chore: deprecate tensorflow maintenance support (#7989)

**Context:**

We are deprecating `tensorflow` maintenance support and promoting user
migration to `jax` and `torch` interfaces.

**Description of the Change:**

- Add deprecation warning to `QNode` execution. This will capture
majority of user workflows and ensure deprecation visibility.
- Add deprecation warning to
https://docs.pennylane.ai/en/stable/introduction/interfaces/tf.html
- Add deprecation warning in changelog (which will be promoted to
release notes).
- Cleaned up necessary tests to un-block work (this involved deleting TF
specific `all_interfaces` tests).
- Add no cover to TF logic branches

Here's an example,

```python
import pennylane as qml
import tensorflow as tf

dev = qml.device("default.qubit", wires=1)
params = tf.Variable(0.1)

@qml.qnode(dev)
def circuit(x):
    qml.RX(x, wires=0)
    return qml.expval(qml.PauliZ(0))

circuit(params)
```
```
PennyLaneDeprecationWarning: Support for the TensorFlow interface is deprecated and will be removed in v0.44. Future versions of PennyLane are not guaranteed to work with TensorFlow. Please migrate your workflows to JAX or torch to benefit from enhanced support and features.
  circuit(params)
  
<tf.Tensor: shape=(), dtype=float64, numpy=0.9950041833264242>
```

**Benefits:** No longer have to deal with maintaining TF.

**Possible Drawbacks:**

This could have impact on our eco-system:

Catalyst: N/A
Lightning: PennyLaneAI/pennylane-lightning#1225

QML: Some
[demos](https://github.com/search?q=repo%3APennyLaneAI%2Fqml%20import%20tensorflow&type=code)
need changes. Being taken care of by product here
PennyLaneAI/qml/pull/1505.

Plug-ins: N/A 

[sc-92521]

---------

Co-authored-by: Pietropaolo Frisoni <[email protected]>
Co-authored-by: Mudit Pandey <[email protected]>
Co-authored-by: Isaac De Vlugt <[email protected]>
Co-authored-by: Isaac De Vlugt <[email protected]>

Author: 4 people

.coveragerc

@@ -5,12 +5,16 @@ omit =
     pennylane/devices/tests*
     pennylane/labs/*
     pennylane/compiler/python_compiler/*
+    pennylane/workflow/interfaces/tensorflow.py
+    pennylane/workflow/interfaces/tensorflow_autograph.py
 
 [report]
 # Regexes for lines to exclude from consideration
 exclude_lines =
     # Have to re-enable the standard pragma
     pragma: no cover
+
+    pragma: no cover (TensorFlow tests were disabled during deprecation)
 
     # Ignore type checking 
     if TYPE_CHECKING:
@@ -33,7 +37,6 @@ exclude_lines =
     # Ignore overload stubs
     @overload
 
-
 ignore_errors = True
 
 [html]

.github/durations/tf_tests_durations.json

@@ -22,11 +22,6 @@ on:
         required: false
         type: string
         default: '0.6.2'
-      tensorflow_version:
-        description: The version of TensorFlow to use for testing
-        required: false
-        type: string
-        default: '2.19.0'
       torch_version:
         description: The version of PyTorch to use for testing
         required: false
@@ -39,9 +34,6 @@ on:
       catalyst-jax-version:
         description: The version of JAX to use along with Catalyst
         value: ${{ jobs.default-dependency-versions.outputs.catalyst-jax-version }}
-      tensorflow-version:
-        description: The version of TensorFlow to use
-        value: ${{ jobs.default-dependency-versions.outputs.tensorflow-version }}
       pytorch-version:
         description: The version of PyTorch to use
         value: ${{ jobs.default-dependency-versions.outputs.pytorch-version }}
@@ -65,10 +57,6 @@ jobs:
         id: catalyst-jax
         run: echo "version=${{ inputs.catalyst_jax_version }}" >> $GITHUB_OUTPUT
 
-      - name: Default Tensorflow Version
-        id: tensorflow
-        run: echo "version=${{ inputs.tensorflow_version }}" >> $GITHUB_OUTPUT
-      
       - name: Default PyTorch Version
         id: pytorch
         run: echo "version=${{ inputs.torch_version }}" >> $GITHUB_OUTPUT
@@ -84,7 +72,6 @@ jobs:
     outputs:
       catalyst-jax-version: jax==${{ steps.catalyst-jax.outputs.version }} jaxlib==${{ steps.catalyst-jax.outputs.version }}
       jax-version: jax==${{ steps.jax.outputs.version }} jaxlib==${{ steps.jax.outputs.version }}
-      tensorflow-version: tensorflow~=${{ steps.tensorflow.outputs.version }} tf-keras~=${{ steps.tensorflow.outputs.version }}
       pytorch-version: torch~=${{ steps.pytorch.outputs.version }}
       catalyst-nightly: ${{ steps.catalyst.outputs.nightly }}
       pennylane-lightning-latest: ${{ steps.pennylane-lightning.outputs.latest }}

.github/stable/tf.txt

@@ -155,7 +155,6 @@ jobs:
           {
             "default": ["3.11", "3.12", "3.13"],
             "torch-tests": ["3.11", "3.13"],
-            "tf-tests": ["3.11", "3.12"],
             "jax-tests": ["3.11", "3.13"],
             "capture-jax-tests": ["3.11", "3.13"],
             "all-interfaces-tests": ["3.11"],
@@ -183,7 +182,6 @@ jobs:
             "core-tests": 6,
             "gradients-tests": 2,
             "jax-tests": 4,
-            "tf-tests": 3,
             "device-tests": 1
           }
           EOF
@@ -193,7 +191,6 @@ jobs:
             "default": 1,
             "core-tests": 6,
             "jax-tests": 8,
-            "tf-tests": 6,
             "torch-tests": 2,
             "device-tests": 1
           }
@@ -303,46 +300,6 @@ jobs:
       pytest_xml_file_path: '${{ inputs.job_name_prefix }}autograd-tests (${{ matrix.python-version }})${{ inputs.job_name_suffix }}.xml'
       pytest_markers: autograd and not qcut and not finite-diff and not param-shift
 
-
-  tf-tests:
-    needs:
-      - setup-ci-load
-      - determine_runner
-      - default-dependency-versions
-      - warnings-as-errors-setup
-    strategy:
-      fail-fast: ${{ needs.warnings-as-errors-setup.outputs.fail_fast == 'default' }}
-      max-parallel: >-
-        ${{
-           fromJSON(needs.setup-ci-load.outputs.matrix-max-parallel).tf-tests
-           || fromJSON(needs.setup-ci-load.outputs.matrix-max-parallel).default
-         }}
-      matrix:
-        group: [1, 2, 3]
-        python-version: >-
-          ${{
-            fromJSON(needs.setup-ci-load.outputs.python-version).tf-tests
-            || fromJSON(needs.setup-ci-load.outputs.python-version).default
-           }}
-    if: ${{ !contains(fromJSON(needs.setup-ci-load.outputs.jobs-to-skip), 'tf-tests') }}
-    uses: ./.github/workflows/unit-test.yml
-    with:
-      job_runner_name: ${{ needs.determine_runner.outputs.runner_group }}
-      job_name: ${{ inputs.job_name_prefix }}tf-tests (${{ matrix.group }}, ${{ matrix.python-version }})${{ inputs.job_name_suffix }}
-      branch: ${{ inputs.branch }}
-      coverage_artifact_name: core-interfaces-coverage-tf-${{ matrix.python-version }}-${{ matrix.group }}
-      python_version: ${{ matrix.python-version }}
-      additional_pip_packages: |
-        ${{ needs.default-dependency-versions.outputs.tensorflow-version }}
-        ${{ inputs.additional_python_packages }}
-      additional_pip_packages_post: ${{ needs.default-dependency-versions.outputs.pennylane-lightning-latest }}
-      pytest_coverage_flags: ${{ inputs.pytest_coverage_flags }}
-      pytest_markers: tf and not qcut and not finite-diff and not param-shift
-      pytest_additional_args: --splits 3 --group ${{ matrix.group }} ${{ needs.warnings-as-errors-setup.outputs.pytest_warning_args }}
-      pytest_durations_file_path: '.github/durations/tf_tests_durations.json'
-      pytest_xml_file_path: '${{ inputs.job_name_prefix }}tf-tests (${{ matrix.group }}, ${{ matrix.python-version }})${{ inputs.job_name_suffix }}.xml'
-      requirements_file: ${{ github.event_name == 'schedule' && strategy.job-index == 0 && 'tf.txt' || '' }}
-
   jax-tests:
     needs:
       - setup-ci-load
@@ -490,7 +447,6 @@ jobs:
       python_version: ${{ matrix.python-version }}
       additional_pip_packages: |
         ${{ needs.default-dependency-versions.outputs.jax-version }}
-        ${{ needs.default-dependency-versions.outputs.tensorflow-version }}
         ${{ needs.default-dependency-versions.outputs.pytorch-version }}
         ${{ inputs.additional_python_packages }}
       additional_pip_packages_post: ${{ needs.default-dependency-versions.outputs.pennylane-lightning-latest }}
@@ -536,7 +492,6 @@ jobs:
         pyzx matplotlib stim quimb mitiq ply optax scipy-openblas32>=0.3.26 qualtran openqasm3 antlr4_python3_runtime xdsl==0.46 filecheck
         ${{ needs.default-dependency-versions.outputs.jax-version }}
         git+https://github.com/PennyLaneAI/pennylane-qiskit.git@master
-        ${{ needs.default-dependency-versions.outputs.tensorflow-version }}
         ${{ needs.default-dependency-versions.outputs.catalyst-nightly }}
         ${{ inputs.additional_python_packages }}
 
@@ -578,7 +533,6 @@ jobs:
         kahypar==1.3.5 
         opt_einsum
         ${{ needs.default-dependency-versions.outputs.jax-version }}
-        ${{ needs.default-dependency-versions.outputs.tensorflow-version }}
         ${{ needs.default-dependency-versions.outputs.pytorch-version }}
         ${{ inputs.additional_python_packages }}
       additional_pip_packages_post: ${{ needs.default-dependency-versions.outputs.pennylane-lightning-latest }}
@@ -654,7 +608,6 @@ jobs:
       pytest_xml_file_path: '${{ inputs.job_name_prefix }}gradients-tests (${{ matrix.config.suite }}, ${{ matrix.python-version }})${{ inputs.job_name_suffix }}.xml'
       additional_pip_packages: |
         ${{ needs.default-dependency-versions.outputs.jax-version }}
-        ${{ needs.default-dependency-versions.outputs.tensorflow-version }}
         ${{ needs.default-dependency-versions.outputs.pytorch-version }}
         ${{ inputs.additional_python_packages }}
       additional_pip_packages_post: ${{ needs.default-dependency-versions.outputs.pennylane-lightning-latest }}
@@ -735,7 +688,6 @@ jobs:
       python_version: ${{ matrix.python-version }}
       additional_pip_packages: |
         ${{ !contains(matrix.config.skip_interface, 'jax') && needs.default-dependency-versions.outputs.jax-version || '' }}
-        ${{ !contains(matrix.config.skip_interface, 'tf') && needs.default-dependency-versions.outputs.tensorflow-version || '' }}
         ${{ !contains(matrix.config.skip_interface, 'torch') && needs.default-dependency-versions.outputs.pytorch-version || '' }}
         ${{ inputs.additional_python_packages }}
       additional_pip_packages_post: ${{ needs.default-dependency-versions.outputs.pennylane-lightning-latest }}
@@ -749,7 +701,6 @@ jobs:
     needs:
       - torch-tests
       - autograd-tests
-      - tf-tests
       - jax-tests
       - capture-jax-tests
       - core-tests
@@ -808,7 +759,6 @@ jobs:
       - determine_runner
       - torch-tests
       - autograd-tests
-      - tf-tests
       - jax-tests
       - capture-jax-tests
       - core-tests

.github/workflows/interface-dependency-versions.yml

@@ -22,7 +22,6 @@ jobs:
       python_warning_level: 'error'
       run_lightened_ci: false
       skip_ci_test_jobs: |
-        tf-tests
         all-interfaces-tests
         external-libraries-tests
         qcut-tests

.github/workflows/interface-unit-tests.yml

@@ -24,7 +24,6 @@ jobs:
       additional_python_packages: 'numpy~=1.26.0'
       upload_to_codecov: false
       skip_ci_test_jobs: |
-        tf-tests
         all-interfaces-tests
         external-libraries-tests
         qcut-tests

.github/workflows/package_warnings_as_errors.yml

@@ -39,7 +39,6 @@ jobs:
           mkdir durations
           jq -s 'add' durations-core-*/*.json > durations/core_tests_durations.json
           jq -s 'add' durations-jax-*/*.json > durations/jax_tests_durations.json
-          jq -s 'add' durations-tf-*/*.json > durations/tf_tests_durations.json
 
       - name: Upload combined durations artifacts
         uses: actions/upload-artifact@v4

.github/workflows/test_numpy_1_compat.yml

@@ -2,20 +2,20 @@
 # A comma-separated list of package or module names from where C extensions may
 # be loaded. Extensions are loading into the active Python interpreter and may
 # run arbitrary code
-extension-pkg-whitelist=numpy,scipy,autograd,toml,appdir,autograd.numpy,autograd.numpy.linalg,autograd.numpy.builtins,packaging,torch,tensorflow,tensorflow.contrib,tensorflow.contrib.eager,LazyLoader,networkx,networkx.dag
+extension-pkg-whitelist=numpy,scipy,autograd,toml,appdir,autograd.numpy,autograd.numpy.linalg,autograd.numpy.builtins,packaging,torch,LazyLoader,networkx,networkx.dag
 
 [TYPECHECK]
 
 # List of module names for which member attributes should not be checked
 # (useful for modules/projects where namespaces are manipulated during runtime
 # and thus existing member attributes cannot be deduced by static analysis. It
 # supports qualified module names, as well as Unix pattern matching.
-ignored-modules=jax,numpy,scipy,autograd,toml,appdir,autograd.numpy,autograd.numpy.linalg,autograd.numpy.builtins,packaging,torch,tensorflow,tensorflow.contrib,tensorflow.contrib.eager,LazyLoader,networkx,networkx.dag,math,pennylane.numpy
+ignored-modules=jax,numpy,scipy,autograd,toml,appdir,autograd.numpy,autograd.numpy.linalg,autograd.numpy.builtins,packaging,torch,LazyLoader,networkx,networkx.dag,math,pennylane.numpy
 
 # List of classes names for which member attributes should not be checked
 # (useful for classes with attributes dynamically set). This supports can work
 # with qualified names.
-ignored-classes=jax,numpy,scipy,autograd,toml,appdir,autograd.numpy,autograd.numpy.linalg,autograd.numpy.builtins,packaging,torch,tensorflow,tensorflow.contrib,tensorflow.contrib.eager,LazyLoader,networkx,networkx.dag,math,pennylane.numpy,pennylane.numpy.random,pennylane.numpy.linalg,pennylane.numpy.builtins,pennylane.operation,rustworkx,kahypar
+ignored-classes=jax,numpy,scipy,autograd,toml,appdir,autograd.numpy,autograd.numpy.linalg,autograd.numpy.builtins,packaging,torch,LazyLoader,networkx,networkx.dag,math,pennylane.numpy,pennylane.numpy.random,pennylane.numpy.linalg,pennylane.numpy.builtins,pennylane.operation,rustworkx,kahypar
 
 [MESSAGES CONTROL]
 

.github/workflows/update-durations.yml

@@ -9,6 +9,14 @@ deprecations are listed below.
 Pending deprecations
 --------------------
 
+* Maintenance support for the ``tensorflow`` interface has been deprecated and will be dropped in PennyLane v0.44.
+  Future versions of PennyLane are not guaranteed to work with TensorFlow.
+  Instead, we recommend using the :doc:`jax </introduction/interfaces/jax>` or :doc:`torch </introduction/interfaces/torch>` interface for
+  machine learning applications to benefit from enhanced support and features.
+  
+  - Deprecated in v0.43
+  - Will be removed in v0.44
+  
 * ``pennylane.devices.DefaultExecutionConfig`` is deprecated and will be removed in v0.44.
   Instead, use ``qml.devices.ExecutionConfig()`` to create a default execution configuration.