Improve sage_getfile by looking at __init__

Author: user202729

src/sage/misc/sageinspect.py

@@ -1328,6 +1328,16 @@ def sage_getfile(obj):
         if isinstance(obj, functools.partial):
             return sage_getfile(obj.func)
         return sage_getfile(obj.__class__)  # inspect.getabsfile(obj.__class__)
+    else:
+        try:
+            objinit = obj.__init__
+        except AttributeError:
+            pass
+        else:
+            pos = _extract_embedded_position(_sage_getdoc_unformatted(objinit))
+            if pos is not None:
+                (_, filename, _) = pos
+                return filename
 
     # No go? fall back to inspect.
     try:
@@ -1336,6 +1346,10 @@ def sage_getfile(obj):
         return ''
     for suffix in import_machinery.EXTENSION_SUFFIXES:
         if sourcefile.endswith(suffix):
+            # TODO: the following is incorrect in meson editable install
+            # but as long as either the class or its __init__ method has a
+            # docstring, _sage_getdoc_unformatted should return correct result
+            # see https://github.com/mesonbuild/meson-python/issues/723
             return sourcefile.removesuffix(suffix)+os.path.extsep+'pyx'
     return sourcefile