Fix nested Compose map_items in forward and inverse paths

[aymuos15]

Summary

Fixes #7932, #7565

When a child Compose has a different map_items setting than its parent, the parent's apply_transform would expand list/tuple data before the child ever sees it — silently overriding the child's map_items.

This PR makes three coordinated changes so the child's map_items is respected:

• Forward path (apply_transform): Skip list expansion when the transform is a Compose instance, letting it handle expansion via its own map_items in execute_compose.
• Inverse path (_inverse_one helper): Delegate directly to Compose.inverse() for nested Compose objects (including RandomOrder and SomeOf) instead of routing through apply_transform(t.inverse, ...).
• flatten(): Only inline nested Compose objects that share the same map_items as the parent. Children with a different map_items are preserved as-is.

Test plan

• test_child_map_items_false_receives_list — parent map_items=True, child map_items=False: child receives list as-is
• test_inverse_respects_child_map_items — inverse roundtrip with nested Compose
• test_parent_no_map_child_map — parent map_items=False, child map_items=True: child maps over items
• test_flatten_preserves_different_map_items — flatten() does not merge children with different map_items

[coderabbitai]

📝 Walkthrough

Walkthrough

Introduced a module helper _inverse_one(...) to centralize per-transform inversion. Compose.inverse, RandomOrder.inverse, and SomeOf.inverse now use _inverse_one for inverting contained transforms. Compose.flatten() was changed to inline nested Compose instances only when type(t) is Compose and t.map_items == self.map_items, preserving nested Compose with differing map_items. apply_transform() was adjusted so a Compose transform can manage list/tuple expansion itself rather than having the caller expand items. New tests cover nested Compose map_items behavior, inversion, and flattening.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	Title clearly and specifically describes the main change: fixing nested Compose map_items behavior in both forward and inverse paths.
Description check	✅ Passed	PR description covers all key aspects: issues fixed, explanation of three coordinated changes, and test plan with checkmarks. Template sections mostly complete.
Linked Issues check	✅ Passed	PR directly addresses issue #7932 by respecting child Compose map_items settings in forward, inverse, and flatten paths—the core feature request.
Out of Scope Changes check	✅ Passed	All changes (apply_transform, _inverse_one helper, flatten logic, and tests) are tightly scoped to fixing nested Compose map_items handling.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

📝 Coding Plan

• Generate coding plan for human review comments

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[coderabbitai]

🧹 Nitpick comments (1)

monai/transforms/compose.py (1)

40-51: Add Google-style docstring with Args/Returns.

Per coding guidelines, docstrings should describe parameters and return values.

📝 Proposed docstring

 def _inverse_one(
     t: InvertibleTransform,
     data: Any,
     map_items: bool | int,
     unpack_items: bool,
     log_stats: bool | str,
 ) -> Any:
-    """Invert a single transform, delegating directly to nested ``Compose`` objects."""
+    """Invert a single transform, delegating directly to nested ``Compose`` objects.
+
+    Args:
+        t: The invertible transform to invert.
+        data: Data to be inverted.
+        map_items: Whether to map over list/tuple items.
+        unpack_items: Whether to unpack data as parameters.
+        log_stats: Logger name or boolean for logging.
+
+    Returns:
+        The inverted data.
+    """
     if isinstance(t, Compose):
         return t.inverse(data)
     return apply_transform(t.inverse, data, map_items, unpack_items, lazy=False, log_stats=log_stats)

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@monai/transforms/compose.py` around lines 40 - 51, Add a Google-style
docstring to the _inverse_one function describing its purpose, parameters and
return value: state that it inverts a single transform (delegating to
Compose.inverse when t is a Compose), document args t (InvertibleTransform),
data (Any), map_items (bool|int), unpack_items (bool), log_stats (bool|str), and
explain the return value (inverted data of type Any); also mention that
apply_transform is called for non-Compose transforms with lazy=False. Include
short notes on side effects (calls to Compose.inverse/apply_transform) if
relevant.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@monai/transforms/compose.py`:
- Around line 40-51: Add a Google-style docstring to the _inverse_one function
describing its purpose, parameters and return value: state that it inverts a
single transform (delegating to Compose.inverse when t is a Compose), document
args t (InvertibleTransform), data (Any), map_items (bool|int), unpack_items
(bool), log_stats (bool|str), and explain the return value (inverted data of
type Any); also mention that apply_transform is called for non-Compose
transforms with lazy=False. Include short notes on side effects (calls to
Compose.inverse/apply_transform) if relevant.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 13d05d32-401c-4be3-a001-687e58886c54

📥 Commits

Reviewing files that changed from the base of the PR and between daaedaa and 26c051f.

📒 Files selected for processing (3)

• monai/transforms/compose.py
• monai/transforms/transform.py
• tests/transforms/compose/test_compose.py

[coderabbitai]

🧹 Nitpick comments (1)

monai/transforms/compose.py (1)

354-361: flatten() doesn't preserve parent attributes (unlike OneOf.flatten()).

Line 361 returns Compose(new_transforms) with defaults. If someone calls flatten() expecting an equivalent executable pipeline, map_items, unpack_items, log_stats, lazy, and overrides are lost.

Current internal usage only reads .transforms, so no bug today.

Proposed fix

-        return Compose(new_transforms)
+        return Compose(new_transforms, self.map_items, self.unpack_items, self.log_stats, self.lazy, self.overrides)

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@monai/transforms/compose.py` around lines 354 - 361, Compose.flatten()
currently builds and returns a new Compose instance with only new_transforms,
dropping parent attributes; update Compose.flatten to preserve and pass through
the parent's configuration (map_items, unpack_items, log_stats, lazy, overrides)
when constructing the returned Compose so the flattened pipeline is equivalent
to the original (mirroring OneOf.flatten behavior). Locate the Compose.flatten
implementation and change the return from Compose(new_transforms) to
Compose(new_transforms, map_items=self.map_items,
unpack_items=self.unpack_items, log_stats=self.log_stats, lazy=self.lazy,
overrides=self.overrides) or otherwise propagate those attributes from self into
the new Compose instance.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Nitpick comments:
In `@monai/transforms/compose.py`:
- Around line 354-361: Compose.flatten() currently builds and returns a new
Compose instance with only new_transforms, dropping parent attributes; update
Compose.flatten to preserve and pass through the parent's configuration
(map_items, unpack_items, log_stats, lazy, overrides) when constructing the
returned Compose so the flattened pipeline is equivalent to the original
(mirroring OneOf.flatten behavior). Locate the Compose.flatten implementation
and change the return from Compose(new_transforms) to Compose(new_transforms,
map_items=self.map_items, unpack_items=self.unpack_items,
log_stats=self.log_stats, lazy=self.lazy, overrides=self.overrides) or otherwise
propagate those attributes from self into the new Compose instance.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 4cdba609-bf44-46ad-a65c-afd42771ee1d

📥 Commits

Reviewing files that changed from the base of the PR and between 4595a45 and f732583.

📒 Files selected for processing (2)

• monai/transforms/compose.py
• tests/transforms/compose/test_compose.py

🚧 Files skipped from review as they are similar to previous changes (1)

• tests/transforms/compose/test_compose.py