buildsys: use clap for env vars

Required input in the form of environment variables was sprinkled
throughout the code. Here we aggregate the inputs into a CLI interface
using Clap, while still allowing all to specified via environment
variables.

tools/buildsys/Cargo.toml

@@ -10,6 +10,7 @@ exclude = ["README.md"]
 
 [dependencies]
 bottlerocket-variant = { version = "0.1", path = "../bottlerocket-variant" }
+clap = { version = "4", features = ["derive", "env"] }
 duct = "0.13"
 hex = "0.4"
 lazy_static = "1"

tools/buildsys/src/args.rs

@@ -0,0 +1,188 @@
+/*!
+
+These structs provide the CLI interface for buildsys which is called from Cargo.toml and accepts all
+of its input arguments from environment variables.
+
+!*/
+
+use clap::{Parser, Subcommand};
+use std::path::PathBuf;
+
+/// A list of environment variables and the type of build that should be rerun if that environment
+/// variable changes. The build type is represented with bit flags so that we can easily list
+/// multiple build types for a single variable. See `[BuildType]` and `[rerun_for_envs]` below to
+/// see how this list is used.
+const REBUILD_VARS: [(&str, u8); 13] = [
+    ("BUILDSYS_ARCH", PACKAGE | VARIANT),
+    ("BUILDSYS_NAME", VARIANT),
+    ("BUILDSYS_OUTPUT_DIR", VARIANT),
+    ("BUILDSYS_PACKAGES_DIR", PACKAGE),
+    ("BUILDSYS_PRETTY_NAME", VARIANT),
+    ("BUILDSYS_ROOT_DIR", PACKAGE | VARIANT),
+    ("BUILDSYS_STATE_DIR", PACKAGE | VARIANT),
+    ("BUILDSYS_TIMESTAMP", VARIANT),
+    ("BUILDSYS_VARIANT", VARIANT),
+    ("BUILDSYS_VERSION_BUILD", VARIANT),
+    ("BUILDSYS_VERSION_IMAGE", VARIANT),
+    ("TLPRIVATE_SDK_IMAGE", PACKAGE | VARIANT),
+    ("TLPRIVATE_TOOLCHAIN", PACKAGE | VARIANT),
+];
+
+/// A tool for building Bottlerocket images and artifacts.
+#[derive(Debug, Parser)]
+pub(crate) struct Buildsys {
+    #[command(subcommand)]
+    pub(crate) command: Command,
+}
+
+#[derive(Subcommand, Debug)]
+pub(crate) enum Command {
+    BuildPackage(BuildPackageArgs),
+    BuildVariant(BuildVariantArgs),
+}
+
+impl Command {
+    pub(crate) fn build_type(&self) -> BuildType {
+        match self {
+            Command::BuildPackage(_) => BuildType::Package,
+            Command::BuildVariant(_) => BuildType::Variant,
+        }
+    }
+}
+
+/// Arguments common to all subcommands.
+#[derive(Debug, Parser)]
+pub(crate) struct Common {
+    #[arg(long, env = "BUILDSYS_ARCH")]
+    pub(crate) arch: String,
+
+    #[arg(long, env = "BUILDSYS_OUTPUT_DIR")]
+    pub(crate) output_dir: PathBuf,
+
+    #[arg(long, env = "BUILDSYS_ROOT_DIR")]
+    pub(crate) root_dir: PathBuf,
+
+    #[arg(long, env = "BUILDSYS_STATE_DIR")]
+    pub(crate) state_dir: PathBuf,
+
+    #[arg(long, env = "BUILDSYS_TIMESTAMP")]
+    pub(crate) timestamp: String,
+
+    #[arg(long, env = "BUILDSYS_VERSION_FULL")]
+    pub(crate) version_full: String,
+
+    #[arg(long, env = "CARGO_MANIFEST_DIR")]
+    pub(crate) cargo_manifest_dir: PathBuf,
+
+    #[arg(long, env = "TLPRIVATE_SDK_IMAGE")]
+    pub(crate) sdk_image: String,
+
+    #[arg(long, env = "TLPRIVATE_TOOLCHAIN")]
+    pub(crate) toolchain: String,
+}
+
+/// Build RPMs from a spec file and sources.
+#[derive(Debug, Parser)]
+pub(crate) struct BuildPackageArgs {
+    #[arg(long, env = "BUILDSYS_PACKAGES_DIR")]
+    pub(crate) packages_dir: PathBuf,
+
+    #[arg(long, env = "BUILDSYS_VARIANT")]
+    pub(crate) variant: String,
+
+    #[arg(long, env = "BUILDSYS_SOURCES_DIR")]
+    pub(crate) sources_dir: PathBuf,
+
+    #[arg(long, env = "CARGO_PKG_NAME")]
+    pub(crate) cargo_package_name: String,
+
+    #[command(flatten)]
+    pub(crate) common: Common,
+}
+
+/// Build filesystem and disk images from RPMs.
+#[derive(Debug, Parser)]
+pub(crate) struct BuildVariantArgs {
+    #[arg(long, env = "BUILDSYS_NAME")]
+    pub(crate) name: String,
+
+    #[arg(long, env = "BUILDSYS_PRETTY_NAME")]
+    pub(crate) pretty_name: String,
+
+    #[arg(long, env = "BUILDSYS_VARIANT")]
+    pub(crate) variant: String,
+
+    #[arg(long, env = "BUILDSYS_VERSION_BUILD")]
+    pub(crate) version_build: String,
+
+    #[arg(long, env = "BUILDSYS_VERSION_IMAGE")]
+    pub(crate) version_image: String,
+
+    #[command(flatten)]
+    pub(crate) common: Common,
+}
+
+/// Returns the environment variables that need to be watched for a given `[BuildType]`.
+fn sensitive_env_vars(build_type: BuildType) -> impl Iterator<Item = &'static str> {
+    REBUILD_VARS
+        .into_iter()
+        .filter(move |(_, flags)| build_type.includes(*flags))
+        .map(|(var, _)| var)
+}
+
+/// Emits the cargo directives for a the list of sensitive environment variables for a given
+/// `[BuildType]`.
+pub(crate) fn rerun_for_envs(build_type: BuildType) {
+    for var in sensitive_env_vars(build_type) {
+        println!("cargo:rerun-if-env-changed={}", var)
+    }
+}
+
+/// The thing that buildsys is building.
+#[repr(u8)]
+#[derive(Debug, Clone, Copy)]
+pub(crate) enum BuildType {
+    Package = 0b00000001,
+    Variant = 0b00000010,
+}
+
+impl BuildType {
+    fn includes(&self, flags: u8) -> bool {
+        let this = *self as u8;
+        let and = flags & this;
+        and == this
+    }
+}
+
+const PACKAGE: u8 = BuildType::Package as u8;
+const VARIANT: u8 = BuildType::Variant as u8;
+
+#[test]
+fn build_type_includes_test() {
+    // true
+    assert!(BuildType::Package.includes(PACKAGE | VARIANT));
+    assert!(BuildType::Variant.includes(VARIANT));
+    assert!(BuildType::Variant.includes(VARIANT | PACKAGE));
+
+    // false
+    assert!(!BuildType::Package.includes(VARIANT));
+    assert!(!BuildType::Variant.includes(PACKAGE));
+    assert!(!BuildType::Variant.includes(32));
+    assert!(!BuildType::Variant.includes(0));
+}
+
+#[test]
+fn test_sensitive_env_vars_variant() {
+    let list: Vec<&str> = sensitive_env_vars(BuildType::Variant).collect();
+    assert!(list.contains(&"BUILDSYS_ARCH"));
+    assert!(list.contains(&"BUILDSYS_VARIANT"));
+    assert!(!list.contains(&"BUILDSYS_PACKAGES_DIR"));
+}
+
+#[test]
+fn test_sensitive_env_vars_package() {
+    let list: Vec<&str> = sensitive_env_vars(BuildType::Package).collect();
+    assert!(list.contains(&"BUILDSYS_ARCH"));
+    assert!(list.contains(&"BUILDSYS_PACKAGES_DIR"));
+    assert!(!list.contains(&"BUILDSYS_VARIANT"));
+}