feat(wfe-rustlang): add Rust toolchain step executors

New crate providing cargo and rustup step types for WFE workflows:

Cargo steps: build, test, check, clippy, fmt, doc, publish
Rustup steps: rust-install, rustup-toolchain, rustup-component, rustup-target

Shared CargoConfig base with toolchain, package, features, release,
target, profile, extra_args, env, working_dir, and timeout support.
Toolchain override via rustup run for any cargo command.

wfe-rustlang/src/cargo/config.rs

@@ -0,0 +1,301 @@
+use std::collections::HashMap;
+
+use serde::{Deserialize, Serialize};
+
+/// Which cargo subcommand to run.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "kebab-case")]
+pub enum CargoCommand {
+    Build,
+    Test,
+    Check,
+    Clippy,
+    Fmt,
+    Doc,
+    Publish,
+    Audit,
+    Deny,
+    Nextest,
+    LlvmCov,
+    DocMdx,
+}
+
+impl CargoCommand {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            Self::Build => "build",
+            Self::Test => "test",
+            Self::Check => "check",
+            Self::Clippy => "clippy",
+            Self::Fmt => "fmt",
+            Self::Doc => "doc",
+            Self::Publish => "publish",
+            Self::Audit => "audit",
+            Self::Deny => "deny",
+            Self::Nextest => "nextest",
+            Self::LlvmCov => "llvm-cov",
+            Self::DocMdx => "doc-mdx",
+        }
+    }
+
+    /// Returns the subcommand arg(s) to pass to cargo.
+    /// Most commands are a single arg, but nextest needs "nextest run".
+    /// DocMdx uses `rustdoc` (the actual cargo subcommand).
+    pub fn subcommand_args(&self) -> Vec<&'static str> {
+        match self {
+            Self::Nextest => vec!["nextest", "run"],
+            Self::DocMdx => vec!["rustdoc"],
+            other => vec![other.as_str()],
+        }
+    }
+
+    /// Returns the cargo-install package name if this is an external tool.
+    /// Returns `None` for built-in cargo subcommands.
+    pub fn install_package(&self) -> Option<&'static str> {
+        match self {
+            Self::Audit => Some("cargo-audit"),
+            Self::Deny => Some("cargo-deny"),
+            Self::Nextest => Some("cargo-nextest"),
+            Self::LlvmCov => Some("cargo-llvm-cov"),
+            _ => None,
+        }
+    }
+
+    /// Returns the binary name to probe for availability.
+    pub fn binary_name(&self) -> Option<&'static str> {
+        match self {
+            Self::Audit => Some("cargo-audit"),
+            Self::Deny => Some("cargo-deny"),
+            Self::Nextest => Some("cargo-nextest"),
+            Self::LlvmCov => Some("cargo-llvm-cov"),
+            _ => None,
+        }
+    }
+}
+
+/// Shared configuration for all cargo step types.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct CargoConfig {
+    pub command: CargoCommand,
+    /// Rust toolchain override (e.g. "nightly", "1.78.0").
+    #[serde(default)]
+    pub toolchain: Option<String>,
+    /// Target package (`-p`).
+    #[serde(default)]
+    pub package: Option<String>,
+    /// Features to enable (`--features`).
+    #[serde(default)]
+    pub features: Vec<String>,
+    /// Enable all features (`--all-features`).
+    #[serde(default)]
+    pub all_features: bool,
+    /// Disable default features (`--no-default-features`).
+    #[serde(default)]
+    pub no_default_features: bool,
+    /// Build in release mode (`--release`).
+    #[serde(default)]
+    pub release: bool,
+    /// Compilation target triple (`--target`).
+    #[serde(default)]
+    pub target: Option<String>,
+    /// Build profile (`--profile`).
+    #[serde(default)]
+    pub profile: Option<String>,
+    /// Additional arguments appended to the command.
+    #[serde(default)]
+    pub extra_args: Vec<String>,
+    /// Environment variables.
+    #[serde(default)]
+    pub env: HashMap<String, String>,
+    /// Working directory.
+    #[serde(default)]
+    pub working_dir: Option<String>,
+    /// Execution timeout in milliseconds.
+    #[serde(default)]
+    pub timeout_ms: Option<u64>,
+    /// Output directory for generated files (e.g., MDX docs).
+    #[serde(default)]
+    pub output_dir: Option<String>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    #[test]
+    fn serde_round_trip_minimal() {
+        let config = CargoConfig {
+            command: CargoCommand::Build,
+            toolchain: None,
+            package: None,
+            features: vec![],
+            all_features: false,
+            no_default_features: false,
+            release: false,
+            target: None,
+            profile: None,
+            extra_args: vec![],
+            env: HashMap::new(),
+            working_dir: None,
+            timeout_ms: None,
+            output_dir: None,
+        };
+        let json = serde_json::to_string(&config).unwrap();
+        let de: CargoConfig = serde_json::from_str(&json).unwrap();
+        assert_eq!(de.command, CargoCommand::Build);
+        assert!(de.features.is_empty());
+        assert!(!de.release);
+    }
+
+    #[test]
+    fn serde_round_trip_full() {
+        let mut env = HashMap::new();
+        env.insert("RUSTFLAGS".to_string(), "-D warnings".to_string());
+
+        let config = CargoConfig {
+            command: CargoCommand::Clippy,
+            toolchain: Some("nightly".to_string()),
+            package: Some("my-crate".to_string()),
+            features: vec!["feat1".to_string(), "feat2".to_string()],
+            all_features: false,
+            no_default_features: true,
+            release: true,
+            target: Some("x86_64-unknown-linux-gnu".to_string()),
+            profile: None,
+            extra_args: vec!["--".to_string(), "-D".to_string(), "warnings".to_string()],
+            env,
+            working_dir: Some("/src".to_string()),
+            timeout_ms: Some(60_000),
+            output_dir: None,
+        };
+        let json = serde_json::to_string(&config).unwrap();
+        let de: CargoConfig = serde_json::from_str(&json).unwrap();
+        assert_eq!(de.command, CargoCommand::Clippy);
+        assert_eq!(de.toolchain, Some("nightly".to_string()));
+        assert_eq!(de.package, Some("my-crate".to_string()));
+        assert_eq!(de.features, vec!["feat1", "feat2"]);
+        assert!(de.no_default_features);
+        assert!(de.release);
+        assert_eq!(de.extra_args, vec!["--", "-D", "warnings"]);
+        assert_eq!(de.timeout_ms, Some(60_000));
+    }
+
+    #[test]
+    fn command_as_str() {
+        assert_eq!(CargoCommand::Build.as_str(), "build");
+        assert_eq!(CargoCommand::Test.as_str(), "test");
+        assert_eq!(CargoCommand::Check.as_str(), "check");
+        assert_eq!(CargoCommand::Clippy.as_str(), "clippy");
+        assert_eq!(CargoCommand::Fmt.as_str(), "fmt");
+        assert_eq!(CargoCommand::Doc.as_str(), "doc");
+        assert_eq!(CargoCommand::Publish.as_str(), "publish");
+        assert_eq!(CargoCommand::Audit.as_str(), "audit");
+        assert_eq!(CargoCommand::Deny.as_str(), "deny");
+        assert_eq!(CargoCommand::Nextest.as_str(), "nextest");
+        assert_eq!(CargoCommand::LlvmCov.as_str(), "llvm-cov");
+        assert_eq!(CargoCommand::DocMdx.as_str(), "doc-mdx");
+    }
+
+    #[test]
+    fn command_serde_kebab_case() {
+        let json = r#""build""#;
+        let cmd: CargoCommand = serde_json::from_str(json).unwrap();
+        assert_eq!(cmd, CargoCommand::Build);
+
+        let serialized = serde_json::to_string(&CargoCommand::Build).unwrap();
+        assert_eq!(serialized, r#""build""#);
+
+        // External tools
+        let json = r#""llvm-cov""#;
+        let cmd: CargoCommand = serde_json::from_str(json).unwrap();
+        assert_eq!(cmd, CargoCommand::LlvmCov);
+
+        let json = r#""nextest""#;
+        let cmd: CargoCommand = serde_json::from_str(json).unwrap();
+        assert_eq!(cmd, CargoCommand::Nextest);
+
+        let json = r#""doc-mdx""#;
+        let cmd: CargoCommand = serde_json::from_str(json).unwrap();
+        assert_eq!(cmd, CargoCommand::DocMdx);
+    }
+
+    #[test]
+    fn subcommand_args_single() {
+        assert_eq!(CargoCommand::Build.subcommand_args(), vec!["build"]);
+        assert_eq!(CargoCommand::Audit.subcommand_args(), vec!["audit"]);
+        assert_eq!(CargoCommand::LlvmCov.subcommand_args(), vec!["llvm-cov"]);
+    }
+
+    #[test]
+    fn subcommand_args_nextest_has_run() {
+        assert_eq!(CargoCommand::Nextest.subcommand_args(), vec!["nextest", "run"]);
+    }
+
+    #[test]
+    fn subcommand_args_doc_mdx_uses_rustdoc() {
+        assert_eq!(CargoCommand::DocMdx.subcommand_args(), vec!["rustdoc"]);
+    }
+
+    #[test]
+    fn install_package_external_tools() {
+        assert_eq!(CargoCommand::Audit.install_package(), Some("cargo-audit"));
+        assert_eq!(CargoCommand::Deny.install_package(), Some("cargo-deny"));
+        assert_eq!(CargoCommand::Nextest.install_package(), Some("cargo-nextest"));
+        assert_eq!(CargoCommand::LlvmCov.install_package(), Some("cargo-llvm-cov"));
+    }
+
+    #[test]
+    fn install_package_builtin_returns_none() {
+        assert_eq!(CargoCommand::Build.install_package(), None);
+        assert_eq!(CargoCommand::Test.install_package(), None);
+        assert_eq!(CargoCommand::Check.install_package(), None);
+        assert_eq!(CargoCommand::Clippy.install_package(), None);
+        assert_eq!(CargoCommand::Fmt.install_package(), None);
+        assert_eq!(CargoCommand::Doc.install_package(), None);
+        assert_eq!(CargoCommand::Publish.install_package(), None);
+        assert_eq!(CargoCommand::DocMdx.install_package(), None);
+    }
+
+    #[test]
+    fn binary_name_external_tools() {
+        assert_eq!(CargoCommand::Audit.binary_name(), Some("cargo-audit"));
+        assert_eq!(CargoCommand::Deny.binary_name(), Some("cargo-deny"));
+        assert_eq!(CargoCommand::Nextest.binary_name(), Some("cargo-nextest"));
+        assert_eq!(CargoCommand::LlvmCov.binary_name(), Some("cargo-llvm-cov"));
+    }
+
+    #[test]
+    fn binary_name_builtin_returns_none() {
+        assert_eq!(CargoCommand::Build.binary_name(), None);
+        assert_eq!(CargoCommand::Test.binary_name(), None);
+    }
+
+    #[test]
+    fn config_defaults() {
+        let json = r#"{"command": "test"}"#;
+        let config: CargoConfig = serde_json::from_str(json).unwrap();
+        assert_eq!(config.command, CargoCommand::Test);
+        assert!(config.toolchain.is_none());
+        assert!(config.package.is_none());
+        assert!(config.features.is_empty());
+        assert!(!config.all_features);
+        assert!(!config.no_default_features);
+        assert!(!config.release);
+        assert!(config.target.is_none());
+        assert!(config.profile.is_none());
+        assert!(config.extra_args.is_empty());
+        assert!(config.env.is_empty());
+        assert!(config.working_dir.is_none());
+        assert!(config.timeout_ms.is_none());
+        assert!(config.output_dir.is_none());
+    }
+
+    #[test]
+    fn config_with_output_dir() {
+        let json = r#"{"command": "doc-mdx", "output_dir": "docs/api"}"#;
+        let config: CargoConfig = serde_json::from_str(json).unwrap();
+        assert_eq!(config.command, CargoCommand::DocMdx);
+        assert_eq!(config.output_dir, Some("docs/api".to_string()));
+    }
+}