happen if we've got an overload with a different
+                # decorator too -- we gave up on the types.
+                if impl_type is None or isinstance(impl_type, AnyType) or sig1 is None:
+                    return
+
+                assert isinstance(impl_type, CallableType)
+                assert isinstance(sig1, CallableType)
+                if not is_callable_subtype(impl_type, sig1, ignore_return=True):
+                    self.msg.overloaded_signatures_arg_specific(i + 1, defn.impl)
+                impl_type_subst = impl_type
+                if impl_type.variables:
+                    impl_type_subst = unify_generic_callable(impl_type, sig1, ignore_return=False)
+                    if impl_type_subst is None:
+                        self.fail("Type variable mismatch between " +
+                                  "overload signature {} and implementation".format(i + 1),
+                                  defn.impl)
+                        return
+                if not is_subtype(sig1.ret_type, impl_type_subst.ret_type):
+                    self.msg.overloaded_signatures_ret_specific(i + 1, defn.impl)
 
     # Here's the scoop about generators and coroutines.
     #
@@ -2107,9 +2149,7 @@ def visit_decorator(self, e: Decorator) -> None:
         e.func.accept(self)
         sig = self.function_type(e.func)  # type: Type
         # Process decorators from the inside out.
-        for i in range(len(e.decorators)):
-            n = len(e.decorators) - 1 - i
-            d = e.decorators[n]
+        for d in reversed(e.decorators):
             if isinstance(d, NameExpr) and d.fullname == 'typing.overload':
                 self.fail('Single overload definition, multiple required', e)
                 continue
@@ -2133,7 +2173,8 @@ def check_incompatible_property_override(self, e: Decorator) -> None:
                     continue
                 if (isinstance(base_attr.node, OverloadedFuncDef) and
                         base_attr.node.is_property and
-                        base_attr.node.items[0].var.is_settable_property):
+                        cast(Decorator,
+                             base_attr.node.items[0]).var.is_settable_property):
                     self.fail(messages.READ_ONLY_PROPERTY_OVERRIDES_READ_WRITE, e)
 
     def visit_with_stmt(self, s: WithStmt) -> None:

diff --git a/mypy/checkmember.py b/mypy/checkmember.py
@@ -75,7 +75,8 @@ def analyze_member_access(name: str,
         if method:
             if method.is_property:
                 assert isinstance(method, OverloadedFuncDef)
-                return analyze_var(name, method.items[0].var, typ, info, node, is_lvalue, msg,
+                first_item = cast(Decorator, method.items[0])
+                return analyze_var(name, first_item.var, typ, info, node, is_lvalue, msg,
                                    original_type, not_ready_callback)
             if is_lvalue:
                 msg.cant_assign_to_method(node)

diff --git a/mypy/fastparse.py b/mypy/fastparse.py
@@ -2,9 +2,12 @@
 import sys
 
 from typing import Tuple, Union, TypeVar, Callable, Sequence, Optional, Any, cast, List, Set
-from mypy.sharedparse import special_function_elide_names, argument_elide_name
+from mypy.sharedparse import (
+    special_function_elide_names, argument_elide_name,
+)
 from mypy.nodes import (
-    MypyFile, Node, ImportBase, Import, ImportAll, ImportFrom, FuncDef, OverloadedFuncDef,
+    MypyFile, Node, ImportBase, Import, ImportAll, ImportFrom, FuncDef,
+    OverloadedFuncDef, OverloadPart,
     ClassDef, Decorator, Block, Var, OperatorAssignmentStmt,
     ExpressionStmt, AssignmentStmt, ReturnStmt, RaiseStmt, AssertStmt,
     DelStmt, BreakStmt, ContinueStmt, PassStmt, GlobalDecl,
@@ -222,11 +225,12 @@ def as_block(self, stmts: List[ast3.stmt], lineno: int) -> Block:
 
     def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
         ret = []  # type: List[Statement]
-        current_overload = []
+        current_overload = []  # type: List[OverloadPart]
         current_overload_name = None
-        # mypy doesn't actually check that the decorator is literally @overload
         for stmt in stmts:
-            if isinstance(stmt, Decorator) and stmt.name() == current_overload_name:
+            if (current_overload_name is not None
+                    and isinstance(stmt, (Decorator, FuncDef))
+                    and stmt.name() == current_overload_name):
                 current_overload.append(stmt)
             else:
                 if len(current_overload) == 1:

diff --git a/mypy/fastparse2.py b/mypy/fastparse2.py
@@ -18,7 +18,9 @@
 import sys
 
 from typing import Tuple, Union, TypeVar, Callable, Sequence, Optional, Any, cast, List, Set
-from mypy.sharedparse import special_function_elide_names, argument_elide_name
+from mypy.sharedparse import (
+    special_function_elide_names, argument_elide_name,
+)
 from mypy.nodes import (
     MypyFile, Node, ImportBase, Import, ImportAll, ImportFrom, FuncDef, OverloadedFuncDef,
     ClassDef, Decorator, Block, Var, OperatorAssignmentStmt,
@@ -31,7 +33,7 @@
     UnaryExpr, FuncExpr, ComparisonExpr, DictionaryComprehension,
     SetComprehension, ComplexExpr, EllipsisExpr, YieldExpr, Argument,
     Expression, Statement, BackquoteExpr, PrintStmt, ExecStmt,
-    ARG_POS, ARG_OPT, ARG_STAR, ARG_NAMED, ARG_STAR2
+    ARG_POS, ARG_OPT, ARG_STAR, ARG_NAMED, ARG_STAR2, OverloadPart,
 )
 from mypy.types import (
     Type, CallableType, AnyType, UnboundType, EllipsisType
@@ -225,11 +227,12 @@ def as_block(self, stmts: List[ast27.stmt], lineno: int) -> Block:
 
     def fix_function_overloads(self, stmts: List[Statement]) -> List[Statement]:
         ret = []  # type: List[Statement]
-        current_overload = []
+        current_overload = []  # type: List[OverloadPart]
         current_overload_name = None
-        # mypy doesn't actually check that the decorator is literally @overload
         for stmt in stmts:
-            if isinstance(stmt, Decorator) and stmt.name() == current_overload_name:
+            if (current_overload_name is not None
+                    and isinstance(stmt, (Decorator, FuncDef))
+                    and stmt.name() == current_overload_name):
                 current_overload.append(stmt)
             else:
                 if len(current_overload) == 1:

diff --git a/mypy/fixup.py b/mypy/fixup.py
@@ -106,6 +106,8 @@ def visit_overloaded_func_def(self, o: OverloadedFuncDef) -> None:
             o.type.accept(self.type_fixer)
         for item in o.items:
             item.accept(self)
+        if o.impl:
+            o.impl.accept(self)
 
     def visit_decorator(self, d: Decorator) -> None:
         if self.current_info is not None:

diff --git a/mypy/messages.py b/mypy/messages.py
@@ -833,6 +833,14 @@ def overloaded_signatures_overlap(self, index1: int, index2: int,
         self.fail('Overloaded function signatures {} and {} overlap with '
                   'incompatible return types'.format(index1, index2), context)
 
+    def overloaded_signatures_arg_specific(self, index1: int, context: Context) -> None:
+        self.fail('Overloaded function implementation does not accept all possible arguments '
+                  'of signature {}'.format(index1), context)
+
+    def overloaded_signatures_ret_specific(self, index1: int, context: Context) -> None:
+        self.fail('Overloaded function implementation cannot produce return type '
+                  'of signature {}'.format(index1), context)
+
     def operator_method_signatures_overlap(
             self, reverse_class: str, reverse_method: str, forward_class: str,
             forward_method: str, context: Context) -> None:

diff --git a/mypy/nodes.py b/mypy/nodes.py
@@ -372,21 +372,29 @@ def fullname(self) -> str:
         return self._fullname
 
 
+OverloadPart = Union['FuncDef', 'Decorator']
+
+
 class OverloadedFuncDef(FuncBase, SymbolNode, Statement):
-    """A logical node representing all the variants of an overloaded function.
+    """A logical node representing all the variants of a multi-declaration function.
+
+    A multi-declaration function is often an @overload, but can also be a
+    @property with a setter and a/or a deleter.
 
     This node has no explicit representation in the source program.
     Overloaded variants must be consecutive in the source file.
     """
 
-    items = None  # type: List[Decorator]
+    items = None  # type: List[OverloadPart]
+    impl = None  # type: Optional[OverloadPart]
 
-    def __init__(self, items: List['Decorator']) -> None:
+    def __init__(self, items: List['OverloadPart']) -> None:
         self.items = items
+        self.impl = None
         self.set_line(items[0].line)
 
     def name(self) -> str:
-        return self.items[0].func.name()
+        return self.items[0].name()
 
     def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_overloaded_func_def(self)
@@ -397,12 +405,17 @@ def serialize(self) -> JsonDict:
                 'type': None if self.type is None else self.type.serialize(),
                 'fullname': self._fullname,
                 'is_property': self.is_property,
+                'impl': None if self.impl is None else self.impl.serialize()
                 }
 
     @classmethod
     def deserialize(cls, data: JsonDict) -> 'OverloadedFuncDef':
         assert data['.class'] == 'OverloadedFuncDef'
-        res = OverloadedFuncDef([Decorator.deserialize(d) for d in data['items']])
+        res = OverloadedFuncDef([
+            cast(OverloadPart, SymbolNode.deserialize(d))
+            for d in data['items']])
+        if data.get('impl') is not None:
+            res.impl = cast(OverloadPart, SymbolNode.deserialize(data['impl']))
         if data.get('type') is not None:
             res.type = mypy.types.deserialize_type(data['type'])
         res._fullname = data['fullname']
@@ -587,6 +600,7 @@ class Decorator(SymbolNode, Statement):
     func = None  # type: FuncDef                # Decorated function
     decorators = None  # type: List[Expression] # Decorators, at least one  # XXX Not true
     var = None  # type: Var                     # Represents the decorated function obj
+    type = None  # type: mypy.types.Type
     is_overload = False
 
     def __init__(self, func: FuncDef, decorators: List[Expression],