Switch to TOML for configuration

cli/src/settings/util.rs

@@ -0,0 +1,41 @@
+use anyhow::{anyhow, bail, Result};
+use toml::value::Table;
+
+/// Check that the input is a table and contains no keys not in the given list, returning
+/// the table.
+pub(super) fn table_with_keys<'a>(cfg: &'a toml::Value, keys: &[&str]) -> Result<&'a Table> {
+    let table = cfg.as_table().ok_or_else(|| anyhow!("not a table"))?;
+
+    for tk in table.keys() {
+        if !keys.iter().any(|k| k == tk) {
+            bail!("unknown table key `{}`", tk);
+        }
+    }
+    Ok(table)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use toml::toml;
+
+    #[test]
+    fn test_dissect_table_missing() {
+        let val = toml! { bar = true };
+        let diss = table_with_keys(&val, &["foo", "bar"]).unwrap();
+        assert_eq!(diss.get("bar"), Some(&toml::Value::Boolean(true)));
+        assert_eq!(diss.get("foo"), None);
+    }
+
+    #[test]
+    fn test_dissect_table_extra() {
+        let val = toml! { nosuch = 10 };
+        assert!(table_with_keys(&val, &["foo", "bar"]).is_err());
+    }
+
+    #[test]
+    fn test_dissect_table_not_a_table() {
+        let val = toml::Value::Array(vec![]);
+        assert!(table_with_keys(&val, &["foo", "bar"]).is_err());
+    }
+}