fix(core): Backtrace Filtering (#11)

This PR improves the stacktrace by:
1) Filter out unnecessary stack frames in `func.h`, `func_details.h`,
etc;
2) Fix a bug when handling errors that have no error message, e.g.
`NotImplementedError`

cpp/traceback.cc

@@ -1,6 +1,7 @@
 #ifndef _MSC_VER
 #include "./traceback.h"
 #include <backtrace.h>
+#include <cstring>
 #include <cxxabi.h>
 #include <iostream>
 #include <mlc/c_api.h>
@@ -11,7 +12,8 @@ namespace {
 
 static int32_t MLC_TRACEBACK_LIMIT = GetTracebackLimit();
 static backtrace_state *_bt_state = backtrace_create_state(
-    /*filename=*/nullptr,
+    /*filename=*/
+    nullptr,
     /*threaded=*/1,
     /*error_callback=*/
     +[](void * /*data*/, const char *msg, int /*errnum*/) -> void {
@@ -43,7 +45,8 @@ MLCByteArray TracebackImpl() {
     }
     if (!symbol) {
       backtrace_syminfo(
-          /*state=*/_bt_state, /*addr=*/pc, /*callback=*/
+          /*state=*/
+          _bt_state, /*addr=*/pc, /*callback=*/
           +[](void *data, uintptr_t /*pc*/, const char *symname, uintptr_t /*symval*/, uintptr_t /*symsize*/) {
             *reinterpret_cast<const char **>(data) = symname;
           },
@@ -54,11 +57,22 @@ MLCByteArray TracebackImpl() {
     if (IsForeignFrame(filename, lineno, symbol)) {
       return 1;
     }
-    reinterpret_cast<TracebackStorage *>(data)->Append(filename)->Append(lineno)->Append(symbol);
+    if (!EndsWith(filename, "core.pyx") &&       //
+        !EndsWith(filename, "func.h") &&         //
+        !EndsWith(filename, "func_details.h") && //
+        !EndsWith(filename, "mlc/core/all.h") && //
+        !EndsWith(filename, "mlc/base/all.h")    //
+    ) {
+      TracebackStorage *storage = reinterpret_cast<TracebackStorage *>(data);
+      storage->Append(filename);
+      storage->Append(lineno);
+      storage->Append(symbol);
+    }
     return 0;
   };
   backtrace_full(
-      /*state=*/_bt_state, /*skip=*/1, /*callback=*/callback,
+      /*state=*/
+      _bt_state, /*skip=*/1, /*callback=*/callback,
       /*error_callback=*/[](void * /*data*/, const char * /*msg*/, int /*errnum*/) {},
       /*data=*/&storage);
   return {static_cast<int64_t>(storage.buffer.size()), storage.buffer.data()};

include/mlc/printer/ir_printer.h

@@ -54,10 +54,14 @@ struct IRPrinterObj : public Object {
       Optional<Str> name = (*it).second->name;
       return Id(name.value());
     }
-    // Legalize characters in the name
-    for (char &c : name_hint) {
-      if (c != '_' && !std::isalnum(c)) {
-        c = '_';
+    bool needs_normalize =
+        std::any_of(name_hint->begin(), name_hint->end(), [](char c) { return c != '_' && !std::isalnum(c); });
+    if (needs_normalize) {
+      name_hint = Str(name_hint->c_str());
+      for (char &c : name_hint) {
+        if (c != '_' && !std::isalnum(c)) {
+          c = '_';
+        }
       }
     }
     // Find a unique name

python/mlc/_cython/base.py

@@ -245,6 +245,7 @@ def _bytes_info() -> bytes:
             bytes_info.append(str_py2c(code.co_filename))
             tb = tb.tb_next
         bytes_info.append(str_py2c(str(exception)))
+        bytes_info = [b if b else b"<null>" for b in bytes_info]
         bytes_info.reverse()
         bytes_info.append(b"")
         return b"\0".join(bytes_info)

tests/python/test_cython_traceback.py

@@ -2,21 +2,21 @@
 from io import StringIO
 
 import mlc
+import pytest
 
 
 def test_throw_exception_from_c() -> None:
     func = mlc.Func.get("mlc.testing.throw_exception_from_c")
-    try:
+    with pytest.raises(ValueError) as exc_info:
         func()
-    except ValueError:
-        msg = traceback.format_exc().strip().splitlines()
-        assert "Traceback (most recent call last)" in msg[0]
-        assert "in test_throw_exception_from_c" in msg[1]
-        assert "ValueError: This is an error message" in msg[-1]
-        if mlc._cython.SYSTEM != "Darwin":
-            # FIXME: for some reason, `c_api.cc` is not in the traceback on macOS
-            # TODO: fix macOS libbacktrace integration on macOS
-            assert "c_api.cc" in msg[-3]
+
+    msg = traceback.format_exception(exc_info.type, exc_info.value, exc_info.tb)
+    msg = "".join(msg).strip().splitlines()
+    assert "Traceback (most recent call last)" in msg[0]
+    assert "in test_throw_exception_from_c" in msg[1]
+    assert "ValueError: This is an error message" in msg[-1]
+    if mlc._cython.SYSTEM != "Darwin":
+        assert "c_api.cc" in msg[-3]
 
 
 def test_throw_exception_from_ffi() -> None:
@@ -41,18 +41,26 @@ def _inner() -> None:
 
         _inner()
 
-    try:
+    with pytest.raises(ValueError) as exc_info:
+        mlc.Func.get("mlc.testing.throw_exception_from_ffi_in_c")(throw_ValueError)
+
+    msg = traceback.format_exception(exc_info.type, exc_info.value, exc_info.tb)
+    msg = "".join(msg).strip().splitlines()
+    assert "Traceback (most recent call last)" in msg[0]
+    assert "in test_throw_exception_from_ffi_in_c" in msg[1]
+    assert "ValueError: This is a ValueError" in msg[-1]
+    if mlc._cython.SYSTEM != "Darwin":
+        idx_c_api_tests = next(i for i, line in enumerate(msg) if "c_api.cc" in line)
+        idx_handle_error = next(i for i, line in enumerate(msg) if "_func_safe_call_impl" in line)
+        assert idx_c_api_tests < idx_handle_error
+
+
+def test_throw_NotImplementedError_from_ffi_in_c() -> None:
+    def throw_ValueError() -> None:
+        def _inner() -> None:
+            raise NotImplementedError
+
+        _inner()
+
+    with pytest.raises(NotImplementedError):
         mlc.Func.get("mlc.testing.throw_exception_from_ffi_in_c")(throw_ValueError)
-    except ValueError:
-        msg = traceback.format_exc().strip().splitlines()
-        assert "Traceback (most recent call last)" in msg[0]
-        assert "in test_throw_exception_from_ffi_in_c" in msg[1]
-        assert "ValueError: This is a ValueError" in msg[-1]
-        if mlc._cython.SYSTEM != "Darwin":
-            # FIXME: for some reason, `c_api.cc` is not in the traceback on macOS
-            # TODO: fix macOS libbacktrace integration on macOS
-            idx_c_api_tests = next(i for i, line in enumerate(msg) if "c_api.cc" in line)
-            idx_handle_error = next(
-                i for i, line in enumerate(msg) if "_func_safe_call_impl" in line
-            )
-            assert idx_c_api_tests < idx_handle_error

tests/python/test_printer_ir_printer.py

@@ -7,6 +7,12 @@ def test_var_print() -> None:
     assert mlcp.to_python(a) == "a"
 
 
+def test_var_print_name_normalize() -> None:
+    a = Var(name="a/0/b")
+    assert mlcp.to_python(a) == "a_0_b"
+    assert mlcp.to_python(a) == "a_0_b"
+
+
 def test_add_print() -> None:
     a = Var(name="a")
     b = Var(name="b")