install: Warn on unknown keys

Out of general principle, since we're adding new ones.

Signed-off-by: Colin Walters <walters@verbum.org>

lib/Cargo.toml

@@ -34,6 +34,7 @@ regex = "1.7.1"
 rustix = { "version" = "0.38", features = ["thread", "fs", "system", "process"] }
 schemars = { version = "0.8.6", features = ["chrono"] }
 serde = { features = ["derive"], version = "1.0.125" }
+serde_ignored = "0.1.9"
 serde_json = "1.0.64"
 serde_yaml = "0.9.17"
 serde_with = ">= 1.9.4, < 2"

lib/src/install.rs

@@ -413,8 +413,15 @@ pub(crate) mod config {
         let mut config: Option<InstallConfiguration> = None;
         for (_name, path) in fragments {
             let buf = std::fs::read_to_string(&path)?;
-            let c: InstallConfigurationToplevel =
-                toml::from_str(&buf).with_context(|| format!("Parsing {path:?}"))?;
+            let mut unused = std::collections::HashSet::new();
+            let de = toml::Deserializer::new(&buf);
+            let c: InstallConfigurationToplevel = serde_ignored::deserialize(de, |path| {
+                unused.insert(path.to_string());
+            })
+            .with_context(|| format!("Parsing {path:?}"))?;
+            for key in unused {
+                eprintln!("warning: {path:?}: Unknown key {key}");
+            }
             if let Some(config) = config.as_mut() {
                 if let Some(install) = c.install {
                     tracing::debug!("Merging install config: {install:?}");