Make CONTRIBUTORS.txt optional in license headers

.github/workflows/pull_request.yml

@@ -8,6 +8,10 @@ on:
     types: [opened, reopened, synchronize]
 
 jobs:
+  shell_tests:
+    name: Shell Tests
+    uses: ./.github/workflows/shell_tests.yml
+
   tests_with_docker_embedded_swift:
     name: Test Embedded Swift SDKs
     uses: ./.github/workflows/swift_package_test.yml

.github/workflows/scripts/check-license-header.sh

@@ -122,10 +122,20 @@ while IFS= read -r file_path; do
     | sed -E -e 's/20[12][0123456789] ?[-–] ?20[12][0123456789]/YEARS/' -e 's/20[12][0123456789]/YEARS/' \
   )
 
-  if ! diff -u \
+  if ! diff_output=$(diff -u \
     --label "Expected header" <(echo "${expected_file_header}") \
-    --label "${file_path}" <(echo "${normalized_file_header}")
+    --label "${file_path}" <(echo "${normalized_file_header}"))
   then
+    expected_file_header_without_contributors=$(echo "${expected_file_header}" | sed '/CONTRIBUTORS\.txt/d')
+    normalized_file_header_without_contributors=$(echo "${normalized_file_header}" | sed '/CONTRIBUTORS\.txt/d')
+    if [ "${expected_file_header}" != "${expected_file_header_without_contributors}" ] \
+      && diff -u \
+        --label "Expected header" <(echo "${expected_file_header_without_contributors}") \
+        --label "${file_path}" <(echo "${normalized_file_header_without_contributors}") > /dev/null
+    then
+      continue
+    fi
+    echo "${diff_output}"
     paths_with_missing_license+=("${file_path} ")
   fi
 done <<< "$file_paths"

.github/workflows/shell_tests.yml

@@ -0,0 +1,20 @@
+name: Shell Tests
+
+on:
+  workflow_call:
+
+permissions:
+  contents: read
+
+jobs:
+  license-header-check:
+    name: License header check tests
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+      - name: Test license header check
+        run: bash tests/check-license-header.sh

tests/check-license-header.sh

@@ -0,0 +1,58 @@
+#!/bin/bash
+##===----------------------------------------------------------------------===##
+##
+## This source file is part of the Swift.org open source project
+##
+## Copyright (c) 2026 Apple Inc. and the Swift project authors
+## Licensed under Apache License v2.0 with Runtime Library Exception
+##
+## See https://swift.org/LICENSE.txt for license information
+##
+##===----------------------------------------------------------------------===##
+
+set -euo pipefail
+
+repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
+tmpdir=$(mktemp -d)
+trap 'rm -rf "${tmpdir}"' EXIT
+
+mkdir -p "${tmpdir}/.github/workflows/scripts"
+cp "${repo_root}/.github/workflows/scripts/check-license-header.sh" "${tmpdir}/.github/workflows/scripts/check-license-header.sh"
+
+cd "${tmpdir}"
+git init -q
+
+cat > WithContributors.swift <<'EOF'
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Logging API open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift Logging API project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift Logging API project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+EOF
+
+cat > WithoutContributors.swift <<'EOF'
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Logging API open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift Logging API project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+EOF
+
+git add WithContributors.swift WithoutContributors.swift
+
+PROJECT_NAME="Swift Logging API" .github/workflows/scripts/check-license-header.sh