fix: ensure the xcodeproj project generation uses the correct Bazel binary in the firebase_example (#1401)

The `rules_xcodeproj` project generator calls Bazel. By default, it
looks for `bazel` on the `PATH`. When running under
`rules_bazel_integration_test` this will pick up the default Bazel
version on the system. If that is Bazelisk, it will pull down the latest
Bazel. The fix is to explicitly tell `xcodeproj` which Bazel binary to
use.

- Add `tools/bazel` to the `firebase_example`. It inspects environment
variables to determine the Bazel version to use and writes
`tools/bazel_for_xcodeproj` which executes Bazel commands against the
correct Bazel binary.
- Use `sanbox` for `rules_xcodeproj` builds in firebase example. This
avoids the duplicate definition error.
- Add `print_and_run` bash function to
`examples/firebase_example/do_test` to ease debugging future issues.

Author: cgrindel

.gitignore

@@ -20,3 +20,6 @@ local.bazelrc
 
 # Ignore vscode settings
 .vscode
+
+# This is generated by the firebase example's tools/bazel.
+examples/firebase_example/tools/bazel_for_xcodeproj

examples/firebase_example/.bazelrc

@@ -20,3 +20,6 @@ build --cxxopt='-std=gnu++14'
 # Firebase SPM support requires `-ObjC` linker option.
 # https://github.com/firebase/firebase-ios-sdk/blob/master/SwiftPackageManager.md#requirements
 build --linkopt='-ObjC'
+
+# Use sandbox for rules_xcodeproj to avoid duplicate definition errors.
+build:rules_xcodeproj --spawn_strategy=remote,worker,sandboxed,local

examples/firebase_example/analytics/AnalyticsExample/BUILD.bazel

@@ -44,6 +44,9 @@ build_test(
 
 xcodeproj(
     name = "xcodeproj",
+    # The ./tools/bazel_for_xcodeproj is generated by tools/bazel. It should
+    # not be checked into source control.
+    bazel_path = "./tools/bazel_for_xcodeproj",
     project_name = "AnalyticsExample",
     tags = ["manual"],
     top_level_targets = [

examples/firebase_example/do_test

@@ -2,15 +2,23 @@
 
 set -o errexit -o nounset -o pipefail
 
+print_and_run() {
+  local cmd="${1}"
+  shift 1
+  printf >&2 "======================\n%s: %s %s\n======================\n" \
+    "$(basename "${BASH_SOURCE[0]}")" "$(basename "${cmd}")" "$*"
+  "${cmd}" "$@"
+}
+
 # Use the Bazel binary specified by the integration test. Otherise, fall back 
 # to bazel.
 bazel="${BIT_BAZEL_BINARY:-bazel}"
 
 # Generate Swift external deps and update build files
-"${bazel}" run //:tidy
+print_and_run "${bazel}" run //:tidy
 
 # Ensure that it builds and tests pass
-"${bazel}" test //...
+print_and_run "${bazel}" test //...
 
 # The analytics/AnalyticsExample generates an Xcode project using
 # rules_xcodeproj. The following ensures that the project generates properly
@@ -19,8 +27,8 @@ bazel="${BIT_BAZEL_BINARY:-bazel}"
 # https://github.com/MobileNativeFoundation/rules_xcodeproj/issues/2703
 
 # Generate the Xcode project
-"${bazel}" run //analytics/AnalyticsExample:xcodeproj
+print_and_run "${bazel}" run //analytics/AnalyticsExample:xcodeproj
 
 # Build the workspace
-"${bazel}" run //analytics/AnalyticsExample:xcodeproj -- \
+print_and_run "${bazel}" run //analytics/AnalyticsExample:xcodeproj -- \
   --generator_output_groups=all_targets 'build --remote_download_minimal'

examples/firebase_example/tools/bazel

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+
+set -o errexit -o nounset -o pipefail
+
+script_dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" > /dev/null && pwd)"
+
+# Order of Bazel selection:
+# 1. BAZEL_REAL: Use Bazel specified by Bazelisk
+# 2. BIT_BAZEL_BINARY: Use Bazel specified by rules_bazel_integration_test.
+# 3: bazel: Try to find Bazel on the PATH
+#
+# NOTE: Do not put BIT_BAZEL_BINARY first in the evaluation. It can lead to 
+# recursive loop when using rules_bazel_integration_test.
+bazel="${BAZEL_REAL:-${BIT_BAZEL_BINARY:-bazel}}"
+
+# Generate a bazel script for rules_xcodeproj to use. This script ensures that
+# the xcodeproj runner uses the Bazel that is under test. We configure the
+# xcodeproj macro to find this generated bazel script.
+bazel_for_xcodeproj="${script_dir}/bazel_for_xcodeproj"
+cat >"${bazel_for_xcodeproj}" <<-EOF
+#!/usr/bin/env bash
+
+# NOTE: This file is generated by tools/bazel. It is used by the xcodeproj 
+# macro.
+
+set -o errexit -o nounset -o pipefail
+
+# Use the Bazel binary that we specify.
+bazel="${bazel}"
+
+# Execute the Bazel command
+"\${bazel}" "\${@}"
+EOF
+chmod +x "${bazel_for_xcodeproj}"
+
+# Execute the command
+"${bazel}" "${@}"