Initial commit: krust - container image build tool for Rust

krust builds container images for Rust applications without Docker:
- Builds static binaries using musl libc
- Creates minimal OCI container images
- Pushes to any OCI-compliant registry
- Outputs digest to stdout for composability

Inspired by ko.build for Go applications.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/config/mod.rs

@@ -0,0 +1,74 @@
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+#[cfg(test)]
+mod tests;
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct Config {
+    /// Default base image for containers
+    #[serde(default = "default_base_image")]
+    pub base_image: String,
+
+    /// Default registry to push images to
+    pub default_registry: Option<String>,
+
+    /// Build configuration
+    #[serde(default)]
+    pub build: BuildConfig,
+
+    /// Registry authentication configuration
+    #[serde(default)]
+    pub registries: HashMap<String, RegistryAuth>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct BuildConfig {
+    /// Additional environment variables for cargo build
+    #[serde(default)]
+    pub env: HashMap<String, String>,
+
+    /// Default cargo build arguments
+    #[serde(default)]
+    pub cargo_args: Vec<String>,
+
+    /// Target directory for build artifacts
+    pub target_dir: Option<PathBuf>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct RegistryAuth {
+    pub username: Option<String>,
+    pub password: Option<String>,
+    pub auth: Option<String>,
+}
+
+fn default_base_image() -> String {
+    "gcr.io/distroless/static:nonroot".to_string()
+}
+
+impl Default for Config {
+    fn default() -> Self {
+        Self {
+            base_image: default_base_image(),
+            default_registry: None,
+            build: BuildConfig::default(),
+            registries: HashMap::new(),
+        }
+    }
+}
+
+impl Config {
+    pub fn load() -> anyhow::Result<Self> {
+        if let Some(config_dir) = dirs::config_dir() {
+            let config_path = config_dir.join("krust").join("config.toml");
+            if config_path.exists() {
+                let content = std::fs::read_to_string(config_path)?;
+                let config: Config = toml::from_str(&content)?;
+                return Ok(config);
+            }
+        }
+        Ok(Config::default())
+    }
+}

src/config/tests.rs

@@ -0,0 +1,20 @@
+#[cfg(test)]
+mod tests {
+    use super::super::*;
+
+    #[test]
+    fn test_default_config() {
+        let config = Config::default();
+        assert_eq!(config.base_image, "gcr.io/distroless/static:nonroot");
+        assert!(config.default_registry.is_none());
+        assert!(config.registries.is_empty());
+    }
+
+    #[test]
+    fn test_build_config_default() {
+        let build_config = BuildConfig::default();
+        assert!(build_config.env.is_empty());
+        assert!(build_config.cargo_args.is_empty());
+        assert!(build_config.target_dir.is_none());
+    }
+}