[4/n] add configuration for target presets (#72)

Add a `target.preset` table which can be used to define presets for target
configuration. This will be used within omicron-package.

For how this will eventually be used, see
oxidecomputer/omicron#7288.

src/config/identifier.rs

@@ -174,6 +174,10 @@ impl FromStr for ConfigIdent {
     }
 }
 
+// The `Deserialize` implementation for `ConfigIdent` must be manually
+// implemented, because it must go through validation. The `Serialize`
+// implementation can be derived because `ConfigIdent` serializes as a regular
+// string.
 impl<'de> Deserialize<'de> for ConfigIdent {
     fn deserialize<D>(deserializer: D) -> Result<ConfigIdent, D::Error>
     where

src/config/imp.rs

@@ -12,7 +12,7 @@ use std::path::Path;
 use thiserror::Error;
 use topological_sort::TopologicalSort;
 
-use super::PackageName;
+use super::{PackageName, PresetName};
 
 /// Describes a set of packages to act upon.
 ///
@@ -106,6 +106,10 @@ pub struct Config {
     /// Packages to be built and installed.
     #[serde(default, rename = "package")]
     pub packages: BTreeMap<PackageName, Package>,
+
+    /// Target configuration.
+    #[serde(default)]
+    pub target: TargetConfig,
 }
 
 impl Config {
@@ -134,6 +138,14 @@ impl Config {
     }
 }
 
+/// Configuration for targets, including preset configuration.
+#[derive(Clone, Deserialize, Debug, Default)]
+pub struct TargetConfig {
+    /// Preset configuration for targets.
+    #[serde(default, rename = "preset")]
+    pub presets: BTreeMap<PresetName, TargetMap>,
+}
+
 /// Errors which may be returned when parsing the server configuration.
 #[derive(Error, Debug)]
 pub enum ParseError {
@@ -187,6 +199,7 @@ mod test {
                 (pkg_a_name.clone(), pkg_a.clone()),
                 (pkg_b_name.clone(), pkg_b.clone()),
             ]),
+            target: TargetConfig::default(),
         };
 
         let mut order = cfg.packages_to_build(&TargetMap::default()).build_order();
@@ -228,6 +241,7 @@ mod test {
                 (pkg_a_name.clone(), pkg_a.clone()),
                 (pkg_b_name.clone(), pkg_b.clone()),
             ]),
+            target: TargetConfig::default(),
         };
 
         let mut order = cfg.packages_to_build(&TargetMap::default()).build_order();
@@ -253,6 +267,7 @@ mod test {
 
         let cfg = Config {
             packages: BTreeMap::from([(pkg_a_name.clone(), pkg_a.clone())]),
+            target: TargetConfig::default(),
         };
 
         let mut order = cfg.packages_to_build(&TargetMap::default()).build_order();