Add try_deserialize deserialization path error tracking

Cargo.toml

@@ -135,6 +135,7 @@ 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 = "0.1"
 
 [dev-dependencies]
 serde_derive = "1.0"

src/config.rs

@@ -2,6 +2,7 @@ use std::fmt::Debug;
 
 use serde::de::Deserialize;
 use serde::ser::Serialize;
+use serde_path_to_error::{Deserializer, Track};
 
 use crate::builder::{ConfigBuilder, DefaultState};
 use crate::error::{ConfigError, Result};
@@ -142,7 +143,20 @@ impl Config {
 
     /// Attempt to deserialize the entire configuration into the requested type.
     pub fn try_deserialize<'de, T: Deserialize<'de>>(self) -> Result<T> {
-        T::deserialize(self)
+        let mut track = Track::new();
+        match T::deserialize(Deserializer::new(self, &mut track)) {
+            Ok(t) => Ok(t),
+            Err(ConfigError::Message(e)) => {
+                let path = track.path();
+                if path.iter().count() == 0 {
+                    return Err(ConfigError::Message(e));
+                }
+                Err(ConfigError::Message(format!(
+                    "failed reading field `{path}`: {e}"
+                )))
+            }
+            Err(err) => Err(err),
+        }
     }
 
     /// Attempt to serialize the entire configuration from the given type.

tests/testsuite/errors.rs

@@ -316,3 +316,39 @@ fn test_error_root_not_table() {
         },
     }
 }
+
+#[test]
+#[cfg(feature = "json")]
+fn test_json_error_with_path() {
+    #[derive(Debug, Deserialize)]
+    struct InnerSettings {
+        #[allow(dead_code)]
+        value: u32,
+        #[allow(dead_code)]
+        value2: u32,
+    }
+
+    #[derive(Debug, Deserialize)]
+    struct Settings {
+        #[allow(dead_code)]
+        inner: InnerSettings,
+    }
+
+    let c = Config::builder()
+        .add_source(File::from_str(
+            r#"
+{
+    "inner": { "value": 42 }
+}
+        "#,
+            FileFormat::Json5,
+        ))
+        .build()
+        .unwrap();
+
+    let with_path = c.clone().try_deserialize::<Settings>();
+    assert_data_eq!(
+        with_path.unwrap_err().to_string(),
+        str!["failed reading field `inner`: missing field `value2`"]
+    );
+}

tests/testsuite/log.rs

@@ -53,6 +53,6 @@ fn test_load_level_lowercase() {
     assert!(s.is_err());
     assert_data_eq!(
         s.unwrap_err().to_string(),
-        str!["enum Level does not have variant constructor error"]
+        str!["failed reading field `log`: enum Level does not have variant constructor error"]
     );
 }