feat: add helpful info to internal AssertionError excs (#19404)

BobTheBuidler · web-flow · commit a79e85e3958a · 2025-07-09T16:27:01.000+01:00
I added some contextual information to various assert statements throughout the repo. This information is helpful for me while debugging [Issue 1116](mypyc/mypyc#1116) and should be similarly useful in many other debugging contexts.
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -7273,7 +7273,7 @@ def named_type(self, name: str) -> Instance:
         if isinstance(node, TypeAlias):
             assert isinstance(node.target, Instance)  # type: ignore[misc]
             node = node.target.type
-        assert isinstance(node, TypeInfo)
+        assert isinstance(node, TypeInfo), node
         any_type = AnyType(TypeOfAny.from_omitted_generics)
         return Instance(node, [any_type] * len(node.defn.type_vars))
 
@@ -7292,7 +7292,7 @@ def lookup_typeinfo(self, fullname: str) -> TypeInfo:
         # Assume that the name refers to a class.
         sym = self.lookup_qualified(fullname)
         node = sym.node
-        assert isinstance(node, TypeInfo)
+        assert isinstance(node, TypeInfo), node
         return node
 
     def type_type(self) -> Instance:
diff --git a/mypy/checkpattern.py b/mypy/checkpattern.py
@@ -796,9 +796,9 @@ def get_var(expr: Expression) -> Var:
     Warning: this in only true for expressions captured by a match statement.
     Don't call it from anywhere else
     """
-    assert isinstance(expr, NameExpr)
+    assert isinstance(expr, NameExpr), expr
     node = expr.node
-    assert isinstance(node, Var)
+    assert isinstance(node, Var), node
     return node
 
 
diff --git a/mypy/plugins/attrs.py b/mypy/plugins/attrs.py
@@ -458,7 +458,7 @@ def _analyze_class(
             if isinstance(node, PlaceholderNode):
                 # This node is not ready yet.
                 continue
-            assert isinstance(node, Var)
+            assert isinstance(node, Var), node
             node.is_initialized_in_class = False
 
     # Traverse the MRO and collect attributes from the parents.
diff --git a/mypy/plugins/dataclasses.py b/mypy/plugins/dataclasses.py
@@ -610,7 +610,7 @@ def collect_attributes(self) -> list[DataclassAttribute] | None:
                 # We will issue an error later.
                 continue
 
-            assert isinstance(node, Var)
+            assert isinstance(node, Var), node
 
             # x: ClassVar[int] is ignored by dataclasses.
             if node.is_classvar:
diff --git a/mypy/semanal.py b/mypy/semanal.py
@@ -6630,7 +6630,7 @@ def named_type(self, fullname: str, args: list[Type] | None = None) -> Instance:
         sym = self.lookup_fully_qualified(fullname)
         assert sym, "Internal error: attempted to construct unknown type"
         node = sym.node
-        assert isinstance(node, TypeInfo)
+        assert isinstance(node, TypeInfo), node
         if args:
             # TODO: assert len(args) == len(node.defn.type_vars)
             return Instance(node, args)
diff --git a/mypy/semanal_main.py b/mypy/semanal_main.py
@@ -290,7 +290,7 @@ def process_functions(graph: Graph, scc: list[str], patches: Patches) -> None:
 
     for module, target, node, active_type in order_by_subclassing(all_targets):
         analyzer = graph[module].manager.semantic_analyzer
-        assert isinstance(node, (FuncDef, OverloadedFuncDef, Decorator))
+        assert isinstance(node, (FuncDef, OverloadedFuncDef, Decorator)), node
         process_top_level_function(
             analyzer, graph[module], module, target, node, active_type, patches
         )
diff --git a/mypyc/analysis/attrdefined.py b/mypyc/analysis/attrdefined.py
@@ -285,15 +285,15 @@ def mark_attr_initialization_ops(
 def attributes_initialized_by_init_call(op: Call) -> set[str]:
     """Calculate attributes that are always initialized by a super().__init__ call."""
     self_type = op.fn.sig.args[0].type
-    assert isinstance(self_type, RInstance)
+    assert isinstance(self_type, RInstance), self_type
     cl = self_type.class_ir
     return {a for base in cl.mro for a in base.attributes if base.is_always_defined(a)}
 
 
 def attributes_maybe_initialized_by_init_call(op: Call) -> set[str]:
     """Calculate attributes that may be initialized by a super().__init__ call."""
     self_type = op.fn.sig.args[0].type
-    assert isinstance(self_type, RInstance)
+    assert isinstance(self_type, RInstance), self_type
     cl = self_type.class_ir
     return attributes_initialized_by_init_call(op) | cl._sometimes_initialized_attrs
 
diff --git a/mypyc/analysis/selfleaks.py b/mypyc/analysis/selfleaks.py
@@ -92,7 +92,7 @@ def visit_call(self, op: Call) -> GenAndKill:
         fn = op.fn
         if fn.class_name and fn.name == "__init__":
             self_type = op.fn.sig.args[0].type
-            assert isinstance(self_type, RInstance)
+            assert isinstance(self_type, RInstance), self_type
             cl = self_type.class_ir
             if not cl.init_self_leak:
                 return CLEAN
diff --git a/mypyc/codegen/emit.py b/mypyc/codegen/emit.py
@@ -742,7 +742,7 @@ def emit_cast_error_handler(
             self.emit_traceback(error.source_path, error.module_name, error.traceback_entry)
             self.emit_line("goto %s;" % error.label)
         else:
-            assert isinstance(error, ReturnHandler)
+            assert isinstance(error, ReturnHandler), error
             self.emit_line("return %s;" % error.value)
 
     def emit_union_cast(
@@ -871,7 +871,7 @@ def emit_unbox(
         elif isinstance(error, GotoHandler):
             failure = "goto %s;" % error.label
         else:
-            assert isinstance(error, ReturnHandler)
+            assert isinstance(error, ReturnHandler), error
             failure = "return %s;" % error.value
         if raise_exception:
             raise_exc = f'CPy_TypeError("{self.pretty_name(typ)}", {src}); '
diff --git a/mypyc/codegen/emitfunc.py b/mypyc/codegen/emitfunc.py
@@ -160,7 +160,7 @@ def generate_native_function(
     # eliminated during code generation.
     for block in fn.blocks:
         terminator = block.terminator
-        assert isinstance(terminator, ControlOp)
+        assert isinstance(terminator, ControlOp), terminator
 
         for target in terminator.targets():
             is_next_block = target.label == block.label + 1
@@ -309,7 +309,7 @@ def visit_assign(self, op: Assign) -> None:
 
     def visit_assign_multi(self, op: AssignMulti) -> None:
         typ = op.dest.type
-        assert isinstance(typ, RArray)
+        assert isinstance(typ, RArray), typ
         dest = self.reg(op.dest)
         # RArray values can only be assigned to once, so we can always
         # declare them on initialization.
@@ -586,7 +586,7 @@ def visit_method_call(self, op: MethodCall) -> None:
     def emit_method_call(self, dest: str, op_obj: Value, name: str, op_args: list[Value]) -> None:
         obj = self.reg(op_obj)
         rtype = op_obj.type
-        assert isinstance(rtype, RInstance)
+        assert isinstance(rtype, RInstance), rtype
         class_ir = rtype.class_ir
         method = rtype.class_ir.get_method(name)
         assert method is not None
@@ -805,7 +805,7 @@ def visit_get_element_ptr(self, op: GetElementPtr) -> None:
         dest = self.reg(op)
         src = self.reg(op.src)
         # TODO: support tuple type
-        assert isinstance(op.src_type, RStruct)
+        assert isinstance(op.src_type, RStruct), op.src_type
         assert op.field in op.src_type.names, "Invalid field name."
         self.emit_line(
             "{} = ({})&(({} *){})->{};".format(
diff --git a/mypyc/irbuild/builder.py b/mypyc/irbuild/builder.py
@@ -551,8 +551,8 @@ def init_final_static(
         *,
         type_override: RType | None = None,
     ) -> None:
-        assert isinstance(lvalue, NameExpr)
-        assert isinstance(lvalue.node, Var)
+        assert isinstance(lvalue, NameExpr), lvalue
+        assert isinstance(lvalue.node, Var), lvalue.node
         if lvalue.node.final_value is None:
             if class_name is None:
                 name = lvalue.name
@@ -1271,7 +1271,7 @@ def add_local(self, symbol: SymbolNode, typ: RType, is_arg: bool = False) -> Reg
         Args:
             is_arg: is this a function argument
         """
-        assert isinstance(symbol, SymbolNode)
+        assert isinstance(symbol, SymbolNode), symbol
         reg = Register(
             typ, remangle_redefinition_name(symbol.name), is_arg=is_arg, line=symbol.line
         )
@@ -1286,7 +1286,7 @@ def add_local_reg(
         """Like add_local, but return an assignment target instead of value."""
         self.add_local(symbol, typ, is_arg)
         target = self.symtables[-1][symbol]
-        assert isinstance(target, AssignmentTargetRegister)
+        assert isinstance(target, AssignmentTargetRegister), target
         return target
 
     def add_self_to_env(self, cls: ClassIR) -> AssignmentTargetRegister:
@@ -1446,7 +1446,7 @@ def get_default() -> Value:
                         GetAttr(builder.fn_info.callable_class.self_reg, name, arg.line)
                     )
 
-            assert isinstance(target, AssignmentTargetRegister)
+            assert isinstance(target, AssignmentTargetRegister), target
             reg = target.register
             if not reg.type.error_overlap:
                 builder.assign_if_null(target.register, get_default, arg.initializer.line)
diff --git a/mypyc/irbuild/classdef.py b/mypyc/irbuild/classdef.py
@@ -424,7 +424,7 @@ def get_type_annotation(self, stmt: AssignmentStmt) -> TypeInfo | None:
                 type_name = stmt.rvalue.args[index]
                 if isinstance(type_name, NameExpr) and isinstance(type_name.node, TypeInfo):
                     lvalue = stmt.lvalues[0]
-                    assert isinstance(lvalue, NameExpr)
+                    assert isinstance(lvalue, NameExpr), lvalue
                     return type_name.node
         return None
 
@@ -765,7 +765,7 @@ def generate_attr_defaults_init(
         self_var = builder.self()
         for stmt in default_assignments:
             lvalue = stmt.lvalues[0]
-            assert isinstance(lvalue, NameExpr)
+            assert isinstance(lvalue, NameExpr), lvalue
             if not stmt.is_final_def and not is_constant(stmt.rvalue):
                 builder.warning("Unsupported default attribute value", stmt.rvalue.line)
 
@@ -871,7 +871,7 @@ def load_decorated_class(builder: IRBuilder, cdef: ClassDef, type_obj: Value) ->
     dec_class = type_obj
     for d in reversed(decorators):
         decorator = d.accept(builder.visitor)
-        assert isinstance(decorator, Value)
+        assert isinstance(decorator, Value), decorator
         dec_class = builder.py_call(decorator, [dec_class], dec_class.line)
     return dec_class
 
@@ -882,7 +882,7 @@ def cache_class_attrs(
     """Add class attributes to be cached to the global cache."""
     typ = builder.load_native_type_object(cdef.info.fullname)
     for lval, rtype in attrs_to_cache:
-        assert isinstance(lval, NameExpr)
+        assert isinstance(lval, NameExpr), lval
         rval = builder.py_get_attr(typ, lval.name, cdef.line)
         builder.init_final_static(lval, rval, cdef.name, type_override=rtype)
 
diff --git a/mypyc/irbuild/expression.py b/mypyc/irbuild/expression.py
@@ -359,7 +359,7 @@ def translate_method_call(builder: IRBuilder, expr: CallExpr, callee: MemberExpr
         and all(kind in (ARG_POS, ARG_NAMED) for kind in expr.arg_kinds)
     ):
         # Call a method via the *class*
-        assert isinstance(callee.expr.node, TypeInfo)
+        assert isinstance(callee.expr.node, TypeInfo), callee.expr.node
         ir = builder.mapper.type_to_ir[callee.expr.node]
         return call_classmethod(builder, ir, expr, callee)
     elif builder.is_module_member_expr(callee):
@@ -722,7 +722,7 @@ def transform_comparison_expr(builder: IRBuilder, e: ComparisonExpr) -> Value:
             mypy_file = builder.graph["builtins"].tree
             assert mypy_file is not None
             info = mypy_file.names["bool"].node
-            assert isinstance(info, TypeInfo)
+            assert isinstance(info, TypeInfo), info
             bool_type = Instance(info, [])
             exprs = []
             for item in items:
diff --git a/mypyc/irbuild/for_helpers.py b/mypyc/irbuild/for_helpers.py
@@ -902,7 +902,7 @@ def begin_body(self) -> None:
         value = builder.add(TupleGet(self.next_tuple, 3, line))
 
         # Coerce just in case e.g. key is itself a tuple to be unpacked.
-        assert isinstance(self.target_type, RTuple)
+        assert isinstance(self.target_type, RTuple), self.target_type
         key = builder.coerce(key, self.target_type.types[0], line)
         value = builder.coerce(value, self.target_type.types[1], line)
 
diff --git a/mypyc/irbuild/function.py b/mypyc/irbuild/function.py
@@ -136,7 +136,7 @@ def transform_decorator(builder: IRBuilder, dec: Decorator) -> None:
 
 def transform_lambda_expr(builder: IRBuilder, expr: LambdaExpr) -> Value:
     typ = get_proper_type(builder.types[expr])
-    assert isinstance(typ, CallableType)
+    assert isinstance(typ, CallableType), typ
 
     runtime_args = []
     for arg, arg_type in zip(expr.arguments, typ.arg_types):
@@ -269,7 +269,7 @@ def c() -> None:
         # add the generated main singledispatch function
         builder.functions.append(func_ir)
         # create the dispatch function
-        assert isinstance(fitem, FuncDef)
+        assert isinstance(fitem, FuncDef), fitem
         return gen_dispatch_func_ir(builder, fitem, fn_info.name, name, sig)
 
     return func_ir, func_reg
@@ -336,8 +336,9 @@ def gen_func_ir(
         add_get_to_callable_class(builder, fn_info)
         func_reg = instantiate_callable_class(builder, fn_info)
     else:
-        assert isinstance(fn_info.fitem, FuncDef)
-        func_decl = builder.mapper.func_to_decl[fn_info.fitem]
+        fitem = fn_info.fitem
+        assert isinstance(fitem, FuncDef), fitem
+        func_decl = builder.mapper.func_to_decl[fitem]
         if fn_info.is_decorated or is_singledispatch_main_func:
             class_name = None if cdef is None else cdef.name
             func_decl = FuncDecl(
@@ -349,13 +350,9 @@ def gen_func_ir(
                 func_decl.is_prop_getter,
                 func_decl.is_prop_setter,
             )
-            func_ir = FuncIR(
-                func_decl, args, blocks, fn_info.fitem.line, traceback_name=fn_info.fitem.name
-            )
+            func_ir = FuncIR(func_decl, args, blocks, fitem.line, traceback_name=fitem.name)
         else:
-            func_ir = FuncIR(
-                func_decl, args, blocks, fn_info.fitem.line, traceback_name=fn_info.fitem.name
-            )
+            func_ir = FuncIR(func_decl, args, blocks, fitem.line, traceback_name=fitem.name)
     return (func_ir, func_reg)
 
 
@@ -483,7 +480,7 @@ def load_decorated_func(builder: IRBuilder, fdef: FuncDef, orig_func_reg: Value)
     func_reg = orig_func_reg
     for d in reversed(decorators):
         decorator = d.accept(builder.visitor)
-        assert isinstance(decorator, Value)
+        assert isinstance(decorator, Value), decorator
         func_reg = builder.py_call(decorator, [func_reg], func_reg.line)
     return func_reg
 
diff --git a/mypyc/irbuild/generator.py b/mypyc/irbuild/generator.py
@@ -158,7 +158,7 @@ def instantiate_generator_class(builder: IRBuilder) -> Value:
 
 def setup_generator_class(builder: IRBuilder) -> ClassIR:
     mapper = builder.mapper
-    assert isinstance(builder.fn_info.fitem, FuncDef)
+    assert isinstance(builder.fn_info.fitem, FuncDef), builder.fn_info.fitem
     generator_class_ir = mapper.fdef_to_generator[builder.fn_info.fitem]
     if builder.fn_info.can_merge_generator_and_env_classes():
         builder.fn_info.env_class = generator_class_ir
diff --git a/mypyc/irbuild/ll_builder.py b/mypyc/irbuild/ll_builder.py
@@ -432,7 +432,7 @@ def coerce(
 
     def coerce_int_to_fixed_width(self, src: Value, target_type: RType, line: int) -> Value:
         assert is_fixed_width_rtype(target_type), target_type
-        assert isinstance(target_type, RPrimitive)
+        assert isinstance(target_type, RPrimitive), target_type
 
         res = Register(target_type)
 
@@ -538,10 +538,11 @@ def coerce_fixed_width_to_int(self, src: Value, line: int) -> Value:
                 line,
             )
 
-        assert is_fixed_width_rtype(src.type)
-        assert isinstance(src.type, RPrimitive)
         src_type = src.type
 
+        assert is_fixed_width_rtype(src_type), src_type
+        assert isinstance(src_type, RPrimitive), src_type
+
         res = Register(int_rprimitive)
 
         fast, fast2, slow, end = BasicBlock(), BasicBlock(), BasicBlock(), BasicBlock()
@@ -1513,7 +1514,7 @@ def compare_bytes(self, lhs: Value, rhs: Value, op: str, line: int) -> Value:
     def compare_tuples(self, lhs: Value, rhs: Value, op: str, line: int = -1) -> Value:
         """Compare two tuples item by item"""
         # type cast to pass mypy check
-        assert isinstance(lhs.type, RTuple) and isinstance(rhs.type, RTuple)
+        assert isinstance(lhs.type, RTuple) and isinstance(rhs.type, RTuple), (lhs.type, rhs.type)
         equal = True if op == "==" else False
         result = Register(bool_rprimitive)
         # tuples of different lengths
diff --git a/mypyc/irbuild/match.py b/mypyc/irbuild/match.py
@@ -151,7 +151,7 @@ def visit_class_pattern(self, pattern: ClassPattern) -> None:
                 return
 
             node = pattern.class_ref.node
-            assert isinstance(node, TypeInfo)
+            assert isinstance(node, TypeInfo), node
             match_args = extract_dunder_match_args_names(node)
 
             for i, expr in enumerate(pattern.positionals):
@@ -345,7 +345,7 @@ def extract_dunder_match_args_names(info: TypeInfo) -> list[str]:
     ty = info.names.get("__match_args__")
     assert ty
     match_args_type = get_proper_type(ty.type)
-    assert isinstance(match_args_type, TupleType)
+    assert isinstance(match_args_type, TupleType), match_args_type
 
     match_args: list[str] = []
     for item in match_args_type.items:
diff --git a/mypyc/irbuild/nonlocalcontrol.py b/mypyc/irbuild/nonlocalcontrol.py
@@ -175,7 +175,7 @@ def gen_return(self, builder: IRBuilder, value: Value, line: int) -> None:
                 self.ret_reg = Register(builder.ret_types[-1])
         # assert needed because of apparent mypy bug... it loses track of the union
         # and infers the type as object
-        assert isinstance(self.ret_reg, (Register, AssignmentTarget))
+        assert isinstance(self.ret_reg, (Register, AssignmentTarget)), self.ret_reg
         builder.assign(self.ret_reg, value, line)
 
         builder.add(Goto(self.target))
diff --git a/mypyc/irbuild/statement.py b/mypyc/irbuild/statement.py
@@ -785,7 +785,7 @@ def maybe_natively_call_exit(exc_info: bool) -> Value:
             args = [none, none, none]
 
         if is_native:
-            assert isinstance(mgr_v.type, RInstance)
+            assert isinstance(mgr_v.type, RInstance), mgr_v.type
             exit_val = builder.gen_method_call(
                 builder.read(mgr),
                 f"__{al}exit__",
diff --git a/mypyc/lower/list_ops.py b/mypyc/lower/list_ops.py
@@ -22,7 +22,7 @@ def buf_init_item(builder: LowLevelIRBuilder, args: list[Value], line: int) -> V
     base = args[0]
     index_value = args[1]
     value = args[2]
-    assert isinstance(index_value, Integer)
+    assert isinstance(index_value, Integer), index_value
     index = index_value.numeric_value()
     if index == 0:
         ptr = base
diff --git a/mypyc/transform/ir_transform.py b/mypyc/transform/ir_transform.py
@@ -357,7 +357,7 @@ def visit_get_element_ptr(self, op: GetElementPtr) -> None:
     def visit_load_address(self, op: LoadAddress) -> None:
         if isinstance(op.src, LoadStatic):
             new = self.fix_op(op.src)
-            assert isinstance(new, LoadStatic)
+            assert isinstance(new, LoadStatic), new
             op.src = new
 
     def visit_keep_alive(self, op: KeepAlive) -> None:
diff --git a/mypyc/transform/refcount.py b/mypyc/transform/refcount.py

Original file line number	Diff line number	Diff line change
`@@ -290,7 +290,7 @@ def process_functions(graph: Graph, scc: list[str], patches: Patches) -> None:`
`290`	`290`
`291`	`291`	`for module, target, node, active_type in order_by_subclassing(all_targets):`
`292`	`292`	`analyzer = graph[module].manager.semantic_analyzer`
`293`		`- assert isinstance(node, (FuncDef, OverloadedFuncDef, Decorator))`
	`293`	`+ assert isinstance(node, (FuncDef, OverloadedFuncDef, Decorator)), node`
`294`	`294`	`process_top_level_function(`
`295`	`295`	`analyzer, graph[module], module, target, node, active_type, patches`
`296`	`296`	`)`