fix(resolver): properly check if variable is defined

midas/checker/python.py

@@ -107,7 +107,7 @@ class PythonTyper(
         tree: ast.Module = ast.parse(source, filename=path or "<unknown>")
         parser = PythonParser()
         stmts: list[p.Stmt] = parser.parse_module(tree)
-        resolver = Resolver()
+        resolver = Resolver(reporter)
         resolver.resolve(*stmts)
 
         self.env = self.global_env

midas/checker/resolver.py

@@ -1,4 +1,6 @@
 import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.reporter import FileReporter
 
 
 class ResolverError(Exception): ...
@@ -11,9 +13,10 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
     scope is referred to when a variable is referenced
     """
 
-    def __init__(self):
+    def __init__(self, reporter: FileReporter):
         self.locals: dict[p.Expr, int] = {}
         self.scopes: list[dict[str, bool]] = [{}]
+        self.reporter: FileReporter = reporter
 
     def resolve(self, *objects: p.Stmt | p.Expr) -> None:
         """Resolve the given statements or expressions"""
@@ -25,29 +28,28 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         """Begin a new scope inside the current one"""
         self.scopes.append({})
 
-    def end_scope(self):
+    def end_scope(self) -> dict[str, bool]:
-        """Close the current scope"""
+        """Close and return the current scope"""
-        self.scopes.pop()
+        return self.scopes.pop()
 
-    def declare(self, name: str) -> None:
+    def declare(self, location: Location, name: str) -> None:
         """Declare a variable in the current scope
 
         This method must be called *before* evaluating the variable initializer
 
         Args:
             name (str): the name of the variable
-
-        Raises:
-            ResolverError: if the variable has already been declared in the current scope
         """
         if len(self.scopes) == 0:
             return
         scope: dict[str, bool] = self.scopes[-1]
         if name in scope:
-            raise ResolverError(
+            self.reporter.error(
-                f"A variable with the name {name} is already declared in this scope"
+                location,
+                f"A variable with the name '{name}' is already declared in this scope",
             )
-        scope[name] = False
+        else:
+            scope[name] = False
 
     def define(self, name: str) -> None:
         """Define a variable in the current scope
@@ -77,7 +79,7 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
                 self.locals[expr] = i
                 return
 
-    def is_defined(self, name: str) -> bool:
+    def is_declared(self, name: str) -> bool:
         """Check whether the given variable is defined in any scope
 
         Args:
@@ -106,7 +108,7 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
                 self.resolve(param.default)
 
         for param in function.params.all:
-            self.declare(param.name)
+            self.declare(function.location, param.name)
             self.define(param.name)
         self.resolve(*function.body)
         self.end_scope()
@@ -116,14 +118,12 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
 
     def visit_function(self, stmt: p.Function) -> None:
         # Declare before resolving body to allow recursion
-        self.declare(stmt.name)
+        self.declare(stmt.location, stmt.name)
         self.define(stmt.name)
         self.resolve_function(stmt)
 
     def visit_type_assign(self, stmt: p.TypeAssign) -> None:
-        self.declare(stmt.name)
+        self.declare(stmt.location, stmt.name)
-        # NOTE: resolve type here?
-        self.define(stmt.name)
 
     def visit_assign_stmt(self, stmt: p.AssignStmt) -> None:
         self.resolve(stmt.value)
@@ -133,9 +133,9 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
     def _visit_assign(self, target: p.Expr):
         match target:
             case p.VariableExpr(name=name):
-                if not self.is_defined(name):
+                if not self.is_declared(name):
-                    self.declare(name)
+                    self.declare(target.location, name)
-                    self.define(name)
+                self.define(name)
                 target.accept(self)
 
             case p.GetExpr():
@@ -145,7 +145,9 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
                 target.accept(self)
 
             case _:
-                raise Exception(f"Unsupported assignment to {target}")
+                self.reporter.error(
+                    target.location, f"Unsupported assignment to {target}"
+                )
 
     def visit_return_stmt(self, stmt: p.ReturnStmt) -> None:
         if stmt.value is not None:
@@ -162,12 +164,17 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         # Body
         self.begin_scope()
         self.resolve(*stmt.body)
-        self.end_scope()
+        body: dict[str, bool] = self.end_scope()
 
         # Else
         self.begin_scope()
         self.resolve(*stmt.orelse)
-        self.end_scope()
+        else_: dict[str, bool] = self.end_scope()
+
+        # Define variables in this scope if it was defined in both body and else blocks
+        for name, is_defined in body.items():
+            if is_defined and else_.get(name, False):
+                self.define(name)
 
     def visit_pass(self, stmt: p.Pass) -> None:
         pass
@@ -188,7 +195,7 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
     def _resolve_imports(self, imports: list[p.ImportAlias]) -> None:
         for import_ in imports:
             name: str = import_.imported_name
-            self.declare(name)
+            self.declare(import_.location, name)
             self.define(name)
 
     def visit_raw_stmt(self, stmt: p.RawStmt) -> None:
@@ -220,8 +227,9 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
 
     def visit_variable_expr(self, expr: p.VariableExpr) -> None:
         if len(self.scopes) != 0 and self.scopes[-1].get(expr.name) is False:
-            raise ResolverError(
+            self.reporter.error(
-                f"Cannot use local variable '{expr.name}' in its own initializer"
+                expr.location,
+                f"Variable '{expr.name}' is declared but may not be defined",
             )  # aka. UnboundLocalError
         self.resolve_local(expr, expr.name)
 

tests/cases/checker/07_variance.py

@@ -11,16 +11,16 @@ from _ import (
     Unused,
 )
 
-unused: Unused
+unused: Unused = object()
-covariant: Covariant
+covariant: Covariant = object()
-contravariant: Contravariant
+contravariant: Contravariant = object()
-invariant: Invariant
+invariant: Invariant = object()
-coco: Coco
+coco: Coco = object()
-cocontra: Cocontra
+cocontra: Cocontra = object()
-contraco: Contraco
+contraco: Contraco = object()
-contracontra: Contracontra
+contracontra: Contracontra = object()
-t1: T1
+t1: T1 = object()
-t2: T2
+t2: T2 = object()
 
 # Dummy print to prudce judgements for the expressions
 print(
@@ -36,17 +36,17 @@ print(
     t2,
 )
 
-cov1: Covariant[float]
+cov1: Covariant[float] = object()
-cov2: Covariant[int]
+cov2: Covariant[int] = object()
 cov1 = cov2  # Ok because int <: float => Covariant[int] <: Covariant[float]
 cov2 = cov1  # Invalid
 
-contra1: Contravariant[float]
+contra1: Contravariant[float] = object()
-contra2: Contravariant[int]
+contra2: Contravariant[int] = object()
 contra1 = contra2  # Invalid
 contra2 = contra1  # Ok because int <: float => Covariant[float] <: Covariant[int]
 
-inv1: Invariant[float]
+inv1: Invariant[float] = object()
-inv2: Invariant[int]
+inv2: Invariant[int] = object()
 inv1 = inv2  # Invalid
 inv2 = inv1  # Invalid

tests/cases/checker/09_frame_ops.py

@@ -1,8 +1,9 @@
 # type: ignore
 # ruff: disable [F821]
+import pandas as pd
 
-df1: Frame[i:int, a:int, b:float]
+df1 = cast(Frame[i:int, a:int, b:float], pd.DataFrame())
-df2: Frame[i:int, a:int, b:float]
+df2 = cast(Frame[i:int, a:int, b:float], pd.DataFrame())
 
 _: Any