feat(checker): add cast expression

examples/01_simple_type_checking/02_simple_types.py

@@ -3,6 +3,6 @@
 
 midas.using("02_simple_types.midas")
 
-distance: Meter = 123.45
-time: Second = 6.7
+distance: Meter = cast(Meter, 123.45)
+time: Second = cast(Second, 6.7)
 speed = distance / time

gen/python.py

@@ -128,4 +128,9 @@ class SetExpr:
     value: Expr
 
 
+class CastExpr:
+    type: MidasType
+    expr: Expr
+
+
 ###<

midas/ast/printer.py

@@ -555,3 +555,13 @@ class PythonAstPrinter(
             self._write_line("value", last=True)
             with self._child_level(single=True):
                 expr.value.accept(self)
+
+    def visit_cast_expr(self, expr: p.CastExpr) -> None:
+        self._write_line("CastExpr")
+        with self._child_level():
+            self._write_line("type")
+            with self._child_level(single=True):
+                expr.type.accept(self)
+            self._write_line("expr", last=True)
+            with self._child_level(single=True):
+                expr.expr.accept(self)

midas/ast/python.py

@@ -204,6 +204,9 @@ class Expr(ABC):
         @abstractmethod
         def visit_set_expr(self, expr: SetExpr) -> T: ...
 
+        @abstractmethod
+        def visit_cast_expr(self, expr: CastExpr) -> T: ...
+
 
 @dataclass(frozen=True)
 class BinaryExpr(Expr):
@@ -287,3 +290,12 @@ class SetExpr(Expr):
 
     def accept(self, visitor: Expr.Visitor[T]) -> T:
         return visitor.visit_set_expr(self)
+
+
+@dataclass(frozen=True)
+class CastExpr(Expr):
+    type: MidasType
+    expr: Expr
+
+    def accept(self, visitor: Expr.Visitor[T]) -> T:
+        return visitor.visit_cast_expr(self)

midas/checker/checker.py

@@ -291,6 +291,9 @@ class Checker(
 
     def visit_set_expr(self, expr: p.SetExpr) -> Type: ...
 
+    def visit_cast_expr(self, expr: p.CastExpr) -> Type:
+        return expr.type.accept(self)
+
     def visit_base_type(self, node: p.BaseType) -> Type:
         return self.ctx.get_type(node.base)
 

midas/parser/python.py

@@ -7,6 +7,7 @@ from midas.ast.python import (
     BaseType,
     BinaryExpr,
     CallExpr,
+    CastExpr,
     CompareExpr,
     ConstraintType,
     Expr,
@@ -38,6 +39,8 @@ class UnsupportedSyntaxError(Exception):
 
 
 class PythonParser:
+    CAST_FUNCTION = "cast"
+
     def parse_module(self, node: ast.Module) -> list[Stmt]:
         statements: list[Stmt] = []
         for stmt in node.body:
@@ -90,15 +93,14 @@ class PythonParser:
                 value=value,
                 simple=1,
             ):
-                type = self._parse_type(annotation, root=True)
-                if type is not None:
-                    statements.append(
-                        TypeAssign(
-                            location=loc,
-                            name=target,
-                            type=type,
-                        )
+                type = self._parse_type(annotation)
+                statements.append(
+                    TypeAssign(
+                        location=loc,
+                        name=target,
+                        type=type,
                     )
+                )
 
                 if value is not None:
                     statements.append(
@@ -215,9 +217,7 @@ class PythonParser:
             default=default,
         )
 
-    def _parse_type(
-        self, type_expr: ast.expr, root: bool = False
-    ) -> Optional[MidasType]:
+    def _parse_type(self, type_expr: ast.expr) -> MidasType:
         loc: Location = Location.from_ast(type_expr)
         match type_expr:
             case ast.Subscript(value=ast.Name(id="Frame"), slice=schema):
@@ -265,8 +265,6 @@ class PythonParser:
                         )
 
             case _:
-                if root:
-                    return None
                 raise UnsupportedSyntaxError(type_expr)
 
     def _parse_frame_type(self, schema: ast.expr) -> FrameType:
@@ -339,6 +337,9 @@ class PythonParser:
             case ast.Compare():
                 return self.parse_compare(node)
 
+            case ast.Call(func=ast.Name(id=self.CAST_FUNCTION)):
+                return self.parse_cast(node)
+
             case ast.Call():
                 return self.parse_call(node)
 
@@ -407,6 +408,19 @@ class PythonParser:
             )
         return expr
 
+    def parse_cast(self, node: ast.Call) -> CastExpr:
+        match node:
+            case ast.Call(args=[type, expr], keywords=[]):
+                return CastExpr(
+                    location=Location.from_ast(node),
+                    type=self._parse_type(type),
+                    expr=self.parse_expr(expr),
+                )
+            case _:
+                raise InvalidSyntaxError(
+                    f"Invalid call to {self.CAST_FUNCTION}, expected type and expression"
+                )
+
     def parse_call(self, node: ast.Call) -> CallExpr:
         return CallExpr(
             location=Location.from_ast(node),

midas/resolver/resolver.py

@@ -114,3 +114,6 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
     def visit_set_expr(self, expr: p.SetExpr) -> None:
         self.resolve(expr.value)
         self.resolve(expr.object)
+
+    def visit_cast_expr(self, expr: p.CastExpr) -> None:
+        self.resolve(expr.expr)

tests/cases/checker/04_custom_types.py

@@ -3,6 +3,6 @@
 
 midas.using("04_custom_types.midas")
 
-distance: Meter = 123.45
-time: Second = 6.7
+distance: Meter = cast(Meter, 123.45)
+time: Second = cast(Second, 6.7)
 speed = distance / time

tests/cases/checker/04_custom_types.py.ref.json

@@ -1,32 +1,3 @@
 {
-  "diagnostics": [
-    {
-      "type": "Error",
-      "location": {
-        "start": [
-          6,
-          0
-        ],
-        "end": [
-          6,
-          24
-        ]
-      },
-      "message": "Cannot assign BaseType(name='float') to distance of type SimpleType(name='Meter', base=BaseType(name='float'))"
-    },
-    {
-      "type": "Error",
-      "location": {
-        "start": [
-          7,
-          0
-        ],
-        "end": [
-          7,
-          18
-        ]
-      },
-      "message": "Cannot assign BaseType(name='float') to time of type SimpleType(name='Second', base=BaseType(name='float'))"
-    }
-  ]
+  "diagnostics": []
 }

tests/serializer/python.py

@@ -6,6 +6,7 @@ from midas.ast.python import (
     BaseType,
     BinaryExpr,
     CallExpr,
+    CastExpr,
     CompareExpr,
     ConstraintType,
     Expr,
@@ -228,3 +229,10 @@ class PythonAstJsonSerializer(
             "name": expr.name,
             "value": expr.value.accept(self),
         }
+
+    def visit_cast_expr(self, expr: CastExpr) -> dict:
+        return {
+            "_type": "CastExpr",
+            "type": expr.type.accept(self),
+            "expr": expr.expr.accept(self),
+        }