feat: add 'try_deserialize_with_error_path' method

Cargo.toml

@@ -120,6 +120,7 @@ convert-case = ["convert_case"]
 preserve_order = ["indexmap", "toml?/preserve_order", "serde_json?/preserve_order", "ron?/indexmap"]
 async = ["async-trait"]
 toml = ["dep:toml"]
+path_to_error = ["serde_path_to_error"]
 
 [dependencies]
 serde = "1.0"
@@ -135,6 +136,7 @@ indexmap = { version = "2.2", features = ["serde"], optional = true }
 convert_case = { version = "0.6", optional = true }
 pathdiff = "0.2"
 winnow = "0.6.20"
+serde_path_to_error = { version = "0.1", optional = true }
 
 [dev-dependencies]
 serde_derive = "1.0"

src/config.rs

@@ -145,6 +145,21 @@ impl Config {
         T::deserialize(self)
     }
 
+    #[cfg(feature = "path_to_error")]
+    /// Attempt to deserialize the entire configuration into the requested type.
+    /// If fails, the returned error will contain the path where it occurred.
+    pub fn try_deserialize_with_error_path<'de, T: Deserialize<'de>>(
+        self,
+    ) -> std::result::Result<T, Box<serde_path_to_error::Error<ConfigError>>> {
+        use serde_path_to_error::{Deserializer, Error, Track};
+
+        let mut track = Track::new();
+        match T::deserialize(Deserializer::new(self, &mut track)) {
+            Ok(t) => Ok(t),
+            Err(err) => Err(Box::new(Error::new(track.path(), err))),
+        }
+    }
+
     /// Attempt to serialize the entire configuration from the given type.
     pub fn try_from<T: Serialize>(from: &T) -> Result<Self> {
         let mut serializer = ConfigSerializer::default();

tests/testsuite/file_json_error_path.rs

@@ -0,0 +1,46 @@
+#![cfg(all(feature = "json5", feature = "path_to_error"))]
+
+use serde_derive::Deserialize;
+
+use config::{Config, File, FileFormat};
+
+#[derive(Debug, Deserialize)]
+struct InnerSettings {
+    #[allow(dead_code)]
+    value: String,
+}
+
+#[derive(Debug, Deserialize)]
+struct Settings {
+    #[allow(dead_code)]
+    inner: InnerSettings,
+}
+
+#[test]
+fn test_json_foo() {
+    let c = Config::builder()
+        .add_source(File::from_str(
+            r#"
+{
+    "inner": { "value": {} }
+}
+            "#,
+            FileFormat::Json,
+        ))
+        .build()
+        .unwrap();
+
+    match c.try_deserialize_with_error_path::<Settings>() {
+        Ok(_) => panic!("expected a type error"),
+        Err(err) => {
+            let path = err.path().to_string();
+            assert_eq!(path, "inner.value");
+
+            let s = format!("{err}");
+            assert_eq!(
+                s,
+                "inner.value: invalid type: unit value, expected a string for key `inner.value`"
+            );
+        }
+    }
+}

tests/testsuite/main.rs

@@ -11,6 +11,7 @@ pub mod file;
 pub mod file_ini;
 pub mod file_json;
 pub mod file_json5;
+pub mod file_json_error_path;
 pub mod file_ron;
 pub mod file_toml;
 pub mod file_yaml;