twister: Move prep stage to a github runner

Speed things up by using GH runners, we do not need the power of our own
runners to create the test plan. This also simplifies the workflow
considerably.

PRs now will get queued immediately, ie. no need to wait for a Zephyr
hosted runner to create the plan and then wait again for another round
to get more runners for execution.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

.github/workflows/twister-prep.yaml

@@ -24,7 +24,102 @@ concurrency:
 
 jobs:
   twister-build-prep:
-    uses: ./.github/workflows/twister-prep.yaml
+    if: github.repository_owner == 'zephyrproject-rtos'
+    runs-on: ubuntu-24.04
+    outputs:
+      subset: ${{ steps.output-services.outputs.subset }}
+      size: ${{ steps.output-services.outputs.size }}
+      fullrun: ${{ steps.output-services.outputs.fullrun }}
+    env:
+      MATRIX_SIZE: 10
+      PUSH_MATRIX_SIZE: 20
+      WEEKLY_MATRIX_SIZE: 200
+      BSIM_OUT_PATH: /opt/bsim/
+      BSIM_COMPONENTS_PATH: /opt/bsim/components
+      TESTS_PER_BUILDER: 900
+      COMMIT_RANGE: ${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }}
+      BASE_REF: ${{ github.base_ref }}
+    steps:
+      - name: Checkout
+        if: github.event_name == 'pull_request'
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+          fetch-depth: 0
+          path: zephyr
+          persist-credentials: false
+
+      - name: Set up Python
+        if: github.event_name == 'pull_request'
+        uses: actions/setup-python@42375524e23c412d93fb67b49958b491fce71c38 # v5.4.0
+        with:
+          python-version: 3.12
+          cache: pip
+          cache-dependency-path: scripts/requirements-actions.txt
+
+      - name: install-packages
+        working-directory: zephyr
+        if: github.event_name == 'pull_request'
+        run: |
+          pip install -r scripts/requirements-actions.txt --require-hashes
+
+      - name: Setup Zephyr project
+        if: github.event_name == 'pull_request'
+        uses: zephyrproject-rtos/action-zephyr-setup@f7b70269a8eb01f70c8e710891e4c94972a2f6b4 # v1.0.6
+        with:
+          app-path: zephyr
+          toolchains: all
+
+      - name: Environment Setup
+        working-directory: zephyr
+        if: github.event_name == 'pull_request'
+        run: |
+          git config --global user.email "[email protected]"
+          git config --global user.name "Zephyr Bot"
+          rm -fr ".git/rebase-apply"
+          rm -fr ".git/rebase-merge"
+          git rebase origin/${BASE_REF}
+          git clean -f -d
+          git log  --pretty=oneline | head -n 10
+
+      - name: Generate Test Plan with Twister
+        working-directory: zephyr
+        if: github.event_name == 'pull_request'
+        id: test-plan
+        run: |
+          export ZEPHYR_BASE=${PWD}
+          export ZEPHYR_TOOLCHAIN_VARIANT=zephyr
+          python3 ./scripts/ci/test_plan.py -c origin/${BASE_REF}.. --no-detailed-test-id --pull-request -t $TESTS_PER_BUILDER
+          if [ -s .testplan ]; then
+            cat .testplan >> $GITHUB_ENV
+          else
+            echo "TWISTER_NODES=${MATRIX_SIZE}" >> $GITHUB_ENV
+          fi
+          rm -f testplan.json .testplan
+
+      - name: Determine matrix size
+        id: output-services
+        run: |
+          if [ "${{github.event_name}}" = "push" ]; then
+            subset="[$(seq -s',' 1 ${PUSH_MATRIX_SIZE})]"
+            size=${MATRIX_SIZE}
+          elif [ "${{github.event_name}}" = "pull_request" ]; then
+            if [ -n "${TWISTER_NODES}" ]; then
+              subset="[$(seq -s',' 1 ${TWISTER_NODES})]"
+            else
+              subset="[$(seq -s',' 1 ${MATRIX_SIZE})]"
+            fi
+            size=${TWISTER_NODES}
+          elif [ "${{github.event_name}}" = "schedule" -a "${{github.repository}}" = "zephyrproject-rtos/zephyr" ]; then
+            subset="[$(seq -s',' 1 ${WEEKLY_MATRIX_SIZE})]"
+            size=${WEEKLY_MATRIX_SIZE}
+          else
+            size=0
+          fi
+
+          echo "subset=${subset}" >> $GITHUB_OUTPUT
+          echo "size=${size}" >> $GITHUB_OUTPUT
+          echo "fullrun=${TWISTER_FULL}" >> $GITHUB_OUTPUT
 
   twister-build:
     runs-on: