Translate dict(x=y, ...) to {'x': y, ...} internally

Closes #239.

Author: JukkaL

mypy/nodes.py

@@ -88,7 +88,7 @@ def __str__(self) -> str:
             return repr(self)
         return ans
 
-    def set_line(self, target: Union[Token, int]) -> 'Node':
+    def set_line(self, target: Union[Token, 'Node', int]) -> 'Node':
         if isinstance(target, int):
             self.line = target
         else:
@@ -282,7 +282,7 @@ def _initialization_statement(self) -> Optional['AssignmentStmt']:
         assign = AssignmentStmt([lvalue], rvalue)
         return assign
 
-    def set_line(self, target: Union[Token, int]) -> Node:
+    def set_line(self, target: Union[Token, Node, int]) -> Node:
         super().set_line(target)
 
         if self.initializer:
@@ -329,7 +329,7 @@ def __init__(self, arguments: List[Argument], body: 'Block',
     def max_fixed_argc(self) -> int:
         return self.max_pos
 
-    def set_line(self, target: Union[Token, int]) -> Node:
+    def set_line(self, target: Union[Token, Node, int]) -> Node:
         super().set_line(target)
         for arg in self.arguments:
             arg.set_line(self.line)

mypy/semanal.py

@@ -1647,11 +1647,28 @@ def visit_call_expr(self, expr: CallExpr) -> None:
             expr.analyzed = PromoteExpr(target)
             expr.analyzed.line = expr.line
             expr.analyzed.accept(self)
+        elif refers_to_fullname(expr.callee, 'builtins.dict'):
+            expr.analyzed = self.translate_dict_call(expr)
         else:
             # Normal call expression.
             for a in expr.args:
                 a.accept(self)
 
+    def translate_dict_call(self, call: CallExpr) -> Optional[DictExpr]:
+        """Translate 'dict(x=y, ...)' to {'x': y, ...}.
+
+        For other variants of dict(...), return None.
+        """
+        if not call.args:
+            return None
+        if not all(kind == ARG_NAMED for kind in call.arg_kinds):
+            return None
+        expr = DictExpr([(StrExpr(key), value)
+                         for key, value in zip(call.arg_names, call.args)])
+        expr.set_line(call)
+        expr.accept(self)
+        return expr
+
     def check_fixed_args(self, expr: CallExpr, numargs: int,
                          name: str) -> bool:
         """Verify that expr has specified number of positional args.

mypy/test/data/check-expressions.test

@@ -1318,3 +1318,18 @@ def f(x: int) -> Iterator[None]:
     (yield)
 [builtins fixtures/for.py]
 [out]
+
+
+-- dict(x=y, ...)
+-- --------------
+
+
+[case testDictWithKeywordArgs]
+from typing import Dict, Any
+d1 = dict(a=1, b=2) # type: Dict[str, int]
+d2 = dict(a=1, b='') # type: Dict[str, int] # E: Incompatible types in assignment (expression has type Dict[str, object], variable has type Dict[str, int])
+d3 = dict(a=1) # type: Dict[int, int] # E: Incompatible types in assignment (expression has type Dict[str, int], variable has type Dict[int, int])
+d4 = dict(a=1, b=1)
+d4.xyz # E: Dict[str, int] has no attribute "xyz"
+d5 = dict(a=1, b='') # type: Dict[str, Any]
+[builtins fixtures/dict.py]

mypy/test/data/pythoneval.test

@@ -1063,3 +1063,14 @@ t = n * ('',)
 t + 1
 [out]
 _program.py:3: error: Unsupported operand types for + (Tuple[str, ...] and "int")
+
+[case testDictWithKeywordArgs]
+from typing import Dict, Any
+d1 = dict(a=1, b=2) # type: Dict[str, int]
+d2 = dict(a=1, b='') # type: Dict[str, int] # E
+d3 = dict(a=1, b=1)
+d3.xyz # E
+d4 = dict(a=1, b='') # type: Dict[str, Any]
+[out]
+_program.py:3: error: Incompatible types in assignment (expression has type Dict[str, object], variable has type Dict[str, int])
+_program.py:5: error: Dict[str, int] has no attribute "xyz"

mypy/test/data/semanal-expressions.test

@@ -379,3 +379,17 @@ MypyFile:1(
         NameExpr(None [builtins.None]))
       NameExpr(int [builtins.int])
       NameExpr(str [builtins.str]))))
+
+[case testDictWithKeywordArgs]
+dict(a=1, b=str())
+[builtins fixtures/dict.py]
+[out]
+MypyFile:1(
+  ExpressionStmt:1(
+    DictExpr:1(
+      StrExpr(a)
+      IntExpr(1)
+      StrExpr(b)
+      CallExpr:1(
+        NameExpr(str [builtins.str])
+        Args()))))