serde: Fix int_or_string_to_int deserialization helper

It's unclear why the previous method didn't work, but this one definitely does.

ruma-serde/src/strings.rs

@@ -1,11 +1,8 @@
-use std::{
-    collections::BTreeMap,
-    convert::{TryFrom, TryInto},
-};
+use std::{collections::BTreeMap, convert::TryInto, fmt};
 
 use js_int::Int;
 use serde::{
-    de::{Deserializer, Error as _, IntoDeserializer as _},
+    de::{self, Deserializer, IntoDeserializer as _, Visitor},
     Deserialize,
 };
 
@@ -33,25 +30,6 @@ where
     }
 }
 
-// Helper type for deserialize_int_or_string_to_int
-#[derive(Deserialize)]
-#[serde(untagged)]
-enum IntOrString<'a> {
-    Num(Int),
-    Str(&'a str),
-}
-
-impl TryFrom<IntOrString<'_>> for Int {
-    type Error = js_int::ParseIntError;
-
-    fn try_from(input: IntOrString) -> Result<Self, Self::Error> {
-        match input {
-            IntOrString::Num(n) => Ok(n),
-            IntOrString::Str(string) => string.parse(),
-        }
-    }
-}
-
 /// Take either an integer number or a string and deserialize to an integer number.
 ///
 /// To be used like this:
@@ -60,7 +38,61 @@ pub fn int_or_string_to_int<'de, D>(de: D) -> Result<Int, D::Error>
 where
     D: Deserializer<'de>,
 {
-    IntOrString::deserialize(de)?.try_into().map_err(D::Error::custom)
+    struct IntOrStringVisitor;
+
+    impl<'de> Visitor<'de> for IntOrStringVisitor {
+        type Value = Int;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("an integer or a string")
+        }
+
+        fn visit_i8<E: de::Error>(self, v: i8) -> Result<Self::Value, E> {
+            Ok(v.into())
+        }
+
+        fn visit_i16<E: de::Error>(self, v: i16) -> Result<Self::Value, E> {
+            Ok(v.into())
+        }
+
+        fn visit_i32<E: de::Error>(self, v: i32) -> Result<Self::Value, E> {
+            Ok(v.into())
+        }
+
+        fn visit_i64<E: de::Error>(self, v: i64) -> Result<Self::Value, E> {
+            v.try_into().map_err(E::custom)
+        }
+
+        fn visit_i128<E: de::Error>(self, v: i128) -> Result<Self::Value, E> {
+            v.try_into().map_err(E::custom)
+        }
+
+        fn visit_u8<E: de::Error>(self, v: u8) -> Result<Self::Value, E> {
+            Ok(v.into())
+        }
+
+        fn visit_u16<E: de::Error>(self, v: u16) -> Result<Self::Value, E> {
+            Ok(v.into())
+        }
+
+        fn visit_u32<E: de::Error>(self, v: u32) -> Result<Self::Value, E> {
+            Ok(v.into())
+        }
+
+        fn visit_u64<E: de::Error>(self, v: u64) -> Result<Self::Value, E> {
+            v.try_into().map_err(E::custom)
+        }
+
+        fn visit_u128<E: de::Error>(self, v: u128) -> Result<Self::Value, E> {
+            v.try_into().map_err(E::custom)
+        }
+
+        fn visit_str<E: de::Error>(self, v: &str) -> Result<Self::Value, E> {
+            v.parse().map_err(E::custom)
+        }
+    }
+
+    de.deserialize_any(IntOrStringVisitor)
 }
 
 /// Take a BTreeMap with values of either an integer number or a string and deserialize
@@ -73,8 +105,42 @@ where
     D: Deserializer<'de>,
     T: Deserialize<'de> + Ord,
 {
-    BTreeMap::<T, IntOrString>::deserialize(de)?
-        .into_iter()
-        .map(|(k, v)| v.try_into().map(|n| (k, n)).map_err(D::Error::custom))
-        .collect()
+    #[repr(transparent)]
+    struct IntWrap(Int);
+
+    impl<'de> Deserialize<'de> for IntWrap {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            int_or_string_to_int(deserializer).map(IntWrap)
+        }
+    }
+
+    Ok(BTreeMap::<T, IntWrap>::deserialize(de)?.into_iter().map(|(k, IntWrap(v))| (k, v)).collect())
+}
+
+#[cfg(test)]
+mod tests {
+    use js_int::{int, Int};
+    use matches::assert_matches;
+    use serde::Deserialize;
+
+    use super::int_or_string_to_int;
+
+    #[test]
+    fn int_or_string() -> Result<(), serde_json::Error> {
+        #[derive(Debug, Deserialize)]
+        struct Test {
+            #[serde(deserialize_with = "int_or_string_to_int")]
+            num: Int,
+        }
+
+        assert_matches!(
+            serde_json::from_value::<Test>(serde_json::json!({ "num": "0" }))?,
+            Test { num } if num == int!(0)
+        );
+
+        Ok(())
+    }
 }