gh-122255: Synchronize warnings in C and Python implementations of the warnings module (GH-122824)

In the linecache module and in the Python implementation of the
warnings module, a DeprecationWarning is issued when
m.__loader__ differs from m.__spec__.loader (like in the C
implementation of the warnings module).

Lib/linecache.py

@@ -224,21 +224,58 @@ def lazycache(filename, module_globals):
 def _make_lazycache_entry(filename, module_globals):
     if not filename or (filename.startswith('<') and filename.endswith('>')):
         return None
-    # Try for a __loader__, if available
-    if module_globals and '__name__' in module_globals:
-        spec = module_globals.get('__spec__')
-        name = getattr(spec, 'name', None) or module_globals['__name__']
-        loader = getattr(spec, 'loader', None)
-        if loader is None:
-            loader = module_globals.get('__loader__')
-        get_source = getattr(loader, 'get_source', None)
 
-        if name and get_source:
-            def get_lines(name=name, *args, **kwargs):
-                return get_source(name, *args, **kwargs)
-            return (get_lines,)
-    return None
+    if module_globals is not None and not isinstance(module_globals, dict):
+        raise TypeError(f'module_globals must be a dict, not {type(module_globals).__qualname__}')
+    if not module_globals or '__name__' not in module_globals:
+        return None
 
+    spec = module_globals.get('__spec__')
+    name = getattr(spec, 'name', None) or module_globals['__name__']
+    if name is None:
+        return None
+
+    loader = _bless_my_loader(module_globals)
+    if loader is None:
+        return None
+
+    get_source = getattr(loader, 'get_source', None)
+    if get_source is None:
+        return None
+
+    def get_lines(name=name, *args, **kwargs):
+        return get_source(name, *args, **kwargs)
+    return (get_lines,)
+
+def _bless_my_loader(module_globals):
+    # Similar to _bless_my_loader() in importlib._bootstrap_external,
+    # but always emits warnings instead of errors.
+    loader = module_globals.get('__loader__')
+    if loader is None and '__spec__' not in module_globals:
+        return None
+    spec = module_globals.get('__spec__')
+
+    # The __main__ module has __spec__ = None.
+    if spec is None and module_globals.get('__name__') == '__main__':
+        return loader
+
+    spec_loader = getattr(spec, 'loader', None)
+    if spec_loader is None:
+        import warnings
+        warnings.warn(
+            'Module globals is missing a __spec__.loader',
+            DeprecationWarning)
+        return loader
+
+    assert spec_loader is not None
+    if loader is not None and loader != spec_loader:
+        import warnings
+        warnings.warn(
+            'Module globals; __loader__ != __spec__.loader',
+            DeprecationWarning)
+        return loader
+
+    return spec_loader
 
 
 def _register_code(code, string, name):