feat: config crate with legacy env names

crates/config/src/lenient.rs

@@ -0,0 +1,79 @@
+//! Deserializers for values that arrive as strings from the environment but
+//! may be native numbers/bools in a TOML file.
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::str::FromStr;
+
+use serde::Deserializer;
+use serde::de::{self, Visitor};
+
+struct Number<T>(PhantomData<T>);
+
+impl<T: FromStr> Visitor<'_> for Number<T> {
+    type Value = T;
+
+    fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("a number")
+    }
+
+    fn visit_str<E: de::Error>(self, v: &str) -> Result<T, E> {
+        v.trim()
+            .parse()
+            .map_err(|_| E::custom("expected a number in range"))
+    }
+
+    fn visit_u64<E: de::Error>(self, v: u64) -> Result<T, E> {
+        self.visit_str(&v.to_string())
+    }
+
+    fn visit_i64<E: de::Error>(self, v: i64) -> Result<T, E> {
+        self.visit_str(&v.to_string())
+    }
+}
+
+pub fn number<'de, D, T>(d: D) -> Result<T, D::Error>
+where
+    D: Deserializer<'de>,
+    T: FromStr,
+{
+    d.deserialize_any(Number(PhantomData))
+}
+
+struct Flag {
+    accepts_one: bool,
+}
+
+impl Visitor<'_> for Flag {
+    type Value = bool;
+
+    fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("a boolean")
+    }
+
+    fn visit_bool<E: de::Error>(self, v: bool) -> Result<bool, E> {
+        Ok(v)
+    }
+
+    fn visit_str<E: de::Error>(self, v: &str) -> Result<bool, E> {
+        Ok(v == "true" || (self.accepts_one && v == "1"))
+    }
+
+    fn visit_u64<E: de::Error>(self, v: u64) -> Result<bool, E> {
+        Ok(self.accepts_one && v == 1)
+    }
+
+    fn visit_i64<E: de::Error>(self, v: i64) -> Result<bool, E> {
+        Ok(self.accepts_one && v == 1)
+    }
+}
+
+/// `true` only for `true` or `1` (anything else is false, like the old readers).
+pub fn true_or_one<'de, D: Deserializer<'de>>(d: D) -> Result<bool, D::Error> {
+    d.deserialize_any(Flag { accepts_one: true })
+}
+
+/// `true` only for `true`.
+pub fn true_only<'de, D: Deserializer<'de>>(d: D) -> Result<bool, D::Error> {
+    d.deserialize_any(Flag { accepts_one: false })
+}