Attach key to type error generated from Config::get_<type>()

This commit extracts low-level get_value() to preserve the origin as much
as possible. get::<Value>() would run Value-to-Value deserialization, and
the origin field would be lost there.

For scalar types, we could instead leverage get::<T>() as the deserializer
implemented for Value type invokes Value::into_<type>() function:

    fn get_string(&self, key: &str) -> Result<String> { self.get(key) }

Signed-off-by: Yuya Nishihara <yuya@tcha.org>

2 files changed, 74 insertions, 14 deletions

diff --git a/src/config.rs b/src/config.rs
index 320b72e..0f44aae 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -150,7 +150,7 @@ impl Config {
         Ok(())
     }
 
-    pub fn get<'de, T: Deserialize<'de>>(&self, key: &str) -> Result<T> {
+    fn get_value(&self, key: &str) -> Result<Value> {
         let k = key.to_lowercase();
         let key = k.as_str();
         // Parse the key into a path expression
@@ -159,38 +159,44 @@ impl Config {
         // Traverse the cache using the path to (possibly) retrieve a value
         let value = expr.get(&self.cache).cloned();
 
-        match value {
-            Some(value) => {
-                // Deserialize the received value into the requested type
-                T::deserialize(value).map_err(|e| e.extend_with_key(key))
-            }
+        value.ok_or_else(|| ConfigError::NotFound(key.into()))
+    }
 
-            None => Err(ConfigError::NotFound(key.into())),
-        }
+    pub fn get<'de, T: Deserialize<'de>>(&self, key: &str) -> Result<T> {
+        self.get_value(key).and_then(|value| {
+            // Deserialize the received value into the requested type
+            T::deserialize(value).map_err(|e| e.extend_with_key(key))
+        })
     }
 
     pub fn get_string(&self, key: &str) -> Result<String> {
-        self.get(key).and_then(Value::into_string)
+        self.get_value(key)
+            .and_then(|value| value.into_string().map_err(|e| e.extend_with_key(key)))
     }
 
     pub fn get_int(&self, key: &str) -> Result<i64> {
-        self.get(key).and_then(Value::into_int)
+        self.get_value(key)
+            .and_then(|value| value.into_int().map_err(|e| e.extend_with_key(key)))
     }
 
     pub fn get_float(&self, key: &str) -> Result<f64> {
-        self.get(key).and_then(Value::into_float)
+        self.get_value(key)
+            .and_then(|value| value.into_float().map_err(|e| e.extend_with_key(key)))
     }
 
     pub fn get_bool(&self, key: &str) -> Result<bool> {
-        self.get(key).and_then(Value::into_bool)
+        self.get_value(key)
+            .and_then(|value| value.into_bool().map_err(|e| e.extend_with_key(key)))
     }
 
     pub fn get_table(&self, key: &str) -> Result<Map<String, Value>> {
-        self.get(key).and_then(Value::into_table)
+        self.get_value(key)
+            .and_then(|value| value.into_table().map_err(|e| e.extend_with_key(key)))
     }
 
     pub fn get_array(&self, key: &str) -> Result<Vec<Value>> {
-        self.get(key).and_then(Value::into_array)
+        self.get_value(key)
+            .and_then(|value| value.into_array().map_err(|e| e.extend_with_key(key)))
     }
 
     /// Attempt to deserialize the entire configuration into the requested type.
diff --git a/tests/errors.rs b/tests/errors.rs
index 1822bff..54cb93a 100644
--- a/tests/errors.rs
+++ b/tests/errors.rs
@@ -59,6 +59,60 @@ fn test_error_type_detached() {
 }
 
 #[test]
+fn test_error_type_get_bool() {
+    let c = make();
+
+    let res = c.get_bool("boolean_s_parse");
+
+    let path: PathBuf = ["tests", "Settings.toml"].iter().collect();
+
+    assert!(res.is_err());
+    assert_eq!(
+        res.unwrap_err().to_string(),
+        format!(
+            "invalid type: string \"fals\", expected a boolean for key `boolean_s_parse` in {}",
+            path.display()
+        )
+    );
+}
+
+#[test]
+fn test_error_type_get_table() {
+    let c = make();
+
+    let res = c.get_table("debug");
+
+    let path: PathBuf = ["tests", "Settings.toml"].iter().collect();
+
+    assert!(res.is_err());
+    assert_eq!(
+        res.unwrap_err().to_string(),
+        format!(
+            "invalid type: boolean `true`, expected a map for key `debug` in {}",
+            path.display()
+        )
+    );
+}
+
+#[test]
+fn test_error_type_get_array() {
+    let c = make();
+
+    let res = c.get_array("debug");
+
+    let path: PathBuf = ["tests", "Settings.toml"].iter().collect();
+
+    assert!(res.is_err());
+    assert_eq!(
+        res.unwrap_err().to_string(),
+        format!(
+            "invalid type: boolean `true`, expected an array for key `debug` in {}",
+            path.display()
+        )
+    );
+}
+
+#[test]
 fn test_error_enum_de() {
     #[derive(Debug, Deserialize, PartialEq, Eq)]
     enum Diode {