fight with Windows

Signed-off-by: William Woodruff <william@trailofbits.com>

action.yml

@@ -83,6 +83,7 @@ runs:
   using: "composite"
   steps:
     - name: Set up sigstore-python
+      id: setup
       run: |
         # NOTE: Sourced, not executed as a script.
         source "${GITHUB_ACTION_PATH}/setup/setup.bash"
@@ -93,12 +94,13 @@ runs:
     - name: Run sigstore-python
       id: sigstore-python
       run: |
-        "${GITHUB_ACTION_PATH}/.action-env/bin/python" \
+        "${VENV_PYTHON_PATH}" \
           "${GITHUB_ACTION_PATH}/action.py" \
           "${GHA_SIGSTORE_PYTHON_INPUTS}"
       env:
         # The year is 2023, and nonsense like this is still necessary on Windows.
         PYTHONUTF8: "1"
+        VENV_PYTHON_PATH: "${{ steps.setup.outputs.venv-python-path }}"
         GHA_SIGSTORE_PYTHON_IDENTITY_TOKEN: "${{ inputs.identity-token }}"
         GHA_SIGSTORE_PYTHON_SIGNATURE: "${{ inputs.signature }}"
         GHA_SIGSTORE_PYTHON_CERTIFICATE: "${{ inputs.certificate }}"

setup/setup.bash

@@ -50,6 +50,18 @@ min_vers=$(cut -d '.' -f2 <<< "${vers}")
 # therefore be subject to PEP 668. We use a virtual environment unconditionally
 # to prevent that kind of confusion.
 python -m venv "${GITHUB_ACTION_PATH}/.action-env"
-"${GITHUB_ACTION_PATH}/.action-env/bin/python" -m pip install --requirement "${GITHUB_ACTION_PATH}/requirements.txt"
 
-debug "sigstore-python: $("${GITHUB_ACTION_PATH}/.action-env/bin/python" -m sigstore --version)"
+# Annoying: Windows venvs use a different structure, for unknown reasons.
+if [[ -d "${GITHUB_ACTION_PATH}/.action-env/bin" ]]; then
+  VENV_PYTHON_PATH="${GITHUB_ACTION_PATH}/.action-env/bin/python"
+else
+  VENV_PYTHON_PATH="${GITHUB_ACTION_PATH}/.action-env/Scripts/python"
+fi
+
+"${VENV_PYTHON_PATH}" -m pip install --requirement "${GITHUB_ACTION_PATH}/requirements.txt"
+
+debug "sigstore-python: $("${VENV_PYTHON_PATH}" -m sigstore --version)"
+
+# Finally, propagate VENV_PYTHON_PATH so we can actually kick-start
+# the extension from it.
+echo "venv-python-path=${VENV_PYTHON_PATH}" >> "${GITHUB_OUTPUT}"