Only trigger new assertions in tests

python · p-sawicki · Jan 27, 2026 · Jan 23, 2026 · Jan 23, 2026 · Jan 26, 2026
commit f4d483cf52bc0ac7a766bf281c4d1b0a1a58d4a4
diff --git a/mypyc/codegen/emit.py b/mypyc/codegen/emit.py
@@ -103,6 +103,7 @@ class EmitterContext:
     def __init__(
         self,
         names: NameGenerator,
+        strict_traceback_checks: bool,
         group_name: str | None = None,
         group_map: dict[str, str | None] | None = None,
     ) -> None:
@@ -130,6 +131,8 @@ def __init__(
         self.declarations: dict[str, HeaderDeclaration] = {}
 
         self.literals = Literals()
+        # See mypyc/options.py for context.
+        self.strict_traceback_checks = strict_traceback_checks
 
 
 class ErrorHandler:
@@ -1201,7 +1204,8 @@ def _emit_traceback(
         type_str: str = "",
         src: str = "",
     ) -> None:
-        assert traceback_entry[1] >= 0, "Traceback cannot have a negative line number"
+        if self.context.strict_traceback_checks:
+            assert traceback_entry[1] >= 0, "Traceback cannot have a negative line number"
         globals_static = self.static_name("globals", module_name)
         line = '%s("%s", "%s", %d, %s' % (
             func,

diff --git a/mypyc/codegen/emitfunc.py b/mypyc/codegen/emitfunc.py
@@ -921,9 +921,10 @@ def emit_traceback(self, op: Branch) -> None:
 
     def emit_attribute_error(self, op: Branch, class_name: str, attr: str) -> None:
         assert op.traceback_entry is not None
-        assert (
-            op.traceback_entry[1] >= 0
-        ), "AttributeError traceback cannot have a negative line number"
+        if self.emitter.context.strict_traceback_checks:
+            assert (
+                op.traceback_entry[1] >= 0
+            ), "AttributeError traceback cannot have a negative line number"
         globals_static = self.emitter.static_name("globals", self.module_name)
         self.emit_line(
             'CPy_AttributeError("%s", "%s", "%s", "%s", %d, %s);'

diff --git a/mypyc/codegen/emitmodule.py b/mypyc/codegen/emitmodule.py
@@ -249,9 +249,9 @@ def compile_scc_to_ir(
     for module in modules.values():
         for fn in module.functions:
             # Insert checks for uninitialized values.
-            insert_uninit_checks(fn)
+            insert_uninit_checks(fn, compiler_options.strict_traceback_checks)
             # Insert exception handling.
-            insert_exception_handling(fn)
+            insert_exception_handling(fn, compiler_options.strict_traceback_checks)
             # Insert reference count handling.
             insert_ref_count_opcodes(fn)
 
@@ -535,7 +535,7 @@ def __init__(
         """
         self.modules = modules
         self.source_paths = source_paths
-        self.context = EmitterContext(names, group_name, group_map)
+        self.context = EmitterContext(names, compiler_options.strict_traceback_checks, group_name, group_map)
         self.names = names
         # Initializations of globals to simple values that we can't
         # do statically because the windows loader is bad.

diff --git a/mypyc/ir/ops.py b/mypyc/ir/ops.py
@@ -1216,7 +1216,6 @@ class RaiseStandardError(RegisterOp):
 
     def __init__(self, class_name: str, value: str | Value | None, line: int) -> None:
         super().__init__(line)
-        assert line >= 0, "RaiseStandardError cannot have a negative line number"
         self.class_name = class_name
         self.value = value
         self.type = bool_rprimitive

diff --git a/mypyc/options.py b/mypyc/options.py
@@ -19,6 +19,7 @@ def __init__(
         log_trace: bool = False,
         depends_on_librt_internal: bool = False,
         experimental_features: bool = False,
+        strict_traceback_checks: bool = False,
     ) -> None:
         self.strip_asserts = strip_asserts
         self.multi_file = multi_file
@@ -60,3 +61,15 @@ def __init__(
         # experimental mode (e.g. use _experimental suffix in librt run test).
         # These can't be used with a librt wheel installed from PyPI.
         self.experimental_features = experimental_features
+        # If enabled, mypyc will assert that every traceback it generates has a
+        # positive line number.
+        # Currently each AST node is assigned line number -1 by default to indicate
+        # that it's unset. If the line number is never set and a traceback is
+        # generated that points at such node, then the line number will be interpreted
+        # as None instead of an integer by Python and potentially crash code that
+        # expects an integer, such as pytest.
+        # The goal is to prevent the incorrect tracebacks but it will require a lot
+        # of changes across mypyc. In the meantime, this option should be enabled in
+        # tests to make sure that no new code which leads to incorrect tracebacks is
+        # added.
+        self.strict_traceback_checks = strict_traceback_checks
diff --git a/mypyc/test/test_analysis.py b/mypyc/test/test_analysis.py
@@ -42,7 +42,7 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 for fn in ir:
                     if fn.name == TOP_LEVEL_NAME and not testcase.name.endswith("_toplevel"):
                         continue
-                    exceptions.insert_exception_handling(fn)
+                    exceptions.insert_exception_handling(fn, True)
                     actual.extend(format_func(fn))
                     cfg = dataflow.get_cfg(fn.blocks)
                     args: set[Value] = set(fn.arg_regs)

diff --git a/mypyc/test/test_emit.py b/mypyc/test/test_emit.py
@@ -24,7 +24,7 @@
 class TestEmitter(unittest.TestCase):
     def setUp(self) -> None:
         self.n = Register(int_rprimitive, "n")
-        self.context = EmitterContext(NameGenerator([["mod"]]))
+        self.context = EmitterContext(NameGenerator([["mod"]]), True)
         self.emitter = Emitter(self.context, {})
 
         ir = ClassIR("A", "mod")

diff --git a/mypyc/test/test_emitfunc.py b/mypyc/test/test_emitfunc.py
@@ -128,7 +128,7 @@ def add_local(name: str, rtype: RType) -> Register:
         )
         self.st = add_local("st", self.struct_type)
 
-        self.context = EmitterContext(NameGenerator([["mod"]]))
+        self.context = EmitterContext(NameGenerator([["mod"]]), True)
 
     def test_goto(self) -> None:
         self.assert_emit(Goto(BasicBlock(2)), "goto CPyL2;")
@@ -974,7 +974,7 @@ def test_simple(self) -> None:
             [self.block],
         )
         value_names = generate_names_for_ir(fn.arg_regs, fn.blocks)
-        emitter = Emitter(EmitterContext(NameGenerator([["mod"]])), value_names)
+        emitter = Emitter(EmitterContext(NameGenerator([["mod"]]), True), value_names)
         generate_native_function(fn, emitter, "prog.py", "prog")
         result = emitter.fragments
         assert_string_arrays_equal(
@@ -994,7 +994,7 @@ def test_register(self) -> None:
             [self.block],
         )
         value_names = generate_names_for_ir(fn.arg_regs, fn.blocks)
-        emitter = Emitter(EmitterContext(NameGenerator([["mod"]])), value_names)
+        emitter = Emitter(EmitterContext(NameGenerator([["mod"]]), True), value_names)
         generate_native_function(fn, emitter, "prog.py", "prog")
         result = emitter.fragments
         assert_string_arrays_equal(

diff --git a/mypyc/test/test_emitwrapper.py b/mypyc/test/test_emitwrapper.py
@@ -11,7 +11,7 @@
 
 class TestArgCheck(unittest.TestCase):
     def setUp(self) -> None:
-        self.context = EmitterContext(NameGenerator([["mod"]]))
+        self.context = EmitterContext(NameGenerator([["mod"]]), True)
 
     def test_check_list(self) -> None:
         emitter = Emitter(self.context)

diff --git a/mypyc/test/test_exceptions.py b/mypyc/test/test_exceptions.py
@@ -45,8 +45,8 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 for fn in ir:
                     if fn.name == TOP_LEVEL_NAME and not testcase.name.endswith("_toplevel"):
                         continue
-                    insert_uninit_checks(fn)
-                    insert_exception_handling(fn)
+                    insert_uninit_checks(fn, True)
+                    insert_exception_handling(fn, True)
                     insert_ref_count_opcodes(fn)
                     actual.extend(format_func(fn))
                     if testcase.name.endswith("_freq"):

diff --git a/mypyc/test/test_lowering.py b/mypyc/test/test_lowering.py
@@ -48,11 +48,11 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 for fn in ir:
                     if fn.name == TOP_LEVEL_NAME and not testcase.name.endswith("_toplevel"):
                         continue
-                    options = CompilerOptions()
+                    options = CompilerOptions(strict_traceback_checks=True)
                     # Lowering happens after exception handling and ref count opcodes have
                     # been added. Any changes must maintain reference counting semantics.
-                    insert_uninit_checks(fn)
-                    insert_exception_handling(fn)
+                    insert_uninit_checks(fn, True)
+                    insert_exception_handling(fn, True)
                     insert_ref_count_opcodes(fn)
                     lower_ir(fn, options)
                     do_flag_elimination(fn, options)

diff --git a/mypyc/test/test_misc.py b/mypyc/test/test_misc.py
@@ -11,7 +11,7 @@
 class TestMisc(unittest.TestCase):
     def test_debug_op(self) -> None:
         block = BasicBlock()
-        builder = LowLevelIRBuilder(errors=None, options=CompilerOptions())
+        builder = LowLevelIRBuilder(errors=None, options=CompilerOptions(strict_traceback_checks=True))
         builder.activate_block(block)
         builder.debug_print("foo")
 

diff --git a/mypyc/test/test_optimizations.py b/mypyc/test/test_optimizations.py
@@ -44,7 +44,7 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 for fn in ir:
                     if fn.name == TOP_LEVEL_NAME and not testcase.name.endswith("_toplevel"):
                         continue
-                    insert_uninit_checks(fn)
+                    insert_uninit_checks(fn, True)
                     self.do_optimizations(fn)
                     actual.extend(format_func(fn))
 
@@ -58,11 +58,11 @@ class TestCopyPropagation(OptimizationSuite):
     files = ["opt-copy-propagation.test"]
 
     def do_optimizations(self, fn: FuncIR) -> None:
-        do_copy_propagation(fn, CompilerOptions())
+        do_copy_propagation(fn, CompilerOptions(strict_traceback_checks=True))
 
 
 class TestFlagElimination(OptimizationSuite):
     files = ["opt-flag-elimination.test"]
 
     def do_optimizations(self, fn: FuncIR) -> None:
-        do_flag_elimination(fn, CompilerOptions())
+        do_flag_elimination(fn, CompilerOptions(strict_traceback_checks=True))
diff --git a/mypyc/test/test_refcount.py b/mypyc/test/test_refcount.py
@@ -52,7 +52,7 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 for fn in ir:
                     if fn.name == TOP_LEVEL_NAME and not testcase.name.endswith("_toplevel"):
                         continue
-                    insert_uninit_checks(fn)
+                    insert_uninit_checks(fn, True)
                     insert_ref_count_opcodes(fn)
                     actual.extend(format_func(fn))
 

diff --git a/mypyc/test/test_run.py b/mypyc/test/test_run.py
@@ -260,6 +260,7 @@ def run_case_step(self, testcase: DataDrivenTestCase, incremental_step: int) ->
                 strict_dunder_typing=self.strict_dunder_typing,
                 depends_on_librt_internal=librt_internal,
                 experimental_features=experimental_features,
+                strict_traceback_checks=True,
             )
             result = emitmodule.parse_and_typecheck(
                 sources=sources,

diff --git a/mypyc/test/testutil.py b/mypyc/test/testutil.py
@@ -275,7 +275,7 @@ def infer_ir_build_options_from_test_name(name: str) -> CompilerOptions | None:
         return None
     if "_32bit" in name and not IS_32_BIT_PLATFORM:
         return None
-    options = CompilerOptions(strip_asserts="StripAssert" in name, capi_version=(3, 9))
+    options = CompilerOptions(strip_asserts="StripAssert" in name, capi_version=(3, 9), strict_traceback_checks=True)
     # A suffix like _python3_9 is used to set the target C API version.
     m = re.search(r"_python([3-9]+)_([0-9]+)(_|\b)", name)
     if m:

diff --git a/mypyc/transform/exceptions.py b/mypyc/transform/exceptions.py
@@ -39,7 +39,7 @@
 from mypyc.primitives.registry import CFunctionDescription
 
 
-def insert_exception_handling(ir: FuncIR) -> None:
+def insert_exception_handling(ir: FuncIR, strict_traceback_checks: bool) -> None:
     # Generate error block if any ops may raise an exception. If an op
     # fails without its own error handler, we'll branch to this
     # block. The block just returns an error value.
@@ -49,7 +49,7 @@ def insert_exception_handling(ir: FuncIR) -> None:
         if error_label is None and any(op.can_raise() for op in block.ops):
             error_label = add_default_handler_block(ir)
     if error_label:
-        ir.blocks = split_blocks_at_errors(ir.blocks, error_label, ir.traceback_name)
+        ir.blocks = split_blocks_at_errors(ir.blocks, error_label, ir.traceback_name, strict_traceback_checks)
 
 
 def add_default_handler_block(ir: FuncIR) -> BasicBlock:
@@ -62,7 +62,7 @@ def add_default_handler_block(ir: FuncIR) -> BasicBlock:
 
 
 def split_blocks_at_errors(
-    blocks: list[BasicBlock], default_error_handler: BasicBlock, func_name: str | None
+    blocks: list[BasicBlock], default_error_handler: BasicBlock, func_name: str | None, strict_traceback_checks: bool,
 ) -> list[BasicBlock]:
     new_blocks: list[BasicBlock] = []
 
@@ -130,9 +130,10 @@ def split_blocks_at_errors(
                 )
                 branch.negated = negated
                 if op.line != NO_TRACEBACK_LINE_NO and func_name is not None:
-                    assert (
-                        op.line >= 0
-                    ), f"Cannot add a traceback entry with a negative line number for op {op}"
+                    if strict_traceback_checks:
+                        assert (
+                            op.line >= 0
+                        ), f"Cannot add a traceback entry with a negative line number for op {op}"
                     branch.traceback_entry = (func_name, op.line)
                 cur_block.ops.append(branch)
                 cur_block = new_block

diff --git a/mypyc/transform/uninit.py b/mypyc/transform/uninit.py
@@ -23,7 +23,7 @@
 from mypyc.ir.rtypes import bitmap_rprimitive
 
 
-def insert_uninit_checks(ir: FuncIR) -> None:
+def insert_uninit_checks(ir: FuncIR, strict_traceback_checks: bool) -> None:
     # Remove dead blocks from the CFG, which helps avoid spurious
     # checks due to unused error handling blocks.
     cleanup_cfg(ir.blocks)
@@ -33,11 +33,11 @@ def insert_uninit_checks(ir: FuncIR) -> None:
         ir.blocks, cfg, set(ir.arg_regs), all_values(ir.arg_regs, ir.blocks)
     )
 
-    ir.blocks = split_blocks_at_uninits(ir.blocks, must_defined.before)
+    ir.blocks = split_blocks_at_uninits(ir.blocks, must_defined.before, strict_traceback_checks)
 
 
 def split_blocks_at_uninits(
-    blocks: list[BasicBlock], pre_must_defined: AnalysisDict[Value]
+    blocks: list[BasicBlock], pre_must_defined: AnalysisDict[Value], strict_traceback_checks: bool,
 ) -> list[BasicBlock]:
     new_blocks: list[BasicBlock] = []
 
@@ -104,9 +104,10 @@ def split_blocks_at_uninits(
                             op.line,
                         )
 
-                    assert (
-                        op.line >= 0
-                    ), f"Cannot raise an error with a negative line number for op {op}"
+                    if strict_traceback_checks:
+                        assert (
+                            op.line >= 0
+                        ), f"Cannot raise an error with a negative line number for op {op}"
                     raise_std = RaiseStandardError(
                         RaiseStandardError.UNBOUND_LOCAL_ERROR,
                         f'local variable "{src.name}" referenced before assignment',