Skip unneeded copy

Author: crusaderky

array_api_compat/common/_helpers.py

@@ -812,7 +812,7 @@ def is_writeable_array(x):
         return False
     return True
 
-def _parse_copy_param(x, copy: bool | None) -> bool:
+def _parse_copy_param(x, copy: bool | None | Literal["_force_false"]) -> bool:
     """Preprocess and validate a copy parameter, in line with the same
     parameter in np.asarray(), np.astype(), etc.
     """
@@ -821,6 +821,8 @@ def _parse_copy_param(x, copy: bool | None) -> bool:
     if copy is False:
         if not is_writeable_array(x):
             raise ValueError("Cannot avoid modifying parameter in place")
+    elif copy == "_force_false":
+        return False
     elif copy is not True:
         raise ValueError(f"Invalid value for copy: {copy!r}")
     return copy
@@ -909,7 +911,7 @@ def _common(
         self,
         at_op: str,
         y=_undef,
-        copy: bool | None = True,
+        copy: bool | None | Literal["_force_false"] = True,
         **kwargs,
     ):
         """Validate kwargs and perform common prepocessing.
@@ -956,13 +958,13 @@ def get(self, copy: bool | None = True, **kwargs):
                 or (is_numpy_array(self.idx) and self.idx.dtype.kind in "biu")
             )
         ):
-            if copy is True:
-                copy = None
-            elif copy is False:
+            if copy is False:
                 raise ValueError(
                     "Indexing a numpy array with a fancy index always "
                     "results in a copy"
                 )
+            # Skip copy inside _common, even if array is not writeable
+            copy = "_force_false"  # type: ignore
 
         res, x = self._common("get", copy=copy, **kwargs)
         if res is not None: