Add license header check for rust files

Added binary that can check for and add Apache 2.0 licenses.
Run this binary during the build-rust workflow.

rust/tools/file_header.rs

@@ -0,0 +1,78 @@
+// Copyright 2023 Google LLC
+//
+// 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
+//
+//     http://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.
+
+use anyhow::anyhow;
+use clap::Parser as _;
+use file_header::{
+    add_headers_recursively, check_headers_recursively,
+    license::spdx::{YearCopyrightOwnerValue, APACHE_2_0},
+};
+use globset::{Glob, GlobSet, GlobSetBuilder};
+use std::{env, path::PathBuf};
+
+fn main() -> anyhow::Result<()> {
+    let rust_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR")?);
+    let ignore_globset = ignore_globset()?;
+    // Note: when adding headers, there is a bug where the line spacing is off for Apache 2.0 (see https://github.com/spdx/license-list-XML/issues/2127)
+    let header = APACHE_2_0.build_header(YearCopyrightOwnerValue::new(2023, "Google LLC".into()));
+
+    let cli = Cli::parse();
+
+    match cli.subcommand {
+        Subcommand::CheckAll => {
+            let result =
+                check_headers_recursively(&rust_dir, |p| !ignore_globset.is_match(p), header, 4)?;
+            if result.has_failure() {
+                return Err(anyhow!(
+                    "The following files do not have headers: {result:?}"
+                ));
+            }
+        }
+        Subcommand::AddAll => {
+            let files_with_new_header =
+                add_headers_recursively(&rust_dir, |p| !ignore_globset.is_match(p), header)?;
+            files_with_new_header
+                .iter()
+                .for_each(|path| println!("Added header to: {path:?}"));
+        }
+    }
+    Ok(())
+}
+
+fn ignore_globset() -> anyhow::Result<GlobSet> {
+    Ok(GlobSetBuilder::new()
+        .add(Glob::new("**/.idea/**")?)
+        .add(Glob::new("**/target/**")?)
+        .add(Glob::new("**/.gitignore")?)
+        .add(Glob::new("**/CHANGELOG.md")?)
+        .add(Glob::new("**/Cargo.lock")?)
+        .add(Glob::new("**/Cargo.toml")?)
+        .add(Glob::new("**/README.md")?)
+        .add(Glob::new("*.bin")?)
+        .build()?)
+}
+
+#[derive(clap::Parser)]
+struct Cli {
+    #[clap(subcommand)]
+    subcommand: Subcommand,
+}
+
+#[derive(clap::Subcommand, Debug, Clone)]
+enum Subcommand {
+    /// Checks if a license is present in files that are not in the ignore list.
+    CheckAll,
+    /// Adds a license as needed to files that are not in the ignore list.
+    AddAll,
+}