Add optional dependency infra and use for ethos_u and vgf backends (#19149)

Optional dependencies can be installed like
pip install executorch[ethos_u]

- Add --optional-dependency flag to install_executorch.py to include
optional deps when installing from source.

- Add ethos_u and vgf as available optional dependencies The
dependencies match their corresponding requirements.txt files, but there
is no convenient way to share.

- Installation of optional deps using setup.sh is kept for now.

Signed-off-by: Erik Lundell <erik.lundell@arm.com>
Co-authored-by: Rob Elliott <Robert.Elliott@arm.com>

Author: Erik-Lundell

backends/arm/requirements-arm-ethos-u.txt

@@ -3,5 +3,7 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+# These dependencies need to match pyproject.toml
+
 ethos-u-vela == 5.0.0
 pte-adapter-model-explorer == 0.0.2

backends/arm/requirements-arm-tosa.txt

@@ -3,6 +3,8 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+# These dependencies need to match pyproject.toml
+
 ml_dtypes == 0.5.1
 flatbuffers == 24.3.25
 tosa-adapter-model-explorer == 0.1.0

backends/arm/requirements-arm-vgf.txt

@@ -3,6 +3,8 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+# These dependencies need to match pyproject.toml
+
 ai_ml_emulation_layer_for_vulkan == 0.9.0
 ai_ml_sdk_model_converter == 0.9.0
 ai_ml_sdk_vgf_library == 0.9.0

install_executorch.py

@@ -1,5 +1,5 @@
 # Copyright (c) Meta Platforms, Inc. and affiliates.
-# Copyright 2024-25 Arm Limited and/or its affiliates.
+# Copyright 2024-2026 Arm Limited and/or its affiliates.
 # All rights reserved.
 #
 # This source code is licensed under the BSD-style license found in the
@@ -195,6 +195,18 @@ def _parse_args() -> argparse.Namespace:
         help="Only installs necessary dependencies for core executorch and skips "
         " packages necessary for running example scripts.",
     )
+    allowed_optional_dependencies = ["ethos_u", "vgf", "openvino"]
+    parser.add_argument(
+        "--optional-dependency",
+        action="append",
+        choices=allowed_optional_dependencies,
+        default=[],
+        metavar="EXTRA",
+        help="Install a named optional dependency from pyproject.toml. Can be "
+        "passed multiple times, for example "
+        "--optional-dependency ethos_u --optional-dependency openvino. "
+        f"Allowed values: {', '.join(allowed_optional_dependencies)}",
+    )
     return parser.parse_args()
 
 
@@ -219,6 +231,10 @@ def main(args):
     install_requirements(install_pinned_version)
 
     # Step 2: Install core package
+    package_spec = "."
+    if args.optional_dependency:
+        extras = ",".join(dict.fromkeys(args.optional_dependency))
+        package_spec = f".[{extras}]"
     cmd = (
         [
             sys.executable,
@@ -228,7 +244,7 @@ def main(args):
         ]
         + (["--editable"] if args.editable else [])
         + [
-            ".",
+            package_spec,
             "--no-build-isolation",
             "-v",
         ]

pyproject.toml

@@ -77,6 +77,23 @@ dependencies=[
 ]
 
 [project.optional-dependencies]
+vgf = [
+  # AoT vgf dependencies
+  # Keep this in sync with AoT deps from backends/arm/requirements-arm-vgf.txt and
+  # backends/arm/requirements-arm-tosa.txt.
+  "ai_ml_emulation_layer_for_vulkan==0.9.0",
+  "ai_ml_sdk_model_converter==0.9.0",
+  "ml_dtypes==0.5.1",
+  "tosa-tools==2026.2.1",
+]
+ethos_u = [
+  # AoT ethos_u dependencies
+  # Keep this in sync with AoT deps backends/arm/requirements-arm-ethos-u.txt and
+  # backends/arm/requirements-arm-tosa.txt.
+  "ethos-u-vela==5.0.0",
+  "ml_dtypes==0.5.1",
+  "tosa-tools==2026.2.1",
+]
 openvino = [
   "openvino>=2025.1.0,<2026.0.0; platform_system == 'Linux'",
 ]