github: Add basic workflow and docs

Bug: b/340900493
Change-Id: I4ef402c655e8a0ad32104b88885fef8f13d07dd2
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/212952
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Reviewed-by: Ted Pudlik <tpudlik@google.com>
Commit-Queue: Rob Mohr <mohrr@google.com>

.github/workflows/bazel-noenv.yaml

@@ -0,0 +1,27 @@
+name: bazel-noenv
+
+on:
+  push
+
+jobs:
+  bazel-build-test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          submodules: recursive
+      - name: Get Bazel
+        uses: bazel-contrib/setup-bazel@0.8.1
+        with:
+          # Avoid downloading Bazel every time.
+          bazelisk-cache: true
+          # Store build cache per workflow.
+          disk-cache: ${{ github.workflow }}
+          # Share repository cache between workflows.
+          repository-cache: true
+      - name: Bazel Build
+        run: bazel build ...
+      - name: Bazel Test
+        run: bazel test ...

.github/workflows/lintformat.yaml

@@ -0,0 +1,18 @@
+name: lintformat
+
+on:
+  push
+
+jobs:
+  lintformat:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          submodules: recursive
+      - name: Bootstrap
+        run: pw_env_setup/run.sh bootstrap.sh
+      - name: python_format
+        run: pw presubmit --program lintformat --full --keep-going

docs/infra/github.rst

@@ -4,9 +4,8 @@
 GitHub
 ===========
 
---------
 Overview
---------
+========
 
 Pigweed itself uses `LUCI <luci>`_ for
 :abbr:`CI/CD (Continuous Integration/Continuous Deployment)`. LUCI is
@@ -18,13 +17,12 @@ for `GitHub Actions <github-actions>`_ as well.
 Bazel
 =====
 Configuring a Bazel builder that runs on pull requests is straightforward.
-There are four steps: `checkout <github-actions-checkout>`_,
-`get Bazel <github-actions-bazel>`_, build, and test. There are good
-community-managed actions for the first two steps, and the last two steps are
-trivial (and can even be combined).
+There are four steps: `checkout`_, `get Bazel`_, build, and test. There
+are good community-managed actions for the first two steps, and the last two
+steps are trivial (and can even be combined).
 
-.. _github-actions-checkout: https://github.com/marketplace/actions/checkout
-.. _github-actions-bazel: https://github.com/marketplace/actions/setup-bazel-environment
+.. _checkout: https://github.com/marketplace/actions/checkout
+.. _get Bazel: https://github.com/marketplace/actions/setup-bazel-environment
 
 The Bazel version retrieved is configured through a ``.bazelversion`` file in
 the root of the checkout.
@@ -63,5 +61,47 @@ the root of the checkout.
 
 ``pw presubmit``
 ================
-Tests that require using `pw_env_setup <module-pw_env_setup>`_ and
-`pw_presubmit <module-pw_presubmit>`_ are not yet supported.
+Configuring a builder that uses `pw_env_setup <module-pw_env_setup>`_ and
+`pw_presubmit <module-pw_presubmit>`_ is also relatively simple. When run
+locally, ``bootstrap.sh`` has several checks to ensure it's "sourced" instead of
+directly executed. A `trivial wrapper script` is included in ``pw_env_setup``
+that gets around this.
+
+.. _trivial wrapper script: https://cs.opensource.google/pigweed/pigweed/+/main:pw_env_setup/run.sh
+
+When ``pw_env_setup`` is run within a GitHub Action, it recognizes this from the
+environment and writes the environment variables in a way
+`understood by GitHub`_, and GitHub makes those variables available to
+subsequent steps.
+
+.. _understood by GitHub: https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-environment-variable
+
+For Pigweed itself, the only ``pw_presubmit``-based action runs lintformat. To
+test all of Pigweed requires more resources than the free GitHub runners
+provide, but small projects using just part of Pigweed may be more successful.
+
+.. code-block:: yaml
+
+   name: lintformat
+
+   on:
+     pull_request:
+       types: [opened, synchronize, reopened]
+
+   jobs:
+     bazel-build-test:
+       runs-on: ubuntu-latest
+       steps:
+         - name: Checkout
+           uses: actions/checkout@v4
+           with:
+             fetch-depth: 0
+             submodules: recursive
+         - name: Bootstrap
+           run: pw_env_setup/run.sh bootstrap.sh
+         - name: python_format
+           run: pw presubmit --program lintformat --keep-going
+
+Note that Pigweed does not accept pull requests on GitHub, so we do not define
+GitHub actions that trigger from pull requests. Instead, we trigger on pushes to
+GitHub.

pw_env_setup/run.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+# Copyright 2024 The Pigweed Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy of
+# the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations under
+# the License.
+
+# Helper script for when 'bootstrap.sh' needs to be executed instead of
+# sourced.
+
+. "$1"