feat: Content.form_with_key_path()

src/awkward/contents/bitmaskedarray.py

@@ -288,6 +288,16 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> BitMaskedFo
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> BitMaskedForm:
+        return self.form_cls(
+            self._mask.form,
+            self._content._form_with_key_path((*path, None)),
+            self._valid_when,
+            self._lsb_order,
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/bytemaskedarray.py

@@ -218,6 +218,15 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> ByteMaskedF
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> ByteMaskedForm:
+        return self.form_cls(
+            self._mask.form,
+            self._content._form_with_key_path((*path, None)),
+            self._valid_when,
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/content.py

@@ -238,6 +238,12 @@ def _form_with_key(
     ) -> Form:
         raise NotImplementedError
 
+    def form_with_key_path(self, root: (str | None) = ()) -> Form:
+        return self._form_with_key_path(root)
+
+    def _form_with_key_path(self, path: (str | None)) -> Form:
+        raise NotImplementedError
+
     @property
     def form_cls(self) -> type[Form]:
         raise NotImplementedError

src/awkward/contents/emptyarray.py

@@ -118,6 +118,9 @@ def simplified(cls, *, parameters=None, backend=None):
     def _form_with_key(self, getkey: Callable[[Content], str | None]) -> EmptyForm:
         return self.form_cls(form_key=getkey(self))
 
+    def _form_with_key_path(self, path: (str | None)) -> EmptyForm:
+        return self.form_cls(form_key=repr(path))
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/indexedarray.py

@@ -214,6 +214,14 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> IndexedForm
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> IndexedForm:
+        return self.form_cls(
+            self._index.form,
+            self._content._form_with_key_path((*path, None)),
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/indexedoptionarray.py

@@ -202,6 +202,14 @@ def _form_with_key(
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> IndexedOptionForm:
+        return self.form_cls(
+            self._index.form,
+            self._content._form_with_key_path((*path, None)),
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/listarray.py

@@ -207,6 +207,15 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> ListForm:
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> ListForm:
+        return self.form_cls(
+            self._starts.form,
+            self._stops.form,
+            self._content._form_with_key_path((*path, None)),
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/listoffsetarray.py

@@ -199,6 +199,14 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> ListOffsetF
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> ListOffsetForm:
+        return self.form_cls(
+            self._offsets.form,
+            self._content._form_with_key_path((*path, None)),
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/numpyarray.py

@@ -200,6 +200,14 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> NumpyForm:
             form_key=getkey(self),
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> NumpyForm:
+        return self.form_cls(
+            ak.types.numpytype.dtype_to_primitive(self._data.dtype),
+            self.inner_shape,
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/recordarray.py

@@ -316,6 +316,24 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> RecordForm:
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> RecordForm:
+        if self._fields is None:
+            contents = [
+                x._form_with_key_path((*path, i)) for i, x in enumerate(self._contents)
+            ]
+        else:
+            contents = [
+                x._form_with_key_path((*path, k))
+                for k, x in zip(self._fields, self._contents)
+            ]
+
+        return self.form_cls(
+            contents,
+            self._fields,
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/regulararray.py

@@ -211,6 +211,14 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> RegularForm
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> RegularForm:
+        return self.form_cls(
+            self._content._form_with_key_path((*path, None)),
+            self._size,
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/unionarray.py

@@ -460,6 +460,15 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> UnionForm:
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> UnionForm:
+        return self.form_cls(
+            self._tags.form,
+            self._index.form,
+            [x._form_with_key_path((*path, i)) for i, x in enumerate(self._contents)],
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,

src/awkward/contents/unmaskedarray.py

@@ -138,6 +138,13 @@ def _form_with_key(self, getkey: Callable[[Content], str | None]) -> UnmaskedFor
             form_key=form_key,
         )
 
+    def _form_with_key_path(self, path: (str | None)) -> UnmaskedForm:
+        return self.form_cls(
+            self._content._form_with_key_path((*path, None)),
+            parameters=self._parameters,
+            form_key=repr(path),
+        )
+
     def _to_buffers(
         self,
         form: Form,