Implement better error

Include/internal/pycore_lazyimportobject.h

@@ -17,6 +17,9 @@ typedef struct {
     PyObject *lz_import_func;
     PyObject *lz_from;
     PyObject *lz_attr;
+    /* Frame information for the original import location */
+    PyCodeObject *lz_code;     /* code object where the lazy import was created */
+    int lz_instr_offset;       /* instruction offset where the lazy import was created */
 } PyLazyImportObject;
 
 

Objects/lazyimportobject.c

@@ -3,6 +3,9 @@
 #include "Python.h"
 #include "pycore_import.h"
 #include "pycore_lazyimportobject.h"
+#include "pycore_frame.h"
+#include "pycore_ceval.h"
+#include "pycore_interpframe.h"
 
 PyObject *
 _PyLazyImport_New(PyObject *import_func, PyObject *from, PyObject *attr)
@@ -26,6 +29,21 @@ _PyLazyImport_New(PyObject *import_func, PyObject *from, PyObject *attr)
     m->lz_from = from;
     Py_XINCREF(attr);
     m->lz_attr = attr;
+
+    /* Capture frame information for the original import location */
+    m->lz_code = NULL;
+    m->lz_instr_offset = -1;
+
+    _PyInterpreterFrame *frame = _PyEval_GetFrame();
+    if (frame != NULL) {
+        PyCodeObject *code = _PyFrame_GetCode(frame);
+        if (code != NULL) {
+            m->lz_code = (PyCodeObject *)Py_NewRef(code);
+            /* Calculate the instruction offset from the current frame */
+            m->lz_instr_offset = _PyInterpreterFrame_LASTI(frame);
+        }
+    }
+
     PyObject_GC_Track(m);
     return (PyObject *)m;
 }
@@ -37,6 +55,7 @@ lazy_import_dealloc(PyLazyImportObject *m)
     Py_XDECREF(m->lz_import_func);
     Py_XDECREF(m->lz_from);
     Py_XDECREF(m->lz_attr);
+    Py_XDECREF(m->lz_code);
     Py_TYPE(m)->tp_free((PyObject *)m);
 }
 
@@ -72,6 +91,7 @@ lazy_import_traverse(PyLazyImportObject *m, visitproc visit, void *arg)
     Py_VISIT(m->lz_import_func);
     Py_VISIT(m->lz_from);
     Py_VISIT(m->lz_attr);
+    Py_VISIT(m->lz_code);
     return 0;
 }
 
@@ -81,6 +101,7 @@ lazy_import_clear(PyLazyImportObject *m)
     Py_CLEAR(m->lz_import_func);
     Py_CLEAR(m->lz_from);
     Py_CLEAR(m->lz_attr);
+    Py_CLEAR(m->lz_code);
     return 0;
 }
 

Python/import.c

@@ -9,6 +9,8 @@
 #include "pycore_interp.h"        // struct _import_runtime_state
 #include "pycore_long.h"          // _PyLong_GetZero
 #include "pycore_lazyimportobject.h"
+#include "pycore_traceback.h"
+#include "pycore_interpframe.h"
 #include "pycore_magic_number.h"  // PYC_MAGIC_NUMBER_TOKEN
 #include "pycore_moduleobject.h"  // _PyModule_GetDef()
 #include "pycore_namespace.h"     // _PyNamespace_Type
@@ -3780,6 +3782,75 @@ _PyImport_LoadLazyImportTstate(PyThreadState *tstate, PyObject *lazy_import)
     Py_XDECREF(obj);
     obj = NULL;
 
+    /* If an error occurred and we have frame information, add it to the exception */
+    if (PyErr_Occurred() && lz->lz_code != NULL && lz->lz_instr_offset >= 0) {
+        /* Get the current exception - this already has the full traceback from the access point */
+        PyObject *exc = _PyErr_GetRaisedException(tstate);
+
+        /* Get import name - this can fail and set an exception */
+        PyObject *import_name = _PyLazyImport_GetName(lazy_import);
+        if (!import_name) {
+            /* Failed to get import name, just restore original exception */
+            _PyErr_SetRaisedException(tstate, exc);
+            goto ok;
+        }
+
+        /* Resolve line number from instruction offset on demand */
+        int lineno = PyCode_Addr2Line((PyCodeObject *)lz->lz_code, lz->lz_instr_offset);
+
+        /* Get strings - these can return NULL on encoding errors */
+        const char *filename_str = PyUnicode_AsUTF8(lz->lz_code->co_filename);
+        if (!filename_str) {
+            /* Unicode conversion failed - clear error and restore original exception */
+            PyErr_Clear();
+            Py_DECREF(import_name);
+            _PyErr_SetRaisedException(tstate, exc);
+            goto ok;
+        }
+
+        const char *funcname_str = PyUnicode_AsUTF8(lz->lz_code->co_name);
+        if (!funcname_str) {
+            /* Unicode conversion failed - clear error and restore original exception */
+            PyErr_Clear();
+            Py_DECREF(import_name);
+            _PyErr_SetRaisedException(tstate, exc);
+            goto ok;
+        }
+
+        /* Create a cause exception showing where the lazy import was declared */
+        PyObject *msg = PyUnicode_FromFormat(
+            "deferred import of '%U' raised an exception during resolution",
+            import_name
+        );
+        Py_DECREF(import_name);  /* Done with import_name regardless of what happens next */
+
+        if (!msg) {
+            /* Failed to create message - restore original exception */
+            _PyErr_SetRaisedException(tstate, exc);
+            goto ok;
+        }
+
+        PyObject *cause_exc = PyObject_CallOneArg(PyExc_ImportError, msg);
+        Py_DECREF(msg);  /* Done with msg */
+
+        if (!cause_exc) {
+            /* Failed to create exception - restore original */
+            _PyErr_SetRaisedException(tstate, exc);
+            goto ok;
+        }
+
+        /* Add traceback entry for the lazy import declaration */
+        _PyErr_SetRaisedException(tstate, cause_exc);
+        _PyTraceback_Add(funcname_str, filename_str, lineno);
+        PyObject *cause_with_tb = _PyErr_GetRaisedException(tstate);
+
+        /* Set the cause on the original exception */
+        PyException_SetCause(exc, cause_with_tb);  /* Steals ref to cause_with_tb */
+
+        /* Restore the original exception with its full traceback */
+        _PyErr_SetRaisedException(tstate, exc);
+    }
+
 ok:
     Py_XDECREF(fromlist);
     return obj;