[CI] Start testing examples (#412)

[CI] Start testing examples

### Motivation

We're expanding the Examples section and want to verify that they continue to work as the project evolves.

That means that they successfully build, and for those with tests, that the tests are passing.

### Modifications

Added a script that is now triggered by the new `examples` pipeline.

It goes through all the packages in Examples and builds them, and for those with a Tests directory, also tests them.

### Result

More confidence that our Examples are working.

### Test Plan

Ran the test on macOS, ran it in docker-compose, all passed, so did the new CI. Verified in CI logs that the script is actually running and the two existing examples were exercised.



Reviewed by: simonjbeaumont

Builds:
     ✔︎ pull request validation (5.10) - Build finished. 
     ✔︎ pull request validation (5.9) - Build finished. 
     ✔︎ pull request validation (5.9.0) - Build finished. 
     ✔︎ pull request validation (compatibility test) - Build finished. 
     ✔︎ pull request validation (docc test) - Build finished. 
     ✔︎ pull request validation (examples) - Build finished. 
     ✔︎ pull request validation (integration test) - Build finished. 
     ✔︎ pull request validation (nightly) - Build finished. 
     ✔︎ pull request validation (soundness) - Build finished. 

#412

Examples/.gitignore

@@ -0,0 +1 @@
+**/Package.resolved

docker/docker-compose.yaml

@@ -60,4 +60,4 @@ services:
 
   examples:
     <<: *common
-    command: /bin/bash -xcl "swift -version && uname -a && true" # Placeholder to bootstrap pipeline.
+    command: /bin/bash -xcl "swift -version && uname -a && bash ./scripts/test-examples.sh"

scripts/test-examples.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the SwiftOpenAPIGenerator open source project
+##
+## Copyright (c) 2023 Apple Inc. and the SwiftOpenAPIGenerator project authors
+## Licensed under Apache License v2.0
+##
+## See LICENSE.txt for license information
+## See CONTRIBUTORS.txt for the list of SwiftOpenAPIGenerator project authors
+##
+## SPDX-License-Identifier: Apache-2.0
+##
+##===----------------------------------------------------------------------===##
+set -euo pipefail
+
+log() { printf -- "** %s\n" "$*" >&2; }
+error() { printf -- "** ERROR: %s\n" "$*" >&2; }
+fatal() { error "$@"; exit 1; }
+
+log "Checking required executables..."
+SWIFT_BIN=${SWIFT_BIN:-$(command -v swift || xcrun -f swift)} || fatal "SWIFT_BIN unset and no swift on PATH"
+
+CURRENT_SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+REPO_ROOT="$(git -C "${CURRENT_SCRIPT_DIR}" rev-parse --show-toplevel)"
+TMP_DIR=$(/usr/bin/mktemp -d -p "${TMPDIR-/tmp}" "$(basename "$0").XXXXXXXXXX")
+
+PACKAGE_PATH=${PACKAGE_PATH:-${REPO_ROOT}}
+EXAMPLES_PACKAGE_PATH="${PACKAGE_PATH}/Examples"
+
+for EXAMPLE_PACKAGE_PATH in $(find "${EXAMPLES_PACKAGE_PATH}" -maxdepth 2 -name Package.swift -type f -print0 | xargs -0 dirname); do
+
+    EXAMPLE_PACKAGE_NAME="$(basename "${EXAMPLE_PACKAGE_PATH}")"
+    EXAMPLE_COPY_DIR="${TMP_DIR}/${EXAMPLE_PACKAGE_NAME}"
+    log "Copying example ${EXAMPLE_PACKAGE_NAME} to ${EXAMPLE_COPY_DIR}"
+    cp -R "${EXAMPLE_PACKAGE_PATH}" "${EXAMPLE_COPY_DIR}"
+
+    log "Overriding dependency in ${EXAMPLE_PACKAGE_NAME} to use ${PACKAGE_PATH}"
+    "${SWIFT_BIN}" package --package-path "${EXAMPLE_COPY_DIR}" \
+        edit swift-openapi-generator --path "${PACKAGE_PATH}"
+
+    log "Building example package: ${EXAMPLE_PACKAGE_NAME}"
+    "${SWIFT_BIN}" build --package-path "${EXAMPLE_COPY_DIR}"
+    log "✅ Successfully built the example package ${EXAMPLE_PACKAGE_NAME}."
+
+    if [ -d "${EXAMPLE_COPY_DIR}/Tests" ]; then
+        log "Running tests for example package: ${EXAMPLE_PACKAGE_NAME}"
+        "${SWIFT_BIN}" test --package-path "${EXAMPLE_COPY_DIR}"
+        log "✅ Passed the tests for the example package ${EXAMPLE_PACKAGE_NAME}."
+    fi
+done