feat: add corn file format (#694)

This adds `corn` as a new file format.

I've enabled it by default as per the current standards, but did see
discussion in #621 as to possibly changing this approach.

https://cornlang.dev

Author: epage

Cargo.lock

@@ -126,6 +126,7 @@ json = ["serde_json"]
 yaml = ["yaml-rust2"]
 ini = ["rust-ini"]
 json5 = ["json5_rs", "dep:serde-untagged"]
+corn = ["dep:corn"]
 convert-case = ["convert_case"]
 preserve_order = ["indexmap", "toml?/preserve_order", "serde_json?/preserve_order", "ron?/indexmap"]
 async = ["async-trait"]
@@ -141,6 +142,7 @@ yaml-rust2 = { version = "0.10.4", optional = true }
 rust-ini = { version = "0.21.3", optional = true }
 ron = { version = "0.8.1", optional = true }
 json5_rs = { version = "0.4.1", optional = true, package = "json5" }
+corn = { version = "0.10.0", optional = true, package = "libcorn" }
 indexmap = { version = "2.11.4", features = ["serde"], optional = true }
 convert_case = { version = "0.6.0", optional = true }
 pathdiff = "0.2.3"

Cargo.toml

@@ -0,0 +1,39 @@
+use crate::value::{Value, ValueKind};
+use crate::{format, Map};
+use std::error::Error;
+
+pub(crate) fn parse(
+    uri: Option<&String>,
+    text: &str,
+) -> Result<Map<String, Value>, Box<dyn Error + Send + Sync>> {
+    let value = from_corn_value(uri, &corn::parse(text)?);
+    format::extract_root_table(uri, value)
+}
+
+fn from_corn_value(uri: Option<&String>, value: &corn::Value<'_>) -> Value {
+    match value {
+        corn::Value::String(value) => Value::new(uri, ValueKind::String(value.to_string())),
+        corn::Value::Integer(value) => Value::new(uri, ValueKind::I64(*value)),
+        corn::Value::Float(value) => Value::new(uri, ValueKind::Float(*value)),
+        corn::Value::Boolean(value) => Value::new(uri, ValueKind::Boolean(*value)),
+        corn::Value::Object(value) => Value::new(
+            uri,
+            ValueKind::Table(
+                value
+                    .iter()
+                    .map(|(key, value)| (key.to_string(), from_corn_value(uri, value)))
+                    .collect(),
+            ),
+        ),
+        corn::Value::Array(value) => Value::new(
+            uri,
+            ValueKind::Array(
+                value
+                    .iter()
+                    .map(|value| from_corn_value(uri, value))
+                    .collect(),
+            ),
+        ),
+        corn::Value::Null(_) => Value::new(uri, ValueKind::Nil),
+    }
+}

src/file/format/corn.rs

@@ -21,6 +21,9 @@ mod ron;
 #[cfg(feature = "json5")]
 mod json5;
 
+#[cfg(feature = "corn")]
+mod corn;
+
 /// File formats provided by the library.
 ///
 /// Although it is possible to define custom formats using [`Format`] trait it is recommended to use `FileFormat` if possible.
@@ -50,6 +53,10 @@ pub enum FileFormat {
     /// JSON5 (parsed with json5)
     #[cfg(feature = "json5")]
     Json5,
+
+    /// Corn (parsed with `libcorn`)
+    #[cfg(feature = "corn")]
+    Corn,
 }
 
 impl FileFormat {
@@ -67,6 +74,8 @@ impl FileFormat {
             FileFormat::Ron,
             #[cfg(feature = "json5")]
             FileFormat::Json5,
+            #[cfg(feature = "corn")]
+            FileFormat::Corn,
         ]
     }
 
@@ -90,6 +99,9 @@ impl FileFormat {
             #[cfg(feature = "json5")]
             FileFormat::Json5 => &["json5"],
 
+            #[cfg(feature = "corn")]
+            FileFormat::Corn => &["corn"],
+
             #[cfg(all(
                 not(feature = "toml"),
                 not(feature = "json"),
@@ -126,6 +138,9 @@ impl FileFormat {
             #[cfg(feature = "json5")]
             FileFormat::Json5 => json5::parse(uri, text),
 
+            #[cfg(feature = "corn")]
+            FileFormat::Corn => corn::parse(uri, text),
+
             #[cfg(all(
                 not(feature = "toml"),
                 not(feature = "json"),