Add a itf::de::from_bigint deserializer function to convert from `B…

…igInt` via `#[serde(deserialize_with = "...")]`

itf/src/de.rs

@@ -5,6 +5,9 @@ use crate::Value;
 mod error;
 pub use error::Error;
 
+mod helpers;
+pub use helpers::from_bigint;
+
 mod deserializer;
 
 #[doc(hidden)]

itf/src/de/helpers.rs

@@ -0,0 +1,15 @@
+use std::fmt::Display;
+
+use num_bigint::BigInt;
+use serde::de::Error;
+use serde::{Deserialize, Deserializer};
+
+pub fn from_bigint<'de, A, D>(deserializer: D) -> Result<A, D::Error>
+where
+    D: Deserializer<'de>,
+    A: TryFrom<BigInt>,
+    <A as TryFrom<BigInt>>::Error: Display,
+{
+    let bigint = BigInt::deserialize(deserializer).map_err(D::Error::custom)?;
+    A::try_from(bigint).map_err(D::Error::custom)
+}

itf/tests/regression.rs

@@ -153,6 +153,22 @@ fn test_enum_deserialization_failure() {
 
     assert!(itf::from_value::<FooBarInt>(itf.clone()).is_err());
 
+    #[derive(Deserialize, Debug)]
+    #[serde(tag = "typ")]
+    enum FooBarWithInt {
+        // try to deserialize _foo as i64, via a conversion from BigInt
+        Foo {
+            #[serde(deserialize_with = "itf::de::from_bigint")]
+            _foo: i64,
+        },
+        Bar {
+            _bar: String,
+        },
+    }
+    itf::from_value::<FooBarWithInt>(itf.clone()).unwrap();
+
+    assert!(itf::from_value::<FooBarWithInt>(itf.clone()).is_ok());
+
     #[derive(Deserialize, Debug)]
     #[serde(tag = "typ")]
     enum FooBarBigInt {