Add copyright header check to CI.

.github/copyright.sh

@@ -0,0 +1,23 @@
+#!/bin/bash
+
+# If there are new files with headers that can't match the conditions here,
+# then the files can be ignored by an additional glob argument via the -g flag.
+# For example:
+#   -g "!src/special_file.rs"
+#   -g "!src/special_directory"
+
+# Check all the standard Rust source files
+output=$(rg "^// Copyright (19|20)[\d]{2} (.+ and )?the Druid Authors( and .+)?$\n^// SPDX-License-Identifier: Apache-2\.0$\n\n" --files-without-match --multiline -g "*.rs" -g "!{druid-derive/tests/ui,docs/book_examples/src}" .)
+
+if [ -n "$output" ]; then
+	echo -e "The following files lack the correct copyright header:\n"
+	echo $output
+	echo -e "\n\nPlease add the following header:\n"
+	echo "// Copyright $(date +%Y) the Druid Authors"
+	echo "// SPDX-License-Identifier: Apache-2.0"
+	echo -e "\n... rest of the file ...\n"
+	exit 1
+fi
+
+echo "All files have correct copyright headers."
+exit 0

.github/workflows/ci.yml

@@ -27,6 +27,14 @@ jobs:
       - name: cargo fmt
         run: cargo fmt --all --check
 
+      - name: install ripgrep
+        run: |
+          sudo apt update
+          sudo apt install ripgrep
+
+      - name: check copyright headers
+        run: bash .github/copyright.sh
+
   test-stable:
     runs-on: ${{ matrix.os }}
     strategy: