_decide_nvjitlink_or_driver() bug fix and enhancements (NVIDIA#1055)

* _decide_nvjitlink_or_driver(): catch RuntimeError (bug fix), use importlib + ModuleNotFoundError (more selective than ImportError) and produce specific error messages

* Fix misunderstanding: RuntimeError is raised only from inner_nvjitlink._inspect_function_pointer()

* Better way of formatting warning messages.

* Change from importlib.import_module() to plain import (the latter does also raise ModuleNotFoundError)

* Enhance to warning messages, to make them actionable.

* Factor out _nvjitlink_has_version_symbol() for clarity and testability

This aids unit testing by allowing localized stubbing of the version-symbol
check, without needing to patch the full inner nvjitlink module.

* Add test_linker_warnings.py

As generated by ChatGPT 5, with minor manual tweaks.

* Fix "the the" oversight

* Replace "culink APIs" → "driver APIs" in warning message.

* Fix oversight: test_linker_warnings.py needs to be updated after commit 0948942

* fix skipping the check for nvidia-smi (NVIDIA#1084)

* rm cuda_core/tests/test_linker_warnings.py: see NVIDIA#1095

---------

Co-authored-by: Leo Fang <leof@nvidia.com>

Author: rwgk

cuda_core/cuda/core/experimental/_linker.py

@@ -5,6 +5,7 @@
 from __future__ import annotations
 
 import ctypes
+import sys
 import weakref
 from contextlib import contextmanager
 from dataclasses import dataclass
@@ -28,6 +29,11 @@
 _nvjitlink_input_types = None  # populated if nvJitLink cannot be used
 
 
+def _nvjitlink_has_version_symbol(inner_nvjitlink) -> bool:
+    # This condition is equivalent to testing for version >= 12.3
+    return bool(inner_nvjitlink._inspect_function_pointer("__nvJitLinkVersion"))
+
+
 # Note: this function is reused in the tests
 def _decide_nvjitlink_or_driver() -> bool:
     """Returns True if falling back to the cuLink* driver APIs."""
@@ -37,28 +43,36 @@ def _decide_nvjitlink_or_driver() -> bool:
 
     _driver_ver = handle_return(driver.cuDriverGetVersion())
     _driver_ver = (_driver_ver // 1000, (_driver_ver % 1000) // 10)
+
+    warn_txt_common = (
+        "the driver APIs will be used instead, which do not support"
+        " minor version compatibility or linking LTO IRs."
+        " For best results, consider upgrading to a recent version of"
+    )
+
     try:
-        from cuda.bindings import nvjitlink as _nvjitlink
-        from cuda.bindings._internal import nvjitlink as inner_nvjitlink
-    except ImportError:
-        # binding is not available
-        _nvjitlink = None
+        import cuda.bindings.nvjitlink as _nvjitlink
+    except ModuleNotFoundError:
+        warn_txt = f"cuda.bindings.nvjitlink is not available, therefore {warn_txt_common} cuda-bindings."
     else:
-        if inner_nvjitlink._inspect_function_pointer("__nvJitLinkVersion") == 0:
-            # binding is available, but nvJitLink is not installed
-            _nvjitlink = None
-
-    if _nvjitlink is None:
-        warn(
-            "nvJitLink is not installed or too old (<12.3). Therefore it is not usable "
-            "and the culink APIs will be used instead.",
-            stacklevel=3,
-            category=RuntimeWarning,
+        from cuda.bindings._internal import nvjitlink as inner_nvjitlink
+
+        try:
+            if _nvjitlink_has_version_symbol(inner_nvjitlink):
+                return False  # Use nvjitlink
+        except RuntimeError:
+            warn_detail = "not available"
+        else:
+            warn_detail = "too old (<12.3)"
+        warn_txt = (
+            f"{'nvJitLink*.dll' if sys.platform == 'win32' else 'libnvJitLink.so*'} is {warn_detail}."
+            f" Therefore cuda.bindings.nvjitlink is not usable and {warn_txt_common} nvJitLink."
         )
-        _driver = driver
-        return True
-    else:
-        return False
+        _nvjitlink = None
+
+    warn(warn_txt, stacklevel=2, category=RuntimeWarning)
+    _driver = driver
+    return True
 
 
 def _lazy_init():