Add preliminary support for qml.labs module sandboxing (#6369)

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- [x] All new features must include a unit test.
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------------------------------------------------------------------------------------------------------------

**Context:** This PR adds `tach` as a development dependency to ensure
`qml.labs` additions do not migrate into mainline PennyLane.

**Description of the Change:** Configs are added to restrict this
library wide, with pre-commit hook support added to prevent additions
going upstream.

**Benefits:** Prevents `qml.labs` additions entering into the main
PennyLane library.

**Possible Drawbacks:** Currently requires explicit use of pre-commit
hooks. CI settings and partitioning to follow.

**Related GitHub Issues:**

---------

Co-authored-by: Rashid N H M <[email protected]>
Co-authored-by: Mudit Pandey <[email protected]>

.github/workflows/module-validation.yml

@@ -0,0 +1,37 @@
+name: Validate module imports
+
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - ready_for_review
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+
+  tach:
+    if: github.event.pull_request.draft == false
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+
+        with:
+          python-version: "3.10"
+
+      - name: Install dependencies
+        run: pip install tach==0.13.1
+
+      - name: Run tach
+        run: |
+          tach report pennylane/labs
+          tach check
+

.pre-commit-config.yaml

@@ -31,6 +31,10 @@ repos:
           "--filter-files",
         ]
       files: ^(pennylane/|tests/)
+-   repo: https://github.com/gauge-sh/tach-pre-commit
+    rev: v0.13.1
+    hooks:
+    -   id: tach
 - repo: local
   hooks:
     - id: pylint

doc/releases/changelog-dev.md

@@ -35,6 +35,9 @@
 
 <h3>Improvements 🛠</h3>
 
+* Module-level sandboxing added to `qml.labs` via pre-commit hooks.
+  [(#6369)](https://github.com/PennyLaneAI/pennylane/pull/6369)
+
 * `qml.matrix` now works with empty objects (such as empty tapes, `QNode`s and quantum functions that do
   not call operations, single operators with empty decompositions).
   [(#6347)](https://github.com/PennyLaneAI/pennylane/pull/6347)

pennylane/labs/__init__.py

@@ -13,3 +13,6 @@
 # limitations under the License.
 """:code:`pennylane/labs/` module contains experimental features enabling
 advanced quantum computing research."""
+
+
+__all__ = []

requirements-dev.txt

@@ -12,3 +12,4 @@ tomli~=2.0.0 # Drop once minimum Python version is 3.11
 isort==5.13.2
 pylint==2.7.4
 rich>=13.7.1
+tach==0.13.1

requirements.txt

@@ -15,3 +15,4 @@ opt_einsum~=3.3
 requests~=2.31.0
 typing_extensions~=4.5.0
 tomli~=2.0.0 # Drop once minimum Python version is 3.11
+tach~=0.13.1

tach.toml

@@ -0,0 +1,16 @@
+exclude = [
+    ".*__pycache__",
+    ".*egg-info",
+    "docs",
+    "tests",
+]
+source_roots = [
+    ".",
+    "pennylane",
+]
+
+[[modules]]
+path = "pennylane.labs"
+depends_on = [
+    { path = "<root>" },
+]