Re-implement shell expansion with serde_as

`serde_with` offers a much more powerful set of tools for modifying
de/serialization behavior, and as a result allows us to collapse a handful of
nearly-identical utility functions into a single `ShellExpand` utility type.

nativelink-config/BUILD.bazel

@@ -10,9 +10,10 @@ rust_library(
     name = "nativelink-config",
     srcs = [
         "src/cas_server.rs",
+        "src/deser/mod.rs",
+        "src/deser/shellexpand.rs",
         "src/lib.rs",
         "src/schedulers.rs",
-        "src/serde_utils.rs",
         "src/stores.rs",
     ],
     compile_data = [
@@ -23,6 +24,7 @@ rust_library(
         "@crates//:byte-unit",
         "@crates//:humantime",
         "@crates//:serde",
+        "@crates//:serde_with",
         "@crates//:shellexpand",
     ],
 )

nativelink-config/Cargo.toml

@@ -6,9 +6,12 @@ edition = "2021"
 [dependencies]
 byte-unit = { version = "5.1.4", default-features = false, features = ["byte"] }
 humantime = "2.1.0"
-serde = { version = "1.0.204", default-features = false }
+serde = { version = "1.0.204", features = ["derive"] }
 serde_json5 = "0.1.0"
-shellexpand = { version = "3.1.0", default-features = false, features = ["base-0"] }
+shellexpand = { version = "3.1.0", default-features = false, features = [
+    "base-0",
+] }
+serde_with = "3.9.0"
 
 [dev-dependencies]
 pretty_assertions = { version = "1.4.0", features = ["std"] }

nativelink-config/src/deser/mod.rs

@@ -0,0 +1,19 @@
+// Copyright 2024 The NativeLink Authors. All rights reserved.
+//
+// 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.
+
+//! Deserialization utilities for use in parsing and deserializing nativelink configs.
+
+mod shellexpand;
+
+pub use self::shellexpand::{ShellExpand, ShellExpandBytes, ShellExpandSeconds};