MicroPython compatibility

.github/workflows/ci.yml

@@ -123,6 +123,59 @@ jobs:
         if-no-files-found: error
         include-hidden-files: true
 
+  micropython:
+    name: MicroPython compatibility
+    runs-on: ubuntu-latest
+    needs: [ pre-commit, towncrier, package ]
+    steps:
+      - name: Build MicroPython
+        run: |
+          # The following script also works on macOS, except that due to a bug,
+          # threading must be enabled, i.e. THREAD must be omitted from the disabled
+          # feature list.
+          cd $RUNNER_TEMP
+          git clone https://github.com/micropython/micropython -b v1.24.0 --depth 1
+
+          # Create a variant with the same configuration as the PyScript build.
+          cd micropython/ports/unix
+          cp -a variants/standard variants/pyscript
+          grep require ../webassembly/variants/pyscript/manifest.py \
+              >> variants/pyscript/manifest.py
+          for feature in BTREE FFI SOCKET SSL TERMIOS THREAD; do
+              echo "MICROPY_PY_$feature = 0" >> variants/pyscript/mpconfigvariant.mk
+          done
+
+          export VARIANT=pyscript
+          make submodules
+          make -j $(nproc)
+
+      - name: Checkout
+        uses: actions/[email protected]
+
+      - name: Set up Python
+        uses: actions/[email protected]
+        with:
+          python-version: "3.13"
+
+      - name: Get Packages
+        uses: actions/[email protected]
+        with:
+          name: Packages-toga-core
+          path: dist
+
+      - name: Test
+        run: |
+          pip install dist/toga_core-*.whl
+          site_packages=$(python -c '
+          import sys
+          print([path for path in sys.path if "site-packages" in path][0])
+          ')
+
+          cd core
+          export MICROPYPATH="$site_packages:.frozen"
+          $RUNNER_TEMP/micropython/ports/unix/build-pyscript/micropython \
+              micropython_check.py
+
   core-coverage:
     name: Coverage
     needs: core

changes/2976.feature.rst

@@ -0,0 +1 @@
+A subset of Toga is now compatible with MicroPython.

core/micropython_check.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+#
+# This script should be run under MicroPython to check that it can import all the Toga
+# modules required by Invent.
+
+# The top-level Toga module must be imported first, to enable the standard library
+# compatibility shims.
+#
+# isort: off
+import toga
+
+# isort: on
+import sys
+import traceback
+
+# Access attributes to trigger lazy import.
+failures = 0
+for name in [
+    "App",
+    "Font",
+    "Image",
+    "Window",
+    #
+    "Widget",
+    "Box",
+    "Button",
+    "DateInput",
+    "Divider",
+    "ImageView",
+    "Label",
+    "MultilineTextInput",
+    "PasswordInput",
+    "ProgressBar",
+    "Slider",
+    "Switch",
+    "TextInput",
+    "TimeInput",
+]:
+    try:
+        getattr(toga, name)
+    except Exception:
+        failures += 1
+        print(f"Failed to import toga.{name}:")
+        traceback.print_exc()
+        print()
+
+if failures:
+    print(f"{failures} names failed to import")
+    sys.exit(1)
+else:
+    print("All names imported successfully")

core/pyproject.toml

@@ -57,8 +57,6 @@ classifiers = [
 ]
 dependencies = [
     "travertino >= 0.3.0",
-    # limited to <=3.9 for the `group` argument for `entry_points()`
-    "importlib_metadata >= 4.4.0; python_version <= '3.9'",
 ]
 
 [project.optional-dependencies]
@@ -114,6 +112,7 @@ relative_files = true
 # See notes in the root pyproject.toml file.
 source = ["src"]
 source_pkgs = ["toga"]
+omit = ["**/toga/compat/**"]  # Only used by MicroPython.
 
 [tool.coverage.paths]
 source = [

core/src/toga/__init__.py

@@ -1,8 +1,15 @@
-from __future__ import annotations
+# Enable the standard library compatibility shims before doing anything else.
+#
+# __future__ imports must be at the very top of the file, and MicroPython doesn't
+# currently include a __future__ module, so this file can't contain any __future__
+# imports. Other modules imported after `compat` can use __future__ as normal.
+import sys
+
+if sys.implementation.name != "cpython":  # pragma: no cover
+    from . import compat  # noqa: F401
 
-import importlib
 import warnings
-from pathlib import Path
+from importlib import import_module
 
 toga_core_imports = {
     # toga.app imports
@@ -83,15 +90,21 @@
 
 
 def __getattr__(name):
-    try:
-        module_name = toga_core_imports[name]
-    except KeyError:
-        raise AttributeError(f"module '{__name__}' has no attribute '{name}'") from None
-    else:
-        module = importlib.import_module(module_name)
+    if module_name := toga_core_imports.get(name):
+        module = import_module(module_name)
         value = getattr(module, name)
-        globals()[name] = value
-        return value
+    else:
+        # MicroPython apparently doesn't attempt a submodule import when __getattr__
+        # raises AttributeError, so we need to do it manually.
+        try:
+            value = import_module(f"{__name__}.{name}")
+        except ImportError:
+            raise AttributeError(
+                f"module '{__name__}' has no attribute '{name}'"
+            ) from None
+
+    globals()[name] = value
+    return value
 
 
 class NotImplementedWarning(RuntimeWarning):
@@ -104,7 +117,7 @@ def warn(cls, platform: str, feature: str) -> None:
         warnings.warn(NotImplementedWarning(f"[{platform}] Not implemented: {feature}"))
 
 
-def _package_version(file: Path | str | None, name: str) -> str:
+def _package_version(file, name):
     try:
         # Read version from SCM metadata
         # This will only exist in a development environment