Implement a reveal_locals expression (#3425)

`reveal_locals()` is a magic function that causes mypy to display
the types of all variables in the current local scope, analogous
to `reveal_type(e)`.

Author: aisipos

docs/source/common_issues.rst

@@ -430,12 +430,25 @@ understand how mypy handles a particular piece of code. Example:
 
    reveal_type((1, 'hello'))  # Revealed type is 'Tuple[builtins.int, builtins.str]'
 
+You can also use ``reveal_locals()`` at any line in a file
+to see the types of all local varaibles at once. Example:
+
+.. code-block:: python
+
+   a = 1
+   b = 'one'
+   reveal_locals()
+   # Revealed local types are:
+   # a: builtins.int
+   # b: builtins.str
 .. note::
 
-   ``reveal_type`` is only understood by mypy and doesn't exist
-   in Python, if you try to run your program. You'll have to remove
-   any ``reveal_type`` calls before you can run your code.
-   ``reveal_type`` is always available and you don't need to import it.
+   ``reveal_type`` and ``reveal_locals`` are only understood by mypy and
+   don't exist in Python. If you try to run your program, you'll have to
+   remove any ``reveal_type`` and ``reveal_locals`` calls before you can
+   run your code. Both are always available and you don't need to import
+   them.
+
 
 .. _import-cycles:
 

mypy/checkexpr.py

@@ -15,14 +15,14 @@
 from mypy.nodes import (
     NameExpr, RefExpr, Var, FuncDef, OverloadedFuncDef, TypeInfo, CallExpr,
     MemberExpr, IntExpr, StrExpr, BytesExpr, UnicodeExpr, FloatExpr,
-    OpExpr, UnaryExpr, IndexExpr, CastExpr, RevealTypeExpr, TypeApplication, ListExpr,
+    OpExpr, UnaryExpr, IndexExpr, CastExpr, RevealExpr, TypeApplication, ListExpr,
     TupleExpr, DictExpr, LambdaExpr, SuperExpr, SliceExpr, Context, Expression,
     ListComprehension, GeneratorExpr, SetExpr, MypyFile, Decorator,
     ConditionalExpr, ComparisonExpr, TempNode, SetComprehension,
     DictionaryComprehension, ComplexExpr, EllipsisExpr, StarExpr, AwaitExpr, YieldExpr,
     YieldFromExpr, TypedDictExpr, PromoteExpr, NewTypeExpr, NamedTupleExpr, TypeVarExpr,
     TypeAliasExpr, BackquoteExpr, EnumCallExpr,
-    ARG_POS, ARG_NAMED, ARG_STAR, ARG_STAR2, MODULE_REF, TVAR, LITERAL_TYPE,
+    ARG_POS, ARG_NAMED, ARG_STAR, ARG_STAR2, MODULE_REF, TVAR, LITERAL_TYPE, REVEAL_TYPE
 )
 from mypy.literals import literal
 from mypy import nodes
@@ -1802,14 +1802,29 @@ def visit_cast_expr(self, expr: CastExpr) -> Type:
                                context=expr)
         return target_type
 
-    def visit_reveal_type_expr(self, expr: RevealTypeExpr) -> Type:
+    def visit_reveal_expr(self, expr: RevealExpr) -> Type:
         """Type check a reveal_type expression."""
-        revealed_type = self.accept(expr.expr, type_context=self.type_context[-1])
-        if not self.chk.current_node_deferred:
-            self.msg.reveal_type(revealed_type, expr)
-            if not self.chk.in_checked_function():
-                self.msg.note("'reveal_type' always outputs 'Any' in unchecked functions", expr)
-        return revealed_type
+        if expr.kind == REVEAL_TYPE:
+            assert expr.expr is not None
+            revealed_type = self.accept(expr.expr, type_context=self.type_context[-1])
+            if not self.chk.current_node_deferred:
+                self.msg.reveal_type(revealed_type, expr)
+                if not self.chk.in_checked_function():
+                    self.msg.note("'reveal_type' always outputs 'Any' in unchecked functions",
+                                  expr)
+            return revealed_type
+        else:
+            # REVEAL_LOCALS
+            if not self.chk.current_node_deferred:
+                # the RevealExpr contains a local_nodes attribute,
+                # calculated at semantic analysis time. Use it to pull out the
+                # corresponding subset of variables in self.chk.type_map
+                names_to_types = {
+                    var_node.name(): var_node.type for var_node in expr.local_nodes
+                } if expr.local_nodes is not None else {}
+
+                self.msg.reveal_locals(names_to_types, expr)
+            return NoneTyp()
 
     def visit_type_application(self, tapp: TypeApplication) -> Type:
         """Type check a type application (expr[type, ...])."""

mypy/literals.py

@@ -4,7 +4,7 @@
     Expression, ComparisonExpr, OpExpr, MemberExpr, UnaryExpr, StarExpr, IndexExpr, LITERAL_YES,
     LITERAL_NO, NameExpr, LITERAL_TYPE, IntExpr, FloatExpr, ComplexExpr, StrExpr, BytesExpr,
     UnicodeExpr, ListExpr, TupleExpr, SetExpr, DictExpr, CallExpr, SliceExpr, CastExpr,
-    ConditionalExpr, EllipsisExpr, YieldFromExpr, YieldExpr, RevealTypeExpr, SuperExpr,
+    ConditionalExpr, EllipsisExpr, YieldFromExpr, YieldExpr, RevealExpr, SuperExpr,
     TypeApplication, LambdaExpr, ListComprehension, SetComprehension, DictionaryComprehension,
     GeneratorExpr, BackquoteExpr, TypeVarExpr, TypeAliasExpr, NamedTupleExpr, EnumCallExpr,
     TypedDictExpr, NewTypeExpr, PromoteExpr, AwaitExpr, TempNode,
@@ -175,7 +175,7 @@ def visit_yield_from_expr(self, e: YieldFromExpr) -> None:
     def visit_yield_expr(self, e: YieldExpr) -> None:
         return None
 
-    def visit_reveal_type_expr(self, e: RevealTypeExpr) -> None:
+    def visit_reveal_expr(self, e: RevealExpr) -> None:
         return None
 
     def visit_super_expr(self, e: SuperExpr) -> None:

mypy/messages.py

@@ -10,6 +10,7 @@
 checker but we are moving away from this convention.
 """
 
+from collections import OrderedDict
 import re
 import difflib
 
@@ -26,10 +27,9 @@
     TypeInfo, Context, MypyFile, op_methods, FuncDef, reverse_type_aliases,
     ARG_POS, ARG_OPT, ARG_NAMED, ARG_NAMED_OPT, ARG_STAR, ARG_STAR2,
     ReturnStmt, NameExpr, Var, CONTRAVARIANT, COVARIANT, SymbolNode,
-    CallExpr
+    CallExpr, Expression
 )
 
-
 # Constants that represent simple type checker error message, i.e. messages
 # that do not have any parameters.
 
@@ -970,6 +970,16 @@ def invalid_signature(self, func_type: Type, context: Context) -> None:
     def reveal_type(self, typ: Type, context: Context) -> None:
         self.fail('Revealed type is \'{}\''.format(typ), context)
 
+    def reveal_locals(self, type_map: Dict[str, Optional[Type]], context: Context) -> None:
+        # To ensure that the output is predictable on Python < 3.6,
+        # use an ordered dictionary sorted by variable name
+        sorted_locals = OrderedDict(sorted(type_map.items(), key=lambda t: t[0]))
+        self.fail("Revealed local types are:", context)
+        # Note that self.fail does a strip() on the message, so we cannot prepend with spaces
+        # for indentation
+        for line in ['{}: {}'.format(k, v) for k, v in sorted_locals.items()]:
+            self.fail(line, context)
+
     def unsupported_type_type(self, item: Type, context: Context) -> None:
         self.fail('Unsupported type Type[{}]'.format(self.format(item)), context)
 

mypy/nodes.py

@@ -78,6 +78,9 @@ def get_column(self) -> int:
 # XXX what?
 UNBOUND_IMPORTED = 7  # type: int
 
+# RevealExpr node kinds
+REVEAL_TYPE = 0  # type: int
+REVEAL_LOCALS = 1  # type: int
 
 LITERAL_YES = 2
 LITERAL_TYPE = 1
@@ -1595,17 +1598,24 @@ def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_cast_expr(self)
 
 
-class RevealTypeExpr(Expression):
-    """Reveal type expression reveal_type(expr)."""
+class RevealExpr(Expression):
+    """Reveal type expression reveal_type(expr) or reveal_locals() expression."""
 
-    expr = None  # type: Expression
+    expr = None  # type: Optional[Expression]
+    kind = 0  # type: int
+    local_nodes = None  # type: Optional[List[Var]]
 
-    def __init__(self, expr: Expression) -> None:
+    def __init__(
+            self, kind: int,
+            expr: Optional[Expression] = None,
+            local_nodes: 'Optional[List[Var]]' = None) -> None:
         super().__init__()
         self.expr = expr
+        self.kind = kind
+        self.local_nodes = local_nodes
 
     def accept(self, visitor: ExpressionVisitor[T]) -> T:
-        return visitor.visit_reveal_type_expr(self)
+        return visitor.visit_reveal_expr(self)
 
 
 class SuperExpr(Expression):

mypy/semanal.py

@@ -46,7 +46,7 @@
     RaiseStmt, AssertStmt, OperatorAssignmentStmt, WhileStmt,
     ForStmt, BreakStmt, ContinueStmt, IfStmt, TryStmt, WithStmt, DelStmt, PassStmt,
     GlobalDecl, SuperExpr, DictExpr, CallExpr, RefExpr, OpExpr, UnaryExpr,
-    SliceExpr, CastExpr, RevealTypeExpr, TypeApplication, Context, SymbolTable,
+    SliceExpr, CastExpr, RevealExpr, TypeApplication, Context, SymbolTable,
     SymbolTableNode, TVAR, ListComprehension, GeneratorExpr,
     LambdaExpr, MDEF, FuncBase, Decorator, SetExpr, TypeVarExpr, NewTypeExpr,
     StrExpr, BytesExpr, PrintStmt, ConditionalExpr, PromoteExpr,
@@ -56,7 +56,7 @@
     YieldExpr, ExecStmt, Argument, BackquoteExpr, ImportBase, AwaitExpr,
     IntExpr, FloatExpr, UnicodeExpr, EllipsisExpr, TempNode, EnumCallExpr, ImportedName,
     COVARIANT, CONTRAVARIANT, INVARIANT, UNBOUND_IMPORTED, LITERAL_YES, ARG_OPT, nongen_builtins,
-    collections_type_aliases, get_member_expr_fullname,
+    collections_type_aliases, get_member_expr_fullname, REVEAL_TYPE, REVEAL_LOCALS
 )
 from mypy.literals import literal
 from mypy.tvar_scope import TypeVarScope
@@ -2574,7 +2574,38 @@ def visit_call_expr(self, expr: CallExpr) -> None:
         elif refers_to_fullname(expr.callee, 'builtins.reveal_type'):
             if not self.check_fixed_args(expr, 1, 'reveal_type'):
                 return
-            expr.analyzed = RevealTypeExpr(expr.args[0])
+            expr.analyzed = RevealExpr(kind=REVEAL_TYPE, expr=expr.args[0])
+            expr.analyzed.line = expr.line
+            expr.analyzed.column = expr.column
+            expr.analyzed.accept(self)
+        elif refers_to_fullname(expr.callee, 'builtins.reveal_locals'):
+            # Store the local variable names into the RevealExpr for use in the
+            # type checking pass
+            local_nodes = []  # type: List[Var]
+            if self.is_module_scope():
+                # try to determine just the variable declarations in module scope
+                # self.globals.values() contains SymbolTableNode's
+                # Each SymbolTableNode has an attribute node that is nodes.Var
+                # look for variable nodes that marked as is_inferred
+                # Each symboltable node has a Var node as .node
+                local_nodes = cast(
+                    List[Var],
+                    [
+                        n.node for name, n in self.globals.items()
+                        if getattr(n.node, 'is_inferred', False)
+                    ]
+                )
+            elif self.is_class_scope():
+                # type = None  # type: Optional[TypeInfo]
+                if self.type is not None:
+                    local_nodes = cast(List[Var], [st.node for st in self.type.names.values()])
+            elif self.is_func_scope():
+                # locals = None  # type: List[Optional[SymbolTable]]
+                if self.locals is not None:
+                    symbol_table = self.locals[-1]
+                    if symbol_table is not None:
+                        local_nodes = cast(List[Var], [st.node for st in symbol_table.values()])
+            expr.analyzed = RevealExpr(kind=REVEAL_LOCALS, local_nodes=local_nodes)
             expr.analyzed.line = expr.line
             expr.analyzed.column = expr.column
             expr.analyzed.accept(self)
@@ -2826,8 +2857,14 @@ def visit_cast_expr(self, expr: CastExpr) -> None:
         expr.expr.accept(self)
         expr.type = self.anal_type(expr.type)
 
-    def visit_reveal_type_expr(self, expr: RevealTypeExpr) -> None:
-        expr.expr.accept(self)
+    def visit_reveal_expr(self, expr: RevealExpr) -> None:
+        if expr.kind == REVEAL_TYPE:
+            if expr.expr is not None:
+                expr.expr.accept(self)
+        else:
+            # Reveal locals doesn't have an inner expression, there's no
+            # need to traverse inside it
+            pass
 
     def visit_type_application(self, expr: TypeApplication) -> None:
         expr.expr.accept(self)

mypy/semanal_pass1.py

@@ -103,6 +103,9 @@ def visit_file(self, file: MypyFile, fnam: str, mod_id: str, options: Options) -
                     # reveal_type is a mypy-only function that gives an error with
                     # the type of its arg.
                     ('reveal_type', AnyType(TypeOfAny.special_form)),
+                    # reveal_locals is a mypy-only function that gives an error with the types of
+                    # locals
+                    ('reveal_locals', AnyType(TypeOfAny.special_form)),
                 ]  # type: List[Tuple[str, Type]]
 
                 # TODO(ddfisher): This guard is only needed because mypy defines

mypy/semanal_pass3.py

@@ -18,7 +18,7 @@
     Node, Expression, MypyFile, FuncDef, FuncItem, Decorator, RefExpr, Context, TypeInfo, ClassDef,
     Block, TypedDictExpr, NamedTupleExpr, AssignmentStmt, IndexExpr, TypeAliasExpr, NameExpr,
     CallExpr, NewTypeExpr, ForStmt, WithStmt, CastExpr, TypeVarExpr, TypeApplication, Lvalue,
-    TupleExpr, RevealTypeExpr, SymbolTableNode, SymbolTable, Var, ARG_POS, OverloadedFuncDef,
+    TupleExpr, RevealExpr, SymbolTableNode, SymbolTable, Var, ARG_POS, OverloadedFuncDef,
     MDEF,
 )
 from mypy.types import (
@@ -278,8 +278,8 @@ def visit_cast_expr(self, e: CastExpr) -> None:
         self.analyze(e.type, e)
         super().visit_cast_expr(e)
 
-    def visit_reveal_type_expr(self, e: RevealTypeExpr) -> None:
-        super().visit_reveal_type_expr(e)
+    def visit_reveal_expr(self, e: RevealExpr) -> None:
+        super().visit_reveal_expr(e)
 
     def visit_type_application(self, e: TypeApplication) -> None:
         for type in e.types:

mypy/server/subexpr.py

@@ -4,7 +4,7 @@
 
 from mypy.nodes import (
     Expression, Node, MemberExpr, YieldFromExpr, YieldExpr, CallExpr, OpExpr, ComparisonExpr,
-    SliceExpr, CastExpr, RevealTypeExpr, UnaryExpr, ListExpr, TupleExpr, DictExpr, SetExpr,
+    SliceExpr, CastExpr, RevealExpr, UnaryExpr, ListExpr, TupleExpr, DictExpr, SetExpr,
     IndexExpr, GeneratorExpr, ListComprehension, SetComprehension, DictionaryComprehension,
     ConditionalExpr, TypeApplication, LambdaExpr, StarExpr, BackquoteExpr, AwaitExpr,
 )
@@ -72,9 +72,9 @@ def visit_cast_expr(self, e: CastExpr) -> None:
         self.add(e)
         super().visit_cast_expr(e)
 
-    def visit_reveal_type_expr(self, e: RevealTypeExpr) -> None:
+    def visit_reveal_expr(self, e: RevealExpr) -> None:
         self.add(e)
-        super().visit_reveal_type_expr(e)
+        super().visit_reveal_expr(e)
 
     def visit_unary_expr(self, e: UnaryExpr) -> None:
         self.add(e)

mypy/strconv.py

@@ -406,8 +406,12 @@ def visit_comparison_expr(self, o: 'mypy.nodes.ComparisonExpr') -> str:
     def visit_cast_expr(self, o: 'mypy.nodes.CastExpr') -> str:
         return self.dump([o.expr, o.type], o)
 
-    def visit_reveal_type_expr(self, o: 'mypy.nodes.RevealTypeExpr') -> str:
-        return self.dump([o.expr], o)
+    def visit_reveal_expr(self, o: 'mypy.nodes.RevealExpr') -> str:
+        if o.kind == mypy.nodes.REVEAL_TYPE:
+            return self.dump([o.expr], o)
+        else:
+            # REVEAL_LOCALS
+            return self.dump([o.local_nodes], o)
 
     def visit_unary_expr(self, o: 'mypy.nodes.UnaryExpr') -> str:
         return self.dump([o.op, o.expr], o)

mypy/traverser.py

@@ -5,12 +5,12 @@
     Block, MypyFile, FuncItem, CallExpr, ClassDef, Decorator, FuncDef,
     ExpressionStmt, AssignmentStmt, OperatorAssignmentStmt, WhileStmt,
     ForStmt, ReturnStmt, AssertStmt, DelStmt, IfStmt, RaiseStmt,
-    TryStmt, WithStmt, MemberExpr, OpExpr, SliceExpr, CastExpr, RevealTypeExpr,
+    TryStmt, WithStmt, MemberExpr, OpExpr, SliceExpr, CastExpr, RevealExpr,
     UnaryExpr, ListExpr, TupleExpr, DictExpr, SetExpr, IndexExpr,
     GeneratorExpr, ListComprehension, SetComprehension, DictionaryComprehension,
     ConditionalExpr, TypeApplication, ExecStmt, Import, ImportFrom,
     LambdaExpr, ComparisonExpr, OverloadedFuncDef, YieldFromExpr,
-    YieldExpr, StarExpr, BackquoteExpr, AwaitExpr, PrintStmt, SuperExpr,
+    YieldExpr, StarExpr, BackquoteExpr, AwaitExpr, PrintStmt, SuperExpr, REVEAL_TYPE
 )
 
 
@@ -181,8 +181,13 @@ def visit_slice_expr(self, o: SliceExpr) -> None:
     def visit_cast_expr(self, o: CastExpr) -> None:
         o.expr.accept(self)
 
-    def visit_reveal_type_expr(self, o: RevealTypeExpr) -> None:
-        o.expr.accept(self)
+    def visit_reveal_expr(self, o: RevealExpr) -> None:
+        if o.kind == REVEAL_TYPE:
+            assert o.expr is not None
+            o.expr.accept(self)
+        else:
+            # RevealLocalsExpr doesn't have an inner expression
+            pass
 
     def visit_unary_expr(self, o: UnaryExpr) -> None:
         o.expr.accept(self)

mypy/treetransform.py

@@ -11,7 +11,7 @@
     OperatorAssignmentStmt, ExpressionStmt, AssignmentStmt, ReturnStmt,
     RaiseStmt, AssertStmt, DelStmt, BreakStmt, ContinueStmt,
     PassStmt, GlobalDecl, WhileStmt, ForStmt, IfStmt, TryStmt, WithStmt,
-    CastExpr, RevealTypeExpr, TupleExpr, GeneratorExpr, ListComprehension, ListExpr,
+    CastExpr, RevealExpr, TupleExpr, GeneratorExpr, ListComprehension, ListExpr,
     ConditionalExpr, DictExpr, SetExpr, NameExpr, IntExpr, StrExpr, BytesExpr,
     UnicodeExpr, FloatExpr, CallExpr, SuperExpr, MemberExpr, IndexExpr,
     SliceExpr, OpExpr, UnaryExpr, LambdaExpr, TypeApplication, PrintStmt,
@@ -20,7 +20,7 @@
     YieldFromExpr, NamedTupleExpr, TypedDictExpr, NonlocalDecl, SetComprehension,
     DictionaryComprehension, ComplexExpr, TypeAliasExpr, EllipsisExpr,
     YieldExpr, ExecStmt, Argument, BackquoteExpr, AwaitExpr,
-    OverloadPart, EnumCallExpr,
+    OverloadPart, EnumCallExpr, REVEAL_TYPE
 )
 from mypy.types import Type, FunctionLike
 from mypy.traverser import TraverserVisitor
@@ -377,8 +377,13 @@ def visit_cast_expr(self, node: CastExpr) -> CastExpr:
         return CastExpr(self.expr(node.expr),
                         self.type(node.type))
 
-    def visit_reveal_type_expr(self, node: RevealTypeExpr) -> RevealTypeExpr:
-        return RevealTypeExpr(self.expr(node.expr))
+    def visit_reveal_expr(self, node: RevealExpr) -> RevealExpr:
+        if node.kind == REVEAL_TYPE:
+            assert node.expr is not None
+            return RevealExpr(kind=REVEAL_TYPE, expr=self.expr(node.expr))
+        else:
+            # Reveal locals expressions don't have any sub expressions
+            return node
 
     def visit_super_expr(self, node: SuperExpr) -> SuperExpr:
         call = self.expr(node.call)